It blocked the dangerous buildup of greenhouse gases in the atmosphere by sucking excess carbon from the ocean and subducting it underground.
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At other fracture points in the crust, oceanic plates are diving back inside, or subducting, their mass devoured in the mantle's hot belly.
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The Mariana Trench is home to the deepest trough on Earth, the location where the Pacific tectonic plate is subducting beneath the Mariana plate.
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Megathrust faults produce biggest quakes Megathrust faults occur at subduction zones, where Earth's tectonic plates are colliding with each other and one plate is moving (or "subducting") under another.
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Now, the subducting plate has been sitting at the bottom of the ocean for millions of years, and it has soaked up a lot of water over that time.
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"One of the most exciting things about this study is the depth extent over which they can seismically image the water going down into the subducting plate," she told Gizmodo.
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Alaska, where the Pacific Ocean plate is slowly sliding, or subducting, beneath the North American plate, is home to many volcanoes, 52 of which have been active in the last three centuries.
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Oceanic crust, where the telltale mantle exchange zones are located, is recycled through the upwelling and subducting pipeline every 200 million years or so, which means hard evidence of tectonic origins was destroyed long ago.
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Image: USGSIn March of 2011, Japan experienced a massive earthquake when the North American continental plate, which the northern half of the island nation sits on, thrust eastward over the subducting Pacific plate, causing the seabed to rise by up to 100 feet (30 meters) in one go.
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Several forces are involved in the process of slab rollback. Two forces acting against each other at the interface of the two subducting plates exert forces against one another. The subducting plate exerts a bending force (FPB) that supplies pressure during subduction, while the overriding plate exerts a force against the subducting plate (FTS). The slab pull force (FSP) is caused by the negative buoyancy of the plate driving the plate to greater depths.
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The relatively cold and dense subducting plates are pulled into the mantle and help drive mantle convection.
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In the nearby region, the Cocos Plate is subducting beneath the North American Plate, however, this was an intraplate earthquake.
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Near the Salvadorian coast, the Cocos Plate is subducting beneath the Caribbean Plate at the Middle America Trench. This earthquake was an intra-slab, normal-slip subduction earthquake in the subducting plate. The subduction zone and a local system of faults along the volcanic chain are two major sources of the earthquakes in El Salvador.
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The remains of the Farallon Plate are the Juan de Fuca, Explorer and Gorda Plates, subducting under the northern part of the North American Plate; the Cocos Plate subducting under Central America; and the Nazca Plate subducting under the South American Plate. The Farallon Plate is also responsible for transporting old island arcs and various fragments of continental crustal material rifted off from other distant plates and accreting them to the North American Plate. These fragments from elsewhere are called terranes (sometimes, "exotic" terranes). Much of western North America is composed of these accreted terranes.
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Underplating is the accumulation of partial melts at the base of the crust where an ocean plate is subducting under continental crust. Underplating is the result of partial melts being produced in the mantle wedge above a subducting plate. The partial melting is induced by a lowering of the melting temperature, the solidus, by the input of water and other volatiles supplied by phase transitions in the subducting slab. When the buoyant partial melt rises upwards through the mantle, it will usually stall at the base of the crust and pond there.
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The northern side is a convergent boundary subducting under the North American Plate forming the Aleutian Trench and the corresponding Aleutian Islands.
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This is the reason for island arc volcanism at consistent distances from the subducting slab: because the temperature-pressure conditions for flux-melting volcanism due to chlorite destabilization will always occur at the same depth, the distance from the trench to the arc volcanoes is determined only by the dip angle of the subducting slab. On the subducting side of the arc is a deep and narrow oceanic trench, which is the trace at the Earth's surface of the boundary between the down-going and overriding plates. This trench is created by the gravitational pull of the relatively dense subducting plate pulling the leading edge of the plate downward. Multiple earthquakes occur along this subduction boundary with the seismic hypocenters located at increasing depth under the island arc: these quakes define the Wadati–Benioff zones.
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The focal mechanism and hypocentral depth of the earthquake show that the earthquake was a result of normal faulting within the subducting slab.
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This was not an aftershock, but a normal fault event within the outer rise of the subducting plate, triggered by the earlier event.
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A volcanic arc grows above the subducting plate. Magma generated above the subducting slab rose into the North American continental crust about inland. Great arc- shaped volcanic mountain ranges, known as the Sierran Arc, grew as lava and ash spewed out of dozens of individual volcanoes. Beneath the surface, great masses of molten rock were injected and hardened in place.
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The subducting Pacific Plate dips at about 10 degrees and directed 83 degrees west of north. The northern subduction zone is expanding by rifting while the southern contains a strike slip fault. Seismologists have been studying how the subducting slabs underneath the Mariana island arc are entering the lower mantle and being redirected horizontally, deflecting off the upper to lower mantle transition zone.
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The age of the subducting plate is older towards west (Andreanof Island) where LFEs occur at greater depths (~75 km) than in the east where the plate is younger (~45 km near Kodiak Island). This may be because the depths at which the hydrous minerals release water and produce tremors are greater when the plate is older, colder, and subducting faster.
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This also causes the subducting Nazca slab to experience flat slab subduction, one of the few places in the world where this currently occurs.
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This earthquake was a shallow thrust earthquake in the interplate subduction zone, in which the Cocos Plate is subducting beneath the North American Plate.
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File:Volcanic Arc System.png Forearc basins form in subduction zones as sedimentary material is scraped off the subducting oceanic plate, forming an accretionary prism between the subducting oceanic lithosphere and the overriding continental plate. Between this wedge and the associated volcanic arc is a zone of depression in the sea floor. Extensional faulting due to relative motion between the accretionary prism and the volcanic arc may occur.
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BLT formation is driven by westward (i.e. converging and subducting) currents along the equator near the eastern edge of the salinity front that defines the warm pool.
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On the other hand, the dense oceanic slab at the subducting plate prefers to move downward. These opposite forces will generate a tensile force or gravitational instability on the downward slab and lead to the break-off of the slab. The space where the break-off slab separates will form a mantle window. Subsequently, the less dense continental margin forms the overriding plate, while the oceanic plate becomes the subducting slab.
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At a 'typical' subduction zone, an oceanic plate typically sinks at a fairly high angle (see above). A volcanic arc grows above the subducting plate. During the growth of the Rocky Mountains, the angle of the subducting plate may have been significantly flattened, moving the focus of melting and mountain building much farther inland than is normally expected. The Laramide orogeny was caused by subduction at an unusually shallow angle.
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Back-arc basins are found in areas where the subducting plate of oceanic crust is very old. The age need to establish back- arc spreading is oceanic lithosphere that is 55 million years old or older. This includes areas like the western pacific where multiple back-arc spreading centers are located. The dip angle of the subducting slab is shown to be greater than 30° in areas of back-arc spreading.
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The northern part of Honshu lies above the convergent boundary between the over-riding Okhotsk Plate (a proposed microplate within the North American Plate) and the subducting Pacific Plate. This boundary has been associated with a series of large historical earthquakes, originating either from rupture along the plate interface or from deformation within either the over-riding or subducting plates, many of them triggering a destructive tsunami, such as the 1896 Sanriku earthquake.
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A mantle wedge is a triangular shaped piece of mantle that lies above a subducting tectonic plate and below the overriding plate. This piece of mantle can be identified using seismic velocity imaging as well as earthquake maps. Subducting oceanic slabs carry large amounts of water; this water lowers the melting temperature of the above mantle wedge. Melting of the mantle wedge can also be contributed to depressurization due to the flow in the wedge.
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Magmas produced in subduction zone regions have high volatile contents. This water is derived from the breakdown of hydrous minerals in the subducting slab, as well as water in the oceanic plate from percolation of seawater. This water rises from the subducting slab to the overriding mantle wedge. The water lowers the melting temperature of the wedge and leaves behind melt inclusions that can be measured in the associated arc volcanic rocks.
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Arabian plate boundaries with the Eurasian, African and Indian plates The quake reportedly occurred within the subducting Arabian Plate below the overriding Eurasian Plate. The Strait of Hormuz separates two forms of plate collision. To the northwest, continental crust portions of the Arabian and Eurasian Plates are colliding, resulting in compressive faulting. To the southeast, dense oceanic crust of the Arabian Plate is subducting underneath the Eurasian Plate at the Makran Trench.
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Volcanoes near plate boundaries and mid-ocean ridges are built by decompression melting of rock in the upper mantle. The lower density magma rises through the crust to the surface. Volcanoes formed near or above subducting zones are created because the subducting tectonic plate adds volatiles to the overriding plate that lowers its melting point. Which of these two process involved in the formation of a seamount has a profound effect on its eruptive materials.
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As the subducting slab shallowed, crustal garnet-containing lherzolite and granulite-eclogite, contributed both from the crustal basis and forearc rocks that were dragged down by the subducting slab, became an increasingly important component of erupted magmas. Eventually, the Incapillo magma chamber was disconnected from the mantle and lower crust. The Incapillo ignimbrite contains xenoliths with sizes of formed by amphibolite. Amphibole crystals are enclosed in intersitital plagioclase crystals and sometimes contain secondary biotite crystals.
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Recent large scale earthquakes resulting from subduction along the Nankai Trough have occurred in areas of large scale increases in the dip angle of the subducting plate (Hori et al., 2004).
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Geologists continue to gather evidence to explain the rise of the Rockies so much farther inland; the answer most likely lies with the unusual subduction of the Farallon plate, or possibly due to the subduction of an oceanic plateau. At a typical subduction zone, an oceanic plate typically sinks at a fairly steep angle, and a volcanic arc grows above the subducting plate. During the growth of the Rocky Mountains, the angle of the subducting plate may have been significantly flattened, moving the focus of melting and mountain building much farther inland than is normally expected. It is postulated that the shallow angle of the subducting plate greatly increased the friction and other interactions with the thick continental mass above it.
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Britain during this period (late Precambrian/early Cambrian) lay about 70 degrees south of the equator at the margin of a large ocean (to the north) and with a large continental plate to the south, the ocean is accepting sediment from the continental block. The oceanic plate is subducting southwards underneath the continental block which is being buoyed by the rock which is subsequently being melted (partial melting) by the high temperatures and pressures associated with the process. As with all subduction zones an island arc is formed above the subducting plate (due to rising rock melt) with a back-arc basin existing between the island arc and the continental edge. A large continental block existed with oceanic crust subducting underneath it.
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About 5–6 million years ago, the Lau-Havre backarc trough opened up and separated the Kermadec arc from the Colville-Lau arc, where volcanic activity ceased about 5-3.5 million years ago. The subduction of the Louisville seamount chain appears to have altered the behaviour of the backarc since north of the subducting area the Lau Basin is undergoing full-fledged seafloor spreading while the Havre Trough south of the subducting area only features short rift segments.
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Since the Jurassic, subduction has been occurring on the western margin of present-day South America, resulting in variable amounts of volcanic activity. A short interruption of volcanism, associated with a flattening of the subducting plate, occurred in the Oligocene 35-25 mya. Subsequently, renewed melt generation modified the overlying crust until major volcanism, associated with a "flare up" of ignimbritic volcanism occurred 10 mya. beneath the local volcanic zone lies the Benioff zone of the subducting Nazca plate.
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Submarine eruptions may produce seamounts which may break the surface to form volcanic islands and island chains. Submarine volcanism is driven by various processes. Volcanoes near plate boundaries and mid-ocean ridges are built by the decompression melting of mantle rock that rises on an upwelling portion of a convection cell to the crustal surface. Eruptions associated with subducting zones, meanwhile, are driven by subducting plates that add volatiles to the rising plate, lowering its melting point.
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This gap in seismicity indicates that subducting seamounts inhibit or even prevent seismicity at subduction zones, perhaps by increasing intervals between earthquakes, but the mechanism behind this process is poorly understood. Geochemical evidence suggests that the Louisville chain has been subducting under the Tonga-Kermadec Arc since 4 Ma. Seismic studies have identified a southward, along-arc mantle flow that indicate that Pacific mantle is being replaced by Indo-Australian mantle west of the Tonga Trench.
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250px The subducting plate consists of two protoplates, the Indian and Australian plates. Similarly, the overriding plate consists of two microplates, the Sunda and Burma plates. The relative motion of the subducting and overriding plates varies slightly along strike due to these complexities but is always strongly oblique. The strike-slip component of the oblique convergence is accommodated by displacement on the Great Sumatran fault, while the dip-slip component is taken up by the Sunda megathrust.
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At shallow depth, magma generation is dominated by anatexis of the slab. The mantle ahead of the edge of the subducting slab may be dominated by a large slab window. Other volcanic activity occurred in the region farther east, on Hardy Peninsula and some surrounding capes and islands during the Miocene; potassium-argon dating has yielded ages of 18 and 21 million years ago. These volcanic systems may indicate that the Antarctic Plate is subducting beneath the Scotia Plate.
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The state of motion of overriding plates control the geometry of divergent doubled subduction and the position of collision. The length of the subducting slab beneath a stagnant overriding plate is shorter because the mantle flow is weaker and the subduction is slower. In contrast, the length of the subducting slab beneath a free moving plate is longer. Additionally, the position of collision is shifted more to the side with stagnant plate as the rollback is faster on the free moving side.
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Earthquake records for this area of subduction go back to 1586. All of these ruptures were located either on the coast of Peru or within the Peru-Chile Trench between 9°S and 18°S, coincidental with the subducting Nazca Ridge, and include both intraplate and interplate rupturing. No large earthquakes have been located between 14°S and 15.5°S, where the bathymetric high of the ridge is subducting. Interplate earthquakes do not occur in direct conjunction with the Nazca Ridge.
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The states of Guerrero and Oaxaca lie above the convergent boundary where the Cocos Plate is being subducted below the North American Plate at a rate of 6.4 cm/yr (2.5 in/yr). The dip of the subducting slab is about 15° as defined by focal mechanisms and hypocenters of previous earthquakes. Seismicity in this area is characterized by regular megathrust earthquakes along the plate interface. In addition, there have been a series of historic normal fault events within the subducting slab.
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"How Mantle Slabs Drive Plate Tectonics". Science. 298 (5591): 207–209. Bibcode:2002Sci...298..207C. doi:10.1126/science.1074161. PMID 12364804 This force occurs between two colliding plates where one is subducting beneath the other.
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Slab suction occurs when a subducting slab drives flow in the lower mantle by exerting additional force down in the direction of the mantle's convection currents. This flow then exerts shear tractions on the base of nearby plates. This driving force is important when the slabs (or portions thereof) are not strongly attached to the rest of their respective tectonic plate. They cause both the subducting and overriding plate to move in the direction of the subduction zone.Conrad, C. P.; Lithgow-Bertelloni, C (2002).
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Most metamorphic phase transitions that occur within the subducting slab are prompted by the dehydration of hydrous mineral phases. The breakdown of hydrous mineral phases typically occurs at depths greater than 10 km. Each of these metamorphic facies is marked by the presence of a specific stable mineral assemblage, recording the metamorphic conditions undergone but the subducting slab. Transitions between facies causes hydrous minerals to dehydrate at certain pressure-temperature conditions and can therefore be tracked to melting events in the mantle beneath a volcanic arc.
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Currently the Philippine Sea Plate is subducting beneath the continental Amurian Plate and the Okinawa Plate to the south at a speed of 4 cm/year, forming the Nankai Trough and the Ryukyu Trench. The Pacific Plate is subducting under the Okhotsk Plate to the north at a speed of 10 cm/year. The early stages of subduction-accretion have recycled the continental crust margin several times, leaving the majority of the modern Japanese archipelago composed of rocks formed in the Permian period or later.
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22, p. 579-592. Most UHP rocks were metamorphosed at peak conditions of 800 °C and 3 GPa.Hacker, B. R., 2006, Pressures and temperatures of ultrahigh-pressure metamorphism: Implications for UHP tectonics and H2O in subducting slabs.
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The mechanism inferred from data is a low-angle thrust of the Nazca Plate, which is subducting beneath the South American Plate. This earthquake occurred in an area where the Peru–Chile subduction zone is relatively quiet.
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The subducting plate has not reached a depth sufficient for proper volcanic arc volcanism, however. The field bears no trace of glacial erosion on its volcanoes, and reports exist of volcanic activity in 1712, 1820 and 1926.
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At least since the Jurassic, the Nazca Plate has been subducting beneath the South America Plate at a rate of about . Volcanism does not occur along the entire length of the subduction zone; where the subducting plate descends into the mantle at a shallow angle volcanism is absent. There are thus three volcanic zones in South America, the Northern Volcanic Zone, the Central Volcanic Zone and the Southern Volcanic Zone. An additional volcanic belt, the Austral Volcanic Zone, is controlled by the subduction of the Antarctic Plate beneath the South America Plate.
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Subduction zones are defined by the inclined array of earthquakes known as the Wadati–Benioff zone after the two scientists who first identified this distinctive aspect. Subduction zone earthquakes occur at greater depths (up to ) than elsewhere on Earth (typically less than depth); such deep earthquakes may be driven by deep phase transformations, thermal runaway, or dehydration embrittlement. The subducting basalt and sediment are normally rich in hydrous minerals and clays. Additionally, large quantities of water are introduced into cracks and fractures created as the subducting slab bends downward.
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Globally, forearcs have the lowest heatflow from the interior Earth because there is no asthenosphere (convecting mantle) between the forearc lithosphere and the cold subducting plate. The inner trench wall marks the edge of the overriding plate and the outermost forearc. The forearc consists of igneous and metamorphic crust, and this crust may act as buttress to a growing accretionary wedge (formed from sediments scraped off the top of the downgoing plate). If the flux of sediments is high, material transfers from the subducting plate to the overriding plate.
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At the subduction boundary between Pacific plate and Tonga-Kermadec plate, the roll-back of the Tonga trench and Pacific slab caused compensating flow of the mantle beneath the Lau Basin. This fertile mantle then encounters the water released from the dehydrated subducting Pacific slab and undergoes partial melting. This results in the creation of a batch of depleted mantle between the fertile mantle and subducting slab. An upward flow of the depleted layer is then induced by back- arc spreading and slab subduction towards corner region where the mantle is hydrated.
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Orogenic cycle of rifting, subduction, and accretion During the Jurassic period, Pangea began to pull apart causing separation of North America from South America. This rifting produced a subduction zone where the Nazca Plate was subducting to the east under the South American Plate. Part of this subducting plate was the Baudo- Island Arc separated from the South American continent by the marginal Colombian Sea. The formation of the extensional back-arc basin associated with this subduction is the origin of the Middle Magdalena Basin in the late Jurassic.
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Such a scenario suggests that the northern hemispheric crust is a relic oceanic plate. In the preferred reconstruction, a spreading center extended north of Terra Cimmeria between Daedalia Planum and Isidis Planitia. As spreading progressed, the Boreal plate broke into the Acidalia plate with south-dipping subducting beneath Arabia Terra, and the Ulysses plate with east-dipping subducting beneath Tempe Terra and Tharsis Montes. According to this reconstruction, the northern plains would have been generated by a single spreading ridge, with Tharsis Montes qualifying as an island arc.
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The shape of the flat slab is constrained through earthquakes within the subducting slab and the interface between the upper plate and the subducting slab. Flat slab zones along the Andean margin release 3–5 times more energy through upper plate earthquakes than adjacent, more steeply dipping subduction zones. Upper plate earthquake focal mechanisms indicate that stress is aligned parallel with motion of the plate, and that stress is transmitted high into the upper plate from the lower. The reason for this enhanced seismicity is more effective coupling of the upper and lower plates.
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Costa Rica lies above the convergent plate boundary where the Cocos Plate is subducting beneath the Caribbean Plate at a rate of 9 cm per year. Off the Nicoya Peninsula, the Cocos Plate is subducting along the Middle America Trench, and the Nicoya Peninsula is unique in being one of the few landmasses along the Pacific Rim located directly above the seismogenic zone of a subduction megathrust fault. The earthquake is thought to have occurred as a result of thrust faulting on the plate interface. The earthquake has a maximum slip of about 2.5 m.
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The basement of the Sierras Pampeanas was uplifted during the Andean orogeny over a near-horizontal segment of the subducting Nazca Plate. Sierras Pampeanas was also affected by Miocene arc magmatism east of the Chile Trench during this period.
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Subducting slabs are able to move through the 660-km phase transition and collect near the bottom of the mantle in a 'slab graveyard', and may be the driving force for convection in the mantle locally and on a crustal scale.
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In between the continents of India and Australia, the oceanic crust is still subducting under the Sunda plate, forming the Sunda trench and Sunda Arc. Australia and Australian derived micro-plates collided with the Sunda plate and Pacific plate in the Pliocene, creating a complex of subduction zones and island arcs. The Philippine plate has been obliquely subducting the Sunda plate for most of the Cenozoic. The complex interaction of the Sunda, Eurasian, Indo-Australian, Philippine and Pacific plates in the Cenozoic has controlled the evolution of approximately 60 Tertiary sedimentary basins in the Indonesian region.
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The accreted material is often referred to as an accretionary wedge, or prism. These accretionary wedges can be identified by ophiolites (uplifted ocean crust consisting of sediments, pillow basalts, sheeted dykes, gabbro, and peridotite). Subduction may also cause orogeny without bringing in oceanic material that collides with the overriding continent. When the subducting plate subducts at a shallow angle underneath a continent (something called "flat-slab subduction"), the subducting plate may have enough traction on the bottom of the continental plate to cause the upper plate to contract leading to folding, faulting, crustal thickening and mountain building.
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298 (5591): 207–209. Bibcode:2002Sci...298..207C. doi:10.1126/science.1074161. PMID 12364804 Slab suction in coordination with slab pull are used to analyze the speeds of plates work. When you combine the slab pull of the upper mantle slabs with the slab suction of lower mantle slabs you get a model showing that subducting plates move four times faster than non subducting plates. Computing the slab suction force can give us predictions of the plate velocities by using viscous flow driven by the slabs and adding it to the shear tractions the flow exerts of the base of the plates.
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Fiji lies in a complex tectonic setting along the boundary between the Australian Plate and the Pacific Plate. Southwards from Fiji the Pacific Plate is subducting beneath the Australian Plate along the Tonga Trench forming the Tonga Ridge island arc system and the Lau Basin back-arc basin. To the southwest of Fiji the Australian Plate is subducting beneath the Pacific Plate forming the Vanuatu Ridge island arc system and the North Fiji back-arc basin. Hence, the region has undergone a complex process of plate convergence, subduction, and arc volcanism from the Middle Eocene to the Early Pliocene.
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Off the western coast of South America, the Nazca Plate subducts beneath the South America Plate at a rate of about . This subduction process is responsible for the volcanic activity in the Andes. The subducting slab releases fluids which induce the formation of melts which are then erupted on the surface as volcanism. The subduction process is not uniform along the plate margin; variations in the dip of the subducting Nazca plate occur along its length, and volcanic activity is concentrated in three belts (Northern Volcanic Zone, Central Volcanic Zone and Southern Volcanic Zone) where the angle of subduction is steep enough.
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Map showing the location of Nazca Ridge off the west coast of Peru The Nazca Ridge is a submarine ridge, located on the Nazca Plate off the west coast of South America. This plate and ridge are currently subducting under the South American Plate at a convergent boundary known as the Peru-Chile Trench at approximately per year. The Nazca Ridge began subducting obliquely to the collision margin at 11°S, approximately 11.2 Ma, and the current subduction location is 15°S. The ridge is composed of abnormally thick basaltic ocean crust, averaging 18 ±3 km thick.
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As the subducting plate flattens there is an inboard migration in the magmatic arc that can be tracked. In the Chilean flat slab region (~31–32 degrees S), around 7–5 Ma there was an eastward migration, broadening and gradual shutdown down of the volcanic arc associated with slab flattening. This occurs as the previous magmatic arc position on the upper plate (100–150 km above subducting plate) is no longer aligned with the zone of partial melting above the flattening slab. The magmatic arc migrates to a new location that coincides with the zone of partial melting above the flattening slab.
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Arc magmas are produced by partial melting of metasomatic domains in the mantle wedge, which was reacted with liquid phases derived from dehydration melting of minerals contained in the subducting oceanic crust formed at mid-ocean ridges. The subducting oceanic crust consists of a four major units. The topmost unit is a thin cap of pelagic sediments up to 0.3 km thick composed of siliceous and calcareous shells, meteoric dusts, and variable amounts of volcanic ash. The next unit is composed of 0.3–0.7 km thick pillow basalts, formed by the quenching of basaltic magma as it erupts into ocean water.
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Volcanism in the Central Volcanic Zone of the Andes is caused by the subduction of the Nazca Plate beneath the South America Plate in the Peru-Chile Trench at a rate of . It does not cause volcanism among the entire length of the trench; where the slab is subducting beneath the South America Plate at a shallow angle there is no recent volcanic activity. The style of subduction has changed over time. About 27 million years ago, the Farallon Plate which hitherto had been subducting beneath South America broke up and the pace of subduction increased, causing increased volcanism.
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Research by Rezene Mahatsente indicates that the driving stresses caused by ridge push would be dissipated by faulting and earthquakes in plate material containing large quantities of unbound water, but they conclude that ridge push is still a significant driving force in existing plates because of the rarity of intraplate earthquakes in the ocean. In plates with particularly small or young subducting slabs, ridge push may be the predominant driving force in the plate's motion. According to Stefanick and Jurdy, the ridge push force acting on the South American plate is approximately 5 times the slab pull forces acting at its subducting margins because of the small size of the subducting slabs at the Scotia and Caribbean margins. The Nazca plate also experiences relatively small slab pull, approximately equal to its ridge push, because the plate material is young (no more than 50 million years old) and therefore less dense, with less tendency to sink into the mantle.
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At Taiwan the oceanic crust has all been subducted and the arc is colliding with continental crust of the Eurasian Plate. To the north of Taiwan the Philippine Sea Plate is in contrast subducting beneath the Eurasian Plate, forming the Ryukyu Arc.
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The buoyancy of a microcontinent locally slows the rollback of and steepens the dip of subducting mafic lithosphere.Brun, J.-P., and Faccenna, C., 2008, Exhumation of high-pressure rocks driven by slab rollback: Earth and Planetary Science Letters, v. 272, p. 1-7.
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Under Oregon, the Siletz terrane appears to extend 25 to possibly 35 km into the trough between the subducting Juan de Fuca plate and the edge of the continent, where it is slipping over sediments accumulated in the bottom of the trough.
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Earthquakes are common along convergent boundaries. A region of high earthquake activity, the Wadati- Benioff zone, generally dips 45° and marks the subducting plate. Earthquakes will occur to a depth of along the Wadati-Benioff margin. Both compressional and extensional forces act along convergent boundaries.
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Since the Jurassic, the Nazca Plate has been subducting beneath the western margin of South America. This subduction process is responsible for the volcanism in the Central Volcanic Zone of the Andes, one of four volcanic arcs in the Andes.Godoy et al. 2018, p.
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In some places, mixtures of older intrusive rocks and the original oceanic rocks have been distorted and warped under intense heat, weight and stress to create unusual swirled patterns known as migmatite, appearing to have been nearly melted in the procedure. Volcanism began to decline along the length of the arc about 60 million years ago during the Albian and Aptian faunal stages of the Cretaceous period. This resulted from the changing geometry of the Kula Plate, which progressively developed a more northerly movement along the mainland of Western Canada. Instead of subducting beneath Western Canada, the Kula Plate began subducting underneath southwestern Yukon and Alaska during the early Eocene period.
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The Sirena Deep was most probably formed, not through transform fault motion as previously thought, but through a north-south convergence of the Caroline plate and the Pacific plate, in which the Caroline plate is subducting. A group of scientists have hypothesized that the great depth of the Mariana Trench, the Challenger Deep, and the Sirena Deep is due to a tear in the subducting Caroline plate, causing deformation of the Pacific plate above. This tear would be located to the south of Guam, the same location of the deepest portion of the Mariana Trench. The tear would lead to unusual regional tectonics, another possible reason for the extreme depth.
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Ophiolites are viewed as evidence for such mechanisms as high pressure and temperature rocks are rapidly brought to the surface through the processes of slab rollback, which provides space for the exhumation of ophiolites. Slab rollback is not always a continuous process suggesting an episodic nature. The episodic nature of the rollback is explained by a change in the density of the subducting plate, such as the arrival of buoyant lithosphere (a continent, arc, ridge, or plateau), a change in the subduction dynamics, or a change in the plate kinematics. The age of the subducting plates does not have any effect on slab rollback.
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Trenches seem positionally stable over time, but scientists believe that some trenches—particularly those associated with subduction zones where two oceanic plates converge—move backward into the subducting plate. This is called trench rollback or hinge retreat (also hinge rollback) and is one explanation for the existence of back-arc basins. Slab rollback occurs during the subduction of two tectonic plates, and results in seaward motion of the trench. Forces perpendicular to the slab at depth (the portion of the subducting plate within the mantle) are responsible for steepening of the slab in the mantle and ultimately the movement of the hinge and trench at the surface.
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In some places, mixtures of older intrusive rocks and the original oceanic rocks have been distorted and warped under intense heat, weight and stress to create unusual swirled patterns known as migmatite, appearing to have been nearly melted in the procedure. Volcanism began to decline along the length of the arc about 60 million years ago during the Albian and Aptian faunal stages of the Cretaceous period. This resulted from the changing geometry of the Kula Plate, which progressively developed a more northerly movement along the Pacific Northwest. Instead of subducting beneath the Pacific Northwest, the Kula Plate began subducting underneath southwestern Yukon and Alaska and during the early Eocene period.
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This last fact was first pushed by Akiho Miyashiro in 1973 who challenged the common conception of Troodos Ophiolite and proposed an island arc origin for it. This was done arguing that numerous lavas and dykes in the ophiolite had calc-alkaline chemistries. In the early 1980s the term supra-subduction zone was coined to infer the formation of lavas above a subducting lithospheric slab, with no specification of where in relation to the subducting slab they form. From subsequent studies of other ophiolites it has been found that these generally have a similar geochemical signature, and so it is inferred that most are supra-subduction zone related.
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Much less interplate seismicity occurs in Oregon compared to Washington and northern California, although Oregon hosts more volcanic activity than its neighboring states. Intraslab earthquakes, frequently associated with stresses within the subducting plate in convergent margins, occur most frequently in northern Cascadia along the west coast of Vancouver Island and in Puget Sound, and in southern Cascadia within the subducting Gorda Plate, near the Mendocino Triple Junction offshore of northern California. The 1949 Olympia earthquake was a damaging magnitude 6.7 intraslab earthquake that occurred at 52 km depth and caused 8 deaths. Another notable intraslab earthquake in the Puget Sound region was the magnitude 6.8 2001 Nisqually earthquake.
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Mount Nansen is a deeply eroded Mid-Cretaceous stratovolcano located west of Carmacks and west of Victoria Mountain in the central Yukon, Canada. It consists of rhyolite, dacite, andesite flows, breccias and tuff. Mount Nansen was formed during subducting under North America during the Mid-Cretaceous.
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In this case the earthquake can be confidently associated with the plane dipping shallowly to the northeast, as this is the orientation of the subducting slab as defined by historical earthquake locations and plate tectonic models. Sibuet,J-C., Rangin,C., Le Pichon,X., Singh,S.
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The Ōu Mountains began to form in the Pliocene. They sit over the middle of the inner arc of the Northeastern Japan Arc. This is the result of the Pacific Plate subducting under the Okhotsk Plate. A chain of Quaternary volcanoes along the range forms the volcanic front.
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The 7.9 Mw Aleutian Islands earthquake occurred in June 2014 at an intermediate depth of 107 km. The quake was caused by oblique normal faulting along the Aleutian Trench, a convergent boundary where the Pacific plate is subducting underneath the North American plate at around 59 mm/year.
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The Cocos Plate is subducting beneath the North American Plate in the Middle America Trench. This was an intraslab earthquake, and the epicenter had some distance from the Middle American Trench. This was the tenth earthquake since 1864 with magnitude larger than 6.5 and similar location of epicenter.
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An example of a volcanic arc having both island and continental arc sections is found behind the Aleutian Trench subduction zone in Alaska. The arc magmatism occurs one hundred to two hundred kilometers from the trench and approximately one hundred kilometers above the subducting slab. This depth of arc magma generation is the consequence of the interaction between hydrous fluids, released from the subducting slab, and the arc mantle wedge that is hot enough to melt with the addition of water. It has also been suggested that the mixing of fluids from a subducted tectonic plate and melted sediment is already occurring at the top of the slab before any mixing with the mantle takes place.
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Accretion involves the addition of material to a tectonic plate via subduction, the process by which one plate is forced under the other when two plates collide. The plate which is being forced down, the subducted plate, is pushed against the upper, over-riding plate. Sediment on the ocean floor of the subducting plate is often scraped off as the plate descends, this accumulated material is called an accretionary wedge (or accretionary prism), which is pushed against and attaches to the upper plate. In addition to accumulated ocean sediments, volcanic island arcs or seamounts present on the subducting plate may be amalgamated onto existing continental crust on the upper plate, increasing the continental landmass.
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Mariana Plate Boundary. 1 is West Mariana Ridge, 2 is Mariana Trough, 3 is Mariana Arc, 4 is Mariana Fore-Arc, 5 is Mariana Trench The tectonic plate is approximately 100 km thick and converging to the east at a rate of 50–80 mm/yr with the Pacific Plate subducting at 60–100 mm/yr This eastern subduction is divided into the Mariana Trench, which forms the southeastern boundary, and the Izu-Ogasawara Trench the northeastern boundary. The Izu-Ogasawara Trench and Mariana subduction zones are traveling at different rates. While the northern section of the Izu-Ogasawara Trench plate is subducting at 44 mm/yr, the southern section subducts at 14 mm/yr.
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Spatial patterns of seismicity are essential for locating and understanding the morphology and rheology of subducting lithospheric slabs, and this is particularly true for the IBM Wadati–Benioff zone (WBZ). first outlined the most important features of the IBM WBZ. Their study detected a zone of deep earthquakes beneath the southern Marianas and provided some of the first constraints on the deep, vertical nature of subducting Pacific lithosphere beneath southern IBM. They also found a region of reduced shallow seismicity (≤70 km) and an absence of deep (≥ 300 km) events beneath the Volcano Islands adjacent to the junction of the Izu Bonin and Mariana trenches, where the trench trends nearly parallel to the convergence vector.
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Melt production and accretion of melt onto continental crust in a subduction zone A subduction zone is a region of the earth's crust where one tectonic plate moves under another tectonic plate; oceanic crust gets recycled back into the mantle and continental crust gets created by the formation of arc magmas. Arc magmas account for more than 20% of terrestrially produced magmas and are produced by the dehydration of minerals within the subducting slab as it descends into the mantle and are accreted onto the base of the overriding continental plate. Subduction zones host a unique variety of rock types created by the high-pressure, low-temperature conditions a subducting slab encounters during its descent.Zheng, Y.-F.
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The d'Entrecasteaux () Ridge (DER) is a double oceanic ridge in the south-west Pacific Ocean, north of New Caledonia and west of Vanuatu Islands. It forms the northern extension of the New Caledonia–Loyalty Islands arc, and is now actively subducting under the Vanuatu/New Hebrides arc. The subduction of the DER is responsible for the anomalous morphology of the central part of New Hebrides arc whose movement more closely matches the north-east direction of the subducting Australian Plate (the rest of the New Hebrides arc rotate west in front of the southward expanding North Fiji Basin). The name honours French naval officer Antoine Bruni d'Entrecasteaux, explorer of the south-west Pacific in the late 18th century.
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This melt may also rise along pre-existing fractures, and be emplaced in the crust above the subducting slab or erupted at the surface. REE enriched deposits forming from these melts are typically S-Type granitoids. Alkaline magmas enriched with rare-earth elements include carbonatites, peralkaline granites (pegmatites), and nepheline syenite.
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It is part of the Luzon Volcanic Arc. Magma was formed from subducting oceanic crust under compression about 25 km deep. The andesite rock contains some visible crystals of pyroxene or amphibole. The geochemistry of the rock shows it is enriched in potassium, strontium and rubidium and light rare earth elements.
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The magmas originated in a parcel of Earth's mantle that was metasomatized by fluid derived from the tectonic plate that was subducting beneath what is now Chile. A nearby gabbro body, the Coloso Coastal Gabbro, is thought to share the same origin as the volcanic rocks of La Negra Formation.
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Gorda plate motions from magnetic anomaly analysis. Earth and Planetary Science Letters, 51(1), 163-170. The northerly side is a transform boundary with the Juan de Fuca Plate, the Blanco Fracture Zone. The subducting Gorda Plate is connected with the volcanoes in northern California, namely, Mount Shasta and Lassen Peak.
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Crustal erosion of the forearc basin has resulted in the loss of of the South American Plate since 11 Ma. The forearc basin of Pisco located above the subducting ridge has experienced uplift since the Late Pliocene or Pleistocene an uplift that is attributed to the subduction of the Nazca Ridge.
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Malpelo, South American and Caribbean Plates The Bucaramanga-Santa Marta Fault system is located in northwestern South America, on the North Andes Plate, where the /yr east to southeastward moving Caribbean,Egbue et al., 2014, p.9 /yr eastward subducting Malpelo,Colmenares & Zoback, 2003, p.721 and South American Plates converge.
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It is now being squeezed by the Arabian Plate from the east and forced toward the west as the Eurasian Plate to its north is blocking motion in that direction. The African Plate is subducting beneath the Anatolian Plate along the Cyprus and Hellenic Arcs offshore in the Mediterranean Sea.
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Intraslab earthquakes in Cascadia occur in areas where the subducting plate has high curvature. Much of the seismicity that occurs off the coast of northern California is due to intraplate deformation within the Gorda Plate. Similar to the distribution of interplate earthquakes in Cascadia, intraslab earthquakes are infrequent in Oregon.
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The Australian Plate is subducting eastward along the western margin of the NFB, the New Hebrides Trench. The transition between these opposed subduction systems is the Fiji Fracture Zone, a complex left- lateral succession of ridges and faults north of Fiji that extends into the North Fiji and Lau basins respectively.
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This left-lateral strike-slip fault extends NW-SE (N30 – 40 W) accommodating the lateral oblique motion of the subducting Philippine Sea Plate with respect to the Philippine Trench.Besana, G.M., Ando, M., 2005. The central Philippine Fault Zone: Location of great earthquakes, slow events, and creep activity. Earth Planets Science 57, 987–994.
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Oceanic trenches are narrow topographic lows that mark convergent boundaries or subduction zones. Oceanic trenches average wide and can be several thousand kilometers long. Oceanic trenches form as a result of bending of the subducting slab. Depth of oceanic trenches seems to be controlled by age of the oceanic lithosphere being subducted.
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The partial melting of the subducting slab formed granites and volcanic rocks like adakites and sanukitoids. Between 2.0-1.95 billion year ago, sedimentary rocks deposited on the stable passive margins of continent in the northern Ordos Block. The final assembly of the Western Block took place at approximately 1.95 billion years ago.
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Lau Basin is a young basin (<= 5 m.y. old) that separates a previously continuous island arc by extensional rifting. During the Pliocene, the Pacific plate was subducting beneath the Australian plate. The slab of the Pacific plate melted as it was thrust down, and then rose to form the original Tonga-Kermadec Ridge.
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57 The Bucaramanga Fault intersects with the Boconó Fault at the Santander Massif.Diederix et al., 2009, p.19 In this area, the top of the subducting slab has been estimated at an initial depth of approximately , then a horizontal part for about , and a farther descending section to reach a depth of around .
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A single peak is seen in all seismological data at which is predicted by the single transition from α- to β- Mg2SiO4 (olivine to wadsleyite). From the Clapeyron slope the Moho discontinuity is expected to be shallower in cold regions, such as subducting slabs, and deeper in warmer regions, such as mantle plumes.
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The subducting Pacific plate was old, cold and dense, easily sinking into the mantle at a steep angle. The hinge zone of the plate also migrated oceanwards over time. So the trench retreated oceanwards, and the old trench and ocean floor become part of the continental plate. Volcanoes formed inwards from the trench.
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Crystalline igneous rocks of the subducting slab, such as gabbro and basaltic sheeted dikes, remain stable until greater depth, when the sodium endmember of plagioclase feldspar, albite, replaces detrital igneous plagioclase feldspar. Also at greater depth in the zeolite facies, the zeolite laumontite replaces the zeolite heulandite and the phyllosilicate chlorite is common.
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Isacks, B. & Molnar, P. (1971). Distribution of stresses in the descending lithosphere from a global survey of focal-mechanism solutions of mantle earthquakes, Reviews of Geophysics and Space Physics, 9, 103–174.Marius Vassiliou (1984). "Stresses in Subducting Slabs as Revealed by Earthquakes Analysed by Moment Tensor Inversion," Earth Planet. Sci. Lett.
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The origin of igneous rock, or petrogenesis , in continental arcs is more complicated than that in oceanic arcs. The partial melting of the subducting oceanic slab generates primary magma, which would be contaminated by the continental crust materials when it travels through the crust. Because the continental crust is felsic or silica while the juvenile primary magma is typically mafic, the composition of magmas in continental arcs is the product of mixing between igneous differentiation of mafic magmas and felsic or silica crust meltings. The mixing of existing continental crust, lower part of lithosphere or lithospheric mantle under the continental crust, the subducting oceanic crust and sediments, the mantle wedge and the underplates materials together is the main source of continental arc rocks.
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In the area of Laguna del Maule, the subducting Nazca plate reaches a depth of and is 37million years old. During the Late Miocene, the convergence rate was higher than today and the Malargüe fold belt formed east of the main chain in response. The Moho is found at depths of beneath the volcanic field.
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The Charcot Plate was a fragment of the Phoenix Plate. The Charcot Plate is subducting under West Antarctica. The subduction of the Charcot Plate stopped before 83 Ma, and became fused onto the Antarctic Peninsula. Researchers have suggested that there are remnants of the western part of the Charcot Plate in the Bellingshausen Sea.
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Structure of the Cascadia subduction zone. The Juan de Fuca Plate is subducting northeastward under the North American Plate. Nonvolcanic, episodic tremor was first identified in southwest Japan in 2002. Shortly after, the Geological Survey of Canada coined the term "episodic tremor and slip" to characterize observations of GPS measurements in the Vancouver Island area.
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Seismic activity along the Japan Trench occurs along the associated subduction zone at disruptive convergent plate boundaries between the Okhotsk and subducting Pacific plate. The continuing movement along these plate boundaries occur at a depth of about .Table showing earthquakes and their magnitudes observed over the past century along the Japan Trench subduction zone.
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The addition of water lowers the melting point of the mantle material above the subducting slab, causing it to melt. The magma that results typically leads to volcanism. At zones of ocean-to-ocean subduction (e.g. Aleutian islands, Mariana Islands, and the Japanese island arc), older, cooler, denser crust slips beneath less dense crust.
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Volcanic activity in the belt is usually linked to the dehydration of the subducting slabs, which causes water and other subducted components to be added to the overlying mantle. In the case of the CVZ, this addition generates magmas that are further modified by the thick crust in the area, forming andesites, dacites and rhyolites.
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The Tonga plate is subducting the Pacific plate along the Tonga Trench. This subduction turns into a transform fault boundary north of Tonga. An active rift or spreading center separates the Tonga from the Australian plate and the Niuafo’ou microplate to the west. The Tonga plate is seismically very active and is rotating clockwise.
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This was an interplate earthquake between the Eurasian Plate and the Philippine Sea Plate. In this region, the Philippine Sea Plate is subducting beneath the Eurasian Plate. The subduction interface around this region include the Nankai Trough and the Ryukyu Trench. This earthquake is the strongest event recorded in the Hyūga-nada Sea region.
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Subducting plates are colder than the mantle into which they are moving. This creates a fast anomaly that is visible in tomographic images. Both the Farallon plate that subducted beneath the west coast of North America and the northern portion of the Indian plate that has subducted beneath Asia have been imaged with tomography.
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This subducting plate system has formed the Cascade Range, the Cascade Volcanic Arc, and the Pacific Ranges, along the west coast of North America from southern British Columbia to northern California. These in turn are part of the Pacific Ring of Fire, a much larger-scale volcanic feature that extends around much of the rim of the Pacific Ocean.
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Evidence supports that the force of gravity will increase plate velocity. As the relatively cool subducting slab sinks deeper into the mantle, it is heated causing dehydration of hydrous minerals. This releases water into the hotter asthenosphere, which leads to partial melting of asthenosphere and volcanism. Both dehydration and partial melting occurs along the isotherm, generally at depths of .
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A small portion of the continental crust may be subducted until the slab breaks, allowing the oceanic lithosphere to continue subducting, hot asthenosphere to rise and fill the void, and rebound of the continental lithosphere. Evidence of this continental rebound include ultrahigh pressure metamorphic rocks which form at depths of that are exposed at the surface.
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A good example for Cenozoic radiolarites are radiolarian clays from Barbados found within the Oceanic Group. The group was deposited in the time range Early Eocene till Middle Miocene on oceanic crust which is subducting now under the island arc of the Lesser Antilles.Speed, R. C. & Larue, D. K. (1982). Barbados architecture and implications for accretion.
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They can be produced by slip along the subduction thrust fault or slip on faults within the downgoing plate, as a result of bending and extension as the plate is pulled into the mantle. The deep-focus earthquakes along the zone allow seismologists to map the three- dimensional surface of a subducting slab of oceanic crust and mantle.
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This tectonic rotation began in Early Miocene Time and continues today. The total rotation is about 90° in the Western Transverse Ranges and less (about 40°) in the eastern ranges. Catalina Island shows the most rotation: almost 120°. A mechanism proposed for the rotation event is capture of the subducting Monterey plate by the outboard Pacific plate.
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The slip of the earthquake was estimated to be about . The locations of aftershocks were distributed roughly in N-S direction. It has been suggested that this earthquake was related to the dehydration of the Philippine Sea Plate slab. In this region, a strong earthquake occurred in 1905, which was also an intraslab event within the subducting plate.
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Martin et al. (2019) give their preferred location as just west of Simeulue, coincident with a major barrier to rupture propagation along the megathrust caused by a ridge associated with a fracture zone on the subducting plate. This location is in a similar part of the megathrust as the epicentre of the 2010 Mentawai tsunami earthquake.
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As the Pacific Plate subducts beneath the Mariana Plate, it creates a trench. This is the Mariana Trench, and it is the deepest trench in the world. Another result from this subduction are the Mariana Islands. These are formed from dehydration of the subducting, old oceanic crust creates melt, and the melt rises to the surface through a volcano.
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Southwestern Mexico lies above the convergent boundary where the Cocos Plate is being subducted below the North American Plate at a rate of 6.4 cm/yr. The dip of the subducting slab is about 15° as defined by focal mechanisms and earthquake hypocenters. Seismicity in this area is characterised by regular megathrust earthquakes along the plate interface.
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The rupture was on a normal fault, at ~107 km depth. Based on the geometry of the slab, and the relative movement of the tectonic plates, the slip vector is likely to have been oblique down-dip towards the ESE. The fault plane appears to be oblique, striking NW-SE and cutting steeply into the subducting slab.
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Arc magmas and the continental crust formed from arc magmas are enriched in boron, lead, arsenic, and antimony derived from the dehydration within the subducting slab. Hydrothermal fluids released from the slab mobilize these elements and allow them to be incorporated into arc magmas, distinguishing arc magmas from those produced at mid-ocean ridges and hotspots.
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The subducting slab is depleted in these water-mobile elements (e.g., K, Rb, Th, Pb) and thus relatively enriched in elements that are not water-mobile (e.g., Ti, Nb, Ta) compared to both mid-ocean ridge and island arc basalts. Ocean island basalts are also relatively enriched in immobile elements relative to the water-mobile elements.
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The high water contents of back-arc basin basalt magmas is derived from water carried down the subduction zone and released into the overlying mantle wedge. Additional source of water could be the eclogitization of amphiboles and micas in the subducting slab. Similar to mid-ocean ridges, back-arc basins have hydrothermal vents and associated chemosynthetic communities.
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Hypothesized Archean hot subduction induced Archean TTG generation model. The heavier oceanic crust sinks into the lighter mantle. The subducting slab is young and hot, thus when it is heated, it partially melts to generate TTG magmas, which rise and intrude into the continental crust. Light green: continental crust; dark green: oceanic crust; red: TTG melts; orange: mantle.
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Farther south, the Rivera Plate is bordered by the Cocos Plate which is also subducting beneath Mexico. The relatively oblique subduction of the Cocos Plate may be responsible for the Colima graben, while another theory postulates that the Colima graben is an extension of the East Pacific Rise. The Riviera Plate is a remnant of the Farallon Plate.
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The western side, the plate is bounded by the Okhotsk Plate at the Kuril-Kamchatka Trench and the Japan Trench, forms a convergent boundary by subducting under the Philippine Sea Plate creating the Mariana Trench, has a transform boundary with the Caroline Plate, and has a collision boundary with the North Bismarck Plate. In the south-west, the Pacific Plate has a complex but generally convergent boundary with the Indo-Australian Plate, subducting under it north of New Zealand forming the Tonga Trench and the Kermadec Trench. The Alpine Fault marks a transform boundary between the two plates, and further south the Indo-Australian Plate subducts under the Pacific Plate forming the Puysegur Trench. The southern part of Zealandia, which is to the east of this boundary, is the plate's largest block of continental crust.
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South of Taiwan, the Philippine Sea Plate is subducting under the Sunda Plate, forming the Luzon Volcanic Arc (including Green Island and Orchid Island). The east and south of the island are a complex system of belts formed by, and part of the zone of, active collision between the North Luzon Trough portion of the Luzon Volcanic Arc and the Eurasian Plate, where accreted portions of the Luzon Arc and Luzon forearc form the eastern Coastal Range and parallel inland Taitung Longitudinal Valley of Taiwan respectively.Clift, Schouten and Draut (2003) in Intra-Oceanic Subduction Systems: Tectonic and Magmatic Processes, p84–86 To the northeast, the Philippine Sea Plate is subducting under the Okinawa Plate, forming the Ryukyu Volcanic Arc. Taiwan seismicity, showing both magnitude and depth of earthquakes.
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The vector of a plate's motion is a function of all the forces acting on the plate; however, therein lies the problem regarding the degree to which each process contributes to the overall motion of each tectonic plate. The diversity of geodynamic settings and the properties of each plate result from the impact of the various processes actively driving each individual plate. One method of dealing with this problem is to consider the relative rate at which each plate is moving as well as the evidence related to the significance of each process to the overall driving force on the plate. One of the most significant correlations discovered to date is that lithospheric plates attached to downgoing (subducting) plates move much faster than plates not attached to subducting plates.
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This sea-floor formed at the extinct Osbourn Trough, located just north of the Louisville Seamount Chain. Abyssal hills on the subducting sea-floor are oriented perpendicular to the old spreading centre and the sea-floor is 72–80 Ma near the Louisville seamounts at the northern end and more than 100 Ma near Hikurangi Plateau at the southern end. There are no seamounts on the sea-floor near the Kermadec Trench except one sitting on the trench slope at which has been dated to 54.8±1.9 Ma. The Hikurangi Plateau formed part of the Ontong-Java-Manihiki-Hikurangi large igneous province (LIP) during the Ontong Java Event 120 . The Manihiki Plateau is currently subducting under the southern part of the Kermadec Arc but most of it has already been subducted.
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Orogeny is the process of mountain building. Subducting plates can lead to orogeny by bringing oceanic islands, oceanic plateaus, and sediments to convergent margins. The material often does not subduct with the rest of the plate but instead is accreted (scraped off) to the continent, resulting in exotic terranes. The collision of this oceanic material causes crustal thickening and mountain-building.
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These convection cells bring hot mantle material to the surface along spreading centers creating new crust. As this new crust is pushed away from the spreading center by the formation of newer crust, it cools, thins, and becomes denser. Subduction initiates when this dense crust converges with the less dense crust. The force of gravity helps drive the subducting slab into the mantle.
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When oceanic lithosphere and continental lithosphere collide, the dense oceanic lithosphere subducts beneath the less dense continental lithosphere. An accretionary wedge forms on the continental crust as deep-sea sediments and oceanic crust are scraped from the oceanic plate. Volcanic arcs form on continental lithosphere as the result of partial melting due to dehydration of the hydrous minerals of the subducting slab.
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More importantly, there is a relatively thin magmatic arc and pre-existing fault dipping towards the subducting plate at the overriding plate. The detachment of the pre-existing fault occurs when buoyant continental margin is in contact with the overriding plate. It is because the buoyant margin resists subduction and significantly increases the frictional force in the contact region. The subduction then stops.
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Power outage occurred in the prefectures of Hiroshima, Ehime, Okayama, Yamaguchi, and Kōchi. The maximum intensity was shindo lower 6 in Hiroshima. This earthquake could be felt along the eastern and southern coasts of South Korea. The released seismic moment of the earthquake was 1.3×1019 Nm. This earthquake is a normal faulting intraslab event within the subducting Philippine Sea Plate.
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Sakhalin Island Arc is an ancient volcanic arc dating from the Early Miocene. The arc was a result of the Okhotsk Plate subducting beneath the Eurasian Plate in the convergence zone. The arc runs from mainland Asia through Sakhalin Island into central Hokkaido and the collision zone around the Daisetsuzan Volcanic Group, where the Kuril Island Arc and the Northeastern Japan Arc meet.
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These tomographic images show a low velocity, high attenuation region above the subducting slab. The slowest velocities in these volcanic arc regions are Vp= 7.4 km·s−1 and Vs= 4 km·s−1. Mantle wedge regions that do not have associated arc volcanism do not show such low velocities. This can be attributed to the melt production in the mantle wedge.
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This is the most common theory on flow within the mantle, although opposing theories do exist (6). Flow within the mantle wedge is parallel to the crust until it reaches the relatively cooler nose of the wedge, then is overturned and is parallel to the subducting slab. The nose of the wedge is generally isolated from the overall mantle flow.
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The Timor Plate is a microplate in southeast Asia carrying the island of Timor and surrounding islands. The Australian Plate is subducting under the southern edge of the plate, while a small divergent boundary is located on the eastern edge. Another convergent boundary exists with the Banda Sea Plate to the north, and to the west is a transform boundary.
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This subducting slab melted, and the rising magma gravitationally differentiated into a more granitic composition, characteristic of continental crust. The result of testing and putting together information has led scientists to believe that crustal growth began approximately 3.8 billion years ago. and continued building slowly, in a sequence of comparatively brief episodes. Then crust quickly stabilized about 2.975 billion years ago.
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During the Cretaceous, the Tethys Sea was rich in limestone deposits. By subducting this carboniferous platform, the resulting magma would have become more carbon dioxide rich. Because carbon dioxide dissolves into melts well, it would have remained dissolved until the confining pressure of the magma was low enough to de-gas and release massive quantities of carbon dioxide into the atmosphere causing warming.
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This deformation may have been a result of the coupling between the subducting Farallon plate and the overlying North American plate. Crustal thickening occurred due to Laramide compression. After the Laramide Orogeny and until 20 Ma, a major period of volcanic activity occurred throughout the southwestern United States. Injection of hot magmas weakened the lithosphere and allowed for later extension of the region.
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The reaction is listed below. Antigorite = Forsterite + Enstatite + H2O Transition into the eclogite facies is proposed to be the source of earthquakes at depths greater than 70 km. These earthquakes are caused by the contraction of the slab as minerals transition into more compact crystal structures. The depth of these earthquakes on the subducting slab is known as the Wadati–Benioff zone.
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The yellow line is the Suruga trough, part of the longer Nankai trough in red is a trough that lies off the coast of Suruga Bay in Japan, forming part of the Nankai Trough, the latter being responsible the source of many large earthquakes in Japan's history. Both mark the boundary of the Philippine Sea Plate subducting under the Amurian Plate.
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Seismic tomography can resolve anisotropy, anelasticity, density, and bulk sound velocity. Variations in these parameters may be a result of thermal or chemical differences, which are attributed to processes such as mantle plumes, subducting slabs, and mineral phase changes. Larger scale features that can be imaged with tomography include the high velocities beneath continental shields and low velocities under ocean spreading centers.
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The Ocean Bottom Seismology (OBS) Lab develops and operates instruments used to measure deformation of the ocean floor in cooperation with the NSF's National Ocean Bottom Seismograph Instrumentation Pool (OBSIP). These instruments permit the study of such phenomena as seafloor spreading and the formation of new crust, convective and hydrothermal processes beneath the seafloor, and the fate of subducting slabs.
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The Punta de Choros Metamorphic Complex is a large coherent group of metamorphic rocks –in other words a geologic complex– of the Chilean Coast Range in northern Chile. It consists mainly of micaschists, greenschists and other low-grade metasediment. The complex was formed by the metamorphism of sediments and associated mafic rocks at the interface between a subducting plate and the overriding plate.
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Like the earlier Intermontane Islands, the large size of the islands prevented them from being pushed under the North American Plate. Instead, the Insular Islands were crumpled and crushed along the shoreline of North America to become part of the continent. The Insular Plate stopped subducting under North America; the subduction zone moved to the Farallon Trench further westward."The Coast Range Episode".
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These terranes represent a variety of tectonic environments. Some are ancient island arcs, similar to Japan, Indonesia and the Aleutians; others are fragments of oceanic crust obducted onto the continental margin while others represent small isolated mid-oceanic islands. Sketch of an oceanic plate subducting beneath a continental plate at a collisional plate boundary. The oceanic plate typically sinks at a high angle (exaggerated here).
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The subducting slab undergoes backward sinking due to the negative buoyancy forces causing a retrogradation of the trench hinge along the surface. Upwelling of the mantle around the slab can create favorable conditions for the formation of a back-arc basin. Seismic tomography provides evidence for slab rollback. Results demonstrate high temperature anomalies within the mantle suggesting subducted material is present in the mantle.
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In Turonian times frontal elements of the Fatric Nappe System of the Inner Western Carpathians were emplaced onto the southern parts of the Vahic Ocean. In the Upper Cretaceous to Paleocene the Vahic Ocean began to close. The Oravic units were detached from its subducting basement and formed a fold and thrust belt. After first phase of folding and thrusting sedimentation of turbiditic sequences was restored.
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The magma source is the western extremity of the Ryukyu Volcanic Arc formed when the subducting Philippine Sea Plate was compressed below the edge of the Eurasian Plate at about 20 to 30 km deep. The magma was contaminated with continental crust material. Geochemistry of the rock shows that iron, aluminium, titanium, potassium, rubidium and strontium are enriched, but sodium, magnesium and nickel are impoverished.
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Deep-focus earthquakes have been shown to contain a combination of these sources. The focal mechanisms of deep earthquakes depend on their positions in subducting tectonic plates. At depths greater than 400 km, down-dip compression dominates, while at depths of 250-300 km (also corresponding to a minimum in earthquake numbers vs. depth), the stress regime is more ambiguous but closer to down-dip tension.
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Pocho volcanic field is a volcanic field in Argentina. It is associated with a crustal lineament known as the Ojo de Agua Lineament. It is located in the Sierras de Cordoba mountain chain. It formed during the late Miocene, when a progressive shallowing of the subducting Nazca Plate caused volcanic activity to retreat from the main Andes into the land behind the mountain chain.
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The Okinawa trough in context of back-arc basins of the world. The (also called ', literally China-Ryukyu Border Trough' ) is a seabed feature of the East China Sea. It is an active, initial back-arc rifting basin which has formed behind the Ryukyu arc-trench system in the West Pacific. It developed where the Philippine Sea Plate is subducting under the Eurasia Plate.
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She showed that young volcanoes could flex the lithosphere, influencing the elevation of nearby volcanoes, and used a 3-D analysis of topography and gravity data to show that the Australian plate could be strong on short time scales and weak on long scales. She also showed how subducting ocean plates could weaken and identified a large topographic feature called the South Pacific superswell.
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During the last half of the Mesozoic Era, the Age of the Dinosaurs, much of today's California, Oregon, and Washington were added to North America. western North America suffered the effects of repeated collision as slabs of ocean crust sank beneath the continental edge. Slivers of continental crust, carried along by subducting ocean plates, were swept into the subduction zone and scraped onto North America's edge.
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The Ogasawara (Bonin) Islands were formed around 48 million years ago. They are a part of the Izu-Bonin-Mariana Arc known geologically as a fore arc. They lie above a subduction zone between the Pacific Plate and the Philippine Sea Plate. The Pacific Plate is subducting under the Philippine Sea Plate, which creates an oceanic trench to the east of the islands: the Bonin Trench.
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The Jom-Bolok volcanic field lies in the over high East Sayan Mountains and is far removed from the major plate boundaries around Asia. It may be under the influence of the subducting Pacific plate regardless, as well as of the India-Asia collision. Other volcanic fields within of Jom-Bolok are the Hangai, Khamar-Daban, Oka, Tuva and Vitim fields. These volcanic fields extend into Mongolia.
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Tectonically, movements of the plates and a sea level fall could cause an additional 4.8 degrees Celsius globally. The combined effect between magmatic and tectonic processes could have placed the Cretaceous Earth 7.6 to 12.5 degrees Celsius higher than today. A second theory on the warm Cretaceous is the subduction of carbonate materials. By subducting carboniferous materials, a release of carbon dioxide would emit from volcanoes.
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This fast subduction has broken off the southern part of the South American Plate between the north- eastern end of the South Sandwich Arc and the Mid-Atlantic Ridge, leaving a separate microplate called 'Sur' (Spanish for 'South') north of the SAAR. The southern part of this Sur microplate has probably also been broken off and is subducting independently under the South Sandwich Arc.
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The conditions within the subducting slab as it plunges toward the mantle in a subduction zone also produce regional metamorphic effects, characterized by paired metamorphic belts. The techniques of structural geology are used to unravel the collisional history and determine the forces involved. Regional metamorphism can be described and classified into metamorphic facies or metamorphic zones of temperature/pressure conditions throughout the orogenic terrane.
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Many seismologists refer to the active segment as the Mendocino Fault or Mendocino fault zone. The fault section demarcates the boundary between the northwestward-moving Pacific Plate and the eastward-moving Gorda Plate. The Gorda Plate is subducting beneath the North American Plate just offshore of Cape Mendocino. Where the Mendocino Fault intersects the undersea trench of the subduction zone, it also meets the San Andreas Fault.
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Central Chile lies on the destructive plate boundary where the Nazca Plate is being subducted beneath the South American Plate. The rate of convergence at this boundary in central Chile is about 74 mm per year. The boundary has a long history of destructive earthquakes and damaging tsunamis. Events occur on the plate interface and within both the subducting slab and the over-riding plate.
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The main components of the rocks at La Breña-El Jagüey are clinopyroxene, ilmenite, olivine, plagioclase and titanomagnetite, with rocks sporting variable textures. The participation of water in the formation process of these magmas is debatable; the rocks may have been influenced by sediments from the uppermost part of the subducting Farallon slab. These rocks are of mafic intraplate geochemistry. The rocks contain mantle xenoliths.
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Aside from triggering mantle melt, this reaction may also trigger partial melting of the subducting slab itself. Phlogopite + Diopside + Orthopyroxene = H2O + Melt Lawsonite remains stable up to 1080 °C and 9.4 GPa. the breakdown of lawsonite releases massive amounts of H2O into the mantle that can trigger partial melting of the slab and of the overlying mantle. The breakdown reaction of lawsonite is listed below.
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Sediment cover slows the cooling and reduces the flow of water. There is little evidence of microbe activity in older (more than 10 million year old) crust. Near subduction zones, volcanoes can form in island arcs and back- arc regions. The subducting plate releases volatiles and solutes to these volcanoes, resulting in acidic fluids with higher concentrations of gases and metals than in the mid-ocean ridge.
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The extension of the crust behind volcanic arcs is believed to be caused by processes in association with subduction. As the subducting plate descends into the asthenosphere it is heated up causing the volcanism at the island arcs. Another result of this heating is a convection cell is formed (See figure 1). The rising magma and heat in the convection cell cause a rift to form.
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In the Lau Basin east of the NFB the Pacific plate is subducting westward under Tonga trench in the highest rate of back-arc rifting known — where the Louisville seamount chain subducts under the Tonga trench rifting propagates at . This seamount chain–trench intersection propagates southward at a rate of and, as a consequence, Tonga Islands rotate clockwise at a rate of 9.3°/Ma.
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The primary tectonic driving force behind this explosive volcanic activity is slab rollback. During the Laramide orogeny, the subducting Farallon Plate subducted at a very shallow angle. When this stopped, the mantle wedge was opened up, and the result was the flare-up. The specifics of this opening, including possible windows or buckling of the plate, can explain specific volcanic trends within the flare-up.
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Since then, geologists have applied this model to other regions such as the Solonker Suture Zone of the Central Asian Orogenic belt, the Jiangnan Orogen, the Lhasa–Qiangtang collision zone and the Baker terrane boundary. Active examples of this system are 1) the Molucca Sea Collision Zone in Indonesia, in which the Molucca Sea plate subducts below the Eurasian plate and the Philippine Sea plate on two sides, and 2) the Adria microplate in the Central Mediterranean, subducting both on its western side (beneath the Apennines and Calabria) and on its eastern side (beneath the Dinarides). Note that the term "divergent" is used to describe one oceanic plate subducting in different directions on two opposite sides. It should not be confused with use of the same term in 'divergent plate boundary' which refers to a spreading center that separates two plates moving away from each other.
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As the Farallon Plate made contact with the North American Plate and began subducting beneath it, it fragmented into the Juan de Fuca Plate and Cocos Plate, and then later fragmented further to form the Rivera Plate. Once the Pacific-Farallon Ridge began subducting beneath the North American Plate, the remains of the Farallon Plate broke apart to form the Monterey, Arguello, Magdalena, and Guadelupe Microplates, and the southern portion of the ridge rotated in a clockwise manner. The contact of the ridge with North America marked a transition of the Pacific-Farallon Ridge from being a globally oriented spreading ridge system to a locally oriented one. The distinction between these systems is that slab pull and gravitational gliding forces determine the characteristics of the globally oriented whereas those of the locally oriented are influenced by the contact of the ridge with the North American Plate.
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Today the Japanese archipelago is considered a mature island arc and is the result of several generations of subducting plates. Approximately 15,000 km of oceanic floor has passed under the Japanese area in the last 450 million years, with most being fully subducted. Japan is situated in a volcanic zone on the Pacific Ring of Fire. Frequent low intensity earth tremors and occasional volcanic activity are felt throughout the islands.
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As data accumulated, a common view developed that one large oceanic plate, the Farallon plate, acted as a conveyor belt, conveying terranes to North America's west coast, where they accreted. As the continent overran the subducting Farallon plate, the denser plate became subducted into the mantle below the continent. When the plates converged, the dense oceanic plate sank into the mantle to form a slab below the lighter continent..
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Taiwan has a history of many strong earthquakes. The island is located within a complex zone of convergence between the Philippine Sea Plate and Eurasian Plate. At the location of the earthquake, these plates converge at a rate of 75 mm per year. To the south of Taiwan, oceanic crust of the Eurasian Plate is subducting beneath the Philippine Sea Plate creating an island arc, the Luzon Arc.
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The volume of water escaping from within and beneath the forearc results in some of Earth's most dynamic and complex interactions between aqueous fluids and rocks. Most of this water is trapped in pores and fractures in the upper lithosphere and sediments of the subducting plate. The average forearc is underrun by a solid volume of oceanic sediment that is thick. This sediment enters the trench with 50–60% porosity.
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Accretionary wedges (also called accretionary prisms) form as sediment is scraped from the subducting lithosphere and emplaced against the overriding lithosphere. These sediments include igneous crust, turbidite sediments, and pelagic sediments. Imbricate thrust faulting along a basal decollement surface occurs in accretionary wedges as forces continue to compress and fault these newly added sediments. The continued faulting of the accretionary wedge leads to overall thickening of the wedge.
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The great thickness of the lithosphere requires that this bending be gentle. As the subducting plate approaches the trench, it first bends upwards to form the outer trench swell, then descends to form the outer trench slope. The outer trench slope is typically disrupted by a set of sub-parallel normal faults that 'staircase' the seafloor down to the trench. The plate boundary is defined by the trench axis itself.
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Subsequently, the new subducting slab develops at an overriding plate with the continuous compression. The new developing slab eventually penetrates and breaks the old slab. A new subduction zone is formed with an opposite polarity to the previous one. In reality, the magmatic arc is a relatively weak zone at the overriding plate because it has a thin lithosphere and is further weakened by high heat flow and hot fluid.
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There is also very little seismic evidence that the Juan de Fuca Plate is actively subducting. As a result, the existence of active volcanism in the Cascade Volcanic Arc is the best evidence for ongoing subduction. However, volcanic activity along the Cascade Arc has been declining over the last few million years. The probable explanation lies in the rate of convergence between the Juan de Fuca and North American plates.
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In the 1980s and 1990s, a number of teams began mapping the structures in the lower crust by seismology. The result was a number of detailed geological cross-sections of the deep structures below the Alps. When seismic research is combined with insights from gravitational research and mantle tomography the subducting slab of the European plate can be mapped. Tomography also shows some older detached slabs deeper in the mantle.
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The Grenada Basin has no active spreading center. The basin geology is influence by the interactions between the Caribbean Plate and the North and South American Plates. The eastern edge of the Caribbean plate is marked by subduction zones, with the North American plate and South American plate subducting beneath the Caribbean plate. The Caribbean plate is currently migrating eastward at 20mm/yr relative to the North and South American plates.
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Mathematical modelling has successfully reproduced the periodicity of episodic tremor and slip in the Cascadia region by incorporating this dehydration effect. In this interpretation, tremor may be enhanced where the subducting oceanic crust is young, hot, and wet as opposed to older and colder. However, alternative models have also been proposed. Tremor has been demonstrated to be influenced by tides or variable fluid flow through a fixed volume.
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Many estimates have been made for the epicentre of this earthquake. Most of the early estimates of the location place it in the outer rise of the subducting plate rather than on the plate interface. Such earthquakes can generate tsunamis, but are highly unlikely to be tsunami earthquakes. More recent estimates give a range of epicentres, including some located on a shallow part of the megathrust, although the uncertainties remain large.
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The San Andreas Fault is a northwest-striking transform fault that accommodates motion between the Pacific and North American Plates. The Mendocino Triple Junction is an area of high seismicity, and marks its northern extremity at the Gorda Plate, which is subducting beneath the North American Plate. Three moderate events in the San Francisco Bay Area occurred on or near the San Andreas Fault in the early nineteenth-century.
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The Solomon archipelago was formed by the convergence of the Indo-Australian and Pacific Plates. The Indo-Australian Plate and the smaller Solomon Sea Plate are subducting beneath the Pacific Plate along the New Britain–San Cristobal oceanic trench, which runs south of and parallel to the archipelago in the Solomon Sea.Holl, Heinz-Gerd. (2013). Geology of the Solomon Islands and Geological Fieldwork Savo Island, April 2013. 10.13140/RG.2.2.18448.00001.
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The Peru–Chile Trench, also known as the Atacama Trench, is an oceanic trench in the eastern Pacific Ocean, about off the coast of Peru and Chile. It reaches a maximum depth of below sea level in Richards Deep () and is approximately long; its mean width is and it covers an expanse of some . The trench delineates the boundary between the subducting Nazca Plate and the overriding South American Plate.
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The andesite line is the most significant regional geologic distinction in the Pacific Ocean basin. It separates the mafic basaltic volcanic rocks of the Central Pacific Basin from the partially submerged continental areas of more felsic andesitic volcanic rock on its margins. The andesite line parallels the subduction zones and deep oceanic trenches around the Pacific basin. It is the surface expression of melting within and above the plunging subducting slab.
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By contrast, the Kermadec and Tonga trenches represent the parts of the subduction zone where oceanic crust of the Pacific Plate is subducting beneath oceanic crust of the Indo-Australian Plate. Although shallower than the trenches north of it, the Hikurangi Trench reaches depths of 3,000 metres as close as 80 kilometres from shore. Its maximum depth is about .Keith B. Lewis, Jean-Yves Collott and Serge E. Lallemand (1998).
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This means lawsonite is capable of conveying appreciable water to shallow depths in subducting oceanic lithosphere (Clarke et al., 2006). Experimentation on lawsonite to vary its responses at different temperatures and different pressures is among its most studied aspects, for it is these qualities that affect its abilities to carry water down to mantle depths, similar to other OH-containing phases like antigorite, talc, phengite, staurolite, and epidote (Comodi et al.
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Regional metamorphism at extreme conditions: Implications for orogeny at convergent plate margins. Journal of Asian Earth Sciences 145, 46-73. Zeolite and prehnite-pumpellyite facies assemblages may or may not be present, thus the onset of metamorphism may only be marked by blueschist facies conditions. Subducting slabs are composed of basaltic crust topped with pelagic sediments; however, the pelagic sediments may be accreted onto the forearc-hanging wall and not subducted.
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Based on inspection of extreme metamorphism and post-subduction magmatism at convergent plate margins, paired metamorphic belts are further extended to two contrasting metamorphic facies series: one is blueschist to eclogite facies series that was produced by subducting metamorphism at low thermal gradients of <10 °C/km, and the other is amphibolite to granulite facies series that was produced by rifting metamorphism at high thermal gradients of >30 °C/km.
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"Ringwoodite lamellae in olivine: Clues to olivine–ringwoodite phase transition mechanisms in shocked meteorites and subducting slabs". PNAS. Natural ringwoodite generally contains much more Mg than Fe but can form a gapless solid solution series from the pure Mg endmember to the pure Fe endmember. The latter has been discovered in a natural sample only recently and was named ahrensite, in honor of US mineral physicist Thomas J. Ahrens (1936–2010).
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Coastal regions of Peru and Chile lie above the convergent boundary, where the Nazca Plate is being subducted beneath the South American Plate along the line of the Peru–Chile Trench. The rate of convergence across this boundary is measured at about per year. This boundary has been the site of many great megathrust earthquakes, in addition to events caused by faulting within both the subducting and over-riding plates.
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Monte Burney seen from space Monte Burney is the most southern stratovolcano of the Austral Volcanic Zone. Six Quaternary volcanoes form this long volcanic arc. The Antarctic Plate subducts beneath the South America Plate and the Scotia Plate at a pace of about , causing the volcanism. The young age of the subducting crust (12-24 million years old) gives the volcanic rocks a unique chemical composition including adakitic rocks.
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The Shetland Plate started forming 3 to 4 million years ago. Prior to formation, the Shetland Plate was part of the Antarctic Plate adjacent to the Antarctic Peninsula. During this period, the Phoenix Plate to the northwest, was subducting under the Antarctic Peninsula and the South Shetland Islands, which created the South Shetland Trench. Approximately 3 million years ago spreading stopped at the Antarctic-Phoenix spreading center in Drake Passage.
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This interpretation is based upon the abundance of phlogopite and geochemistry of light rare-earth elements that imply a geochemical contribution from subducting slab material. The composition of these ultramafic rocks is consistent with their origin by simple fractional crystallization within a pluton.Seaman, SJ, KE Karlstrom, ML Williams, and AJ Petruski (1997) Proterozoic Ultramafic Bodies in the Grand Canyon. Geological Society of America, Abstracts with Programs. 29(6):A-89.
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The U.S. Pacific Tsunami Warning Center instead reported the quake as 7.4. Venezuela's coast at Cariaco lies on the El Pilar fault of the Caribbean and South American plates, with the latter subducting under the former when the fault turns perpendicular to the coastline. Though Caracas is a long distance from the epicentre, because it is still on the fault line at the San Sebastian fault the tremor was still quite powerful. A seismologist from the University of Southampton said that the two plates usually experience "horizontal differential motion" (the Caribbean plate moves eastward, the South American plate moves westward, and they strike and catch against each other) but that the earthquake being so deep indicated that it was not "directly related to transform faulting [or] strike-slip faulting", suggesting that the quake may have been caused by the "edge of the South American plate that is subducting under the Lesser Antilles arc" being involved.
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Mexico's southwestern coast is parallel to the Middle America Trench (MAT), where the oceanic Cocos plate (a remnant of the ancient Farallon plate) is being subducted under the North American plate, resulting in many major earthquakes.. Most earthquakes observed in this region are similar to earthquakes seen at other subduction zones, but in the vicinity of Ometepec they tend to occur as doublets.. This earthquake is unique in being (circa 2013) the "best documented doublet and for which near and teleseismic data are available", and has been extensively studied.. The interruption of the main rupture that results in a doublet earthquake has been attributed to "asperities", patches in the fault where harder rock resists immediate rupture. However, study of this earthquake's aftershocks shows a discontinuity in their spatial distribution.. This has been interpreted as indicating a split in the subducting plate, where the plate is subducting at slightly different down angles on either side of the split..
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The Mount Skukum Volcanic Complex is an early Eocene caldera complex, located 43 km west of Carcross and 32 km northeast of Mount Porsild in the Yukon Territory, Canada. The complex composes the Skukum Group. It is a northeast- trending complex of subaerial volcanic and volcaniclastic rocks covering 140 km2. The Mount Skukum Volcanic Complex was formed when the ancient Kula Plate was subducting under North America during the early Eocene period.
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The Nankai Trough is the surface expression of the subduction zone between the Philippine Sea and Amur plates. Honshu itself is formed from the island arc developed over the subducting plate. The megathrust boundary extends about 700 km from the southern end of Kyūshū to the triple junction with the Okhotsk Plate near Mount Fuji. At its southwestern end, there is another triple junction, where the overriding plate becomes the Okinawa Plate.
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This earthquake occurred where the Pacific Plate is subducting under the plate beneath northern Honshu. The Pacific plate, which moves at a rate of 8 to 9 cm (3.1 to 3.5 in) per year, dips under Honshu's underlying plate, building large amounts of elastic energy. This motion pushes the upper plate down until the accumulated stress causes a seismic slip-rupture event. The break caused the sea floor to rise by several metres.
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Seafloor spreading helps explain continental drift in the theory of plate tectonics. When oceanic plates diverge, tensional stress causes fractures to occur in the lithosphere. The motivating force for seafloor spreading ridges is tectonic plate slab pull at subduction zones, rather than magma pressure, although there is typically significant magma activity at spreading ridges. Plates that are not subducting are driven by gravity sliding off the elevated mid-ocean ridges a process called ridge push.
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Subduction zones are sites of gravitational sinking of Earth's lithosphere (the crust plus the top non-convecting portion of the upper mantle). Subduction zones exist at convergent plate boundaries where one plate of oceanic lithosphere converges with another plate. The descending slab, the subducting plate, is over-ridden by the leading edge of the other plate. The slab sinks at an angle of approximately twenty-five to forty-five degrees to Earth's surface.
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Not all non-accretionary convergent margins are associated with primitive arcs. Trenches adjacent to continents where there is little influx of sediments carried by rivers, such as the central part of the Peru–Chile Trench, may also lack an accretionary prism. Igneous basement of a nonaccretionary forearc may be continuously exposed by subduction erosion. This transfers material from the forearc to the subducting plate and can be accomplished by frontal erosion or basal erosion.
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The lithosphere break-up model is simulated by hydrocarbon experiments in the laboratory. The researchers set up the setting of subduction zone which are analogized by hydrocarbons with different densities representing various layers in the subduction zone. The initial setting of the simulated subduction zone model is confined by two pistons. The piston connected to the overriding plate is locked, while the piston linking to subducting plate is subjected to a constant rate of compression.
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The main mineral is calcium rich plagioclase. The magma source is the western extremity of the Ryukyu Volcanic Arc formed when the subducting Philippines Sea Plate was compressed below the edge of the Eurasian Plate at about 20 to 30 km deep. The magma was contaminated with continental crust material. Geochemistry of the rock shows that iron, aluminium, titanium, potassium, rubidium and strontium are enriched, but sodium, magnesium and nickel are impoverished.
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The events of AD 365 and 1303 are likely to have been much larger than this. In mainland Greece, normal faulting gives earthquakes up to 7 in magnitude, while in the northern Aegean, strike-slip events with a magnitude of 7.2 have been recorded. Large intermediate depth (>50 km) earthquakes of magnitude >7 from within the subducting African Plate have been recorded but such events cause little damage, although they are widely felt.
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As a result, to the northeast of the subducting edge lies the continuous arc of volcanos —also known as the Central America Volcanic Arc— stretching from Costa Rica to Guatemala, and a belt of earthquakes that extends farther north, into Mexico. The northern boundary of the Cocos Plate is the Middle America Trench. The eastern boundary is a transform fault, the Panama Fracture Zone. The southern boundary is a mid- oceanic ridge, the Galapagos Rise.
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The total thickness of the sedimentary infill in a sag basins can thus exceed 10 km. A third type of basin exists along convergent plate boundaries – places where one tectonic plate moves under another into the asthenosphere. The subducting plate bends and forms a fore-arc basin in front of the overriding plate – the an elongated, deep asymmetric basin. Fore-arc basins are filled with deep marine deposits and thick sequences of turbidites.
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Magma chambers above a subducting plate Magma rises through cracks from beneath and across the crust because it is less dense than the surrounding rock. When the magma cannot find a path upwards it pools into a magma chamber. These chambers are commonly built up over time, by successive horizontal or vertical magma injections. Influx of new magma causes reaction of pre-existing crystals and the pressure in the chamber to increase.
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Most events occur along the main ranges running from Fiordland in the southwest to East Cape in the northeast. This axis follows the boundary between the Indo-Australian and Pacific plates. Large earthquakes are less common along the central Alpine Fault, where the plates are not subducting and the forces are accommodated in different ways. The largest city within the highest-risk zone is the nation's capital, Wellington, followed by Hastings then Napier.
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The Lau Basin in the upper part of the arc-backarc complex The Lau Basin is a back-arc basin (also addressed as “interarc basin”) at the Australian-Pacific plate boundary. It is formed by the Pacific plate subducting under the Australian plate. The Tonga-Kermadec Ridge, a frontal arc, and the Lau- Colville Ridge, a remnant arc, sit to the eastern and western sides of the basin, respectively.Gill, J. B. 1976.
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Most of Alaska consists of terranes accreted by collisions with island arcs carried in over the last 160 million years. These terranes were caused by the subduction of the Farallon, Kula, and Pacific plates sequentially. Currently, the Pacific plate is subducting beneath Alaska, producing the Aleutian arc series of volcanoes through the Alaskan Peninsula and Aleutian Islands. One of the sutures left by terrane addition is the Denali Fault, which curves through south-central Alaska.
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In general, the sedimentary basement terranes become younger from West to East across the country, as the newer terranes were scraped off the subducting paleo-Pacific Plate, and accreted to the boundary of Gondwana over hundreds of millions of years. Many rocks in the Eastern Province have been metamorphosed into the Haast Schist, due to exposure to high pressures and temperatures. Rocks grade continuously from greywacke (e.g., in Canterbury) to high-grade schist (e.g.
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388x388px The generation of tonalitic-trondhjemitic- granodioritic gneiss is associated with the formation of the magmatic arc during subduction. The geochemistry of tonalitic-trondhjemitic-granodioritic gneiss is similar to that of the calc-alkaline rocks in a continental arc under modern plate tectonics. Within the continental arc system, the subducting oceanic plate and lower continental crust were partially melted. As a result, there is a slight difference in the composition of tonalitic- trondhjemitic-granodioritic gneiss.
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Subduction has been occurring off the western margin of South America for the past 200 million years. Presently, the Nazca Plate is subducting eastward below South America. The subduction is responsible for the formation of the Altiplano high plateau; the Tibetan Plateau is the only other place in the world where oceanic subduction has generated a high plateau. Volcanism in the Andes occurs in a frontal volcanic arc, but also in the back-arc region.
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The Caribbean plate has been migrating eastward from the Pacific region and eventually collided with the South American plate in the middle Paleocene. This collision transformed the passive margin of northern South America into an active margin. The Caribbean plate had subducted significant amounts of oceanic Proto-Caribbean crust by this time and was now subducting beneath the South American crust. This boundary interaction was greatly affecting the region of northwestern South America.
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Discussed in the text are a subducting plate (5); an island arc (15) overlying a mantle wedge; a mid-ocean ridge (12); and a hotspot (3). Water is not just present as a separate phase in the ground. Seawater percolates into oceanic crust and hydrates igneous rocks such as olivine and pyroxene, transforming them into hydrous minerals such as serpentines, talc and brucite. In this form, water is carried down into the mantle.
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Nicaragua lies above the convergent boundary where the Cocos Plate is being subducted beneath the Caribbean Plate. The convergence rate across this boundary is about 73 mm per year. There have been many large earthquakes in this part of the plate boundary, including events in 1982, 2001, 2012 and 2014. The 2001 and 2014 events were a result of normal faulting within the subducting Cocos Plate, with the others representing faulting along the plate interface.
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Volcanism and tectonism in the Central Andes has been ongoing since the late Oligocene. Volcanism has been occurring in two broad regions, the principal volcanic arc and a secondary volcanic arc in the Cordillera Oriental whose origin is less clear. In that area, the Brazilian Shield subducts beneath the Andean orogen. The origin of the Macusani volcanics has been variously attributed to frictional heating of the subducting Brazilian shield, the subduction itself or a hotspot.
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A number of mechanisms have been proposed to interpret the origin of volcanism in the Anahim Volcanic Belt. This includes rift propagation and melting of mantle associated with lithospheric fracturing due to flexuring of the crust along the northern edge of the subducting Juan de Fuca Plate. However, insignificant evidence exists to support these hypotheses. The most common and best mechanism used to explain Anahim Belt volcanic activity is a stationary hotspot.
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Serpentinites are hydrated (15-16 wt.% H2O) ultramafic rocks that are composed of predominately serpentine, a weak and buoyant mineral with a broad P-T stability field, and are generally associated with subduction zones. Protoliths of serpentinites are olivine- and pyroxene-dominated. The formation of serpentinites is caused by the release of fluids from subducting hydrated oceanic slabs as they become heated with depth to a maximum temperature of 650-700 °C.
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Bicol region is highly volcanic in origin and part of the Pacific Ring of Fire. Known as the Bicol Volcanic Arc or Chain, the volcanoes are the results of the Philippine Sea Plate subducting under the Philippine Mobile Belt, along the Philippine Trench. Volcanism is evident by the number of hot springs, crater lakes, and volcanoes that dot the region starting from Mount Labo in Camarines Norte to the Gate Mountains in Matnog, Sorsogon.McDermott, Delfin, Defant, et al. (2005).
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Vrátna dolina, Slovakia The area now occupied by the Carpathians was once occupied by smaller ocean basins. The Carpathian mountains were formed during the Alpine orogeny in the MesozoicPlašienka, D., 2002, Origin and growth of the Western Carpathian orogenetic wedge during the mesozoic. (PDF) in Geologica Carpathica Special Issues 53 Proceedings of XVII. Congress of Carpathian-Balkan Geological Association Bratislava, 1–4 September 2002 and Tertiary by moving the ALCAPA, Tisza and Dacia plates over subducting oceanic crust.
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During the formation of the GLTZ, the MRV protocontinent consumed the Superior province's oceanic crust as the subprovince came in from the south. Suturing of one continental block onto another usually occurs because a subduction zone exists beneath one of the blocks. The subduction zone consumes the oceanic crust connected to the other block. After the oceanic crust is consumed, the two blocks meet and the subducting oceanic crust pulls the attached continental block under the other.
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This steadiness can be attributed to many different causes. In the case of ridge-to-ridge transforms, the constancy is caused by the continuous growth by both ridges outward, canceling any change in length. The opposite occurs when a ridge linked to a subducting plate, where all the lithosphere (new seafloor) being created by the ridge is subducted, or swallowed up, by the subduction zone. Finally, when two upper subduction plates are linked there is no change in length.
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In the north, high-velocities may reflect the remains of batholithic roots that formed as a result of continuous subduction along the northern continental margin 150 to 50 million years ago. High velocities in the south represent the subducting Juan de Fuca slab. Centered near Nazko Cone, the low-velocity zone extends to a depth of approximately . However, it may extend deeper southward beneath the Juan de Fuca Plate through the transition zone into the lower mantle.
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The North Andean convergent margin is a region of large crustal deformation. The North Andes block moves northeastwards relative to the South America at a rate of 6±2 mm/yr. The Nazca Plate is subducting beneath the South American Plate along the Colombia-Ecuador Trench. The subduction of the Carnegie Ridge into the Colombia-Ecuador Trench affected the crustal deformation in this region and the coupling between the Nazca Plate and the South America Plate.
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When the subducting slab broke off (known as slab breakoff, slab pull) and fell away, the subducted crust began moving up. This led to the uplift of the thickened continental crust which led, in the Miocene, to extension. In the case of the Alps, the extension could only take place in a west–east direction because the Adriatic plate was still converging from the south. An enormous thrustzone evolved that would later become the Periadriatic Seam.
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El Salvador lies above the convergent boundary where oceanic crust of the Cocos Plate is being subducted beneath the Caribbean Plate at rate of about 72 mm per year along the Middle America Trench. This boundary is associated with earthquakes resulting from movement on the plate interface itself, such as the 7.7 1992 Nicaragua earthquake, and from faulting within both the overriding Caribbean Plate and the subducting Cocos Plate, such as the 1982 El Salvador earthquake.
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The forearc mantle extends from where the subducting slab meets the cold nose of the mantle wedge, this occurs at depths from 10–40 km. Low seismic attenuation, and high seismic velocities characterize this region. There is a boundary between this low attenuation region and a high attenuation region on the forearc side of the arc volcanoes. To image the mantle wedge region below volcanic arcs P-wave, S-wave and seismic attenuation images should be used in coordination.
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The Queen Charlotte Basin was formed during the last 43 Ma by episodes of extension paired with a belt of subsidence and uplift. Periods of igneous activity in the Queen Charlotte Islands have corresponded with periods of extension. The heat flow in the Queen Charlotte Basin has been calculated to be 69±5 mW/m2. To the southeast the heat flow is reduced through cooling by the subducting plate, and increased to the northwest through crustal extension.
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Another model of Archean SCLM formation suggests that the SCLM formed in a subduction environment in which new Archean crust was created through slab melting. If the primitive mantle is the starting composition for this SCLM formation event, subducting slab would be composed of TTG crust, then the removal of basaltic melt and the enrichment of the mantle wedge with felsic melts could explain the formation of the depleted Archean subcontinental lithosphere. For more information, see Archean subduction.
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The Philippine Mobile Belt is between the Eurasia Plate and the Philippine Sea Plate. The Philippine Sea Plate is subducting along the Philippine Trench in this region. At the latitude of the earthquake, the Philippine Sea Plate moves in the WNW direction at a velocity of approximately 100 mm/yr with respect to the Sunda Plate. This earthquake was an intraplate earthquake greater than 50 kilometers to the east of the boundary of the Philippine Sea Plate.
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There is narrow band of deep earthquakes beneath southern IBM between ~21°N and ~17°N, but south of this there are extremely few deep events. Although early studies assumed that seismicity demarcated the upper boundary of the slab, more recent evidence has shown that many of these earthquakes occur within the slab. For instance, a study by showed that a region of events beneath northernmost IBM region occur ~20 km beneath the top of the subducting plate.
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The spatial distribution of heat flow in the vicinity of the MTJ is similar to what would be expected in a subduction environment. That is, heat flow is low above the subducting Gorda slab, between 40–50 mW/m². South of the MTJ, heat flow through the California coast is higher, around 90 mW/m². The distance south of the MTJ over which heat flow increases gives an indication of the timing of development of the heat flow anomaly.
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At the edge of the subducting Flysch Belt, sedimentary rocks are up to four kilometers thick. Central Carpathian rocks are not folded. Molasse deposits laid down in the Oligocene span into southern Slovakia from the Pannonian Basin in Hungary. The back-arc molasse formed several large basins, including the Vienna Basin, Danube Basin, South Slovak Basin and East Slovak Basin in the Neogene (the Danuba, South Slovak and East Slovak are all subdivisions of the Pannonian Basin).
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The timing of the accretion of the insular belt is uncertain, although the closure did not occur until at least 115 million years ago. Other Mesozoic terranes that accreted onto the continent include the Klamath Mountains, the Sierra Nevada, and the Guerrero super-terrane of western Mexico. 80 to 90 million years ago the subducting Farallon plate split and formed the Kula Plate to the North. Many of the major batholiths date from the late Cretaceous.
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Other Mesozoic terranes that accreted onto the continent include the Klamath Mountains, the Sierra Nevada, and the Guerrero super-terrane of western Mexico. 80 to 90 million years ago the subducting Farallon plate split and formed the Kula Plate to the North. This formed an area in what is now Northern California, where the plates converged forming a Mélange. North of this was the Columbia Embayment, where the continental margin was east of the surrounding areas.
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Japan subduction setting. The discovery of LFEs originates in Japan at the Nankai trough and is in part due to the nationwide collaboration of seismological research following the Kobe earthquake of 1995. Low frequency earthquakes in Japan were first observed in a subduction setting where the Philippine Sea plate subducts at the Nankai trough near Shikoku. The low-frequency continuous tremor researchers observed was initially interpreted to be a result of dehydration reactions in the subducting plate.
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At paths up to 220–320 °C and below 4.5 kbars, subducting slabs may encounter the prehnite-pumpellyite facies, characterized by the presence of the hydrous chlorite, prehnite, albite, pumpellyite, tremolite, and epidote and the loss of the zeolites heulandite and laumonite. Actinolite may occur at higher grade. Aside from albite, these characteristic minerals are water bearing, and may contribute to mantle melting. These minerals are also vital in the formation of glaucophane, which is associated with blueschist facies.
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The arc crust is under extension or rifting as a result of the sinking of the subducting slab. Back-arc basins were initially a surprising result for plate tectonics theorists, who expected convergent boundaries to be zones of compression, rather than major extension. However, they are now recognized as consistent with this model in explaining how the interior of Earth loses heat. Cross- section sketch showing the development of a back-arc basin by rifting the arc longitudinally.
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Therefore, back-arc basins form when the overriding plate is under extension. In some cases, extension is triggered by the entrance of a buoyant feature in the subduction zone, which locally slows down subduction and induce the subducting plate to rotate adjacent to it. This rotation is associated with trench retreat and overriding plate extension.[9] For back-arc extension to form, a subduction zone is required, but not all subduction zones have a back-arc extension feature.
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The Juan de Fuca Plate is being subducted under the North American Plate, generating gradual, diverse volcanism. The Cascade Range was produced by convergence of the North American Plate with the subducting Juan de Fuca Plate. Active volcanism has taken place for approximately 36 million years; the nearby Challis Range features complexes as old as 55 mya. Most geologists believe that activity in the Cascades has been relatively intermittent, producing up to 3,000 volcanic calderas at a time.
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Plate tectonics along the west coast of North America 130 million years ago The Insular Plate was an ancient oceanic plate that began subducting under the west-coast of North America around the early Cretaceous period. The Insular Plate had a chain of active volcanic islands that were called the Insular Islands. These volcanic islands, however, collided then fused onto the west- coast of North America when the Insular Plate jammed then shut down ending the subduction zone.
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West of South America, the Nazca Plate subducts beneath the South America Plate. This process has formed the Andean Volcanic Belt, which is subdivided into the Northern Volcanic Zone, the Central Volcanic Zone and the Southern Volcanic Zone. These belts have different underlying crusts and thus have different typical magma compositions. These volcanic zones are separated from each other by zones where there is no volcanism, associated with a shallow dip of the seismic zone of the subducting plate.
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Modified from Moyen & Martin, 2012. Geochemical similarity shared between TTGs and adakites was long noted by researchers. Adakites are one type of modern arc lavas, which differ from common arc lavas (mostly granitoids) in their felsic and sodic nature with high LREE but low HREE content. Their production is interpreted to be the partial melting of young and hot subducting oceanic slabs with minor interaction with surrounding mantle wedges, rather than mantle wedge melts like other arc-granitoids.
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The thickness of sedimentation in the trench does not have a correlation with presence of tremor. For example, there is ~1 km-thick late Quaternary-Holocene sediment underneath Kodiak, and ~ 200 m-thick sediment underneath the Andreanof Islands. Kodiak Island had LFE epicenters at depths of 45–60 km while Andreanof Islands had epicenters at ~60–70 km depths. However, tremor does seem to occur at a specific depth related to the age of the subducting plate.
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Located along the Cascadia accretionary marginPhilip, B., Denny, A., Solomon, E., & Kelley, D. (2016). Time‐series measurements of bubble plume variability and water column methane distribution above Southern Hydrate Ridge, Oregon. Geochemistry, Geophysics, Geosystems,17(3), 1182-1196., sediment build-up in this region is driven by two subduction-related processes: #Scraping of sediments off of the subducting Juan de Fuca plate onto the overlying North American plate, and #Underplating of subducted sediments onto the overlying plate.
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Such a variety of volcanic rocks has been found at the adjacent volcanic fields of Ayutla, Los Volcanes and Tapalpa. As a plate subducts and sinks into the mantle, it loses water to the abovelying mantle wedge. This water also transports material from the subducting slab into the mantle wedge, modifying its chemistry. The melting of this modified mantle wedge appears to be the source of Mascota magmas, albeit with some magmas being modified by interactions with the crust.
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This shallowing forms the limit between the volcanically active Central Volcanic Zone and the magmatically inactive Pampean flat slab region farther south. This magmatic inactivity occurs because the flat slab removes the asthenospheric wedge. Incapillo is part of a volcanic system active between 3.5 and 2mya that includes Ojos del Salado and Nevado Tres Cruces. It was the last volcanic centre formed in the region; subsequently, the shallowing of the subducting slab prevented volcanism east and south of it.
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The overall chemical composition is potassium-rich calc-alkaline. Thermobarometry indicates that the older magmas crystallized at pressures of while younger ones crystallized at and temperatures of about . These magma compositions indicate that the magmas are the result of complex mixing processes and also involve the transitional nature of the mantle beneath Tuzgle, where the more northern steep slab encounters the shallower southern subducting slab. Crystal fractionation and melting of upper crustal rocks further complicate the pattern.
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For these two masses of magma to exist, the temperature of the magma at the Cobb Hotspot must be of a particularly high temperature. It is undetermined whether the hotspot was created from mantle-core boundary convection, as the end of the chain is subducting under another. The initial plume of magma would leave behind geologic evidence at the surface, but due to the consumption of the older end of the chain this evidence isn't visible.
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USGS image The Juan de Fuca Plate is a tectonic plate generated from the Juan de Fuca Ridge that is subducting under the northerly portion of the western side of the North American Plate at the Cascadia subduction zone. It is named after the explorer of the same name. One of the smallest of Earth's tectonic plates, the Juan de Fuca Plate is a remnant part of the once-vast Farallon Plate, which is now largely subducted underneath the North American Plate.
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At this point, the India Plate subducts beneath the Burma Plate, which carries the Nicobar Islands, the Andaman Islands, and northern Sumatra. The India Plate sinks deeper and deeper beneath the Burma Plate until the increasing temperature and pressure drive volatiles out of the subducting plate. These volatiles rise into the overlying plate, causing partial melting and the formation of magma. The rising magma intrudes into the crust above and exits the Earth's crust through volcanoes in the form of a volcanic arc.
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In this case an accretionary prism grows and the location of the trench migrates progressively away from the volcanic arc over the life of the convergent margin. Convergent margins with growing accretionary prisms are called accretionary margins and make up nearly half of all convergent margins. If the incoming sediment flux is low, material is scraped from the overriding plate by the subducting plate in a process called subduction erosion. This material is then carried down into the subduction zone.
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The phenomenon of subduction polarity reversal has been identified in the collision of an intra-oceanic subduction system, which is the collision of two oceanic plates. When two oceanic plates migrate towards each other, one subducts below the other. Generally, the oceanic plate with higher density subducts beneath and the other one overrides the down-going slab. The process continues until a buoyant continental margin sitting on the top of the subducting plate is introduced into the down-going slab.
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The Appalachian Orogeny, a result of three separate continental collisions. USGS As mentioned previously, the Acadian Orogeny formed from the oblique convergence or major transcurrent movement along a large strike-slip fault moving in a southeasterly direction. Avalonian terranes accreted to the eastern margin of Laurentia during the Late to Middle Devonian. This was a continent-continent collision with Baltica/Avalonia obliquely subducting below the eastern Laurentia margin, which closed the southern Iapetus ocean and created a high mountain belt.
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The absolute motion of the Nazca Plate has been calibrated at 3.7 cm/yr east motion (88°), one of the fastest absolute motions of any tectonic plate. The subducting Nazca Plate, which exhibits unusual flat slab subduction, is tearing as well as deforming as it is subducted (Barzangi and Isacks). The subduction has formed, and continues to form, the volcanic Andes Mountain Range. Deformation of the Nazca Plate even affects the geography of Bolivia, far to the east (Tinker et al.).
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This southwards migration results in a steepening of the subducting plate behind the ridge, causing decompression melting. Between 1:4 to 1:6 of the generated melts are erupted to the surface as ignimbrites. Mafic rocks are associated with strike-slip faults and normal faults and are found in the southern Puna and Altiplano. The southern Puna has calc-alkaline andesites erupted after 7 mya, with the least evolved magmas being the 6.7 mya Cerro Morado and 8–7 m Rachaite complex flows.
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The main shock was a reverse fault (thrust), with the Indo-Australian Plate subducting beneath the Pacific Plate. The earthquake lifted a large area of land around the epicenter approximately 1 metre. New Zealand's Institute of Geological and Nuclear Sciences (GNS Science) initially measured the earthquake at magnitude 6.6, but later revised the magnitude to 7.8. The reported energy release was compared to "500 million tonnes of TNT,[and] 25,000 times more powerful than the atomic bomb dropped on Nagasaki in 1945".
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The earthquake on March 3 had a magnitude of 7.4 , with a hypocentral depth of 225.6 km. The focal mechanism is consistent with reverse faulting within subducting oceanic crust. Comparison with similar earthquakes in 1993 and 2015, which have very similar depths and epicenters, suggests that the major component of the slip in all three events occurred on the same part of the fault. The earthquake on March 25 had a magnitude of 6.1 , with a hypocentral depth of 8.0 km.
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Studies have shown that magmas that produce island arcs are more oxidized than the magmas that are produced at mid-ocean ridges. This relative degree of oxidation has been determined by the iron oxidation state of fluid inclusions in glassy volcanic rocks. It has been determined that this state of oxidation is correlated with the water content of the mantle wedge. Water itself is a poor oxidant and therefore the oxidizing agent must be transported as a dissolved ion in subducting slab.
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Gulick, S., Meltzer, A., and S. Clarke (1998) Seismic structure of the southern Cascadia subduction zone and accretionary prism north of the Mendocino triple junction. Journal of Geophysical Research-Solid Earth, 103(B11). Stresses from the neighboring North American Plate and Pacific Plate cause frequent earthquakes in the interior of the plate, including the 1980 Eureka earthquake (also known as the Gorda Basin event). The easterly side is a convergent boundary subducting under the North American Plate in northern California.
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South of New Zealand the boundary becomes a transitional transform-convergent boundary, the Macquarie Fault Zone, where the Australian Plate is beginning to subduct under the Pacific Plate along the Puysegur Trench. Extending southwest of this trench is the Macquarie Ridge. The southerly side is a divergent boundary with the Antarctic Plate called the Southeast Indian Ridge (SEIR). The subducting boundary through Indonesia is not parallel to the biogeographical Wallace line that separates the indigenous fauna of Asia from that of Australasia.
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The western part of Washington State lies above the Cascadia subduction zone, where the Juan de Fuca Plate is being subducted beneath the North American Plate. The seismicity of this region consists of rare great megathrust earthquakes, like the 1700 Cascadia earthquake and more common earthquakes originating from within the subducting slab. These events relate to normal faulting, associated with the bending of the slab, possibly related to a phase change below about 40 km from basalt/gabbro to eclogite.
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This extensional deformation is associated with a steeply dipping slab. The extreme cases of these two types of back-arc deformation can be found in Chile and at the Marianas arc. The shallow dipping slab subducting beneath Chile at an angle of about 10–15° causes a compressional stress on the back-arc region behind the Andes. On the other extreme, the slab going down into the mantle at the Marianas subduction zone is so steep it is nearly vertical.
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Off southwesternmost South America, the Antarctic Plate subducts beneath the South America Plate at a rate of . This subduction is responsible for the volcanism in the Austral Volcanic Zone, whereas earthquake activity is low; this is possibly because the subducting plate is too hot and too slow moving. The basement below Aguilera is of Paleozoic-early Mesozoic age and consists of metamorphic rocks. The volcano sits at the easterly margin of the Patagonian Batholith, a Mesozoic-Cenozoic igneous rock province.
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The Hikurangi Plateau is an oceanic plateau on the Pacific Plate that attached to the Chatham Ridge after partially subducted under it, and is now subducting under the North Island. It likely formed in one of the world's largest volcanic outpourings, the greater Ontong Java event. Ophiolites, volcanic deposits from the ocean floor, have been incorporated into the continental basement of New Zealand in the Dun Mountain Ophiolite Belt, found at both ends of the South Island, and in Northland.
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The mechanism of arc subduction is well understood to be the location where new continental crust is formed and is presumably also the site of subcontinental mantle genesis. Firstly, hydrated oceanic crust slabs begin subducting which releases fluids (subduction zone metamorphism) to the mantle wedge above. Continued subduction of the slab leads to further hydration of the mantle which causes partial melting in the mantle wedge. It is expected then that the modern subcontinental mantle is a former, melt-depleted mantle wedge.
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The Philippine Trench (also called the Mindanao Trench) is a submarine trench in length found directly east of the Philippine Mobile Belt and is the result of a collision of tectonic plates. The Philippine Sea Plate is subducting under the Philippine Mobile Belt at the rate of about per year. Its deepest point, the Galathea Depth, has a depth of . The Philippine Fault System consists of a series of seismic faults that produce several earthquakes per year, most of which are not felt.
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About 200–300 miles inland, magma generated above the subducting slab rose into the North American continental crust. Great arc-shaped volcanic mountain ranges grew as lava and ash spewed out of dozens of individual volcanoes. Beneath the surface, great masses of molten rock were injected and hardened in place. For 100 million years the effects of plate collisions were focused very near the edge of the North American plate boundary, far to the west of the Rocky Mountain region.
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It was not until 70 million years ago that these effects began to reach the Rockies. The growth of the Rocky Mountains has been one of the most perplexing of geologic puzzles. Normally, mountain building is focused between 200 and 400 miles inland from a subduction zone boundary, yet the Rockies are hundreds of miles farther inland. Although geologists continue to gather evidence to explain the rise of the Rockies, the answer most likely lies with an unusual subducting slab.
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It is postulated that the shallow angle of the subducting plate greatly increased the friction and other interactions with the thick continental mass above it. Tremendous thrusts piled sheets of crust on top of each other, building the extraordinarily broad, high Rocky Mountain range. As of 60 million years ago, the Rockies were like Tibet: a high plateau, probably above sea level. Since then, erosion stripped away the high rocks, revealing the ancestral rocks beneath, and forming the current landscape of the Rockies.
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With the collision being an active ongoing process, it progressively generates weight which resulted a downward flexing of the subducting Indian plate and created an accommodation space to be filled with sediments. The flexural subsidence of the basin is slow as a result of the hard and rigid precambrian basement making a relatively shallow foreland basin. Topographic load exerted from the developing Himalayan mountain range results in the downward flexing of the Indian Plate. Modified from Egan and Williams, Dept.
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Schematic cartoon of the Bransfield Basin tectonic setting. The Bransfield Basin is considered to be a back-arc basin that is located behind the South Shetland Islands. The Islands are believed to have formed from a period of subduction that occurred between the Phoenix Plate and the Antarctic plate starting roughly 200 million years ago during the Mesozoic. It is believed that the Phoenix plate stopped subducting under the Antarctic plate at least 4 million years ago during the Pliocene.
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Both glaciers start from about and flow northwards to below . The glaciers are heavily covered in rocky debris due to the crumbling nature of the Tusk's rock. The Black Tusk is a member of the chain of volcanic peaks that run from southwestern British Columbia to northern California. The peaks formed in the past 35 million years as the Juan de Fuca, Gorda and Explorer plates to its west have been subducting under the North American Plate at the Cascadia subduction zone.
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Debris from a larger subducted seamount probably dammed the trench from 2 Ma to 0.5 Ma and similar events probably redirected sediments in similar ways before that. Two oceanic plates meet at the Kermadec Trench which is located far from any larger landmass. Because of this, the Pacific Plate as well as the trench itself is only covered by of sediments. The trench is almost perfectly straight and its simple geometry is the result of the uniformity of the subducting sea-floor.
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Kick 'em Jenny (also: Kick-'em-Jenny or Mt. Kick-'Em-Jenny) is an active submarine volcano or seamount on the Caribbean Sea floor, located north of the island of Grenada and about west of Ronde Island in the Grenadines. Kick-'em- Jenny rises above the sea floor on the steep inner western slope of the Lesser Antilles ridge. The South American tectonic plate is subducting the Caribbean tectonic plate to the east of this ridge and under the Lesser Antilles island arc.
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This geological setting would have been analogous to the modern-day subduction zone of the Pacific Ocean plate colliding and subducting beneath the North and South American continental plate. Sark also exercises jurisdiction over the island of Brecqhou, only a few hundred feet west of Greater Sark. It is a private island, but it has recently been opened to some visitors. Since 1993, Brecqhou has been owned by David Barclay, one of the Barclay brothers who are co-owners of The Daily Telegraph.
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Northland-East Cape was an undersea basin. Much of the land that now forms Northland-East Cape was higher land to the Northeast (composed of rocks formed 90–25 Ma). The Pacific-Australian plate boundary was further to the Northeast, with the Pacific Plate subducting under the Australian Plate. Layers of rocks were peeled off the higher land, from the top down, and slid Southwest under the influence of gravity, to be stacked the right way up, but in reverse order.
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Because the Australian Plate is subducting under the Pacific Plate in Fiordland, there are frequent deep earthquakes near Fiordland, with the earthquakes being deeper to the east and shallower near the west. Shallow earthquakes are more widespread, occurring almost everywhere throughout New Zealand (especially the Bay of Plenty, East Cape to Marlborough, and Alpine Fault). However, Northland, Waikato, and Otago are relatively stable. Canterbury had been without a major earthquake in recorded history until the 7.1 Canterbury earthquake on 4 September 2010.
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Flat slab subduction is characterized by a low subduction angle (<30 degrees to horizontal) beyond the seismogenic layer and a resumption of normal subduction far from the trench. A slab refers to the subducting lower plate. Although, some would characterize flat slab subduction as any shallowly dipping lower plate as in western Mexico. Flat slab subduction is associated with the pinching out of the asthenosphere, an inland migration of arc magmatism (magmatic sweep), and an eventual cessation of arc magmatism.
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There are two competing interpretations for this. In the context of mantle plumes, the near-surface material is postulated to have been transported down to the core-mantle boundary by subducting slabs, and to have been transported back up to the surface by plumes. In the context of the Plate hypothesis, subducted material is mostly re-circulated in the shallow mantle and tapped from there by volcanoes. Stable isotopes like Fe are used to track processes that the uprising material experiences during melting.
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Sicily lies on part of the complex convergent boundary where the African Plate is subducting beneath the Eurasian Plate. This subduction zone is responsible for the formation of the stratovolcano Mount Etna and considerable seismic activity. Most damaging earthquakes however, occur on the Siculo-Calabrian rift zone. This zone of extensional faulting runs for about , forming three main segments through Calabria, along the east coast of Sicily and immediately offshore, and finally forming the southeastern margin of the Hyblaean Plateau.
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Southward subduction of the Asian Plate and the northward one of the Indian Plate have been found. Mélange from these subducting plates forms the source material of the magmas of the volcanic fields in northwestern Tibet, although isotope data suggest that the Ashikule magma may not derive from subduction. Magma generation in Ashikule could have been affected by garnet or garnet-containing crustal layers. More generally, the crust beneath northern and central Tibet is suspected to be partially molten between of depth.
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The Buffalo Head Hills kimberlite field is an atypical diamond deposit. The lack of indicator minerals such as harzburgitic garnet suggests a mantle composition different from those of other diamond occurrences. An unusual occurrence of Type II and Type IaB diamonds is indicative of a sub-lithospheric origin, such as a subducting oceanic slab, and the presence of a lherzolitic garnet suggests a formation depth of some . 26 of the 38 kimberlite pipes in the Buffalo Head Hills kimberlite field are, nevertheless, diamondiferous.
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Indonesia has relatively high tectonic and volcanic activities. It lies on the convergence between the Eurasian, Indo-Australian, Pacific, and Philippine Sea Plate. The Sunda megathrust is a 5,500 km long fault located off southern coasts of Sumatra, Java and Lesser Sunda Islands, where the Pacific Plate is thrusting northeastward towards the subducting Sunda Plate. Tectonic movement in this fault is responsible for the creation of the Sunda Trench, and mountain ranges across Sumatra, Java, and the Lesser Sunda Islands.
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Of these volcanic zones, the Central Volcanic Zone of which Lascar is a member of is the largest, covering parts of Peru, Bolivia, Argentina and Chile. The Central Volcanic Zone is located between two areas where subduction is shallower and volcanic activity is absent. In the Central Volcanic Zone, volcanism has been active for 120 million years, although it has undergone eastward migration during this time. Water released from the subducting plate triggers the formation of basaltic magmas that are then injected into the crust.
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The Tethyan Trench formed when the Cimmerian Plate was subducting under eastern Laurasia, around 200 million years ago, in the Early Jurassic. The Tethyan Trench extended at its greatest during Late Cretaceous to Paleocene, from what is now Greece to the Western Pacific Ocean. Subduction at the Tethyan Trench probably caused the continents Africa and India to move towards Eurasia, which resulted in the opening of the Indian Ocean. When the Arabian and Indian plates collided with Eurasia, the Tethys Ocean and the trench closed.
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However these models cannot conclude that the lack of lateral displacement demonstrates that the Extrusion Model must be false. A narrow proto-South China Sea or other crustal deformation could potentially have accommodated the subducting proto South China Sea and account for the lack of displacement along strike-slip faults.The continental rift basin model where the line with triangles represents subduction. Subduction to the south of Borneo pulls the plate that Borneo is on causing extension in the South China sea to the north.
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A pair of paragliders take flight at Mussel Rock Beach near Daly City, California.Mussel Rock is a "greenstone assemblage" which is part of the Franciscan Complex, which is the bedrock under San Francisco, and was transported to the site by a subducting plate about 80 or 90 million years ago. It is older than the nearby sedimentary rocks which are part of the Merced Formation, which are about 3 million years old. A paragliding flight over the Mussel Rock Gliding Bluffs in Pacifica, California.
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Oceanic trench formed along an oceanic-oceanic convergent boundary The Mariana trench contains the deepest part of the world's oceans, and runs along an oceanic- oceanic convergent boundary. It is the result of the oceanic Pacific plate subducting beneath the oceanic Mariana plate. Trenches distant from an influx of continental sediments lack an accretionary prism, and the inner slope of such trenches is commonly composed of igneous or metamorphic rocks. Non- accretionary convergent margins are characteristic of (but not limited to) primitive arc systems.
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As the oceanic slab sinks deep into the Earth's interior beneath the continental plate, high temperatures and pressures allow water molecules locked in the minerals of solid rock to escape. The water vapor rises into the pliable mantle above the subducting plate, causing some of the mantle to melt. This newly formed magma ascends upward through the crust along a path of least resistance, both by way of fractures and faults as well as by melting wall rocks. The addition of melted crust changes the geochemical composition.
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The Ring of Fire is also known for its frequent earthquakes. The volcanoes and earthquakes arise from a common source: subduction, where the dense Juan de Fuca oceanic plate plunges beneath the North American Plate. As the oceanic slab sinks deep into the Earth's interior beneath the continental plate, high temperatures and pressures allow water molecules locked in the minerals of solid rock to escape. The water vapor rises into the pliable mantle above the subducting plate, causing some of the mantle to melt.
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Subduction of the Nazca Plate beneath the South America Plate is responsible for the volcanism of the Andes. This volcanism does not occur along the entire strike of the Andes, but in three selected volcanic belts, the Northern Volcanic Zone, the Central Volcanic Zone and the Southern Volcanic Zone. A fourth volcanic zone, the Austral Volcanic Zone, lies south of the Southern Volcanic Zone. These volcanically active belts are separated by gaps where recent volcanism is absent and the subducting plate descends in a much shallower angle.
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Nevado de Acay lies northeast just outside the caldera margin, and the town of San Antonio de los Cobres only about northwest. The cities of Salta and Jujuy lie about east of Negra Muerta. The region has an arid climate, thus geological features are often buried beneath uneroded rocks and difficult to access. The south Central Andes in the past were the site of large scale dacitic ignimbrite-forming eruptions and the formation of calderas, linked to the interaction between a subducting slab and the overlying crust.
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To get a basalt from melting an eclogite (i.e.; a rock with basalt composition) it has to undergo 100% partial melting. Instead, basalts can be modelled as having been produced by 1 to 25% partial melting of peridotite, such as harzburgite and lherzolite. Some andesite-like rocks could be produced from partial melting of eclogite; for instance, an unusual rock type called adakite (first described from Adak Island in the Aleutians) has been proposed to be a product of partial melting of eclogite in subducting oceanic crust.
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The Needle Range ash flow tuff is the most extensive, covering 13,000 square miles in southwest Utah and eastern Nevada. While most tuffs are rhyolite, the Needles Range tuff includes amphibolite, biotite and plagioclase phenocrysts. Volcanism was related to the subducting Farallon Plate and took place from 35 to 19 million years ago, predating the block faulting of the Basin and Range Province making tuff useful for stratigraphic comparisons. Several unusual laccolith intrusions formed including the Henry, La Sal, Abajo and Three Peaks mountains.
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The subduction event between the Phoenix plate and the Antarctic plate have built a volcanic arc consisting of low potassium to medium potassium content along the Antarctic Peninsula and South Shetland Islands. Volcanism occurred in multiple events during 130-110, 90-70, 60-40, and 30 -20 million years ago. The paucity can be interpreted as subducting younger crust or subsidence the post 20 million years arc after the basin formed. Volcanism is widespread within the Quaternary which created a series of submarine volcanoes.
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Areas of Mexico's coastline on the Gulf of California, including the Baja California Peninsula, are riding northwestward on the Pacific plate. Rather than one plate subducting, the Pacific and North American plates grind past each other, creating a slip fault that is the southern extension of the San Andreas fault in California. Motion along this fault in the past pulled Baja California away from the coast, creating the Gulf of California. Continued motion along this fault is the source of earthquakes in western Mexico.
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Rifting is said to have begun in the Late Cretaceous epoch to Paleogene period. At that time the African plate was experiencing far-field stresses caused by portions of the northern boundary of the African plate subducting under the Eurasian plate. Today, the Arabian plate is experiencing a crustal down pull, or slab pull, that has separated from the African plate. At the same time of the subduction in the north there was mantle upwelling causing the crust to down warp and swell into domes.
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The Peruvian flat slab is the largest in the world, and extends ~700 km inboard from the trench axis. The subducting plate starts at a dip of 30 degrees then flattens out at a depth of 100 km under the Eastern Cordillera and Subandean zone. The segment is visually correlated with the subduction of the Nazca Ridge, an aseismic ridge with thickened crust. The second highest zone in the Andes, Cordillera Blanca, is associated with the Peruvian flat slab segment and uplift of basement-cored blocks.
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The subducting oceanic crust is thought to split from the continental margin to aid subduction. In the event that the rate of trench retreat is greater than that of the island arc complex's progression, trench rollback will take place, and by consequence, extension of the overriding plate will occur to allow the island arc complex to match the trench retreat's speed. The extension, a back-arc basin, generates oceanic crust: ophiolites. Finally, when the oceanic lithosphere is entirely subducted, the island arc complex's extensional regime becomes compressional.
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This trench is created by the downward gravitational pull of the relatively dense subducting plate on the leading edge of the plate. Multiple earthquakes occur along this subduction boundary with the seismic hypocenters located at increasing depth under the island arc: these quakes define the Benioff zone. Island arcs can be formed in intra- oceanic settings, or from the fragments of continental crust that have migrated away from an adjacent continental land mass or at subduction-related volcanoes active at the margins of continents.
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Subduction zones are places where two plates, usually an oceanic plate and a continental plate, collide. In this case, the oceanic plate subducts, or submerges, under the continental plate, forming a deep ocean trench just offshore. In a process called flux melting, water released from the subducting plate lowers the melting temperature of the overlying mantle wedge, thus creating magma. This magma tends to be extremely viscous because of its high silica content, so it often does not attain the surface but cools and solidifies at depth.
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The uplift and subsequent weathering and erosion have exposed ancient oceanic Jurassic and Cretaceous age rocks that now form the summit. The mountain grows from three to five millimeters each year. The upper portion of the mountain is made up of volcanic and sedimentary deposits of what once was one or more island arcs of the Farallon Plate dating back to the Jurassic and Cretaceous periods, between 90 and 190 million years ago. During this time, the Farallon Plate was subducting beneath the North American continent.
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Analysis of this earthquake using modern techniques has been possible due to the large collection of seismograms recording this event published in 1907. They came from 78 stations around the world and included details of the characteristics of the individual seismometers. The focal mechanism of the earthquake has been determined from the seismograms as a normal faulting event within the subducting slab, with a large component of left-lateral strike-slip faulting. A tsunami was recorded in both Japan and Hawaii in the hours following the earthquake.
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Sites such as the Wopmay Orogen provide evidence for early and ongoing plate tectonics. Traces of old oceanic crust, island arcs, and colliding continents indicate that the same forces at work today have been at work in the early Proterozoic and probably earlier. Alignments of magnetic particles in rocks demonstrate that continents were drifting across the surface of the Earth relative to the magnetic poles then as now, and that the ocean floor was rifting and subducting, all at least 1.5 billion years ago. Retrieved May 2016.
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Understanding predictions of mantle dynamics helps geoscientists predict where subducted crust will end up. Crustal recycling is a tectonic process by which surface material from the lithosphere is recycled into the mantle by subduction erosion or delamination. The subducting slabs carry volatile compounds and water into the mantle, as well as crustal material with an isotopic signature different from that of primitive mantle. Identification of this crustal signature in mantle-derived rocks (such as mid-ocean ridge basalts or kimberlites) is proof of crustal recycling.
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The Gorda Ridge runs in a north-easterly direction, bounded at both ends by transform faults. At the southern end, the ridge meets the Mendocino transform fault, while the northern end butts against the Blanco transform fault. To its east is the Gorda Plate, which together with the Juan de Fuca Plate to its north, is what remains of the once-vast Farallon Plate. These two oceanic plates are currently moving east, subducting underneath the North American Plate in what is known as the Cascadia Subduction Zone.
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Bernal Hill, along with the other hills in the San Francisco area, is a folded hill, created by the "wrinkling up" effect of the Pacific plate subducting under the North American plate, when the North American and Pacific plates were converging, around 150 million years ago. Near the summit are folded layers of very hard rock called radiolarian chert. It is a sedimentary silicate rock which gets its silica content from the shells of microscopic creatures called radiolaria. The red color comes from iron oxide.
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This fault system takes up part of the motion due to the subducting plates and produces large earthquakes. Southwest of Luzon is a collision zone where the Palawan micro-block collides with SW Luzon, producing a highly seismic zone near Mindoro island. Southwest Luzon is characterized by a highly volcanic zone, called the Macolod Corridor, a region of crustal thinning and spreading. Using geologic and structural data, seven principal blocks were identified in Luzon in 1989: the Sierra Madre Oriental, Angat, Zambales, Central Cordillera of Luzon, Bicol, and Catanduanes Island blocks.
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Terranes started to collide with the western edge of North America in the Mississippian age (approximately 350 million years ago), causing the Antler orogeny. During the last half of the Mesozoic Era, much of today's California, British Columbia, Oregon, and Washington were added to North America. Western North America suffered the effects of repeated collision as the Kula and Farallon plates sank beneath the continental edge. Slivers of continental crust, carried along by subducting ocean plates, were swept into the subduction zone and scraped onto North America's western edge.
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Stable subduction zones involve the oceanic lithosphere of one plate sliding beneath the continental or oceanic lithosphere of another plate due to the higher density of the oceanic lithosphere. This means that the subducted lithosphere is always oceanic while the overriding lithosphere may or may not be oceanic. Subduction zones are sites that usually have a high rate of volcanism and earthquakes. Furthermore, subduction zones develop belts of deformation and metamorphism in the subducting crust, whose exhumation is part of orogeny and also leads to mountain building in addition to collisional thickening.
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This sinking is driven by the temperature difference between the subducting oceanic lithosphere and the surrounding mantle asthenosphere, as the colder oceanic lithosphere has, on average, a greater density. At a depth of greater than 60 kilometers, the basalt of the oceanic crust is converted to a metamorphic rock called eclogite. At that point, the density of the oceanic crust increases and provides additional negative buoyancy (downwards force). It is at subduction zones that Earth's lithosphere, oceanic crust and continental crust, sedimentary layers and some trapped water are recycled into the deep mantle.
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Slab suction is one of the four main forces that drive plate tectonics. It creates a force that pulls down plates as they are subducting and speeds up their movement, creating larger amounts of displacement. It is because of these forces, slab pull, ridge push, mantle convection, and slab suction that the earth's crust is able to move and orient itself in various arrangements. This is how throughout the earth's history there has been the ability to create super continents where all of the land mass has converged into one (for example, Pangaea).
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The Hunter-Bowen event produced a ~3,000 km long structural foredeep above a Late Carboniferous and Palaeozoic margin to the weakly consolidated Australian continental mass which was part of the Gondwana Supercontinent at this time; the orogen developed to the east of the Palaeozoic Lachlan Orogen and the Proterozoic terranes of the Mount Isa Inlier. Before the orogeny the rocks of the coastal area were formed. During Late Carboniferous there was a continental margin with an oceanic trench subducting the ocean floor off the coast. To the east there was a magmatic arc.
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Locals who ventured to the island shortly after it formed heard a hissing noise at one end and started a fire which was difficult to extinguish. There are several mud volcanoes inland near Zalzala Jazeera and they are common in the vicinity of subducting plate boundaries; in fact, similar islands have appeared in the same region following earthquakes in 1945, 1999, 2001, and 2010. Because of its composition of softer sediments, the sea was predicted to erode the island completely within a few months. By the end of 2016, the island had completely disappeared.
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The epicenter of the 1920 earthquake lay within the inner zone of the Northern Apennines, which has been affected by extensional tectonics since the Late Miocene to Pliocene epochs. This extension is a result of the same process that opened the Tyrrhenian Sea during the same period, the rollback of the subducting Adriatic Plate. The continuing extension has resulted in a series of northwest- southeast trending normal faults bounding basins filled by the Pliocene to recent sediments. Near Garfagnana, there are two such basins, the Serchio and Magra grabens.
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Even subducted sediment may rise as diapirs from the subducting plate and accumulate to form UHP terrains.Currie, C. A., Beaumont, C., and Huismans, R. S., 2007, The fate of subducted sediments: A case for backarc intrusion and underplating: Geology, v. 35, p. 1111-1114. Studies of numerical geodynamics suggest that both subducted sediment and crystalline rocks may rise through the mantle wedge diapirically to form UHP terranes.Stöckhert, B., and Gerya, T. V., 2005, Pre-collisional high pressure metamorphism and nappe tectonics at active continental margins: a numerical simulation: Terra Nova, v. 17, p. 102-110.
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The January 13 earthquake was a result of normal faulting within the subducting Cocos Plate as shown by the hypocentral depth and published focal mechanisms. Of the two possible fault planes indicated, analysis of observed seismic waves supports the solution with a fault plane dipping moderately to the northeast. It was followed by a series of aftershocks, including 70 greater than M 4 of which 10 were greater than M 5 in the period up to February 2, 2020. The largest aftershock was an M 5.8 event at 12:20 on January 15.
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GPS measurements from Victoria, British Columbia show periodic reversals in crustal deformation in the North American region of the Cascadia Subduction Zone. In the Cascadia subduction zone, the Juan de Fuca Plate, a relic of the ancient Farallon Plate, is actively subducting eastward underneath the North American Plate. The boundary between the Juan de Fuca and North American plates is generally "locked" due to interplate friction. A GPS marker on the surface of the North American plate above the locked region will trend eastward as it is dragged by the subduction process.
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The geologic characteristics displayed on the surrounding islands provide insight regarding the complex plate movement of the divergent double subducting plate. Detached ophiolitic series and thick melanges are overlain by forearc deposits; subduction-driven east-west shortening of the Snellius Plateau caused the thrust melanges to reactivate and deform the forearc series. Exposed ophiolitic rocks can be found on the islands of the submarine Talaud-Mayu Ridge, which bisects the arc-arc collision zone of the Molucca Sea Plate; these ophiolites provide insight regarding the relationship between earthquakes and uplift surrounding the plate.
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In a continental collision, a subducting tectonic plate pushes on the plate above it, making the rock fold, often to the point where thrust faults form, and a mountain chain rises. On the upper plate, the land between the mountains and the undeformed continent bends downward, forming a foreland basin. If the basin forms slowly, as in the northern Appalachians, it fills with shallow-water sediments. If it forms rapidly, as in the east side of the North American Cordillera, then sea water may rush in, and the first sedimentary deposits are deep water deposits.
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A peak is seen in seismological data at about 410 km as is predicted by the transition from α- to β- Mg2SiO4 (olivine to wadsleyite). From the Clapeyron slope, this change is predicted to occur at shallower depths in cold regions, such as where subducting slabs penetrate into the transition zone, and at greater depths in warmer regions, such as where mantle plumes pass through the transition zone.C.M.R. Fowler, The Solid Earth (2nd Edition), Cambridge University Press 2005. Therefore, the exact depth of the "410 km discontinuity" can vary.
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The northeasterly side is a complex but generally convergent boundary with the Pacific Plate. The Pacific Plate is subducting under the Australian Plate, which forms the Tonga and Kermadec Trenches, and the parallel Tonga and Kermadec island arcs. It has also uplifted the eastern parts of New Zealand's North Island. The continent of Zealandia, which separated from Australia 85 million years ago and stretches from New Caledonia in the north to New Zealand's subantarctic islands in the south, is now being torn apart along the transform boundary marked by the Alpine Fault.
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Bernal Hill, along with the other hills in the San Francisco area, is a folded hill, created by the "wrinkling up" effect of the Pacific Plate subducting under the North American Plate, when the North American and Pacific plates were converging, around 150 million years ago. Near the summit you will find folded layers of very hard rock called radiolarian chert. It is a high in silica sedimentary rock which gets its silica content from the shells of microscopic creatures called radiolaria. The red color comes from iron oxide.
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Mexico lies within two seismically active earthquake zones. The Baja California peninsula lies near the boundary of the Pacific Plate and the North American Plate, while southern Mexico lies just north of the boundary between the North American Plate and the Cocos and Rivera tectonic plates. The Cocos Plate is subducting under the North American Plate at a rate of per year, while the Pacific and Rivera plates are moving northwest relative to the North American Plate. Southern Mexico also contains numerous faults, which causes that section of the country to have high tectonic activity.
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The trench-chain collision zone is moving southward at a rate of / because of the oblique angle between the trench and the Louisville chain. This further shortens the seamount's lifespan. The flat top of the seamount is currently tilting down toward the trench because the seamount is sitting on the edge of the trench where the Australian Plate is being bent by subduction. A bathymetric high north-west of the Osbourn Seamount has been interpreted as the currently subducting portion of the Louisville chain, but this continuation is not aligned with the existent chain.
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Sediment samples within the Japan Trench consist mainly of highly localized clay-rich material. The subducting Pacific Plate creates basins along the ocean floor of the Japan Trench, accommodating the deposition of fine-grained turbidites and interseismic sediment deposits through turbidity currents. These turbidites preserve the sediment deposits as a geologic record of past large earthquakes by indicating the change in sediment deposition through sediment gravity flow. The small deep-sea basins with high sedimentation rates found along the Japan Trench pose favorable environmental conditions for the studying of turbidite paleoseismology.
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It was also felt in other Eastern Caribbean islands, from Puerto Rico to the north to Trinidad and Tobago to the south. It could also be felt in part of South America such as in Venezuela, Guyana, Suriname, and French Guiana. In Caracas, Venezuela, some people evacuated office buildings. The intensity reached VI to VII on the EMS98 scale in Martinique and Dominica.Loi d'atténuation B-Cube pour l’évaluation rapide des intensités sismiques probables dans l'Archipel de Guadeloupe In the surrounding region, the South American Plate is subducting beneath the Caribbean Plate.
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Similar to mineralization processes that takes place within rocks, mineralization can also occur under the sea. The rate of dissolution of carbon dioxide from atmosphere to oceanic regions relies upon the circulation period of the ocean and buffering ability of subducting surface water. Researches have demonstrated that the carbon dioxide marine storage at several kilometers deep could be viable for up to 500 years, but is dependent on injection site and conditions. Several studies have shown that although it may fix carbon dioxide effect, carbon dioxide may be released back to the atmosphere over time.
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Late Eocene compressional structures in the Taranaki Basin correspond with a period of elevated uplift rates along the Alpine Fault on New Zealand's South Island that has also been attributed to the nearby subduction zone. Kapuni is located on the Australian Plate, west of the plate boundary zone and above the subducting Pacific Plate. Current geothermal gradients in the Taranaki Basin vary from 33-35 °C/km offshore near the Maui Field and in northern portions of the Taranaki Peninsula to 25 °C/km in Kapuni and other southeast portions of the Taranaki Peninsula.
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Aguilera has erupted dacites with intermediate contents of potassium, defining a calc-alkaline suite with adakitic characteristics. Phenocrysts include amphibole, biotite, clinopyroxene, hornblende and plagioclase; plagioclase and also orthoclase and pyroxene often occur as xenoliths. Melts of subducted sediment and from the subducting slab give rise to the magmas of Aguilera and other volcanoes of the northern Austral Volcanic Zone, but they are subsequently modified by interactions with the mantle wedge and in the case of Aguilera, Lautaro and Viedma further interaction takes place with the Paleozoic crust.
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The Manila Trench near western Luzon and Mindoro, the Philippine Trench in the east, and the Philippine Mobile Belt. The Manila Trench is an oceanic trench in the Pacific Ocean, located west of the islands of Luzon and Mindoro in the Philippines. The trench reaches a depth of about , in contrast with the average depth of the South China Sea of about . It is created by subduction, in which the Sunda Plate (part of Eurasian Plate) is subducting under the Philippine Mobile Belt, producing this almost N-S trending trench.
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The Manila Trench was formed by the subduction of the Eurasian Plate underneath the Philippine Sea Plate, which initiated during the Middle Miocene (22-25 million years ago). A characteristic feature of this plate boundary is the gradual change from normal subduction (on the southern margin) to a collisional regime (on the northern margin) which produces the Taiwan orogeny. The dip angle of the subducting plate also increases from south to north in the northern section of the trench.; The structure of the northern Manila Trench has been studied extensively.
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Earthquakes are common in Sumatra as it lies at the convergent boundary where the Sunda Plate is subducting beneath the Indo-Australian Plate. The plates are converging obliquely at a rate of 60 mm per year and the right lateral component is accommodated by strike-slip faulting within Sumatra, mainly on the Great Sumatran fault. In 2004, Sumatra was devastated by the Sumatra–Andaman earthquake and resulting tsunami that killed tens of thousands in the area and 230,000 people around the Indian Ocean. In 2009, an earthquake near Padang on Sumatra killed more than 1,000.
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Ovalle National Theatre after the earthquake. Chile lies above the convergent plate boundary where the Nazca Plate is subducting beneath the South American Plate, at a location where they converge at a rate of seventy millimeters a year. This quake was an oceanic interplate type, occurred in the downgoing slab of the Nazca Plate and not on the interface between the two plates. This event took place under the area of Chile, between 27° and 33° S, where the slab is nearly horizontal and there is a high degree of mechanical coupling between the plates.
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For northern IBM, used a refined earthquake relocation scheme to detect a DSZ between depths of 300 km and 400 km, which also has a spacing of 30 35 km between the upper and lower zones. They interpreted data from S to P converted phases and thermal modeling to propose that the DSZ results from transformational faulting of a metastable olivine wedge in the slab. Recent work suggests that compositional variations in the subducting slab may also contribute to double seismic zone , or that DSZs represent the locus of serpentine dehydration in the slab .
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Bathymetry of the northeast corner of the Caribbean Plate showing the major faults and plate boundaries; view looking south-west. The main bathymetric features of this area include: the Lesser Antilles volcanic arc; the old inactive volcanic arc of the Greater Antilles (Virgin Islands, Puerto Rico, and Hispaniola); the Muertos Trough; and the Puerto Rico Trench formed at the plate boundary zone between the Caribbean and obliquely subducting North American Plates. Vertical exaggeration is 5:1. The Lesser Antilles Volcanic Arc is a volcanic arc that forms the eastern boundary of the Caribbean Plate.
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The Hellenic arc is an arcuate tectonic feature related to the subduction of the African Plate beneath the Aegean Sea Plate. It is one of the most active seismic zones in western Eurasia and has a history of large earthquakes that also affect Egypt. Large earthquakes with epicentres near Crete and to the north of the island are typically intermediate depth events located at the subducting plate interface. Such events are often M>7, but due to their depths cause relatively little damage for their size, while being very widely felt.
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The formation of the Koh-i-Sultan volcano is related to the subduction of the Arabian Plate under the Eurasian Plate Pakistan is part of the active tectonic belt which is responsible for the formation of the Himalayas following the collision of India and Asia. As a result of this activity, hydrothermal alteration and hydrothermal activity are expected to be widespread in Pakistan. Koh-i-Sultan is the youngest volcano in Pakistan. It is tectonically influenced by the Arabian Plate subducting beneath the Eurasian Plate, forming the Chagai volcanic zone.
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There was an aftershock two hours later at 2.12 am, followed over several days by frequent small tremors; up to 21 September there were 6365 aftershocks. Fiordland is one of the seismically active parts of the country according to GNS seismologist Dr Warwick Smith, as they are a relief mechanism for stresses as the Australian and Pacific tectonic plates are being forced together in the area, with the Pacific Plate subducting under the Australian Plate. In August 2004 there was another large earthquake of magnitude 7.1 MW in Fiordland.
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This Image shows where the Yakutat microplate is subducting beneath the North American Plate. Red indicates the region where the microplate has already been subducted, while the yellow indicates where it is still present at the surface. Alaskan tectonism is mainly dominated by the subduction of the Pacific Plate beneath the North American Plate. The subduction boundary is marked by a 4,000 km long trench known as the Aleutian Trench, where seismic activity is common and the volcanic arc produced is part of the Pacific Ring of Fire.
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Lava flows from mid-ocean ridge and plate boundary seamounts are mostly basaltic (both tholeiitic and alkalic), whereas flows from subducting ridge volcanoes are mostly calc-alkaline lavas. Compared to mid-ocean ridge seamounts, subduction zone seamounts generally have more sodium, alkali, and volatile abundances, and less magnesium, resulting in more explosive, viscous eruptions. All volcanic seamounts follow a particular pattern of growth, activity, subsidence and eventual extinction. The first stage of a seamount's evolution is its early activity, building its flanks and core up from the sea floor.
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The island of Bali forms part of the Sunda Arc, which formed above the convergent boundary where the Australian Plate is subducting beneath the Sunda Plate. The rate of convergence across the line of the Sunda-Java Trench is 7.5 cm per year. Eastwards from Bali, the Sunda Arc is also being thrust over the Bali and Flores back-arc basins on a series of south-dipping thrusts. Focal mechanisms for earthquakes near Bali are dominantly thrust sense on both the subduction interface and the system of thrust faults to the north.
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El Salvador lies above the convergent boundary where oceanic crust of the Cocos Plate is being subducted beneath the Caribbean Plate at rate of about 72 mm per year along the Middle America Trench. This boundary is associated with earthquakes resulting from movement on the plate interface itself, such as the 7.7 1992 Nicaragua earthquake, and from faulting within both the overriding Caribbean Plate associated with the active volcanic belt, such as the destructive 1936 San Salvador earthquake, and the subducting Cocos Plate, such as the 1982 El Salvador earthquake.
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By the early Devonian, magmatic activity was taking place in the northern Tien Shan mountains, likely as a result of the subducting Turkestan crust. Sedimentation occurred in shallow seas and on the passive margin of the Tarim-Alay Block. Magmatic activity resumed in the Carboniferous, with spreading in the Turkestan Ocean and renewed subduction under the Kyrgyz Block. By the late Carboniferous, collision between the Tarim-Alay microcontinent and the Kyrgyz Block was underway, emplacing large nappe features with ophiolite deposits on top of the Tarim-Alay basement rocks.
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Jotabeche is located at the southern end of the Maricunga belt, which was active starting from the Oligocene until the Pliocene. The formation of this volcanic belt was influenced by the changes in the subduction of the Nazca plate, which included the shallowing of the subducting plate and the formation of the Puna plateau. Jotabeche, belonging to the fourth stage of Maricunga belt activity after the third stage of Copiapo, is the youngest eruption of the Maricunga belt, whose activity ended with the Jotabeche caldera forming eruption. Volcanism afterwards shifted eastwards.
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Most of western Turkey lies in an area of extensional tectonics that extends into the Aegean Sea. The cause of the extension is thought to be the rollback of the subducting slab of the African Plate that dips northwards beneath the Aegean. The overall N–S extension has resulted in a series of NW–SE to W–E trending seismically active normal faults with associated rift basins. The Afyon–Akşehir Graben lies in the hanging-wall of the low-angle Sultandağı Fault and contains nearly 1 km of late Miocene to Quaternary sedimentary fill.
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The dammed Hikurangi Trough: a channel-fed trench blocked by subducting seamounts and their wake avalanches (New Zealand-France GeodyNZ Project), Basin Research 10, 441-468. At the southern end of the trench, off the coast of the Marlborough region, the seabed rises sharply, and because of the prevailing winds and tides in this area, many deep water species are found close to the shore. This food source attracts the whales for which the town of Kaikoura is famous. The plate boundary continues inland along the Marlborough Fault System, linking through to the Alpine Fault.
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LFE P-waves, when successfully detected, have first motions indicative of compressional stress, indicating that thrust-sense slip is responsible for their generation. Extracting high quality P-wave data out of LFE waveforms can be quite difficult, however, and is furthermore important for accurate hypocentral depth determinations. The detection of high quality P-wave arrivals is a recent advent thanks to the deployment of highly sensitive seismic monitoring networks. The depth occurrence of LFEs are generally determined by P-wave arrivals but have also been determined by mapping LFE epicenters against subducting plate geometries.
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Capitanio et al. attributes the rise of Altiplano and the bending of the Bolivian Orocline to the varying ages of the subducted Nazca Plate with the older parts of the plate subducting at the centre of the orocline. As Andrés Tassara puts it the rigidity of the Bolivian Orocline crust is derivative of the thermal conditions. The crust of the western region (forearc) of the orocline has been cold and rigid, resisting and damming up the westward flow of warmer and weaker ductile crustal material from beneath the Altiplano.
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Peru lies above the convergent boundary where the Nazca Plate is subducting beneath the South American Plate at a rate of 61 mm per year. It has been the location for many large and damaging earthquakes since historical records began, most of which triggered devastating tsunamis. The southern segment of the Peruvian part of this plate boundary is affected by the presence of the Nazca aseismic ridge, on the downgoing plate. It also marks a major change in the subduction geometry between 'flat-slab' subduction to the northwest and normally dipping subduction to the southeast.
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Italy lies on the southern extent of the Eurasian Plate, which is surrounded by the Aegean Sea Plate, the Adriatic Plate, and the Anatolian Plate. The Apennine Mountains contain numerous faults that run along the entire Italian peninsula and form the majority of the destructive boundary between the Eurasian and the Adriatic plates, thus causing Italy to have high amounts of tectonic activity. In addition, Sicily and Calabria are located near the boundary where the African plate is subducting below the Eurasian plate, which was responsible for forming the stratovolcano known as Mount Etna.
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Antofalla and other Andean volcanoes form because the Nazca Plate is subducting beneath the South America Plate. Antofalla volcano is located in a region with a "basins and ranges" topography, where during the Miocene ranges were uplifted and basins formed through tectonic movement. It sits on a basement formed by Eocene-Miocene sedimentary units over a much older crystalline basement. Antofalla is formed by a principal volcano, the high Antofalla volcano proper, and a surrounding complex of smaller volcanic systems that are formed by lava flows and pyroclastic material.
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The deep water cycle, or geologic water cycle, involves exchange of water with the mantle, with water carried down by subducting oceanic plates and returning through volcanic activity, distinct from the water cycle process that occurs above and on the surface of Earth. Some of the water makes it all the way to the lower mantle and may even reach the outer core. Mineral physics experiments show that hydrous minerals can carry water deep into the mantle in colder slabs and even "nominally anhydrous minerals" can store several oceans' worth of water.
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The fault zone that separates the two is the Periadriatic Seam that runs through the Alps. Studies indicate that in addition to deforming, the Eurasian continental crust has actually subducted to some extent below the Adriatic/Apulian Plate, an unusual circumstance in plate tectonics. Oceanic crust of the African Plate is also subducting under the Adriatic/Apulian Plate off the western and southern coasts of the Italian Peninsula, creating a berm of assorted debris which rises from the seafloor and continues onshore. This subduction is also responsible for the volcanics of southern Italy.
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The island of Bali forms part of the Sunda Arc, which formed above the convergent boundary where the Australian Plate is subducting beneath the Sunda Plate. The rate of convergence across the line of the Sunda–Java Trench is 7.5 cm per year. Eastwards from Bali, the Sunda Arc is also being thrust over the Bali and Flores back-arc basins on a series of south-dipping thrusts. Focal mechanisms for earthquakes near Bali are dominantly thrust sense on both the subduction interface and the system of thrust faults to the north.
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The island of Bali forms part of the Sunda Arc, which formed above the convergent boundary where the Australian Plate is subducting beneath the Sunda Plate. The rate of convergence across the line of the Sunda-Java Trench is 7.5 cm per year. Eastwards from Bali, the Sunda Arc is also being thrust over the Bali and Flores back-arc basins on a series of south-dipping thrusts. Focal mechanisms for earthquakes near Bali are dominantly thrust sense on both the subduction interface and the system of thrust faults to the north.
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The Aleutian subduction zone is a ~2500 mile-long convergence boundary between the North American Plate and the Pacific Plate, that extends from the Alaska Range to the Kamchatka Peninsula. Here, the Pacific Plate is being subducted underneath the North American plate and the rate of subduction changes from west to east from 7.5 cm/yr to 5.1 cm/yr. The Aleutian subduction zone includes two prominent features _,_ the Aleutian arc and the Aleutian trench. The island arc was created via volcanic eruptions from dehydration of the subducting slab at ~100 km depth.
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144, Orient Blackswan, However, blue diamonds have also been discovered in the Cullinan Mine in South Africa and the Golconda region. A few blue diamonds have been discovered in the Argyle Mine in Western Australia as well, and are offered at their annual Argyle Tender when they are found. It is thought that blue diamonds, unlike most other diamonds, are formed in the lower part of Earth’s mantle, and that the boron creating their blue color originates from serpentinite carried down to the mantle by subducting ocean tectonic plates.
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Incapillo is found on a crust thick, among the thickest in volcanic regions of the Earth. Several studies by Suzanne Mahlburg Kay and others indicate that trends in the isotope ratios are because of a thickening crust and increased contribution thereof to the magmas. At the latitude of Incapillo, the northern Antofalla terrane borders the Cuyania terrane, both of which were attached to South America during the Ordovician but are of different provenance. At the latitude of Incapillo, the Nazca plate subducting beneath the South America plate abruptly shallows towards the south.
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Since real data on exoplanets is currently limited, a large amount of the dialogue regarding rocky exoplanet tectonics has been driven by the results of numerical modeling studies. In such models, different planetary physical parameters are manipulated (i.e. mantle viscosity, core- mantle boundary temperature, insolation, “wetness” or hydration of subducting lithosphere) and the resultant impact on the geodynamic regime is reported. Due to computational limitations the large amount of variables that control planet geodynamics in real life cannot be accounted for; models therefore ignore certain parameters believed to be less important and emphasize others to try to isolate disproportionately important driving factors.
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Bear Glacier, the longest glacier in the park The park's landscape has been shaped by plate tectonics, with the Pacific Plate subducting beneath the North American Plate. The process has lowered the elevation of the Kenai Mountains, gradually pulling glacial features down into the sea, which is at the same time rising. The floors of the fjords can be from below the present sea level. The motion of the North Pacific Plate has accreted a variety of terranes against the shoreline, so that the coastal region is a mixture of rocks that originated elsewhere, together with local igneous rock.
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Although it is now well accepted that subducting slabs cross the mantle transition zone and descend into the lower mantle, debate about the existence and continuity of plumes persists, with important implications for the style of mantle convection. This debate is linked to the controversy regarding whether intraplate volcanism is caused by shallow, upper-mantle processes or by plumes from the lower mantle. Many geochemistry studies have argued that the lavas erupted in intraplate areas are different in composition from shallow-derived mid-ocean ridge basalts (MORB). Specifically, they typically have elevated Helium-3 – Helium-4 ratios.
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The strains caused by plate convergence in subduction zones cause at least three types of earthquakes. Earthquakes mainly propagate in the cold subducting slab and define the Wadati–Benioff zone. Seismicity shows that the slab can be tracked down to the upper mantle/lower mantle boundary (approximately six hundred kilometer depth). Nine of the ten largest earthquakes of the last 100 years were subduction zone events, which included the 1960 Great Chilean earthquake, which, at M 9.5, was the largest earthquake ever recorded; the 2004 Indian Ocean earthquake and tsunami; and the 2011 Tōhoku earthquake and tsunami.
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Oceanic crust is formed at an oceanic ridge, while the lithosphere is subducted back into the asthenosphere at trenches Oceanic trenches are topographic depressions of the seafloor, relatively narrow in width, but very long. These oceanographic features are the deepest parts of the ocean floor. Oceanic trenches are a distinctive morphological feature of convergent plate boundaries, along which lithospheric plates move towards each other at rates that vary from a few millimeters to over ten centimeters per year. A trench marks the position at which the flexed, subducting slab begins to descend beneath another lithospheric slab.
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There are, nevertheless, traces in seamounts on Hikurangi of a second Late Cretaceous magmatic event contemporaneous with volcanism on New Zealand and associated with the final break-up of Gondwana. The Hikurangi Plateau has been partly subducted under the Chatham Rise, probably during the Cretaceous, and probably resulting in a slab more than long. The western margin of the plateau is actively subducting under the North Island of New Zealand to a depth of . With these missing portions of the plateau added to it, the Hikurangi Plateau originally must have covered , an area similar to that of the Manihiki Plateau to the north.
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As one plate subducts, it sets up convection currents in the upper mantle that exert a net trenchward pull, and acts to suck both the plates together. Slab suction compared to slab pull is weaker, but not as much you might expect, considering slab pull is the strongest of the driving forces. When measuring the forces of these two mechanisms, slab pull in subducting plate boundaries for upper mantle slabs is 1.9 × 10^21 N. In comparison slab suction in the upper and lower mantle totaled 1.6 × 10^21 N.Conrad, C. P.; Lithgow-Bertelloni, C (2002). "How Mantle Slabs Drive Plate Tectonics". Science.
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Greece is located at the complex boundary zone in the eastern Mediterranean between the African Plate and the Eurasian Plate. The northern part of Greece lies on the Eurasian Plate while the southern part lies on the Aegean Sea Plate. The Aegean Sea Plate is moving southwestward with respect to the Eurasian Plate at about 30 mm/yr while the African Plate is subducting northwards beneath the Aegean Sea Plate at a rate of about 40 mm/yr. The northern plate boundary is a relatively diffuse divergent boundary while the southern convergent boundary forms the Hellenic arc.
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The angle of dip of the subducting slab, and therefore the Benioff seismic zone, is dominantly controlled by the negative buoyancy of the slab and forces from the flowing of the asthenosphere. Younger lithosphere is hotter and more buoyant, resulting in shallow-dipping Benioff zones, whereas older lithosphere is denser and colder, causing steeper dips. The Benioff zone spans from near-surface to depths of up to 670 km. The upper bound is just beneath the weak sediments in the toe of the wedge of the subduction zone, and the lower bound is where the brittle-ductile transition occurs.
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The positive buoyancy of the continental slab—in opposition principally to ridge push—can then drive exhumation of the subducting crust at a rate and mode determined by plate geometry and the rheology of the crustal materials. The Norwegian Western Gneiss Region is the archetype for this exhumation mode, which has been termed 'eduction' or subduction inversion.Andersen, T. B., Jamtveit, B., Dewey, J. F., and Swensson, E., 1991, Subduction and eduction of continental crust: major mechanism during continent-continent collision and orogenic extensional collapse, a model based on the south Caledonides: Terra Nova, v. 3, p. 303-310.
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Depending on assumptions, this part of the boundary accommodates 134–139 mm per year of relative plate motion. The southern boundary of the Bismarck Sea Plate is formed by a convergent boundary where oceanic crust of the Solomon Sea Plate is subducting northwards along the New Britain Trench, forming the New Britain island arc. It is unclear how these two boundaries link together, as the Weitin Fault becomes difficult to trace southeast of New Ireland. To the southeast, the New Britain Trench links to the Solomon Islands Trench along which the Solomon Sea Plate subducts beneath the Pacific Plate.
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Roughly 205 million years ago (during the Jurassic period) the Pangaea supercontinent began to break up as a rift separated the North American Plate from what is now Europe, and pushed it west against the Farallon Plate. During the subsequent Cretaceous Period (144 to 66 Ma ago) the entire Pacific coast of North America, from Alaska to Central America, was a subduction zone. The Farallon plate is notable for having been very large, and for subducting nearly horizontally under much of the United States and Mexico; it is likely connected with the Laramide Orogeny. ; Burke Museum.
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The Insular Mountains have much seismic activity, with the Juan de Fuca Plate subducting at the Cascadia subduction zone and the Pacific Plate sliding along the Queen Charlotte Fault. Large earthquakes have led to collapsing mountains, landslides, and the development of fissures.Insular Mountains in the Canadian Mountain Encyclopedia. Retrieved on 2007-12-02 Flood basalts on Vancouver Island form a geologic formation called the Karmutsen Formation, which is perhaps the thickest accreted section of an oceanic plateau worldwide, exposing up to of basal sediment-sill complexes, basaltic to picritic pillow lavas, pillow breccia, and thick, massive basalt flows.
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Cross section across the Mariana Plate The Mariana Plate is a micro tectonic plate located west of the Mariana Trench which forms the basement of the Mariana Islands which form part of the Izu-Bonin-Mariana Arc. It is separated from the Philippine Sea Plate to the west by a divergent boundary with numerous transform fault offsets. The boundary between the Mariana and the Pacific Plate to the east is a subduction zone with the Pacific Plate subducting beneath the Mariana. This eastern subduction is divided into the Mariana Trench, which forms the southeastern boundary, and the Izu-Ogasawara Trench the northeastern boundary.
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Mount Cleveland is located from the western end of the Aleutian Arc, a long volcanic chain extending off the coast of Alaska. Containing over 75 volcanoes, this volcanic arc occurs above the subduction zone where the Pacific Plate plunges under the North American plate. As the plate moves deeper into the earth, the increasing pressure results in the loss of volatiles, certain elements and compounds with low boiling points, from various hydrous minerals. One of these compounds is water; its addition to the mantle wedge formed between the subducting and overriding plates lowers the melting point enough to allow magma to form.
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Map of earthquake locations, showing depth contours on top of downgoing slab At the Kurile-Kamchatka Trench, the Pacific Plate is subducting beneath the Okhotsk Plate, a microplate formerly considered to be part of the North American Plate. The convergence rate ranges from ≈75 mm/yr in the north to ≈83 mm/yr at the southern end. Obliquity of convergence increases to the south, where the transpressional stress is partitioned into trench-normal thrust earthquakes and trench-parallel strike-slip earthquakes. This partitioning results in westward translation of the Kurile forearc relative to the North American Plate.
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This shallow earthquake occurred in a seismically active zone near the coast of central Mexico. The earthquake occurred near the juncture of three tectonic plates: the North American Plate to the northeast, the Rivera Plate to the northwest, and the Cocos Plate to the south. Both the Rivera Plate and the Cocos Plate are being subsumed beneath the North American Plate. The slower subducting Rivera Plate is moving northwest at about 2 cm per year relative to the North American Plate and the faster Cocos plate is moving in a similar direction at a rate of about 4.5 cm per year.
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The Nazca Plate began subducting into the Peru-Chile trench 11.2 Ma at 11°S. Due to the oblique orientation of the ridge to the Nazca-South American plate collision zone, the ridge has migrated south along the active margin to its current location at 15°S. Based on Tuamotu Plateau mirror relationship, it is estimated that of the Nazca Ridge has already subducted. The speed of migration has slowed over time, with the ridge migrating at per year until 10.8 Ma, then slowing to per year from 10.8-4.9 Ma. The current ridge migration rate is per year.
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Large magnitude and frequent earthquake activity occurring at the northern Japan Trench may be explained by variations in surface roughness of the subducting Pacific plate. Regions of smooth ocean floor subduction are correlated with typically large under-thrust earthquakes within the deeper part of the plate interface zone. No earthquakes have been observed or reported from the shallow aseismic zone of the north Japan Trench. Regions of rough ocean bottom subduction are correlated with large normal faulting earthquakes within the outer-rise region, along with larger tsunami earthquakes occurring at the shallow region of the plate interface (megathrust events) .
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Prior to Garibaldi Belt formation, a number of older, but related volcanic belts were constructed along the Southern Coast of British Columbia. This includes the east-west trending Alert Bay Volcanic Belt on northern Vancouver Island and the Pemberton Volcanic Belt along the coastal mainland. The Pemberton Belt began its formation when the former Farallon Plate was subducting under the British Columbia Coast 29 million years ago during the Oligocene epoch. At this time, the north-central portion of the Farallon Plate was just starting to subduct under the U.S. state of California, splitting it into northern and southern sections.
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The Bennett Lake Volcanic Complex was formed when the ancient Kula Plate was subducting under North America during the early Eocene period.Crustal recycling during subduction at the Eocene Cordilleran margin of North America Retrieved on 2007-06-26 Cataclysmic eruptions from the Bennett Lake Volcanic Complex were from vents along arcuate fracture systems that ejected out about of glowing avalanches of pyroclastic rock called pyroclastic flows. Evacuation of the underlying magma chamber was followed by several stages of collapse to form two calderas, one nested inside the other, that produced an elliptical depression by across. The calderas were from to deep.
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The Iapetus Ocean was an ancient ocean which existed in the Southern Hemisphere approximately 600 million years ago and was bordered by several paleocontinents: Laurentia, Ganderia, Carolinia, Avalonia, and Baltica. During a series of geological events, the Salinic orogeny and Caledonian orogeny all three land masses began to converge upon each other slowly diminishing the ocean by subducting the oceanic crust. By the end of the Silurian period, approximately 420 million years ago, the ocean had disappeared. The geological fault zone resulting from the continental collision is known as the Iapetus Suture, named after the ocean it replaced.
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Vailulu'u lies at the eastern end of the Samoan volcanic chain and is considered to be the present-day location of the Samoa hotspot; this interpretation is based on both the position of the seamount and the isotope ratios of rocks taken from it. Young rock ages have also been observed on Malumalu Seamount, implying that the hotspot is currently feeding both volcanoes and forming two separate volcanic chains. These two volcanoes are the endpoints of two separate volcano lineaments in the Samoa islands. Samoa is located just northeast of the northern corner of the Tonga Trench, where the Pacific Plate is subducting.
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The TAO evolved through a series of extensional back-arcs separated by compressional events when the subducting oceanic plate got stuck in Gondwana's margin. As Gondwana was amalgamated in the Early Palaeozoic during the so-called Pan-African orogenies the TAO propagated along the southern (modern coordinates) Proto-Pacific/Iapetus margin of the supercontinent. The TAO ended with the Gondwanide orogeny. This and younger orogens covers most of the outboard margin of the TAO, and, likewise, the inboard margin is almost entirely covered by younger deposits and ice but remains exposed in Australia along the Torrens Hinge Line or Delamarian orogeny.
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The Cascade Range is formed by an active continental margin A slice of the Earth from the Pacific Ocean through the Pacific Northwest might look something like the adjacent image. Beneath the Cascades, a dense oceanic plate plunges beneath the North American Plate; a process known as subduction. As the oceanic slab sinks deep into the Earth's interior beneath the continental plate, high temperatures and pressures allow water molecules locked in the minerals of solid rock to escape. The water vapor rises into the pliable mantle above the subducting plate, causing some of the mantle to melt.
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The width of the Cascadia subduction zone varies along its length, depending on the angle of the subducted oceanic plate, which heats up as it is pushed deeper beneath the continent. As the edge of the plate sinks and becomes hotter and more molten, the subducting rock eventually loses the ability to store mechanical stress; earthquakes may result. On the Hyndman and Wang diagram (not shown, click on reference link below) the "locked" zone is storing up energy for an earthquake, and the "transition" zone, although somewhat plastic, could probably rupture. USGS (dead link) See fig.
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The accommodation of this plate configuration results in a transform boundary along the Mendocino Fracture Zone, and a divergent boundary at the Gorda Ridge. Due to the relative plate motions, the triple junction has been migrating northwards for the past 25–30 million years, and assuming rigid plates, the geometry requires that a void, called slab window, develop southeast of the MTJ. At this point, removal of the subducting Gorda lithosphere from beneath North America causes asthenospheric upwelling. This instigates different tectonic processes, which include surficial uplift, crustal deformation, intense seismic activity, high heat flow, and even the extrusion of volcanic rocks.
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Koryaksky lies on the Pacific Ring of Fire, at a point where the Pacific Plate is sliding underneath the Eurasian Plate at about per year. A wedge of mantle material lying between the subducting Pacific Plate and the overlying Eurasian Plate is the source of dynamic volcanism over the whole Kamchatka Peninsula. The volcano has probably been active for tens of thousands of years. Geological records indicate that there have been three major eruptions in the last 10,000 years, at 5500 BC, 1950 BC and 1550 BC. These three eruptions seem to have been mainly effusive, generating extensive lava flows.
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"The transition between Makran subduction and the Zagros collision: recent advances in its structure and Active deformation", V. Regard et al, Geological Society of London 330 (2010) 41-64 ,DOI : 10.1144/SP330.4 (2010) Iran lies on the fault line between the Arabian plate and the Eurasian plate. The collision of these two plates cause most of the earthquakes that strike Iran. The specific area of the fault that lies below the Sistan and Baluchestan Province is referred to as the Makran region. In this area the Arabian Plate is folding under, or subducting, the Eurasia Plate.
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W H K Lee, H Kanamori, P C Jennings, and C. Kisslinger, Academic Press, The maximum observed lengths of ruptures and mapped faults (which may break in a single rupture) are approximately . Examples are the earthquakes in Alaska (1957), Chile (1960), and Sumatra (2004), all in subduction zones. The longest earthquake ruptures on strike-slip faults, like the San Andreas Fault (1857, 1906), the North Anatolian Fault in Turkey (1939), and the Denali Fault in Alaska (2002), are about half to one third as long as the lengths along subducting plate margins, and those along normal faults are even shorter.
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That spreading ridges could be subducted was recognized early in the development of plate tectonic theory, but there was little consideration of the ensuing effects. In the 1980s came realization that the magma welling up from the asthenosphere through the subducted ridge would not reach seawater, and thus not be quenched to form rock and close the gap. Continued spreading would lead to a widening gap or "window" in the subducting plate through which there could be increased flow of magma.. The implications of this for Siletzia were first shown by and (following the pioneering work by ).; .
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The western edge of the North American continent was later pushed against the oceanic plate under the adjacent ocean. An area of great compression called a subduction zone was formed in the early-to-mid Mesozoic, which replaced the quiet, sea-covered continental margin with erupting volcanoes and uplifting mountains. A chain of volcanoes pushed through the continental crust parallel to the deep trench, fed by magma rising from the subducting oceanic plate as it entered the Earth's hot interior. Thousands of feet (hundreds of meters) of lavas erupted, pushing the ocean over to the west.
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Map of the Zealandia continent The Hikurangi Trench, also called the Hikurangi Trough, is an oceanic trench in the bed of the Pacific Ocean off the east coast of the North Island of New Zealand, lying between the southern end of the Cook Strait and the Chatham Rise. It is the southward continuation of the much deeper Kermadec Trench. It lies in the Hikurangi Margin subduction zone, which is the southern extension of the Kermadec-Tonga subduction zone. The Hikurangi Margin is the subduction zone where the thick oceanic Hikurangi Plateau is subducting beneath continental crust of the Indo-Australian Plate.
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South of Crater Lake in Oregon, the belt bends in southeastern direction until reaching Lassen Peak. The eastern boundary of the Southern Cascades known as the Hat Creek Graben region is cut by many faults and incorporates several tectonic provinces and volcanoes. It also resides at the transition zone between the subducting Gorda tectonic plate, which is also moving under the North American Plate, the Klamath Mountain Region where the Earth's crust is shortening, and an area of normal faults. In this region, more than 500 volcanic vents have erupted in the past 7 million years.
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In normal subduction zones the coupling interface, the area in which the two plates are in close proximity, between the two plates is ~100–200 km long, but in flat slab subduction zones the coupling interface is much longer, 400–500 km. Although the lower lithosphere of the upper deforms plastically, numerical modeling has shown stress can be transmitted to crustal regions which behave in a brittle fashion. Along the subducting plate seismicity is more variable, especially intermediate-depth earthquakes. The variability may be controlled by the thickness of the crust and how efficiently it can release water.
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Volcanism in the Andes is caused by the subduction of the Nazca Plate and the Antarctic Plate beneath the South America Plate. The Nazca Plate subducts at a speed of and the Antarctic Plate at a speed of . Volcanism does not occur along a continuous chain; there are four separate regions named: the Northern Volcanic Zone, the Central Volcanic Zone, the Southern Volcanic Zone, and the Austral Volcanic Zone. The formation of magma results from the release of water and other volatile material from the subducting plate, which is then injected into the above-lying mantle wedge.
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This resulted in rapid formation of oceanic crust at ridges and hot spots, and rapid recycling of oceanic crust at subduction zones. There are at least three hypotheses of how cratons have been formed: 1) surface crust was thickened by a rising plume of deep molten material, 2) successive subducting plates of oceanic lithosphere became lodged beneath a proto-craton in an under-plating process, 3) accretion from island arcs or continental fragments rafting together to thicken into a craton.Petit (2010) p. 26 Earth's surface was probably broken up into many small plates with volcanic islands and arcs in great abundance.
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This work showed that during westward flow, the BLT in the western Pacific along the equator (138oE-145oE, 2oN-2oS) was between 18 m – 35 m corresponding with warm SST and serving as an efficient storage mechanism for heat. Barrier layer formation is driven by westward (i.e. converging and subducting) currents along the equator near the eastern edge of the salinity front that defines the warm pool. These westward currents are driven by downwelling Rossby waves and represent either a westward advection of BLT or a preferential deepening of the deeper thermocline versus the shallower halocline due to Rossby wave dynamics (i.e.
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Low frequency earthquakes were first classified in 1999 when the Japan Meteorological Agency (JMA) began differentiating LFE's seismic signature in their seismicity catalogue. The discovery and understanding of LFEs at subduction zones is due in part to the fact that the seismic signatures of these events were found away from volcanoes. Prior to their discovery, tremor events of this style were mainly associated with volcanism where the tremor is generated by partial coupling of flowing magmatic fluids. Japanese researchers first detected "low-frequency continuous tremor" near the top of the subducting Philippine Sea plate in 2002.
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The Pacific coast of Nicaragua lies above the convergent plate boundary where the Cocos Plate is subducting beneath the Caribbean Plate, at a rate of 83 mm per year. The direction of convergence is significantly oblique to the plate boundary, leading to an element of left lateral strike-slip movement within the overriding plate. Unlike the obliquely convergent boundary in Sumatra, where the strike-slip element is accommodated by displacement along the trench parallel Great Sumatran fault, no major NW-SE trending fault structure is known in Nicaragua. The most commonly mapped faults are SW-NE trending left lateral in type.
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Serpentine is also an important hydrous phase (13 wt% H2O) that is only present in oceanic crust created at a slow spreading ridge where ultramafic rocks are emplaced at shallow levels. Lawsonite does not release water until approximately 300 km depth and is the last hydrous mineral to do so. Metamorphic dehydration reactions are prominent within the subducting slab during subduction, giving rise to liquid phases that contain of fluid-mobile trace elements due to the breakdown of hydrous minerals such as phengite, lawsonite and zoisite. This creates a unique type of trace element distribution pattern for arc magma.
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Cross-sectional diagram of magmatic processes in a continental arc The dehydration of the downgoing slab and the partial melting of asthenosphere together generate the primary magma of continental arcs. Primary magma is composed of olivine tholeiitic basalt because of mixture of peridotites from the mantle wedge and large ion lithophile enriched (LIL- enriched) fluids from the dehydrating subducting plate. Because the larger thickness and lower density, the continental crust is likely to prevent the upwards rising of primary magma. Ascending primary magma is likely to pond at the bottom of continental crust, forming a magma chamber.
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This was done by constructing fault plane solutions of earthquakes in oceanic faults, which showed beach ball plots of strike slip nature (see figures), with one nodal plane parallel to the fault and the slip in the direction required by the idea of sea floor spreading from the ridges.Sykes, L.R. (1967). Mechanism of earthquakes and nature of faulting on the mid-oceanic ridges, Journal of Geophysical Research, 72, 5–27. Fault plane solutions also played the key role in the discovery that the deep earthquake zones in some subducting slabs are under compression, others are under tension.
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The Intra-Pontide Ocean stopped subducting with the collision between the Western Pontides terrain and the Eastern Pontides terrain. The Aplide orogeny stopped deposition and uplifted the Zonguldak basin during the Eocene epoch beginning at 42 Ma. The coal bearing formations experienced the highest temperatures at the onset of the Alpide orogeny. For example, the base of the Kozlu Fm experienced temperatures of 125, 175, and 140 °C in the Armutcuk, the Zonguldak, and the Amasra regions, respectively. The Alpide tectonic provinces in Anatolia, from north to south, are the Pontides, Anatolides, Tarides, and Border Folds.
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The volcanic zones of the Andes The oceanic Nazca tectonic plate is subducting at a rate of beneath the continental part of the South American tectonic plate, and this process is responsible for volcanic activity and the uplift of the Andes mountains and Altiplano plateau. The subduction is oblique, leading to strike-slip faulting. Volcanic activity does not occur along the entire length of the Andes; where subduction is shallow, there are gaps with little volcanic activity. Between these gaps lie volcanic belts: the Northern Volcanic Zone, the Central Volcanic Zone, the Southern Volcanic Zone and the Austral Volcanic Zone.
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The region probably formed far south-west of its present location where it was subsequently rifted apart when the South Fiji Basin opened in the Early Oligocene. From the Early Oligocene to Miocene the region was part of an arc that formed the northern margin of the Australian plate. The NFB back-arc basin broke through this margin 12 and has since the Late Miocene rotated the New Hebrides Arc 30° clockwise and Fiji at least 100° counter-clockwise. Today the Pacific Plate is subducting westward along the eastern margin of the NFB, the Tonga-Kermadec Trench.
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Volcanism in the Andes occurs in four distinct regions: the Northern Volcanic Zone, the Central Volcanic Zone, the Southern Volcanic Zone, and the Austral Volcanic Zone. All but the last are geographically associated with the subduction of the Nazca Plate beneath the South American Plate; the Austral Volcanic Zone involves the subduction of the Antarctic Plate beneath the South American Plate. Magmatic processes important in the Central Andes include the partial melting of the subducting plate and its sediments and of mantle peridotite, and fractional crystallization in the crust. Large scale assimilation of the crust has not been reported at Lastarria.
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Rupture areas for the 1861, 1833 and 2004 earthquakes and area of main shock and aftershocks for the 2005 event, showing similarity to 1861 quake At this plate boundary, earthquakes occur along the Sunda megathrust and within both the subducting and overriding plates. The largest earthquakes are generated when the megathrust itself ruptures. Studies of both recent and historical earthquakes show that the megathrust is segmented. The largest earthquakes occur on separate 'patches' along the megathrust surface (1797, 1833, 1861, 2004, 2005 & 2007), with smaller events occurring at the boundaries between these patches (1935, 1984, 2000 & 2002).
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Volcanic activity in the Andes and the region between the Andes and the Atlantic Ocean is caused by the subduction of the Nazca plate beneath the South America plate. While the main volcanic arc is formed by the dehydration of the descending slab of oceanic lithosphere, the origin of volcanism beneath the main volcanic arc is unclear. One of these volcanic structures is the Payenia volcanic field between 34°30′–38°S southern latitude; it was probably formed by magmas generated by asthenosphere overriding a steepening subducting Nazca plate. This province, with a surface area of , includes Payún Matrú and Llancanelo volcanic field.
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The fault is divided into three sections based on fault trace geometry, Northern extending between 41–46 km in length, Central extending between 48–53 km in length, and Southern extending 26 km in length. The fault displays a right-lateral (horizontal) motion and has formed in response to stresses from the Nazca Plate subducting under the South American Plate. It is a major fault with crustal significance. The Andes Mountain belt trends with respect to the Nazca Plate/South American Plate convergence zone, and deformation is divided between the Precordilleran thrust faults and the El Tigre strike-slip motion.
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About 50 million years ago this fast moving Indo-Australian Plate had completely closed the Tethys Ocean, the existence of which has been determined by sedimentary rocks settled on the ocean floor and the volcanoes that fringed its edges. Since both plates were composed of low density continental crust, they were thrust faulted and folded into mountain ranges rather than subducting into the mantle along an oceanic trench. An often-cited fact used to illustrate this process is that the summit of Mount Everest is made of marine limestone from this ancient ocean.Mount Everest – Overview and Information by Matt Rosenberg.
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The Austral Volcanic Zone was identified as such in 1976, but some volcanoes were identified and localized later. Owing to their similar composition the three northerly volcanoes Lautaro, Viedma and Aguilera are grouped as the "northern Austral Volcanic Zone". Volcanism in the Austral Volcanic Zone is not well known before the Holocene; it is likely that a lull of volcanism occurred before the Pliocene while the Chile Triple Junction was being subducted in the region. Magmas from the Austral Volcanic Zone are adakitic owing to the melting of the subducting slab and the interaction of these melts with the crust and mantle.
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At first the driving force for spreading was argued to be convection currents in the mantle. Since then, it has been shown that the motion of the continents is linked to seafloor spreading by the theory of plate tectonics, which is driven by convection that includes the crust itself as well. The driver for seafloor spreading in plates with active margins is the weight of the cool, dense, subducting slabs that pull them along, or slab pull. The magmatism at the ridge is considered to be passive upwelling, which is caused by the plates being pulled apart under the weight of their own slabs.
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Finney reconsidered the possibility of micro- continent model through U-Pb zircon dating and discovered that the dating result favours the Gondwana province instead of a drifting model from Laurentia. He raised multiple ideas, such as reconsidering Western Sierras Pampeanas as autochthonous to Gondwana; the rocks between Precordillera and Famatina are instead a crustal fragment of Gondwana that cannot be explained by the Laurentian drifting models. He proposed another model saying the Precordillera, or Cuyania was at the Southern margin of Gondwana and started drifting along the transform fault in mid-late Ordovician. Finally it reached the position where it was subducting beneath the Famatinan belt in Devonian.
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Rapid subduction under the southwestern North America continent began 40 to 60 million years ago (Ma), during the mid Paleocene to mid Eocene epochs. This convergent subduction margin created a distinctive geomorphologic feature called an oceanic trench, which occurs at a convergent plate boundaries as a heavy metal rich, lithospheric plate moves below a light silica rich continental plate. The trench marks the position at which the flexed subducting slab begins to descend beneath and deform the continental plate margin. By 43 Ma, during the Eocene, worldwide plate motions changed and the Pacific Plate began to move away from North America and subduction of the Farallon Plate slowed dramatically.
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As of 2013, it is generally accepted that the western quarter of North America consists of accreted terrane accumulated over roughly the past 200 m.y as the remnant Farallon Plate (the Juan De Fuca and Cocos plates) continues to convey oceanic terrane onto the continental margin. This model, however, was unable to explain many terrane complexities, and is inconsistent with seismic tomographic images of subducting slabs which penetrate the lower-mantle. Further study will be needed to understand this inconsistency in data and will, with all luck, provide a solid and concrete understanding of the western continental margin of North America and its complexities upon completion.
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The Izanagi Plate (named after the Shinto god Izanagi) was an ancient tectonic plate, which began subducting beneath the Okhotsk Plate 130–100 Ma years ago. The rapid plate motion of the Izanagi Plate caused north-west Japan and the outer zone of south-west Japan to drift northward. High-pressure metamorphic rocks were formed at the eastern margin of the drifting land mass in the Sanbagawa metamorphic belt, while low-pressure metamorphic rocks were formed at its western margin in the Abukuma metamorphic belt. At approximately 95 Ma, the Izanagi Plate was completely subducted and replaced by the western Pacific Plate, which also subducted in the north-western direction.
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A separate terrane with its own tectonic history, the Caroline Plate has been considered part of the Pacific Plate because of sparse seismicity and low velocities along its boundaries. It includes the West and East Caroline basins and the inactive Eauripik Rise separating them, but neither the Caroline Islands nor the Caroline Ridge. It is subducting under the Bird's Head and Woodlark plates along the New Guinea Trench to the south. The boundary with the Philippine Sea to the west has two segments: the southern segment, the Ayu Trough was spreading at a rate of 8 mm/yr 25–2 Ma but has been slowing down since.
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As the central oceanic plate subducts on both sides into the two overriding plates, the subducting oceanic slab brings fluids down and the fluids are released in the mantle wedge. This initiates the partial melting of the mantle wedge and the magma eventually rise into the overriding plates, resulting in the formation of two volcanic arcs on the two overriding plates. At the same time, sediment deposits on the two margins of the overriding plates, forming two accretionary wedges. As the plate subducts and rollback occurs, the ocean becomes narrower and the subduction rate reduces as the oceanic plate becomes closer to an inverted "U" shape.
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The Pelham dome—a large upland structure running north–south east of Amherst—appears to contain 600-million-year-old Avalon terrane rocks. These rocks were likely the subducting edge of the Avalon terrane which were later uplifted west of other intervening terranes sometime in the Devonian. After the Bronson Hill island arc, one of the next terranes to collide was the Merrimack terrane, which trends west to east in Ware, Gardner, and Southbridge, as well as encompassing the rocks of Mount Wachusett. A large number of Merrimack terrane rocks are west-dipping and date to the Silurian, including the Oakdale and Eliot formations or the Paxton schist.
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Daiichi- Kashima lies south of the Japan Trench on a seafloor of Valanginian age, very close to the trench. The Pacific Plate is subducting beneath Japan at a rate of and close to the Daiichi-Kashima Seamount lies the Boso Triple Junction between the Japan Trench, the Sagami Trench and the Izu-Bonin Trench. The subduction process may cause the downgoing oceanic plate to buckle and form normal faults that run parallel to the trench. Since about 100,000 years, the western half of Daiichi-Kashima is being subducted in the Japan Trench and about one third to one quarter of the seamount has been subducted already.
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Break-off of the subducting slab following the end of subduction would lead to the upwelling of hot asthenosphere, causing melting of the overlying lithosphere producing lamprophyric magmas, underplating and injecting into the crust. The granitic magmas may be a result of either partially melting the lamprophyric underplate or by differentiation from the lamprophyric magmas. Further upwelling would lead to an increase degree of melting within the crust, contributing to a decrease in the amount of mantle component in the granitic melts. This is consistent with an overall change from more basic to more acidic with time observed in the plutons and a reduction of Barium and Strontium.
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Schematic depiction of the process of slab detachment. OC=oceanic crust, OLM=oceanic lithospheric mantle, CC=continental crust, CLM=continental lithospheric mantle In plate tectonics, slab detachment or slab break-off may occur during continent-continent or arc-continent collisions. When the continental margin of the subducting plate reaches the oceanic trench of the subduction zone, the more buoyant continental crust will in normal circumstances experience only a limited amount of subduction into the asthenosphere. The slab pull forces will, however, still be present and this normally leads to the breaking off or detachment of the descending slab from the rest of the plate.
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Whether formed far offshore as seamounts, or close inshore by a slab window, the Siletzian basalts were laid down on a subducting oceanic plate: the Siletz terrane on the Farallon plate, and the Crescent terrane most likely on the adjoining Resurrection plate (previously broken away from the Kula plate, which had previously broken away from the Farallon plate). In both cases the Siletzia mass was drawn toward the subduction zone, which possibly ran diagonally across what is now Washington, approximately at the position of the Olympic-Wallowa Lineament., figure 5; see also . This would be the Challis subduction zone, but there is some question about it.
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The Valdivia earthquake released almost a quarter of all global seismic energy between 1906 and 2005 The earthquake was a megathrust earthquake resulting from the release of mechanical stress between the subducting Nazca Plate and the South American Plate, on the Peru–Chile Trench. The focus was relatively shallow at , considering that earthquakes in northern Chile and Argentina may reach depths of . Subduction zones are known to produce the strongest earthquakes on earth, as their particular structure allows more stress to build up before energy is released. Geophysicists consider it a matter of time before this earthquake will be surpassed in magnitude by another.
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The Rocky Mountains were formed by a series of events, the last of which is the Laramide Orogeny. One of the outstanding features of the Rocky Mountains is the distance of the range from a subducting plate; this has led to the theory that the Laramide Orogeny took place when the Farallon plate subducted at a low angle, causing uplift far from the margin under which the plate subducted. The lithology of the Rocky Mountains in western Canada includes a thin-skinned fold and thrust belt involving Neoproterozoic through Mississippian series of carbonates, shales, argillites and sandstones. The Colorado Plateau is a stable region dating back at least 600 million years.
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It is a thrust fault that marks the northernmost exposure of the Crescent terrane (part of Siletzia), where basalt of the Metchosin Igneous Complex (correlative with the Crescent Formation on the Olympic Peninsula) is dragged under Vancouver Island by the subducting Juan de Fuca Plate. About ten kilometers north the nearly parallel San Juan Fault marks the southern limit of rock of the Wrangellia terrane, which underlies most of Vancouver Island. Between these two northeast-dipping thrust faults are the Leech River Complex and (near Port Renfrew, but also outcrops near Victoria) the Pandora Peak Unit.The principal authority for the Leech River Fault is , summarized in .
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Diagram of the geological process of subduction An accretionary wedge or accretionary prism forms from sediments accreted onto the non-subducting tectonic plate at a convergent plate boundary. Most of the material in the accretionary wedge consists of marine sediments scraped off from the downgoing slab of oceanic crust, but in some cases the wedge includes the erosional products of volcanic island arcs formed on the overriding plate. An accretionary complex is a current (in modern use) or former accretionary wedge. Accretionary complexes are typically made up of a mix of turbidites of terrestrial material, basalts from the ocean floor, and pelagic and hemipelagic sediments.
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The volcanic zones are separated by areas where the subducting plate subducts at a flatter angle and volcanism is absent. The Peruvian flat slab between the Northern and the Central Volcanic Zones is associated with the subduction of the Nazca Ridge, the Pampean flat slab between the Central and the Southern Volcanic Zone is associated with the subduction of the Juan Fernandez Ridge, and the Patagonian volcanic gap between the Southern and the Austral Volcanic Zone is associated with the Chile Triple Junction. About 178 volcanoes are found in the Andes, 60 of which have been active in historical times. In addition, large calderas and monogenetic volcanoes exist in the Andes.
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A hypothesis based on research conducted on the Bay of Islands complex in Newfoundland suggests that an irregular continental margin colliding with an island arc complex causes ophiolite generation in a back-arc basin and obduction due to compression.Cawood, P.A. and Suhr, G., (1992) The continental margin, promontories and reentrants along its length, is attached to the subducting oceanic crust, which dips away from it underneath the island arc complex. As subduction takes place, the buoyant continent and island arc complex converge, initially colliding with the promontories. However, oceanic crust is still at the surface between the promontories, not having been subducted beneath the island arc yet.
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These terranes were subjected to extreme warping from continued subduction of the Kula plate, leading to the formation of the distorted Insular Mountains. Much of the central mountainous region around Strathcona Park is part of the Karmutsen Formation, which is a sequence of tholeiitic pillow basalts and breccias. Since Vancouver Island has become an accretionary wedge on the North American continent, the Kula Plate has fully subducted beneath it and the remnants of the Farallon Plate, the Juan de Fuca Plate, are now subducting below the island. This process has led to Vancouver Island being one of the most seismically active regions in Canada.
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At the Cascadia subduction zone, the distribution of LFEs form a surface roughly parallel to intercrustal seismic events, but displaced 5–10 kilometers down-dip, providing evidence that LFEs are generated at the plate interface. Subducting plate geometry and the kinematically defined interplate zones. The locked zone is the most shallow where the two plates are locked together, the transient slip zone is downdip of the locked zone and is the site of SSEs, and the stable slip zone is where the two plates are continuously slipping at their interface. Low frequency earthquakes are an active area of research and may be important seismic indicators for higher magnitude earthquakes.
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Receiver functions contain detailed information on the average seismic velocities within the crust and on the depth of the Moho at a specific location. This data alone can be useful in obtaining information about a specific location. But when receiver function data from one seismic station is combined with data from many other stations, it is possible to build a detailed map of the Moho depth and of seismic velocity across a large geographic area. The dipping top surfaces of subducting lithosphere is often sufficiently sharp to generate P-to-S converted phases that can be detected a depths up to 100 km or more.
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Heart Peaks is part of the Northern Cordilleran Volcanic Province, a long volcanic chain extending from just north of the city of Prince Rupert in British Columbia through Yukon to the Alaska border. Along this line, the North American Plate has been rupturing. Earth's lithosphere consists of several large tectonic plates, which slowly move towards and away from one another, either converging and subducting or diverging and rifting; volcanoes and earthquakes are generated by these activities. The west coast of North America is the site of plate margins between the large Pacific and North American plates, and also between the smaller Juan de Fuca and Cocos plates.
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It is the interaction of this down-welling mantle with aqueous fluids rising from the sinking slab that is thought to produce partial melting of the mantle as it crosses its wet solidus. In addition, some melts may result from the up-welling of hot mantle material within the mantle wedge. If hot material rises quickly enough so that little heat is lost, the reduction in pressure may cause pressure release or decompression partial melting. On the subducting side of the island arc is a deep and narrow oceanic trench, which is the trace at the Earth's surface of the boundary between the down-going and overriding plates.
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The Northern Cordilleran Volcanic Province rift The Northern Cordilleran Volcanic Province has been a zone of active volcanism since it began to form 20 million years ago. Unlike other parts of the Pacific Ring of Fire, the Northern Cordilleran Volcanic Province has its origins in continental rifting—an area where the Earth's crust and lithosphere is being pulled apart. This differs from other portions of the Pacific Ring of Fire as it consists largely of volcanic arcs formed by subducting oceanic crust at oceanic trenches along continental margins circling the Pacific Ocean. The continental crust at the Northern Cordilleran Volcanic Province is being stretched at a rate of about per year.
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Late Cretaceous paleogeographic map of the United States, showing Elkhorn volcanoes in the northwestThe rocks of the Elkhorns were formed about 74 to 81 million years ago (Late Cretaceous time) as a result of the Farallon tectonic plate subducting beneath western North America and allowing magma to rise to the surface. The Elkhorn Mountains Volcanics are extrusive rocks related to the plutonic granites of the Boulder Batholith. Volcanic flows, lahars, and ash falls from sources in the Elkhorn Mountains reach as far as Choteau, Montana, but the thickest deposits lie within a radius of about from the Elkhorns. The volcanics probably originally covered an area of about .
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Barkley Canyon extends from the continental shelf edge at 400 m down the continental slope to the canyon axis at 985 m water depth. Located at the leading edge of the Cascadia subduction zone, this site supports the study of the accretionary prism, where the sediments pile along the continental slope as they are scraped off the subducting or descending tectonic plate. This is also a location where pressure, temperature, gas saturation, and local biological and chemical conditions are just right for exposed gas hydrates to be stable on the seafloor. Gas hydrates have gas molecules, typically methane in marine environments, trapped within “cages” of water molecules.
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The Aleutian Islands are a volcanic arc lying above the convergent boundary where the Pacific Plate is being subducted beneath the North American Plate. Earthquakes in the area are caused by movement along the plate interface (such as the 1965 Rat Islands earthquake), normal faulting within the outer rise and within the subducting slab. The earthquake's epicenter lies close to a major break in the Aleutian chain, between the Andreanof Islands to the east and the Rat Islands to the west, along what is known as the Amchitka channel. In this region there is evidence for a tear in the lithosphere of the descending slab.
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The Pacific Plate is moving in a northwest direction, creating a divergence with the Gorda Plate at a speed of 5 cm per year. The Juan de Fuca Plate (including the Gorda Plate) is moving east-northeast, subducting under the North America Plate at a much slower rate of 2.5–3 cm per year. Due to the ridge being segmented into three distinct parts, each section has its own spreading rate, caused by the slab-pull and ridge-push of the surrounding tectonic plates. The northern segment is the narrowest, with portions as narrow as 3 km across, and has the fastest spreading rate of 2.9 cm per year (half-rate).
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Large magnitude earthquakes beneath the NFB have been attributed to a detached slab segment of the subducted Australian plate which collided with the subducting Pacific plate at a depth of 5 Ma. The earthquakes are the result of these colliding slabs settling on the 660 km discontinuity. Beneath Tonga at a depth of the number of earthquakes increases dramatically while the shape of the Pacific becomes complex. Hundreds of these earthquakes occur outside the Wadati- Benioff zone (top of slab) along an horizontal plane. The eastward subduction of the Australian plate (together with the now-fused South Fiji plate) under NFB created the New Hebrides and south Solomon Islands.
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The seamounts, including the Sabine Bank which reaches bsl, are the volcanic remnants of an old island arc. A -deep scarp separates the southern ridge from the North Loyalty Basin to the south. The Bougainville Guyot, south of Santos, forms the eastern continuation of the seamount chain and is a Middle Miocene andesitic volcano covered by Oligocene to Miocene lagoonal limestone. The northern ridge, a more continuous ridge similar in composition to the Mariana fore-arc, forms part of an abandoned, north-facing oceanic trench which has been subducting under the New Hebrides island arc during the last 2–3 Ma. The northern DER reaches bsl.
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Main faults of the Siculo-Calabrian rift zone Sicily lies on part of the complex convergent boundary where the African Plate is subducting beneath the Eurasian Plate. This subduction zone is responsible for the formation of the stratovolcano Mount Etna. Most of the damaging earthquakes occur on the Siculo-Calabrian rift zone, a zone of extensional faulting which runs for about , forming three main segments through Calabria, along the east coast of Sicily and immediately offshore, and finally forming the southeastern margin of the Hyblean Plateau, a carbonate platform in southeastern Sicily. Faults in the Calabrian segment were responsible for the 1783 Calabrian earthquakes sequence.
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As a slab window develops, the mantle in that region becomes increasingly hot and dry. The decrease in hydration causes arc volcanism to diminish or stop entirely, as magma production in subduction zones generally results from hydration of the mantle wedge due to de-watering of the subducting slab. Slab-window magmatism may then replace this melting, and can be produced by multiple processes, including increased temperatures, mantle circulation producing interaction of supra- and sub-slab mantle, partial melting of subducted slab edges and extension in the upper plate. Mantle flowing upward through the slab window in order to compensate for the decreased lithospheric volume can also produce decompression melting.
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Atwater's research paper, "Implications of Plate Tectonics for the Cenozoic Tectonic Evolution of Western North America", established the essential framework for the plate tectonics of western North America. In her work, she explains that approximately 40 million years ago, the Farallon Plate was subducting underneath the North American Plate and the Pacific Plate. The lower half of the Farallon plate was entirely subducted under Southern California and the upper half did not sink, which eventually became known as the Juan de Fuca Plate.Since the southern section of Farallon completely disappeared, the boundary of southern California was now between the Pacific Plate and the North American Plate.
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Map of South Sandwich Plate (SAN) shows its position between the Scotia Plate (SCO), South American Plate (SAM) and the Antarctic Plate (ANT). There are also visible The East Scotia Ridge (ESR), South Sandwich Islands (SSI) and the South Sandwich Trench (SST). The South Sandwich Plate or Sandwich Plate is a minor tectonic plate bounded by the subducting South American Plate to the east, the Antarctic Plate to the south and the Scotia Plate to the west. The plate is separated from the Scotia Plate by the East Scotia Rise, a back arc spreading ridge formed by the subduction zone on its eastern margin.
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Map of the Wells Gray- Clearwater volcanic field The Wells Gray-Clearwater volcanic field began forming approximately 3,500,000 years ago and has grown steadily since then. The tectonic causes of the volcanism that have produced the Wells Gray- Clearwater volcanic field are not yet clear and are therefore a matter of ongoing research. It is approximately inland from the north-south trending Garibaldi Volcanic Belt and is along-strike from the Nootka Fault on the British Columbia Coast, which has been subducting under the North American Plate at the Cascadia subduction zone. The Wells Gray volcanics are mostly alkali olivine basalt, with some lava flows comprising mantle xenoliths.
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Formation of the Juan de Fuca (including Explorer and Gorda) and Cocos plates (including Rivera) and of the San Andreas Fault from the Farallon plate Region of the modern Cascadia subduction zone A software model by NASA of the remnants of the Farallon Plate, deep in Earth's mantle. The Farallon Plate was an ancient oceanic plate that began subducting under the west coast of the North American Plate—then located in modern Utah—as Pangaea broke apart during the Jurassic period. It is named for the Farallon Islands, which are located just west of San Francisco, California. Over time, the central part of the Farallon Plate was completely subducted under the southwestern part of the North American Plate.
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Tectonic plates boundaries detailed-en Sunda Plate map-fr The Cenozoic plate tectonics of the Indonesian region have generated a complex assemblage of micro-continental blocks and marginal ocean basins surrounded by extensional margins, subduction zones and major transcurrent faults. The island of Borneo and the Kutai basin are located on the Sunda micro-plate, which is bounded to the north and west by the Eurasian plate, to the south by the Indo-Australian plate and to the west by the Philippine and Pacific oceanic plates. In the Cenozoic, the Indo-Australian plate has been moving north and subducting under Eurasia. The collision of the Indian continent with Eurasia halted subduction and uplifted the Himalayas.
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By far the most active deep focus faulting zone in the world is that caused by the Pacific Plate subducting under the Australian Plate, Tonga Plate, and Kermadec Plate. Earthquakes have been recorded at depths of over , the deepest in the planet. The large area of subduction results in a broad swath of deep-focus earthquakes centered from Papua New Guinea to Fiji to New Zealand, although the angle of the plates' collision causes the area between Fiji and New Zealand to be the most active, with earthquakes of 4.0 or above occurring on an almost daily basis. Notable deep-focus earthquakes in this region include a 8.2 and 7.9 earthquake in 2018, and a 7.8 earthquake in 1919.
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Cross Section of Molucca Sea Collision Zone modified by Zhang et al. While the scientific community has not come to a consensus as to when the Molucca Sea Plate became fully subducted, the dominant theory is that the Molucca Sea Plate has been completely subducted beneath the overriding Halmahera and Sangihe Plates. When actively subducting, the crustal collision of the Molucca Sea Plate was formed by surface intersection of “oppositely dipping Benioff zones” (also known as divergent double subduction) which results in the Sangihe and Halmahera volcanic arcs. The force exerted by the thick overlying collision complex of the Halmahera and Sangihe Plates effectively depressed the crust of the Molucca Sea Plate.
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A map of the Gorda and neighboring Juan de Fuca Plates subducting under the North American plate The Gorda Plate, located beneath the Pacific Ocean off the coast of northern California, is one of the northern remnants of the Farallon Plate. It is sometimes referred to (by, for example, publications from the USGS Earthquake Hazards Program) as simply the southernmost portion of the neighboring Juan de Fuca Plate, another Farallon remnant. Unlike most tectonic plates, the Gorda Plate experiences significant intraplate deformation inside its boundaries. Numerous faults have been mapped in both the sediments and basement of the Gorda Basin, which is in the interior of the plate south of 41.6°N.
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Bathymetry of the Kermadec volcanic island arc and surrounding areas The Kermadec scalyfin – part of the rich marine biota of the Kermadecs The islands are a volcanic island arc, formed at the convergent boundary where the Pacific Plate subducts under the Indo-Australian Plate. The subducting Pacific Plate created the Kermadec Trench, an 8 km deep submarine trench, to the east of the islands. The islands lie along the undersea Kermadec Ridge, which runs southwest from the islands towards the North Island of New Zealand and northeast towards Tonga (Kermadec-Tonga Arc). The four main islands are the peaks of volcanoes that rise high enough from the seabed to project above sea level.
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The remainder appear to originate in the upper mantle and have been suggested to result from the breakup of subducting lithosphere.Vincent Courtillot, Anne Davaille, Jean Besse, & Joann Stock; Three distinct types of hotspots in the Earth’s mantle; Earth and Planetary Science Letters; V. 205; 2003; pp.295–308 Recent imaging of the region below known hotspots (for example, Yellowstone and Hawaii) using seismic-wave tomography has produced mounting evidence that supports relatively narrow, deep-origin, convective plumes that are limited in region compared to the large-scale plate tectonic circulation in which they are imbedded. Images reveal continuous but torturous vertical paths with varying quantities of hotter material, even at depths where crystallographic transformations are predicted to occur.
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The Phoenix Plate (also known as the Aluk Plate or Drake Plate) was a tectonic plate that existed during the early Paleozoic through late Cenozoic time. It formed a triple junction with the Izanagi and Farallon plates in the Panthalassa Ocean as early as 410 million years ago, during which time the Phoenix Plate was subducting under eastern Gondwana. By the Late Jurassic–Early Cretaceous 150–130 million years ago, the Pacific Plate arose from the Izanagi-Farallon-Phoenix triple junction, resulting in the creation of the Izanagi-Pacific-Phoenix and Farallon-Pacific-Phoenix triple junctions. Subduction ceased east of Australia about 120 million years ago, during which time a transform/transpressional boundary formed.
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The most recent estimate of the subduction angle for the Nazca Plate is 20° to a depth of at inland. At depth, approximately inland, the plate shifts to a horizontal orientation, and continues to travel horizontally for up to inland, before resuming subduction into the asthenosphere. Image showing the lack of continental volcanism adjacent to subducting ridges Large magnitude earthquakes occur in association with the area around the Nazca Ridge subduction zone, known at the Peru megathrust. These include, but are not limited to, a magnitude 8.1 earthquake in 1942, a magnitude 8.0 earthquake in 1970, a magnitude 7.7 earthquake in 1996, a magnitude 8.4 earthquake in 2001, and a magnitude 8.0 earthquake in 2007.
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A back-arc basin is formed when a subducting plate creates accommodation space behind a volcanic arc During the Cretaceous, the basins of northern South America were connected in a back-arc basin setting. The first phase of the Andean orogeny uplifted the Western Ranges and was characterised by magmatism in the Sierra de San Lucas in the northern Central Ranges, dated to the Albian to Cenomanian epochs. Sedimentation on the northern South American platform was of siliciclastic and carbonate character, the latter more dominant in the northern areas. In the Cesar-Ranchería Basin, this led to the deposition of the main source rock formations of the basin, most notably La Luna.
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As Wellington rises, and Marlborough sinks, Cook Strait is being shifted further south.New Zealand uplift and sinking from Te Ara: The Encyclopedia of New Zealand Great stress is built up in the earth's crust due to the constant movement of the tectonic plates. This stress is released by earthquakes, which can occur on the plate boundary or on any of thousands of smaller faults throughout New Zealand. Because the Pacific Plate is subducting under the eastern side of the North Island, there are frequent deep earthquakes east of a line from the Bay of Plenty to Nelson (the approximate edge of the subducted plate), with the earthquakes being deeper to the west, and shallower to the east.
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This is thought to be related to northward tectonic movement of the West Coast relative to the rest of North America. Since about 35 million years ago, oceanic crust from the Pacific Ocean has been subducting under the continental margin, which has formed the current volcanoes as well as a number of igneous intrusions composed of diorite and gabbro. The current uplift of the Cascade Range began around 8 million years ago. Northern flank of Coquihalla Mountain Rocks similar to those in the North Cascades continue north to the vicinity of Mount Meager massif in the Coast Mountains, where they abut the Stikinia Terrane of the Omineca-Intermontane Province that dominates the Interior Plateau of British Columbia.
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Since slow slip events and their corresponding LFE signals have been recorded, none of them have been accompanied by a megathrust earthquake, however, SSEs act to increase the stress in the seismogenic zone by forcing the locked interval between the subducting and overriding plate to accommodate for down-dip movement. Some calculations find that the probability of a large earthquake occurring during a slow slip event are 30–100 times greater than background probabilities. Understanding the seismic hazard that LFEs might herald is among the primary reasons for their research. Additionally, LFEs are useful for the tomographic imaging of subduction zones because their distributions accurately map the deep plate contact near the Mohorovicic discontinuity.
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The Kantō Region lies at the complex triple junction, where the convergent boundaries between the subducting Pacific and Philippine Sea Plates and the overriding North American Plate meet. Earthquakes with epicenters in the Kanto region may occur within the Eurasian Plate, at the Eurasian Plate/Philippine Sea Plate interface, within the Philippine Sea Plate, at the Philippine Sea Plate/Pacific Plate interface or within the Pacific Plate. In addition to this set of major plates it has been suggested that there is also a separate 25 km thick, 100 km wide body, a fragment of Pacific Plate lithosphere. The 1703 earthquake is thought to have involved rupture of the interface between the Eurasian Plate and the Philippine Sea Plate.
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The islands comprising the Japanese Archipelago were separated from mainland Asia by back- arc spreading The islands of Japan are primarily the result of several large oceanic movements occurring over hundreds of millions of years from the mid- Silurian to the Pleistocene as a result of the subduction of the Philippine Sea Plate beneath the continental Amurian Plate and Okinawa Plate to the south, and subduction of the Pacific Plate under the Okhotsk Plate to the north. Japan was originally attached to the eastern coast of the Eurasian continent. The subducting plates, being deeper than the Eurasian plate, pulled Japan eastward, opening the Sea of Japan around 15 million years ago. The Strait of Tartary and the Korea Strait opened much later.
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Montana Mountain is a deeply eroded Late Cretaceous stratovolcano located south of Carcross, Yukon, Canada. As well as its main peak, the mountain includes many sub-peaks and contains felsic pyroclastics and flows;Jurassic to Cretaceous volcanics Retrieved on 2007-07-04 typically altered and orange- weathering. Montana Mountain was formed when the ancient Kula Plate was subducting under southwestern Yukon during the Late Cretaceous period. A flurry of quartz mining activity took place on Montana Mountain starting in 1899, peaking in 1905-1906 when American mining promoter John Conrad consolidated claims on Montana Mountain and built three tramways to carry the ore back down, including a 4-mile-long one from Windy Arm on Tagish Lake to the Mountain Hero mine.
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The Sunda Arc marks an active convergent boundary between the East Eurasian plates that underlie Indonesia, especially the Sunda Plate and the Burma Plate, with the India and Australian Plates that form the seabed of the Indian Ocean and the Bay of Bengal. The Sunda Arc is a classic example of a volcanic island arc, in which all the elements of such geodynamic features can be identified. The Indo-Australian Plate is subducting beneath the Sunda and Burma plates along the Sunda Arc with the plate velocity ranges from 63 mm/yr-70 mm/yr. The tectonic deformation along this subduction zone in the Java Trench (also known as the Sunda Trench) caused the 2004 Indian Ocean earthquake of 26 December 2004.
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The different volcanic zones are intercalated by volcanic gaps, zones that, despite lying at the right distance from an oceanic trench, lack volcanic activity. The Andes has three major volcanic gaps the Peruvian flat-slab segment (3 °S–15 °S), the Pampean flat- slab segment (27 °S–33 °S) and the Patagonian Volcanic Gap (46 °S–49 °S). The first one separates the Northern from the Central Volcanic Zone, the second the Central from the Southern and the last separates the Southern from the Austral Volcanic Zone. The Peruvian and Pampean gaps coincide with areas of flat slab (low angle) subduction and therefore the lack of volcanism is believed to be caused by the shallow dip of the subducting Nazca Plate in these places.
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During the late 20th century, there was significant debate within the geophysics community as to whether convection is likely to be "layered" or "whole". Although elements of this debate still continue, results from seismic tomography, numerical simulations of mantle convection and examination of Earth's gravitational field are all beginning to suggest the existence of 'whole' mantle convection, at least at the present time. In this model, cold, subducting oceanic lithosphere descends all the way from the surface to the core–mantle boundary (CMB) and hot plumes rise from the CMB all the way to the surface. This picture is strongly based on the results of global seismic tomography models, which typically show slab and plume-like anomalies crossing the mantle transition zone.
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The Hikurangi Plateau first subducted beneath New Zealand around 100 Ma during the Gondwana collision and it is currently subducting a second time as part of the convergence between the Pacific and Australian plates. These subducted parts are reaching into the mantle beneath the North Island and northern South Island. The extent of the Hikurangi Plateau slab suggests that it has played a significant role in the geology of New Zealand during the past 100 Ma. The Southern Alps in central South Island are being uplifted along the plate boundary there, a fault zone which parallels the western edge of the slab of the Hikurangi Plateau. The Australian and Pacific plates converge obliquely in the Tonga-Kermadec- Hikurangi subduction zone.
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Movements of tectonic plates create volcanoes along the plate boundaries, which erupt and form mountains. A volcanic arc system is a series of volcanoes that form near a subduction zone where the crust of a sinking oceanic plate melts and drags water down with the subducting crust. The Dome of Vitosha mountain next to Sofia Most volcanoes occur in a band encircling the Pacific Ocean (the Pacific Ring of Fire), and in another that extends from the Mediterranean across Asia to join the Pacific band in the Indonesian Archipelago. The most important types of volcanic mountain are composite cones or stratovolcanoes (Vesuvius, Kilimanjaro and Mount Fuji are examples) and shield volcanoes (such as Mauna Loa on Hawaii, a hotspot volcano).
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Li, Z., and Gerya, T. V., 2009, Polyphase formation and exhumation of high- to ultrahigh-pressure rocks in continental subduction zone; numerical modeling and application to the Sulu ultrahigh-pressure terrane in eastern China: Journal of Geophysical Research, v. 114. The material within the channel can be exhumed if: # continuous introduction of new material into the channel driven by traction of the subducting plate pushes old channel material upward; # buoyancy in the channel exceeds subduction-related traction and the channel is pushed upward by the asthenospheric mantle intruding between the plates; or # a strong indenter squeezes the channel and extrudes the material within. Buoyancy alone is unlikely to drive exhumation of UHP rocks to Earth's surface, except in oceanic subduction zones.Hacker, B.R., 2007.
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The tectonic history of Baja California was greatly influenced by the collision of the spreading ridge between the Pacific Plate and the Farallon Plate with North America during the Oligocene. Before that time, the crust of the Pacific Ocean had been subducting beneath North America; now two triple junctions formed at the contact site with the San Andreas Fault in between. Later in the Miocene, spreading between the two plates and the subduction west of Baja California ceased about 12.5 million years ago, with the spreading ridge being either subducted or just abandoned outside of the previous trench. 6 million years ago the East Pacific Rise penetrated inland into the Gulf of California, separating Baja California from the North America Plate.
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In front of the block and above the subducting oceanic plate are volcanoes emitting a range of varied deposits that give a spectrum of signatures (basaltic eruption, intermediate eruptions and acidic eruptions, as the material melting and rising changes over the period of the subduction). These volcanic deposits get mixed up with the sediment from the continent (now in the form of a back arc basin). These are the volcaniclastic deposits that we can see today at places such as The Wrekin. During the formation of the volcanoes and their associated deposits of basalt and rhyolite there are melts that never reach the surface and these shallow level intrusions are notable in the forms of their non-extrusive equivalents such as granophyre and rhyolite.
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This eruptive period postdates the formation of the Garibaldi Belt and evidence for more recent volcanism in the Alert Bay Belt has not been found, indicating that volcanism in the Alert Bay Belt is likely extinct. Bedrock under the Garibaldi chain consists of granitic and dioritic rocks of the Coast Plutonic Complex, which makes up much of the Coast Mountains. This is a large batholith complex that was formed when the Farallon and Kula plates were subducting along the western margin of the North American Plate during the Jurassic and Tertiary periods. It lies on island arc remnants, oceanic plateaus and clustered continental margins that were added along the western margin of North America between the Triassic and Cretaceous periods.
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300 px The earthquake was associated with the rupturing of approximately of the Wairarapa Fault. A horizontal displacement of up to was accompanied by uplift and tilting of the Rimutaka Range on the northwestern side of the fault with vertical offsets of about 6 metres near the fault reducing to almost nothing on the western coast of the Wellington Peninsula. The estimated magnitude of about 8.2 is unusually large for an earthquake associated with movement on a mainly strike-slip fault, and the coseismic offset would have been the largest known for such an event. It has been suggested that this was caused by the rupture propagating down to where the fault links through to the top of the subducting Pacific Plate.
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Alaska's network of faults is a result of tectonic activity; the Pacific Plate is actively subducting (sliding under) the North American Plate, and the Denali Fault is located on the boundary between the two plates. The fault's rate of displacement varies from 1 mm to 35 mm per year. It was the main fault along which the 2002 Denali earthquake occurred, which was measured as a magnitude of 7.9 Mw. During the afternoon of November 3, 2002, the water in Seattle's Lake Union suddenly began sloshing hard enough to knock houseboats off their moorings. Water in pools, ponds, and bayous as far away as Texas and Louisiana splashed for nearly half an hour. The earthquake began at 1:12 p.m.
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The Mendocino Triple Junction is located at the eastern end of the Mendocino Fracture Zone where it approaches Cape Mendocino. The Mendocino Triple Junction (MTJ) is the point where the Gorda plate, the North American plate, and the Pacific plate meet, in the Pacific Ocean near Cape Mendocino in northern California. This triple junction is the location of a change in the broad plate motions which dominate the west coast of North America, linking convergence of the northern Cascadia subduction zone and translation of the southern San Andreas Fault system. The Gorda plate is subducting, towards N50ºE, under the North American plate at 2.5 – 3 cm/yr, and is simultaneously converging obliquely against the Pacific plate at a rate of 5 cm/yr in the direction N115ºE.
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The onset of subduction of the Carnegie Ridge beneath the South American Plate has been dated variously from about mid-Miocene (15 Ma) to about Pleistocene (2 Ma). Although there is agreement that the ridge is being subducted, there is little agreement on the effect that this has had on either the subducting or over-riding plates. Some models argue that the buoyancy associated with the thickened crust of the ridge has caused the downgoing Nazca Plate to tear, leaving a relatively flat section carrying the ridge, flanked by two sections with steeper dip. The presence of a flat section is not supported by a more recent study of earthquake hypocenters, which found a constant dip of about 25°-35° down to 200 km.
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Mount Merapi viewed from 9th-century Prambanan Hindu temple, built during Mataram Kingdom era Merapi is the youngest in a group of volcanoes in southern Java. It is situated at a subduction zone, where the Indo-Australian Plate is subducting under the Sunda Plate. It is one of at least 129 active volcanoes in Indonesia, part of the volcano is located in the Southeastern part of the Pacific Ring of Fire–a section of fault lines stretching from the Western Hemisphere through Japan and South East Asia. Stratigraphic analysis reveals that eruptions in the Merapi area began about 400,000 years ago, and from then until about 10,000 years ago, eruptions were typically effusive, and the out flowing lava emitted was basaltic.
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The 2013 Saravan earthquake occurred with a moment magnitude of 7.7 at 15:14 pm IRDT (UTC+4:30) on 16 April. The shock struck a mountainous area between the cities of Saravan and Khash in Sistan and Baluchestan Province, Iran, close to the border with Pakistan, with a duration of about 25 seconds. The earthquake occurred at an intermediate depth in the Arabian plate lithosphere, near the boundary between the subducting Arabian Plate and the overriding Eurasian Plate at a depth of about 80 km. It was the largest earthquake in Iran within the last 40 years, equal in magnitude to the one that shook Tabas in 1978 killing 15,000, and possibly the largest in the last half-century.
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The lower members of this formation consist of coal beds and claystone with conglomerate made of quartzite from the Targhee uplift above.Geology of National Parks, page 568, section 7 The subducting Farallon Plate was eventually completely consumed below the North American Plate, bringing an end to the Laramide orogeny. Hot and semi-plastic rock deep below western North America responded to the lack of compression beginning 30 million years ago by slowly rising; gradually pushing the overlying rock sideways both east and west.Smith, Windows into the Earth (2000), page 103 Blocks of the brittle upper crust responded by breaking along roughly parallel north-to-south trending normal faults that each have a subsiding basin on one side and a mountain range on the other.
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For example, Kohala, the oldest volcano on Hawaii island, is one million years old and last erupted 120,000 years ago, a period of just under 900,000 years; whereas one of the oldest, Detroit Seamount, experienced 18 million or more years of volcanic activity. The oldest volcano in the chain, Meiji Seamount, perched on the edge of the Aleutian Trench, formed 85 million years ago. At its current velocity, the seamount will be destroyed within a few million years, as the Pacific Plate slides under the Eurasian Plate. It is unknown whether the seamount chain has been subducting under the Eurasian Plate, and whether the hotspot is older than Meiji Seamount, as any older seamounts have since been destroyed by the plate margin.
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The magma that forms them arises when water, which is trapped both in hydrated minerals and in the porous basalt rock of the upper oceanic crust, is released into mantle rock of the asthenosphere above the sinking oceanic slab. The release of water from hydrated minerals is termed "dewatering", and occurs at specific pressure/temperature conditions for specific minerals as the plate subducts to lower depths. The water freed from the subducting slab lowers the melting point of the overlying mantle rock, which then undergoes partial melting and rises due to its density relative to the surrounding mantle rock, and pools temporarily at the base of the lithosphere. The magma then rises through the crust, incorporating silica rich crustal rock, leading to a final intermediate composition.
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It passes directly under many settlements on the West Coast of the South Island and shaking from a rupture would likely affect many cities and towns throughout the country. The rapid uplift and high erosion rates within the Southern Alps combine to expose high grade greenschist to amphibolite facies rocks, including the gemstone pounamu (jade). Geologists visiting the West Coast can easily access high-grade metamorphic rocks and mylonites associated with the Alpine Fault, and in certain places can stand astride the fault trace of an active plate boundary. Fiordland is dominated by steep, glacier-carved valleys To the south of New Zealand the Indo-Australian Plate is subducting under the Pacific Plate, and this is beginning to result in back-arc volcanism.
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Magmatism before the Laramide orogeny migrated all the way to western South Dakota. Eventually, the magmatic activity above the flat slab may completely cease as the subducting plate and upper plate pinch out the mantle wedge. Upon the failure of the flat slab, the mantle wedge can again start circulating hot asthenosphere (1300 degrees C) in an area that has been heavily hydrated, but that had not produced any melt; this leads to widespread ignimbritic volcanism, which is seen in both the Andean flat slab effected regions and the western United States. Adakites are dacitic and andesitic magmas that are highly depleted in heavy rare-earth elements and high strontium/yttrium ratios and may be derived of melting of the oceanic crust.
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New Zealand lies along the boundary between the Indo- Australian Plate and Pacific Plates. In the South Island most of the relative displacement between these plates is taken up along a single dextral (right lateral) strike-slip fault with a major reverse component, the Alpine Fault. In the North Island the displacement is mainly taken up along the Hikurangi Subduction Zone, although the remaining dextral strike-slip component of the relative plate motion is accommodated by the North Island Fault System (NIFS). The focal mechanism of the earthquake, its depth and the distribution of aftershocks show that it was a result of oblique normal faulting within the upper part of the subducting Pacific Plate, with the rupture terminating upwards at the plate interface.
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The island of Java is the most densely populated island on Earth, and is vulnerable to both large earthquakes and volcanic eruptions, due to its location near the Sunda Trench, a convergent plate boundary where the Australian tectonic plate is subducting beneath Indonesia. Three great earthquakes occurred in the span of three years to the northwest on the Sumatra portion of the trench. The 2004 M9.15 Sumatra–Andaman, the 2005 M8.7 Nias–Simeulue, and the 2007 M8.4 Mentawai earthquakes produced the largest release of elastic strain energy since the 1957/1964 series of shocks on the Aleutian/Alaska Trench. The southeastern (Java) portion of the Sunda Trench extends from the Sunda Strait in the west to Bali Basin in the east.
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Scientists hypothesize that the shallow angle of the subducting plate increased the friction and other interactions with the thick continental mass above it. Tremendous thrusts piled sheets of crust on top of each other, building the broad, high Rocky Mountain range. Tilted slabs of sedimentary rock in Roxborough State Park near Denver The current southern Rockies were forced upwards through the layers of Pennsylvanian and Permian sedimentary remnants of the Ancestral Rocky Mountains. Such sedimentary remnants were often tilted at steep angles along the flanks of the modern range; they are now visible in many places throughout the Rockies, and are shown along the Dakota Hogback, an early Cretaceous sandstone formation running along the eastern flank of the modern Rockies.
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Bathymetry of the northeast corner of the Caribbean Plate showing the major faults and plate boundaries; view looking south-west. The main bathymetric features of this area include: the Lesser Antilles Volcanic Arc; the old inactive volcanic arc of the Greater Antilles (Virgin Islands, Puerto Rico, and Hispaniola); the Muertos Trough; and the Puerto Rico Trench formed at the plate boundary zone between the Caribbean and obliquely subducting North American Plates. Vertical exaggeration is 5:1. The northern boundary with the North American Plate is a transform or strike-slip boundary which runs from the border area of Belize, Guatemala (Motagua Fault), and Honduras in Central America, eastward through the Cayman trough along the Swan Islands Transform Fault before joining the southern boundary of the Gonâve Microplate.
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However, Newberry Volcano has been transformed by tectonic processes, possibly related to subductive mechanisms that enhance melting of the Juan de Fuca tectonic plate. The High Lava Plains Trend, or the Newberry Trend, moves at an oblique angle to the underlying North American tectonic plate, for which subduction counterflow, gravitational flow along the lithosphere's base, faulting, and extension of the Basin and Range Province have all been proposed as possible mechanisms. At Newberry, the subducting plate has a depth that is shallower than elsewhere in the major crest of the Cascades, accounting for its unique magmas. Newberry Volcano is likely fed by a magma chamber under the large, cauldron-like caldera at its summit. This caldera has dimensions of and formed about 75,000 years ago.
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The name Clayoquot (pronounced “Clah-quot”) is an anglicized version of Tla-o-qui-aht, the largest nation in the Nuu-chah-nulth (Nootka) First Nations, whose people have resided in the Clayoquot Sound region near Tofino and Ucluelet for at least the last 2000 years. The Clayoquot Slope site lies about 1250 m below sea level and approximately 20 km landward of the toe of the Cascadia subduction zone. The Cascadia subduction zone is the area at which the Juan de Fuca plate is subducting (descending) beneath the North American plate. This is a zone where much of the thick layer of sediments deposited on the eastern flank of the Juan de Fuca Ridge are scraped off and accreted as the tectonic plates converge (move together).
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The islands of Japan were separated from mainland Asia by back-arc spreading The islands of Japan are primarily the result of several large ocean movements occurring over hundreds of millions of years from the mid-Silurian to the Pleistocene as a result of the subduction of the Philippine Sea Plate beneath the continental Amurian Plate and Okinawa Plate to the south, and subduction of the Pacific Plate under the Okhotsk Plate to the north. Japan was originally attached to the eastern coast of the Eurasian continent. The subducting plates, being deeper than the Eurasian plate, pulled Japan eastward, opening the Sea of Japan around 15 million years ago. The Strait of Tartary and the Korea Strait opened much later.
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Around 23 million years ago, western Japan was a coastal region of the Eurasia continent. The subducting plates, being deeper than the Eurasian plate, pulled parts of Japan which become modern Chūgoku region and Kyushu eastward, opening the Sea of Japan (simultaneously with the Sea of Okhotsk) around 15-20 million years ago, with likely freshwater lake state before the sea has rushed in. Around 16 million years ago, in the Miocene period, a peninsula attached to the eastern coast of the Eurasian continent was well formed. About 11 million years before present, the parts of Japan which become modern Tōhoku and Hokkaido were gradually uplifted from the seafloor, and terranes of Chūbu region were gradually accreted from the colliding island chains.
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IODP Expedition 370 will seek to find the temperature limit of the deepest life on Earth by drilling in the Nankai Trough, where heat flow is particularly high near its boundary with the subducting young, hot Philippine Sea tectonic plate. At the targeted site, the geothermal gradient is about four times steeper than elsewhere in the Pacific Ocean. Reaching temperatures of approximately 130 °C in other areas would require collecting cores from approximately 4 kilometers below the seafloor, rather than 1.2 kilometers as planned by Expedition 370. Eventually, IODP Expedition 370 reached a temperature of ~120 °C at 1.2 kilometers below the seafloor with mineral evidence showing that there are localized depths with significantly higher temperatures due to hot fluids.
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If these segments are combined and reconstructed back to their original location at the surface, they equal both the NFB and the subducted part of the Australian plate since 12 Ma in area. The Tonga slab is avalanching through the 660 km layer at the southern end of the New Hebrides arc and trench. The Pacific plate has been subducting at the Tonga trench for a long time which led to an accumulation of slab material at the 660 km layer south of the Vitiaz trench while the New Hebrides island arc has been pushed southward and clockwise. It also reversed the direction of subduction and opened the NFB back-arc and pushed the Vitiaz slab into the mantle and initiated the subduction at New Hebrides trench.
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There are multiple processes that can lead to the development of high pressure terranes. First, upper crustal rocks have to be carried to great depths, nearing the mantle boundary. This could be accomplished by continental margin subduction, microcontinent subduction, sediment subduction, intracontinental subduction, subduction erosion, or foundering of a crustal root. After burial at depth, these continental rocks can then return to the surface through: eduction - the process where a slab of continental crust is subducted due to being attached to a denser subducting oceanic plate, and at some point, the downward slab pull force exceeds the strength of the slab, thus causing necking and detachment to occur, and the positive buoyancy of the continental slab leads to its exhumation.
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Location of the ridge The Mediterranean Ridge is a wide ridge in the bed of the Mediterranean Sea, running along a rough quarter circle from Calabria, south of Crete, to the southwest corner of Turkey, and from there eastwards south of Cyprus and Turkey. It is an accretionary wedge caused by the African Plate subducting under the Eurasian and Anatolian plates. As the African Plate moves slowly north-northeastward, it is plowing up the igneous and sedimentary rocks of the Mediterranean seafloor, lifting them from the seabed and creating Cyprus and other islands along the ridge. Along the ridge, five deep basins full of anoxic brine have been found, where Messinian evaporite deposits of brine caught up in this ongoing orogeny have dissolved.
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Considered an outlier of the Cascade Range, the Boring Lava Field lies about to the west of the major Cascade crest. It marks one of five volcanic fields along the Quaternary Cascade arc, along with Indian Heaven, Tumalo in Oregon, the Mount Bachelor chain, and Caribou in California. Like the Cascade Range, the Boring field was also generated by the subduction of the oceanic Juan de Fuca tectonic plate under the North American tectonic plate, but it has a different tectonic position, with its eruptive activity more likely related to tectonic rifting throughout the region. The Boring Lava Field has erupted material derived from hot mantle magma, and the subducting Juan de Fuca plate may be as shallow as in depth at their location.
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The rest of the boundary in the far northwestern part of the plate extends into Siberia. This boundary continues from the end of the Gakkel Ridge as the Laptev Sea Rift, on to a transitional deformation zone in the Chersky Range, then the Ulakhan Fault between it and the Okhotsk Plate, and finally the Aleutian Trench to the end of the Queen Charlotte Fault system. The westerly boundary is the Queen Charlotte Fault running offshore along the coast of Alaska and the Cascadia subduction zone to the north, the San Andreas Fault through California, the East Pacific Rise in the Gulf of California, and the Middle America Trench to the south. On its western edge, the Farallon Plate has been subducting under the North American Plate since the Jurassic Period.
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A study published in 2016 suggested a new parameter to determine a subduction zone's ability to generate mega-earthquakes. By examining subduction zone geometry and comparing the degree of curvature of the subducting plates in great historical earthquakes such as the 2004 Sumatra-Andaman and the 2011 Tōhoku earthquake, it was determined that the magnitude of earthquakes in subduction zones is inversely proportional to the degree of the fault's curvature, meaning that "the flatter the contact between the two plates, the more likely it is that mega- earthquakes will occur." Outer rise earthquakes occur when normal faults oceanward of the subduction zone are activated by flexure of the plate as it bends into the subduction zone. The 2009 Samoa earthquake is an example of this type of event.
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It is proposed that the Philippine Trench and PFZ represent a ‘shear partitioning’ mechanism, where the oblique physical motions of subduction at the convergent zone resulted in the development of the major strike-slip fault. In the Philippine Sea, the oblique motion of the subducting Philippine Sea Plate resulted in the formation of the Philippine trench and the PFZ back arc fault system. The oblique motion is accommodated by two vector components; one vector perpendicular to the converging Philippine Trench and one vector parallel to the PFZ. Approximately 30% of the oblique motion is accommodated by the PFZ while the remaining proportions are displaced along other regional tectonic features as the Philippine Sea Plate currently subducts below the Philippine archipelago at a rate of 6–8 cm/year.
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Initially, there will be decreased alkalic magmatism, horizontal shortening, hydration of the lithosphere above the flat-slab, and low heat flow. Upon a return to normal subduction, the hot asthenosphere will once again interact with the hydrated mantle, causing wet melting, crustal melting will ensue as mantle melts pass through, and lithospheric thinning and weakening due to the increased heat flow. The subducting slab can be lifted by aseismic ridges, seamount chains, or oceanic plateaus – which can provide a favourable environment for the development of a porphyry deposit. This interaction between subduction zones and the aforementioned oceanic features can explain the development of multiple metallogenic belts in a given region; as each time the subduction zone interacts with one of these features it can lead to ore genesis.
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The Tyrrhenian Sea west of Italy is host to a large number of deep-focus earthquakes as deep as below the surface. however, very few earthquakes occur in the region less than deep, the majority originating from a depth of around . Due to the lack of shallow earthquakes, the faulting is believed to originate from an ancient subduction zone that began subducting less than 15 million years ago, and largely finished around 10 million years ago, no longer visible on the surface. Due to the calculated subduction rate, the cause for subduction was likely to be internal stressing on the Eurasian Plate, rather than due to the collision of the African and Eurasian Plates, the cause of modern-day subduction for the nearby Aegean Sea and Anatolian microplates.
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The unusual disparity between the magnitude of the earthquake and the subsequent tsunami may be due to a combination of forces: # the tsunami was caused by a slope failure triggered by the earthquake # the rupture velocity was unusually low Scientists believe the effect of subducted sediment beneath the accretionary wedge was responsible for a slow rupture velocity. The effects of a 20° dipping fault along the top of the subducting plate was found to match both the observed seismic response and tsunami, but required a displacement of 10.4 m. The displacement was reduced to a more reasonable value after the extra uplift caused by the deformation of sediments in the wedge and a shallower fault dip of 10° was considered. This revised fault model gave a magnitude of =8.0–8.1.
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From their trace element contents and stable isotopic compositions it is inferred that the mud water is a mixture of sediment pore water (ancient seawater) and water released from dehydration of clay minerals. The 87Sr/86Sr of mud water (~0.7071) confirms the above inference and points out that altered oceanic crust plays a significant role in controlling the chemistry of water. The formation temperatures of mud ejecta, derived from mineralogical (smectite/illite), chemical (K+/Na+) and isotopic (δD/δ18O) geothermometers, lie in the range of 50 °C to 120 °C — which corresponds to a depth zone of 2 to 6 km within the Andaman forearc. It is believed that the mud volcano ejecta originate at the plate-boundary décollement zone, from the sediments and altered oceanic crust of the subducting Indian plate.
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Some geologists believe some fundamental change in convection within the Earth's mantle caused the rifting event, while others believe the huge oceanic plate became mechanically unstable as it continued to subduct beneath the Pacific Northwest. The Kula Plate once again continued to subduct beneath the continental margin, supporting the Coast Range Arc. Volcanism began to decline along the length of the arc about 60 million years ago during the early Paleogene period of the Cenozoic era as the rapid northern movement of the Kula Plate became parallel with the Pacific Northwest, creating a transform fault plate boundary similar to the Queen Charlotte Fault. During this passive plate boundary, the Kula Plate began subducting underneath Alaska and southwestern Yukon at the northern end of the arc during the early Eocene period.
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Earthquakes and active faults in western and northern Pakistan and adjacent parts of Afghanistan are the result of the Indian plate moving northward at a rate of about 40 mm/yr (1.6 inches/yr) and colliding with the Eurasian plate. Along the northern edge of the Indian subcontinent, the Indian plate is subducting beneath the Eurasian plate, causing uplift that produces the highest mountain peaks in the world, including the Himalayan, the Karakoram, the Pamir and the Hindu Kush ranges. West and south of the Himalayan front, the relative motion between the two plates is oblique, which results in strike-slip, reverse-slip, and oblique-slip earthquakes. The pattern of elastic waves that were radiated by the October 28 and 29, 2008, earthquakes implies that each earthquake was the result of predominantly strike-slip faulting.
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The subduction of bathymetric highs such as aseismic ridges, oceanic plateaus, and seamounts has been posited as the primary driver of flat slab subduction. The Andean flat slab subduction zones, the Peruvian slab and the Pampean (Chilean) flat slab, are spatially correlated with the subduction of bathymetric highs, the Nazca Ridge and the Juan Fernandéz Ridge, respectively. The thick, buoyant oceanic crust lowers the density of the slab, and the slab fails to sink into the mantle after coming to a shallow depth (~100 km) due to the lessened density contrast. This is supported by the fact that all slabs under ~50 Ma. However, there are cases where aseismic ridges on the same scale as the Nazca Ridge are subducting normally, and cases where flat slabs are not associated with bathymetric highs.
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Off the western coast of South America, the Nazca Plate subducts beneath the South America Plate. This subduction is responsible for the volcanism in the volcanic arc, but the presence of the Carnegie Ridge on the subducting plate may modify the extent of volcanism: Whereas the volcanic arc in Colombia is relatively narrow, in Ecuador it is over wide. Pilavo lies west of the main volcanic arc and is constructed on a crust that is in part derived from the Caribbean large igneous province, part of which were integrated on the Ecuadorean coast and gave the crust thus a mafic signature. Otherwise, the basement includes Cretaceous marine and volcanic sequences, and is cut by a number of faults which controlled the location of the volcanic vents including these of Pilavo.
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Off the western coast of South America, the Nazca Plate subducts beneath the South America Plate at a rate of about ; this subduction is responsible for volcanic activity in the Central Volcanic Zone and elsewhere in the Andes. Volcanism does not occur along the entire length of the subduction zone; north of 15° and south of 28° the subducting plate moves downward at a shallower angle and this is associated with the absence of volcanic activity. Other volcanic zones exist in the Andes, including the Northern Volcanic Zone in Colombia and Ecuador and the Southern Volcanic Zone also in Chile. A furtherourth volcanic zone, the Austral Volcanic Zone, is caused by the subduction of the Antarctic Plate beneath the South America Plate and lies south of the Southern Volcanic Zone.
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The subducting Louisville Ridge has caused a significant amount of erosion on the outer edge of the southern Tonga fore-arc and has probably accelerated subsidence in the Tonga Trench, a process which makes the Tonga Trench the second deepest trench on Earth and considerably deeper than the Kermadec Trench. The oldest and westernmost of the Louisville seamounts, the Osbourn Seamount, is sitting on the edge of the trench and its former flat top is currently tilting towards the trench. West of the Osbourn Seamount a broad zone of faulted blocks shallows the trench by while the adjacent fore- arc is elevated by and covered by canyons. The Louisville collision zone correlates with a zone of seismic quiescence along the Tonga-Kermadec Trench known as the "Louisville Gap".
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In a rift setting, the alkaline magma is produced by very small degrees of partial melting (<1%) of garnet peridotite in the upper mantle (200 to 600 km depth). This melt becomes enriched in incompatible elements, like the rare-earth elements, by leaching them out of the crystalline residue. The resultant magma rises as a diapir, or diatreme, along pre-existing fractures, and can be emplaced deep in the crust, or erupted at the surface. Typical REE enriched deposits types forming in rift settings are carbonatites, and A- and M-Type granitoids. Near subduction zones, partial melting of the subducting plate within the asthenosphere (80 to 200 km depth) produces a volatile-rich magma (high concentrations of CO and water), with high concentrations of alkaline elements, and high element mobility that the rare-earths are strongly partitioned into.
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This triggered the formation of evaporite basins containing halite, boron and sulfate and may have generated the nitrate deposits of the Atacama Desert. The sudden increase is explained by a sudden steepening of the subducting plate, similar to the Mid-Tertiary ignimbrite flare-up. In the northern Puna, ignimbrite activity began 10 mya, with large- scale activity occurring 5 to 3.8 Ma in the arc front and 8.4 to 6.4 Ma in the back arc. In the southern Puna, backarc activity set in 14–12 Ma and the largest eruptions occurred after 4 Ma. The start of ignimbritic activity is not contemporaneous in the entire APVC area; north of 21°S the Alto de Pica and Oxaya Formations formed 15–17 and 18–23 mya respectively, whereas south of 21°S large scale ignimbrite activity didn't begin until 10.6 mya.
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Shipping-container crane at Port-au-Prince (Haiti) harbor leaning after earthquake-induced ground failure. Seattle's waterfront faces similar risk The Seattle Fault (and the related Tacoma Fault) is not the only source of earthquake hazard in the Puget Lowland. Other faults in the near surface continental crust, such as the South Whidbey Island Fault (near Everett), and the yet to be studied Olympia Fault (near Olympia), though historically quiescent, are suspected of generating earthquakes of around magnitude 7. Others, such as the 2001 Nisqually earthquake, originate about below Puget Sound in the Benioff zone of the subducting Juan de Fuca Plate; being so deep their energy is dissipated. And there are the infrequent but very powerful great subduction events, such as the magnitude 9 1700 Cascadia earthquake, where the entire Cascadia subduction zone, from Cape Mendocino to Vancouver Island, slips.
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The subducted portion of the plate extends downward to more than 300 km (186 mi) depth, and laterally as far as mainland Canada. The relative buoyancy of the subducting plate and the underlying mantle may be inhibiting the Explorer Plate's ability to descend further into the mantle. There is an ongoing debate regarding the process of subduction of the Explorer Plate and how the boundary between the Explorer plate and the North American Plate are defined: # The Explorer Plate has stopped and may eventually accrete, fusing with the North American plate as the subduction has fully stopped and will eventually become a plate boundary between the North American Plate and Pacific Plate rather than continuing its subduction. # The Explorer Plate consists of two parts with half being fused to the North American Plate and the other half remaining a microplate system.
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The location of Telegraph IslandTelegraph Island (also known as Jazīrat al Maqlab or جزيرة_تليغراف, and Jazīrat Şaghīr) is located in the Elphinstone Inlet or Khor Ash Sham, the inner inlet of Khasab Bay, less than 400 meters off the shore of the Musandam Peninsula, and less than 500 meters south of much larger but also much lesser known Sham Island, both of which are parts of the Sultanate of Oman. It is 160 meters long, and up to 90 meters wide, yielding an area of 1.1 hectares. The name as "Telegraph" comes from the telegraph-cable repeater station built on the island in 1864. The inlet at the island is a fjord surrounded by high mountains, with notable geology in the rock strata which dip downwards under the immense pressures caused by the Arabian tectonic plate meeting (and subducting beneath) the Eurasian plate.
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In the Mesozoic, the subducting Farallon Plate had produced magma and played a role in building the Sierra Nevada mountains, but by 60 million years ago in the Cenozoic, its downward angle decreased and it moved further eastward without producing magma. The plate produced shear stress at the base of the North American Plate, driving the Laramide orogeny, which created the Rocky Mountains. Due to conditions in the underlying crust, inferred to be a thinner section of the Farallon, intense volcanic activity began in the Eocene in northern Nevada around 43 million years ago, reaching the center of the state by the Oligocene and the south by the Miocene. The volcanism was some of the most intense in Earth history, ejecting 17,000 cubic miles of material in 250 major eruptions and layering the landscape in tuff ash falls thousands of feet thick.
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During the subduction to the collisional phases of the orogenic cycle, a tectonic wedge forms on the prowedge (side of the subducting plate) and commonly the retrowedge (continental side) of the orogen. During the continued convergence, the wedge maintains its shape by maintaining its critical angle of taper by the interaction of thickening through basal accretion or foreland propagation (frontal accretion) and thinning through normal faulting and erosion at the upper part of the wedge. Erosion of the wedge significantly impacts the dynamics within the wedge, which promotes exhumation by thrusting mid-crustal rocks to the hanging wall of the wedge. Characteristics of this mode of exhumation include, evidence for strong non coaxial reverse-shearing, pro-grade metamorphism, cooling ages are progressively younger towards deeper structural levels and that exhumation at higher structural levels is coeval to burial of the structural levels.
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The gradual subsidence of the Po Valley (including that of Venice) and the folding of the mountains of eastern Italy have been investigated using seismic wave analysis of the "Apennine Subduction System." Along the Adriatic side of Italy the floor of the Adriatic Sea, referred to as the "Adriatic lithosphere" or the "Adriatic plate," terms whose precise meaning is the subject of ongoing research, is dipping under the slab on which the Apennines have been folded by compressional forces. Subduction occurs along a fault, along which a hanging wall, or overriding slab is thrust over an overridden slab, also called the subducting slab. The fault that acts as the subduction interface is at the bottom of the Apennine wedge, characterized by a deep groove in the surface, typically filled with sediment, as sedimentation here occurs at a much faster rate than subduction.
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The Yukon–Tanana and Cassiar terranes consist of shifted sedimentary and metamorphic rocks that were derived from the North American continent. The southern boundary of the Northern Cordilleran Volcanic Province is parallel with southwestern Stikinia and is characterized by separate volcanic vents and erosional remains of lavas south of the small community of Stewart. The southern boundary of the Northern Cordilleran Volcanic Province also parallels with a gap in modern volcanism and the supposed northern boundary of the Cascadia subduction zone, defined by the eastward extension of the northern edge of the subducting Juan de Fuca Plate. These two zones divide the Northern Cordilleran Volcanic Province from modern volcanic zones further south, including the broad Chilcotin Plateau, the east-west trending Anahim Volcanic Belt and the monogenetic Wells Gray-Clearwater volcanic field in the British Columbia Interior.
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Basalts formed at mid-ocean ridges and hotspots originate in the mantle and are used to provide information on the composition of the mantle. Magma rising to the surface may undergo fractional crystallization in which components with higher melting points settle out first, and the resulting melts can have widely varying water contents; but when little separation has occurred, the water content is between about 0.07–0.6 wt%. (By comparison, basalts in back- arc basins around volcanic arcs have between 1 wt% and 2.9 wt% because of the water coming off the subducting plate.) Mid-ocean ridge basalts (MORBs) are commonly classified by the abundance of trace elements that are incompatible with the minerals they inhabit. They are divided into "normal" MORB or N-MORB, with relatively low abundances of these elements, and enriched E-MORB.
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The Kula Plate began subducting under the Pacific Northwest region of North America during the Late Cretaceous period much like the Pacific Plate does, supporting a large volcanic arc system from northern Washington to southwestern Yukon called the Coast Range Arc. There was a triple junction of three ridges between the Kula Plate to the north, the Pacific Plate to the west and the Farallon Plate to the east. The Kula Plate was subducted under the North American Plate at a relatively steep angle, so that the Canadian Rockies are primarily composed of thrusted sedimentary sheets with relatively little contribution of continental uplift, while the American Rockies are characterized by significant continental uplift in response to the shallow subduction of the Farallon Plate. About 55 million years ago, the Kula Plate began an even more northerly motion.
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According to the USGS: > The Mw 6.8 Honshu earthquake of June 13th 2008 occurred in a region of > convergence between the Pacific Plate and the Okhotsk section of the North > American Plate in northern Japan, where the Pacific plate is moving west- > northwest with respect to North America at a rate of approximately 8.3 > cm/yr. The hypocenter of the earthquake indicates shallow thrusting motion > in the upper (Okhotsk) plate, above the subducting Pacific plate, which lies > at approximately 80 km depth at this location. > The earthquake occurred in a region of upper-plate contraction, probably > within the complicated tectonics of the Ou Backbone Range, known to have > hosted several large earthquakes in historic times. The largest of these > events occurred in 1896, approximately 70km north of the June 13th event, > and killed over 200 people in the local area.
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Variation of seismicity with depth across the Sunda Trench subduction zone, low-angle part is the Sunda megathrust – September 2007 Sumatra earthquake shown by star The Sunda megathrust is a fault that extends approximately 5,500 km (3300 mi) from Myanmar (Burma) in the north, running along the southwestern side of Sumatra, to the south of Java and Bali before terminating near Australia. It is a megathrust, located at a convergent plate boundary where it forms the interface between the overriding Eurasian plate and the subducting Indo-Australian plate. It is one of the most seismogenic structures on Earth, being responsible for many great and giant earthquakes, including the 2004 Indian Ocean earthquake and tsunami that killed over 230,000 people. The Sunda megathrust can be divided into the Andaman Megathrust, Sumatra(n) Megathrust and Java(n) Megathrust.
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In the southern Appalachians of Alabama, Georgia, and North Carolina, the Taconic orogeny was not associated with collision of an island arc with ancient North America (Laurentia). Geologists working in these areas have long puzzled over the "missing" arc terrane typical of Taconic-aged rocks in New England and Canada. Instead, the Iapetus margin of this part of Laurentia appears to have faced a back-arc basin during the Ordovician, suggesting that Iapetus oceanic crust was subducted beneath Laurentia - unlike the New England and Canadian segments of the margin, where Laurentia was on the subducting plate. In contrast to the Ordovician geologic history of New England, rocks in Alabama, Georgia, and North Carolina, including those of the Dahlonega gold belt (GA and NC), Talladega belt (Alabama and Georgia), and eastern Blue Ridge (AL, GA, and NC), are not typical of a volcanic arc in its strictest sense.
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The rest of the material is then carried upwards due to chemical buoyancy and contributes to the high levels of basalt found at the mid-ocean ridge. The resulting motion forms small clusters of small plumes right above the core- mantle boundary that combine to form larger plumes and then contribute to superplumes. The Pacific and African LLSVP, in this scenario, are originally created by a discharge of heat from the core (4000 K) to the much colder mantle (2000 K), the recycled lithosphere is only fuel that helps drive the superplume convection. Since it would be difficult for the Earth's core to maintain this high heat by itself, it gives support for the existence of radiogenic nuclides in the core, as well as the indication that if fertile subducted lithosphere stops subducting in locations preferable for superplume consumption, it will mark the demise of that superplume.
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In the second type, subducting oceanic plates (which largely constitute the upper thermal boundary layer of the mantle) plunge back into the mantle and move downwards towards the core-mantle boundary. Mantle convection occurs at rates of centimeters per year, and it takes on the order of hundreds of millions of years to complete a cycle of convection. Neutrino flux measurements from the Earth's core (see kamLAND) show the source of about two- thirds of the heat in the inner core is the radioactive decay of 40K, uranium and thorium. This has allowed plate tectonics on Earth to continue far longer than it would have if it were simply driven by heat left over from Earth's formation; or with heat produced from gravitational potential energy, as a result of physical rearrangement of denser portions of the Earth's interior toward the center of the planet (i.e.
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The Boring Lava Field has erupted material derived from hot mantle magma, and the subducting Juan de Fuca plate may be as shallow as in depth at their location. The High Cascades, a segment of the Cascade volcanic arc that includes the Boring Lava Field, is characterized by basaltic lava flows with andesite, tuff breccia, and volcanic ash. The High Cascades may lie over a graben (a depressed block of the Earth's crust bordered by parallel faults), and activity at the Boring field and throughout the Portland area may be associated with deformation of the block. Portland lies within the Portland Basin, part of the forearc (the region between an oceanic trench and the associated volcanic arc) between the Cascades major arc and the Pacific Coast Ranges, which consist of Eocene to Miocene marine sedimentary rock deposits and Eocene intrusions and extrusions of basalt that were emplaced on the Siletz terrane.
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Cyprus is located at the boundary between the African and Eurasian plate, an active margin in which the African plate is colliding with the Eurasian plate. This collision between two plates is the cause for the large magnitude and frequent earthquakes, especially seen in the southern portion of the Island where a portion of the African plate is thought to be subducting underneath Cyprus. Historically Cyprus has been affected by 16 destructive earthquakes, 7 or higher on the modified Mercalli scale, from 26 B.C. to 1900 A.D. Six earthquakes of note affected Cyprus during the Roman period. In 26 B.C. an earthquake with an intensity of 7 with an epicenter located southwest of Cyprus caused damage in the city of Paphos. In 15 B.C. many towns in Cyprus experienced a magnitude 8 earthquake, but at Paphos and Kourion it registered as a magnitude 9.
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Nankai megathrust earthquakes are great megathrust earthquakes that occur along the Nankai megathrust – the fault under the Nankai Trough – which forms the plate interface between the subducting Philippine Sea Plate and the overriding Amurian Plate (part of the Eurasian Plate), which dips beneath southwestern Honshu, Japan. The fault is divided into five segments in three zones, which rupture separately or in combination, and depending on location, the resulting earthquakes are subdivided by zone from west to east into Nankai earthquakes, Tōnankai earthquakes, and Tōkai earthquakes. The earthquakes occur with a return period of about 90–200 years, and often occur in pairs, where a rupture along part of the fault is followed by a rupture elsewhere, notably the 1854 Ansei-Tōkai earthquake and the 1854 Ansei-Nankai earthquake the next day, and the 1944 Tōnankai earthquake, followed by the 1946 Nankaidō earthquake. In one recorded case (the 1707 Hōei earthquake) the fault ruptured along its entire length.
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Volcanoes in the Andes occur in four separate regions: the Northern Volcanic Zone between 2°N and 5°S, the Central Volcanic Zone between 16°S and 28°S, the Southern Volcanic Zone between 33°S and 46°S, and the Austral Volcanic Zone, south of the Southern Volcanic Zone. These volcanic zones are separated by areas where recent volcanism is absent; one common theory is that the subduction processes responsible for volcanism form a subducting plate that is too shallow to trigger the formation of magma. This shallow subduction appears to be triggered by the Nazca Ridge and the Juan Fernandez Ridge; the areas where they subduct beneath the Peru-Chile Trench coincide with the limits of the Central Volcanic Zone. It is possible that when these ridges are subducted, the buoyancy they carry disrupts the subduction process and reduces the supply of water, which is important for the formation of melts.
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The Nazca Plate and Antarctic Plate subduct beneath the South America Plate in the Peru-Chile Trench at a pace of and , respectively, resulting in volcanic activity and geothermal manifestations in the Andes. Present-day volcanism occurs within four discrete belts: the NVZ (between 2°N–5°S), the CVZ (16°S–28°S), the SVZ (33°S–46°S) and the Austral Volcanic Zone (AVZ) (49°S-55°S). Between them they contain about 60 active volcanoes and 118 volcanoes which appear to have been active during the Holocene, not including potentially active very large silicic volcanic systems or very small monogenetic ones. These belts of active volcanism occur where the Nazca Plate subducts beneath the South America Plate at a steep angle, while in the volcanically inactive gaps between them the subduction is much shallower; thus there is no asthenosphere between the slab of the subducting plate and the overriding plate in the gaps.
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Subduction zones are important for several reasons: # Subduction Zone Physics: Sinking of the oceanic lithosphere (sediments, crust, mantle), by contrast of density between the cold and old lithosphere and the hot asthenospheric mantle wedge, is the strongest force (but not the only one) needed to drive plate motion and is the dominant mode of mantle convection. # Subduction Zone Chemistry: The subducted sediments and crust dehydrate and release water-rich (aqueous) fluids into the overlying mantle, causing mantle melting and fractionation of elements between surface and deep mantle reservoirs, producing island arcs and continental crust. Hot fluids in subduction zones also alter the mineral compositions of the subducting sediments and potentially the habitability of the sediments for microorganisms. # Subduction zones drag down subducted oceanic sediments, oceanic crust, and mantle lithosphere that interact with the hot asthenospheric mantle from the over-riding plate to produce calc- alkaline series melts, ore deposits, and continental crust.
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North of the Mendocino Triple Junction, the Gorda plate is subducting beneath the North American Plate at the Cascadia subduction zone, with a convergence rate of per year, but comparisons with other subduction zones have led to a belief that the convergence may be taking place aseismically. The distinct lack of interplate events there has generated contention regarding the zone's seismic hazard, though there are strong indications that substantial historic events have occurred in the Pacific Northwest. Submerged wetlands and raised marine terraces both illustrate the presence of past events, and radiocarbon dating of rock layers has revealed that three seismic events took place in the last 2,000 years, with the most recent event being the 1700 Cascadia earthquake. The Gorda Plate is undergoing a process of intraplate deformation and experiences large intraplate earthquakes that may be the result of north- south compression of the oceanic crust along the Mendocino Fracture Zone.
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The Kanto area lies above a complex part of the convergent boundaries between the subducting Pacific and Philippine Sea Plates and the overriding Eurasian and North American Plates. Earthquakes with epicenters in the Kanto region may occur within the Eurasian Plate, at the Eurasian Plate/Philippine Sea Plate interface, within the Philippine Sea Plate, at the Philippine Sea Plate/North American Plate interface (under the Sagami Trough), at the Philippine Sea Plate/Pacific Plate interface (Izu-Bonin-Mariana Arc), or within the Pacific Plate. In addition to this set of major plates it has been suggested that there is also a separate 25 km thick, 100 km wide body, a fragment of Pacific Plate lithosphere. The cause of the 1855 earthquake is unknown; it is consistent with a rupture along the interface between the Eurasian and Philippine Sea Plates, adjacent to, and down dip from, the rupture that caused the 1923 Great Kantō earthquake.
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The map shows the features of the Philippine Sea Plate. Benham Rise is a submerged extinct volcanic ridge located at 16 degrees 30 minutes N, 124 degrees 45 minutes E off the coast of Luzon, with the size of about 250 km in diameter and rises over 2,000 meters (2 km.) above the sea floor, from below 5,000 meters (5 km.) below sea level to above 3,000 meters (3 km.) below sea level. Its area is close to the Benham Seamount, located at 15 degrees 48 minutes N, 124 degrees 15 minutes E. The precise location is somewhere near the east of the Philippine Trench and near the south of the East Luzon Trench, both of which absorb the subducting force of the Philippine Sea Plate under the Philippine Mobile Belt,Hashimoto, M, ed., (1981) Accretion Tectonics in the Circum- Pacific Regions, p299 a collage of large blocks of that crust that amalgamated prior to the collision of the Philippine Sea Plate with the Eurasian Plate.
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Their activity began 16million years ago, when the Chile Rise collided with the Peru-Chile Trench and thus caused a tear in the subducting slab and the formation of a slab window beneath Patagonia; later it was suggested that slab rollback might instead be the mechanism by which volcanism is triggered in the Pali-Aike region. The age trends of volcanism has been interpreted as indicating either a southward migration or a northeastward one in the case of the plateau lavas, following the movement of the triple junction to the north; in that case Pali-Aike would be an exception, probably due to local tectonic effects. However, some older plateau lavas in the north formed in response to an earlier ridge subduction event in the Eocene and Paleocene. farther west from Pali-Aike lies the actual Andean volcanic arc in the form of the Austral Volcanic Zone, a chain of stratovolcanoes and one volcanic field (Fueguino) which is South America's southernmost volcano.
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During the last 66 million years, nearly the entire west coast of North America was dominated by a subduction zone, with the Farallon Plate subducting beneath the North American Plate. Presently, the Juan de Fuca Plate (with its Explorer and Gorda satellite plates) and the Rivera and Cocos Plates are the only remnants of the once much larger Farallon Plate. The plate margin that remains in California is that of the strike-slip San Andreas Fault (SAF), the diffuse Pacific–North American plate boundary that extends east into the Basin and Range Province of eastern California and western Nevada (a seismically active area called Walker Lane) and southwest into the California Continental Borderland region off the central and southern coasts. This system of faults terminates in the north at the Mendocino Triple Junction, one of the most seismically active regions in the state, where earthquakes are occasionally the result of intraplate deformation within the Gorda Plate.
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The Pacific plate, for instance, is essentially surrounded by zones of subduction (the so-called Ring of Fire) and moves much faster than the plates of the Atlantic basin, which are attached (perhaps one could say 'welded') to adjacent continents instead of subducting plates. It is thus thought that forces associated with the downgoing plate (slab pull and slab suction) are the driving forces which determine the motion of plates, except for those plates which are not being subducted. This view however has been contradicted by a recent study which found that the actual motions of the Pacific Plate and other plates associated with the East Pacific Rise do not correlate mainly with either slab pull or slab push, but rather with a mantle convection upwelling whose horizontal spreading along the bases of the various plates drives them along via viscosity-related traction forces. The driving forces of plate motion continue to be active subjects of on-going research within geophysics and tectonophysics.
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About 50 million years ago the Siletzia terrane, being borne to the northeast by the subducting plate, refused to be subducted. It ran it into the edge of the continent and embayed the overlying crust, bending the section of the Wrangellia—Pacific Rim contact now known as the San Juan fault to its current easterly orientation. This also initiated the oblique left-lateral Devils Mountain fault, including the section now known as the Leech River fault, and its right-lateral extension, the Darrington fault, that strikes southward from the town of Darrington to converge with the right-lateral strike-slip Straight Creek Fault at the OWL (see map).If connected strike-slip faults having opposite senses of movement seems strange, consider the Crescent terrane (the part of Siletzia relevant here) as a very blunt arrowhead: the point is now near Darrington (unlabelled black square on map); the Devils Mountain and Darrington faults are the opposite sides of the arrow head.
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The Tonga and Kermadec Plates originated about 4-5 million years ago. Before their creation, the Pacific Plate was subducting under the Australian Plate, producing the Lau-Colville Ridge (now extinct). About 6 million years ago, this region underwent crustal extension and through a complicated series of spreading centers, ultimately leading to the separation of the Pacific and Australian Plate and the creation of what are now Tonga and Kermadec Plates. The Tonga and Kermadec Plates separated because the northern portion of the original plate was growing much more quickly (96 mm/year) than the southern portion (39 mm/year), eventually generating a transform fault between them, creating the Tonga and Kermadec Plates. Just as this phenomenon created the Tonga and Kermadec Plates, it was also the cause of the creation of the Niuafo’ou microplate to the northwest of the Tonga Plate because the Tonga's northern portion is still growing much faster than the southern counterpart.
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