They believed that some of those minerals could be olivine and pyroxene, which are found in asteroids and Earth's upper mantle.
|
|
But Earth's lithosphere, meaning its crust and upper mantle, contains magnetic minerals that contribute a small boost to this defensive field.
|
|
The project started with an attempt to make a detailed map of the thickness of Earth's lithosphere (its crust and upper mantle).
|
|
Although scientists have a detailed understanding of how Earth's tectonic plates interact, the region just below, in the upper mantle, remains relatively unobserved.
|
|
The researchers believe the "great valley" formed as Mercury's interior cooled, which caused the planet's crust and upper mantle to contract and bend.
|
|
Case in point: the Northern Appalachian Anomaly (NAA), a 250 mile (400 km)-wide hotspot centered in the upper mantle beneath southern New Hampshire.
|
|
Hansen suspects the volcano's magma source lies to the east, closer to the rest of the Cascade Arc, where material in the upper mantle is hotter.
|
|
But that still leaves the question of why gooey rock being forced westward, through the crust or upper mantle, to erupt in this one off-kilter location.
|
|
Among the initiatives planned by the IODP for the next three decades is probing the deep Earth -- the moonshot of hitting the upper mantle being one goal.
|
|
"I will be interested to see if the new techniques and data used by the authors to produce this analysis will reveal similar areas in the upper mantle in other unexpected locations around the US," Murray said.
|
|
Because of the diamonds' size and chemistry, Dr. Gillet and his team concluded that the diamonds formed under intense pressure, of about 20 giga-pascals, which is close to the pressure seen 400 miles below Earth's surface where the upper mantle transitions into the lower mantle.
|
|
The entire mantle is thought to deform like a fluid on long timescales, with permanent plastic deformation. The highest pressure of the upper mantle is compared to the bottom of the mantle which is . Estimates for the viscosity of the upper mantle range between 1019 and 1024 Pa·s, depending on depth, temperature, composition, state of stress, and numerous other factors. The upper mantle can only flow very slowly.
|
|
The magma originated in the upper mantle under tension conditions on the continental margin.
|
|
The Ch'iyar Qullu magmas are Central Andes intraplate magmas and originate from the upper mantle.
|
|
Due to the varying temperatures and pressures between the lower and upper mantle, a variety of creep processes can occur with dislocation creep dominating in the lower mantle and diffusional creep occasionally dominating in the upper mantle. However, there is a large transition region in creep processes between the upper and lower mantle and even within each section, creep properties can change strongly with location and thus temperature and pressure. In the power law creep regions, the creep equation fitted to data with n = 3–4 is standard. Since the upper mantle is primarily composed of olivine ((Mg,Fe)2SiO4), the rheological characteristics of the upper mantle are largely those of olivine.
|
|
The melts originally came from the upper mantle which, over time, was progressively depleted by every following melting event.
|
|
Oceanic crust is thinner than continental crust and is generally less than thick. Continental crust is about thick, but the large crustal root under the Tibetan Plateau is approximately thick. The thickness of the upper mantle is about . The entire mantle is about thick, which means the upper mantle is only about 20% of the total mantle thickness.
|
|
Lherz Massif is an upper mantle peridotite body in the French Pyrenees. The rock lherzolite takes its name from this rock body.
|
|
The upper mantle of Earth is composed mainly of olivine and pyroxene. Pyroxene and feldspar are the major minerals in basalt and gabbro.
|
|
Descending slabs have colder than average temperatures. Phase transformations of olivine moving through the upper mantle, transition zone, and lower mantle. In the core, water might be stored as hydrogen bound to iron. The mantle can be divided into the upper mantle (above 410 km depth), transition zone (between 410 km and 660 km), and the lower mantle (below 660 km).
|
|
This melt supply may still be continuing today as indicated by a low-velocity anomaly in the upper mantle beneath the western Lau Basin.
|
|
The seismic data is not sufficient to determine the composition of the mantle. Observations of rocks exposed on the surface and other evidence reveal that the upper mantle are mafic minerals olivine and pyroxene and it has a density of about Upper mantle material which has come up onto the surface is made up of about 55% olivine and 35% pyroxene and 5 to 10% of calcium oxide and aluminum oxide. The upper mantle is dominantly peridotite, composed primarily of variable proportions of the minerals olivine, clinopyroxene, orthopyroxene, and an aluminous phase. The aluminous phase is plagioclase in the uppermost mantle, then spinel, and then garnet below ~100 km.
|
|
The Merlis Serpentinites are an aligned group of small serpentinite outcrops in the northwestern French Massif Central. Their parent rocks were peridotites from the upper mantle.
|
|
This process usually occurs in areas with especially weak crust and upper mantle, such as the Tibetan Plateau (Figure 1). Intraplate deformation brings another aspect to plate tectonic theory.
|
|
C. Mercier, Insight into the upper mantle beneath an active extensional zone: The spinel-peridotite xenoliths from San Quintín (Baja California, México), Contrib. Mineral. Petrol., 100, 374-382, 1988.
|
|
Diatreme formation is sometimes associated with kimberlite magma, which originates in the upper mantle. When a diatreme is formed due to a kimberlite intrusion, there is a possibility that diamonds may be brought up, because diamonds are formed in the upper mantle at depths of 150-200 kilometers. Kimberlite magmas can sometimes include chunks of diamond as xenoliths, making them economically significant. Diatremes are sometimes associated with deposition of economically significant mineral deposits.
|
|
1 = continental crust, 2 = oceanic crust, 3 = upper mantle, 4 = lower mantle, 5+6 = core, A = crust- mantle boundary (Mohorovičić discontinuity) The density profile through Earth is determined by the velocity of seismic waves. Density increases progressively in each layer largely due to compression of the rock at increased depths. Abrupt changes in density occur where the material composition changes. The upper mantle begins just beneath the crust and ends at the top of the lower mantle.
|
|
Glossodoris pallida is semi-translucent-white all over with a thin yellow-margined mantle. It also has opaque white patches on its upper mantle. Both its gills and rhinophores are also white.
|
|
Uranium decay- series disequilibria data has shown that the actively flowing region of the melt zone is km wide at its base and at the upper mantle upwelling, consistent with tomographic measurements.
|
|
1930, Radioactivity and Earth movements. Geological Society of Glasgow Transactions, 18, pp.559-606. However, some studies have shown that the upper mantle (asthenosphere) is too plastic (flexible) to generate enough friction to pull the tectonic plate along. Moreover, mantle upwelling that causes magma to form beneath the ocean ridges appears to involve only its upper 400 km (250 mi), as deduced from seismic tomography and from observations of the seismic discontinuity in the upper mantle at about 400 km (250 mi).
|
|
"The Homestead Kimberlite, Central Montana, USA: Mineralogy, Xenocrysts, and Upper- Mantle Xenoliths." In 8th International Kimberlite Conference: The J. Barry Hawthorn Volume. Vol. 2. T. Stachel, ed. Maryland Heights, Mo.: Gulf Professional Publishing, 2004.
|
|
This dove is about long. The forehead and lores are ashy grey, and the crown is dark slaty. The nape and upper mantle are chestnut. The lower mantle is olive and has bronze reflections.
|
|
View from Balcreuchan Cave entrance down to the beach A basalt boulder near the cave The rocks here are a section of ancient oceanic crust around 500 million years old. This rare rock formation has formed because a fragment of oceanic crust has been emplaced onto continental crust. In the bay, rocks of the upper mantle progress to igneous rocks of the oceanic crust and finally on to the sedimentary rocks of the ancient sea floor. The rarely exposed rocks of the upper mantle are visible.
|
|
Two types of magma have been determined to have generated in the Earth's upper mantle by partial melting of mantle rocks. One of these magma types is basaltic in composition, composed of plagioclase, titanium-rich pyroxene, and olivine. The other magma type crystallized to nepheline, melilite, pyroxene, and, in some of the rocks, plagioclase. Some nepheline-bearing igneous rocks contain rounded inclusions of spinel peridotite, an ultramafic rock that may represent fragments of the upper mantle incorporated into the magma during its ascent to the surface.
|
|
In the deeper crust and upper mantle, the high frequency shear waves split completely into two separate shear waves with different polarizations and a time delay between them that may be up to a few seconds.
|
|
These boulder fields in southeastern Pennsylvania and central New Jersey formed from a group of diabase sills in Newark Basin. The sills were formed when stretching of the Earth's crust allowed mafic magma to travel up from the upper mantle inject into the sedimentary basin 200 million years ago (early Jurassic Period). Phenocrysts of two minerals that had crystallized in the upper mantle, olivine and pyroxene, quickly settled out of the magma and collected along the base of the sills. When fully solidified, this crystal-rich layer formed a separate rock unit thick.
|
|
Mineral transformations in the mantle The top of the mantle is defined by a sudden increase in seismic velocity, which was first noted by Andrija Mohorovičić in 1909; this boundary is now referred to as the Mohorovičić discontinuity or "Moho". The upper mantle is dominantly peridotite, composed primarily of variable proportions of the minerals olivine, clinopyroxene, orthopyroxene, and an aluminous phase. The aluminous phase is plagioclase in the uppermost mantle, then spinel, and then garnet below ~100 km. Gradually through the upper mantle, pyroxenes become less stable and transform into majoritic garnet.
|
|
Pressure increases as depth increases, since the material beneath has to support the weight of all the material above it. The entire mantle, however, is thought to deform like a fluid on long timescales, with permanent plastic deformation accommodated by the movement of point, line, and/or planar defects through the solid crystals composing the mantle. Estimates for the viscosity of the upper mantle range between 1019 and 1024 Pa·s, depending on depth, temperature, composition, state of stress, and numerous other factors. Thus, the upper mantle can only flow very slowly.
|
|
Young, R.E. & M. Vecchione (1999). Pholidoteuthis adami Dermal Cushions. Tree of Life Web Project. It has been proposed that these two species achieve buoyancy by means of the fluid stored in their vacuolate dermal cushions and upper mantle layer.
|
|
The adult male plumage is reached in the second year. Females are brown and shorter-tailed than the males. Females of some subspecies have whitish underparts strongly patterned with black, and in L. n. whiteheadi this extends to the upper mantle.
|
|
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.
|
|
The mechanism behind the lower zone of seismicity, located in the upper mantle portion of the down- going lithosphere, is still debated; the global ubiquity of double Benioff zones indicates that it must be a process that commonly occurs in subduction zones. Some of the suggested instability mechanisms include dehydration embrittlement caused by the breakdown of antigorite or chlorite in a hydrated peridotite upper mantle, and un-bending of the slab. Observations from seismic studies indicate that the lithospheric mantle at the intermediate depths where double Benioff zones occur is dry, which favours the proposed slab-unbending mechanism.
|
|
The upper mantle of the Earth is a very thick layer of rock inside the planet, which begins just beneath the crust (at about under the oceans and about under the continents) and ends at the top of the lower mantle at . Temperatures range from approximately at the upper boundary with the crust to approximately at the boundary with the lower mantle. Upper mantle material which has come up onto the surface is made up of about 55% olivine, 35% pyroxene and 5 to 10% of calcium oxide and aluminum oxide minerals such as plagioclase, spinel or garnet, depending upon depth.
|
|
A lithospheric drip is a geological phenomenon in which a dense and relatively cold mass of lithosphere sinks into the more fluid upper mantle. The regions of descending material have been detected by seismic tomography methods and modeled as near vertically oriented cylindrical masses within the upper mantle. The lithospheric drip discovered below the Great Basin in central Nevada has dimensions of 100 km diameter by 500 km vertical length. Another area underlain by a descending cylindrical mass of dense lithosphere has been reported in the southwestern Sierra Nevada and portions of the San Joaquin Valley of California.
|
|
When plotted in multi-isotope space, ocean island basalts tend to form arrays trending from a central composition out to an endmember with an extreme composition. The depleted mantle, or DM, is one endmember, and is defined by low 87Sr/86Sr, 206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb, and high 143Nd/144Nd and 176Hf/177Hf. The DM is therefore geochemically depleted (as the name states), and relatively unradiogenic. Mid- ocean ridge passively sample the upper mantle and MORBs are typically geochemically depleted, and therefore it is widely accepted that the upper mantle is composed mostly of depleted mantle.
|
|
The northern royal albatross is typically about ,BirdLife International (2008) weighs and has a wingspan from .Robertson, C. J. R. (2003)Answers.com The juvenile has a white head, neck, upper mantle, rump, and underparts. There is dark speckling on the crown and rump.
|
|
Olivine, wadsleyite, and ringwoodite are polymorphs found in the upper mantle of the earth. At depths greater than about 660 km, other minerals, including some with the perovskite structure, are stable. The properties of these minerals determine many of the properties of the mantle.
|
|
The ophiolitic sequence found in this terrane is one of several major ophiolites found in California. Ophiolites are crustal and upper-mantle rocks from the ocean floor that have been moved on land. Ophiolites have been studied extensively regarding the movement of crustal rocks by plate tectonics.
|
|
Eclogites typically result from high to ultrahigh pressure metamorphism of mafic rocks at low thermal gradients of < as they were subducted to the lower crust to upper mantle depths in a subduction zone. They are generally formed from precursor mineral assemblages typical of blueschist-facies metamorphism.
|
|
The sculpture of the shell shows fine radial ribs. The upper mantle fold only slightly envelops the edge of the shell. The apical opening (foramen) is elongate-oval and situated almost in the center. Long papillae extend from the mantle towards the foramen, as in A. nigrita.
|
|
The Descent is a 1999 science fiction/horror novel by American author Jeff Long. It describes the discovery and exploration of an extensive labyrinth of tunnels and passages stretching throughout the Earth's upper mantle, found to be inhabited by a malicious species of alternately-evolved troglofauna hominids.
|
|
The face veil is light with a thin dark border. The top has brown, white and black spots, the spots on the upper mantle are a strong white. The shoulder feathers have black-fringed whitish outer flags. The chest has a thick brown and yellow-brown banding.
|
|
Extensive green gloss to rear crown and hindneck becoming pink on upper mantle. Whitish bill and pale eye. A rare resident breeder in the mountain laurisilva and Canary pine forests, the laurel pigeon builds a stick nest in a tree. There it lays one white egg.
|
|
Ophiolites are fragments of oceanic crust as well as upper mantle material that become tectonically emplaced onto continents during orogenic events, and their occurrence is generally along suture zones. A typical ophiolitic suite contains peridotite and harzburgite, layered gabbro, sheeted dykes, pillow basalts, and pelagic sediments.
|
|
The mantle of Kepler-277b is thought be predominantly composed of ultrahigh-pressure phases of magnesium silicates (MgSiO3). The uppermost mantle of Kepler-277b is thought to consist of olivine, wadsleyite, and ringwoodite while the lower part of Kepler-277b's upper mantle consists of silicate perovskite and post-perovskite.
|
|
Chromodoris strigata is pale blue with black longitudinal lines on its body and upper mantle. It has a bright orange-edged mantle and bright orange gills and rhinophores. This species is easily confused with Chromodoris elisabethina but has a distinctive darker area in the middle of the back.
|
|
In geology, plating is a hypothesized process whereby asthenospheric mantle hardens beneath crustal material, thereby becoming attached to it and thereafter moving together with the crustal material as part of the lithosphere. A complementary process, although it does not necessarily always involve the upper mantle, is called delamination.
|
|
Most of the igneous rocks on the surface probably are not representative of the original magmas formed in the mantle; certain processes, such as separation of phenocrysts from the liquid from which they crystallized have altered their original chemical compositions at depths shallower than the mantle. By inference, the rocks at Pilot Knob crystallized from partial melts of the upper mantle. Only rocks of the second series have been discovered at Pilot Knob; no basaltic rocks have been located. No mantle fragments have been located in Pilot Knob igneous rocks, but their presence is suspected, and some of the olivine phenocrysts in the rocks may be fragments derived from the upper mantle.
|
|
Juveniles can be identified by their shorter crest and tail, paler mask, brownish nape and brighter mantle. Subspecies have subtle variations in plumage: patkaicus' mantle is a darker, richer chestnut; belangeri has white extending lower onto the belly and paler underparts; diardi even more so and with a brighter upper mantle.
|
|
Such changes include the thickening of the lithosphere by overthrusting, changes in rock density of the lithosphere caused by metamorphism or thermal expansion and contraction, increases in the volume of the asthenosphere (part of the upper mantle supporting the lithosphere) caused by hydration of olivine, and orogenic, or mountain- building, movements.
|
|
Charlotte E. Keen (née Davidson) is a Canadian geologist and professor emeritus at the Geological Survey of Canada. Her work focuses on the structure of the earth's crust and the upper mantle using geophysical imaging and magnetic measurements. She was the first woman to go on a Canadian Survey Ship.
|
|
Underparts are heavily and regularly marked with black, white and rufous. Female is more uniformly rufous, with irregular black-tipped white spots on the upper mantle, scapular and underparts. Males duller in color than females. Frogmouths are distinguishable by their large head and body compared to their small legs and feet.
|
|
Zabargad Island, Egypt. Zabargad Island ( ', also known as St. John's Island in English) is the largest of a group of islands in Foul Bay, Egypt. It covers an area of . It is not a quaternary volcanic island, but rather is believed to be an upthrusted part of upper mantle material.
|
|
The source of the Yellowstone hotspot is controversial. Some geoscientists hypothesize that the Yellowstone hotspot is the effect of an interaction between local conditions in the lithosphere and upper mantle convection. Others suggest an origin in the deep mantle (mantle plume).See list of off-line references in mantleplumes.org/CRB.
|
|
Since the Earth formed, the upper mantle has lost 40–90% of its carbon by evaporation and transport to the core in iron compounds. The most rigorous estimate gives a carbon content of 30 parts per million (ppm). The lower mantle is expected to be much less depleted – about 350 ppm.
|
|
The Aztec thrush is long and weighs . The adult male has a dark brown hood, the head, neck and upper mantle being dark brown, with pale flecks or streaks. There may be a pale brown supercilium. The back, scapulars, median coverts and greater coverts are dark brown, the greater coverts having white edges.
|
|
The Chatham albatross weighs and it has a length of . The adult has a dark grey crown, face, upper mantle, back, upperwing, tail, and throat. They have a white rump and underparts. They also have a black thumbmark on the leading edge of the underwings, and a black tip on the wings.
|
|
Oceanic core complex structures form at slow spreading oceanic plate boundaries which have a limited supply of upwelling magma. These zones have low upper mantle temperatures and long transform faults develop. Rift valleys do not develop along the expansion axes of slow spreading boundaries. Expansion takes place along low-angle detachment faults.
|
|
Upper mantle and oceanic crust are exposed along this bank. Ferrogabbro dated at 77 Ma has been intruded. Also at 66 Ma the Canary hotspot mantle plume passed by and caused alkaline magma to intrude. Where there is crust, it is very thin, so that the Moho comes up to the sea floor.
|
|
This reaction marks the boundary between upper mantle and lower mantle. This measurement is estimated from seismic data and high- pressure laboratory experiments. The base of the mesosphere includes the D″ zone which lies just above the mantle–core boundary at approximately . The base of the lower mantle is at about 2700 km.
|
|
The transition zone is part of the Earth's mantle, and is located between the lower mantle and the upper mantle, between a depth of 410 and 660 km (250 to 400 mi). The Earth's mantle, including the transition zone, consists primarily of peridotite, an ultramafic igneous rock. The mantle was divided into the upper mantle, transition zone, and lower mantle as a result of sudden seismic- velocity discontinuities at depths of 410 and 660 km (250 to 400 mi). This is thought to occur as a result of rearrangement of grains in olivine (which constitutes a large portion of peridotite) at a depth of 410 km, to form a denser crystal structure as a result of the increase in pressure with increasing depth.
|
|
Australian National University – Research School of Earth Sciences: : Hrvoje Tkalčić. Retrieved 2018-02-24. He participated in a number of scientific field campaigns to establish temporary seismic networks in remote parts of Australia. The main objective has been to image structure of the Earth's crust and upper mantle using seismic tomography and other imaging techniques.
|
|
Nowadays, the study of geophysics is less present in the base. Nonetheless, several tools are still in use, notably a tide gauge, a cosmic rays detector, a GPS to measure the dip of the Antarctica into the upper mantle, and a lidar, which allows the analysis of the ozone depletion and the ozone holes.
|
|
Hypselodoris purpureomaculosa is white, with a distinct orange fringed mantle, orange gills and rhinophores. The specific epithet purpureomaculosa refers to the purple spots on its upper mantle that vary in colour from red to black in some individuals. This species reaches a length of at least 40 mm.Gosliner, T.M., Behrens, D.W. & Valdés, Á., 2018.
|
|
The weak visibility of the postulated plume in tomographic images of the lower mantle and the geochemical evidence for eclogite in the mantle source have led to the theory that Iceland is not underlain by a mantle plume at all, but that the volcanism there results from processes related to plate tectonics and is restricted to the upper mantle.
|
|
Eclogite Peridotite is the dominant rock type of the upper mantle, not eclogite, as established by seismic and petrologic evidence. Likewise, peridotite is a much more important source rock of common magmas. Melting of eclogite to produce basalt directly is generally not supported in modern petrology. Unreasonably high degrees of partial melting are required to attain basaltic compositions.
|
|
The Deep Carbon Observatory's research considers the global carbon cycle beyond Earth's surface. It explores high-pressure and extreme temperature organic synthesis, complex interactions between organic molecules and minerals, conducts field observations of deep microbial ecosystems and of anomalies in petroleum geochemistry, and constructs theoretical models of lower crust and upper mantle carbon sources and sinks.
|
|
Ukraine (NASU) since 1952 (Director, 1963–1982). NASU Corresponding Member (1964), NASU Academician (1979). Prof. Dolenko proposed the concept of mineral synthesis of oil and gas in the asthenospere of the Earth's upper mantle. State Award laureate (1971) for the prospecting and discovery of oil and gas fields at great depths in the Dnieper-Donets basin and Carpathian Foredeep.
|
|
Male F. c. africana in Morocco The common chaffinch is about long, with a wingspan of and a weight of . The adult male of the nominate subspecies has a black forehead and a blue-grey crown, nape and upper mantle. The rump is a light olive-green; the lower mantle and scapulars form a brown saddle.
|
|
Carbonatites in Finland have wide range in ages but they all derive from a "well-mixed" portion of the upper mantle. The Siilinjärvi carbonatite complex of Archean age is one of the Earth's oldest carbonatites. All known kimberlites are concentrated near the towns of Kuopio and Kaavi. These are grouped in two clusters and include diatremes and dykes.
|
|
This may lead to large scale formation of serpentinite in the upper mantle of the downgoing plate (Ranero et al., 2003). Faulting of the downgoing plate results in a horst and graben structure that allows sediment that reaches the trench to be deposited in graben and carried downward. This faulting also breaks up seamounts as they approach the trench.
|
|
Fetlar has a very complex geology, including gneiss in the west, metamorphosed gabbro and phyllite, and kaolin. There is also antigorite and steatite here. Talc was mined here. The east of the island is part of the Shetland ophiolite complex (a section of the Earth's oceanic crust and the underlying upper mantle that has been uplifted and exposed above sea level).
|
|
Convection within Earth's mantle is the driving force for plate tectonics. Mantle convection is the result of a thermal gradient: the lower mantle is hotter than the upper mantle, and is therefore less dense. This sets up two primary types of instabilities. In the first type, plumes rise from the lower mantle, and corresponding unstable regions of lithosphere drip back into the mantle.
|
|
Planet Mars – volatile gases (Curiosity rover, October 2012) The most common form of volcanism on the Earth is basaltic. Basalts are extrusive igneous rocks derived from the partial melting of the upper mantle. They are rich in iron and magnesium (mafic) minerals and commonly dark gray in color. The principal type of volcanism on Mars is almost certainly basaltic too.
|
|
Coloring: Both adults have variable plumage; red/black face; rest of head brown/red, darker on hindcheeks; underparts dark maroon; dark blue collar across upper mantle, obvious in some birds but in others narrow and nearly absent; upperparts and tail green, feathers on rump in some individuals edged with maroon. Bill grey/black. Dark grey eye ring. Eye orange/yellow.
|
|
Depending on the model, carbon is predicted to contribute between 0.2 and 1 percent by weight in the core. Even at the lower concentration, this would account for half Earth's carbon. Estimates of the carbon content in the upper mantle come from measurements of the chemistry of mid-ocean ridge basalts (MORBs). These must be corrected for degassing of carbon and other elements.
|
|
Oceanic crust is continuously being created at mid- ocean ridges. As plates diverge at these ridges, magma rises into the upper mantle and crust. As it moves away from the ridge, the lithosphere becomes cooler and denser, and sediment gradually builds on top of it. The youngest oceanic lithosphere is at the oceanic ridges, and it gets progressively older away from the ridges.
|
|
31, p.93-120. Weakening and cracking of oceanic crust and upper mantle is likely to occur in the tensional regime. This results in the incorporation of ophiolite slabs into the overriding plate. Progressive packing of ophiolite slices and arc fragments against the leading edge of a continent may continue over a long period of time and lead to a form of continental accretion.
|
|
The bird's chin and throat are covered in a thin layer of white feathers, and the neck is long and slender. The nape is also covered in white feathers, while the hindneck is nearly bare, revealing the orange-yellow skin. The upper mantle is a solid black, merging into a greyish-black lower mantle. The rockfowl's thighs are very muscular and aid its partially terrestrial lifestyle.
|
|
Instead of intrusive magmatic structures, the transitional crust is composed of stretched continental crust and exhumed upper mantle. NVPM are typically submerged and buried beneath thick sediments, so they must be studied using geophysical techniques or drilling. NVPM have diagnostic seismic, gravity, and magnetic characteristics that can be used to distinguish them from VPM and for demarcating the transition between continental and oceanic crust.
|
|
The Moho marks a large density contrast between crust and mantle, typically at least 0.35 g/cm3. The highest amplitudes of the gravity anomaly occur seaward of the continent-ocean transition. High-density upper mantle material is elevated relative to the more landward crustal root. The oceanic crust density is then further enhanced with gabbros and basalts and additionally contributes to the regional gravity trend.
|
|
It is primarily made of silicate rocks with (SiO2) content ranging from 45–77 wt%. The Semail Ophiolite is important because it is rich in copper and chromite ore bodies, and because it also provides valuable information about the ocean floor and the upper mantle on land. Geologists have studied the area, attempting to find the best model explaining the formation of the Semail Ophiolite.
|
|
For instance, olivine (an abundant mineral in the upper mantle) has the chemical formula . Nickel, with very similar chemical behaviour to iron and magnesium, substitutes readily for them and hence is very compatible in the mantle. Compatibility controls the partitioning of different elements during melting. The compatibility of an element in a rock is a weighted average of its compatibility in each of the minerals present.
|
|
This ultimately changes the chemical composition of the melt as different minerals begin to crystallize. Fractional crystallization of elements in basaltic liquids has also been studied to observe the composition of lava in the upper mantle. This concept can be applied by scientists to give insight on the evolution of Earth's mantle and how concentrations of lithophile trace elements have varied over the last 3.5 billion years.
|
|
A major alternative to the plume model is a model in which ruptures are caused by plate-related stresses that fractured the lithosphere, allowing melt to reach the surface from shallow heterogeneous sources. The high volumes of molten material that form the LIPs is postulated to be caused by convection in the upper mantle, which is secondary to the convection driving tectonic plate motion.
|
|
The yellow-billed kingfisher is long, with a wingspan of , and it weighs . Its orange colouring and yellow bill are distinctive; it has an orange head and neck with a black nape patch and white throat. Adult females also have a black crown patch. The upper mantle is blackish grading to olive green on the back, blue-green on rump and with a blue tail.
|
|
The lofty Hajar Mountains and the drowned valleys of Musandam are dramatic reminders of this. Generally speaking Oman is fairly quiescent tectonically. Musandan experiences occasional tremors as the Arabian Plate collides with the Eurasian Plate. During the Cretaceous Period Oman was located adjacent to a subduction zone and a portion of the upper mantle along with overlying seafloor volcanic rocks were thrust over the continental crust.
|
|
However, when large forces are applied to the uppermost mantle it can become weaker, and this effect is thought to be important in allowing the formation of tectonic plate boundaries. Although there is a tendency to larger viscosity at greater depth, this relation is far from linear and shows layers with dramatically decreased viscosity, in particular in the upper mantle and at the boundary with the core.
|
|
The physical appearance differs from other species by a heavier black marking above breast as well as no rufous on breast. Hodgson's frogmouth is the most well-marked sexual dichromatic of all frogmouths. The male is rufous brown. Upper parts are heavily marked with black, especially on the head, with irregular bold whitish markings particularly on scapular and upper mantle which forms a white collar.
|
|
The creation of the dome was caused by a phase of east- west directed extension in the Miocene that occurred throughout the Eastern and Central Alps. This extensional phase was probably a result of slab detachment in the upper mantle. Similar large extensional structures appear in more places in the Alps, examples are the Hohe Tauern window and the smaller Engadin and Rechnitz windows.
|
|
The earthquake's focal mechanism is consistent with normal faulting, trending SW-NE. From the distribution of aftershocks, it is possible to discriminate between the two nodal planes implied by the focal mechanism, indicating that the fault plane dips to the southeast at about 25°. The rupture area is estimated to be about 110 km along strike and 26 km in depth, extending into the upper mantle.
|
|
Significant variation periods are typically from seconds to about an hour, so the induction process involves the upper mantle and lithosphere. Since the largest magnetic field variations are observed at higher magnetic latitudes, GIC have been regularly measured in Canadian, Finnish and Scandinavian power grids and pipelines since the 1970s. GIC of tens to hundreds of amperes have been recorded. GIC have also been recorded at mid- latitudes during major storms.
|
|
Indunstrial & Engineering Chemistry, volume 45, issue 3, pages 567–572. Orthosilicate salts, like sodium orthosilicate, are stable, and occur widely in nature as silicate minerals, being the defining feature of the nesosilicates.Western Oregon University Olivine, a magnesium or iron(II) orthosilicate, is the most abundant mineral in the upper mantle. The orthosilicate anion is a strong base, the conjugate base of the extremely weak orthosilicic acid (pKa2 = 13.2 at 25 °C).
|
|
The mineral olivine () is a magnesium iron silicate with the formula (Mg2+, Fe2+)2. Thus, it is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers quickly on the surface. The ratio of magnesium to iron varies between the two endmembers of the solid solution series: forsterite (Mg-endmember: ) and fayalite (Fe-endmember: ).
|
|
Earth's lithosphere includes the crust and the uppermost mantle, which constitutes the hard and rigid outer layer of the Earth. The lithosphere is subdivided into tectonic plates. The uppermost part of the lithosphere that chemically reacts to the atmosphere, hydrosphere, and biosphere through the soil-forming process is called the pedosphere. The lithosphere is underlain by the asthenosphere which is the weaker, hotter, and deeper part of the upper mantle.
|
|
Geophysical studies in the early 21st century posit that large pieces of the lithosphere have been subducted into the mantle as deep as 2900 km to near the core-mantle boundary, while others "float" in the upper mantle, while some stick down into the mantle as far as 400 km but remain "attached" to the continental plate above, similar to the extent of the "tectosphere" proposed by Jordan in 1988.
|
|
Bringelly Shale and Minchinbury Sandstone are often seen in the greater western parts of Sydney, which are part of the Wianamatta Shale group.Chris Herbert. Geology of the Sydney 1:100,000 Sheet 9130 Prospect Hill in western Sydney is the largest assemblage of igneous rock in Sydney. The oval-shaped ridge was made many millions of years ago when volcanic material from the Earth's upper mantle moved upwards and then sideways.
|
|
The uranium, thorium, and potassium in particular were used to map the location of KREEP (potassium, rare-earth element, and phosphorus containing material, which is thought to have developed late in the formation of the crust and upper mantle, and is therefore important to understanding lunar evolution). The GRS was also capable of detecting fast (epithermal) neutrons, which complemented the neutron spectrometer in the search for water on the Moon.
|
|
S-waves (seismic shear waves) cannot propagate in liquids, leading to negligible velocity in the liquid outer core. The seismic velocities very near the surface () are markedly lower than at greater depths, demarking the LVZ. The low-velocity zone (LVZ) occurs close to the boundary between the lithosphere and the asthenosphere in the upper mantle. It is characterized by unusually low seismic shear wave velocity compared to the surrounding depth intervals.
|
|
The adult bushy-crested jay has a length of . The tail is long and the central feathers are graduated. The sexes look alike; the head, neck, breast and upper mantle are black while the remaining upper parts are dark blue with a sheen of green or violet. The underparts are plain greenish-blue, the undersides of the wings are grey and the underside of the tail is blackish.
|
|
Reaching the discontinuity by drilling remains an important scientific objective. Soviet scientists at the Kola Superdeep Borehole pursued the goal from 1970 until 1992. They reached a depth of , the world's deepest hole, before abandoning the project. One proposal considers a rock-melting radionuclide-powered capsule with a heavy tungsten needle that can propel itself down to the Moho discontinuity and explore Earth's interior near it and in the upper mantle.
|
|
The magmas erupted in the Latir volcanic field show isotopic chemistry indicating the magmas evolved in an open system, with crystal fractionation, magma mixing, and crustal assimilation all playing roles.Johnson et al. 1990 However, the precaldera rocks are overwhelmingly derived from basaltic magmas produced in the upper mantle, rather than melted crust. The precaldera intermediate-composition rocks likely were produced by mixing between fractionated magma and primitive basalt.
|
|
Some geophysical imaging techniques for the Earth's lithosphere and upper mantle include teleseismic tomography, surface-wave tomography, gravity modeling, and electromagnetic methods. Geophysical imaging techniques can be combined to create a more accurate image of the lithosphere. The techniques used to image the lithosphere can be used to map out the thermostructure of the Earth. In turn, the thermostructure reveals near surface processes such as seismicity, magma emplacement, and mineralization events.
|
|
Hess found that the slow shear waves propagated perpendicular to the plane of slip and the higher velocity component was parallel to it. He inferred that the structure of oceanic basins could be recorded quickly and understood better if these techniques were used. Ando (1980) focused on identifying shear-wave anisotropy in the upper mantle. This study focused on shear wave splitting recorded near the Chubu Volcanic Area in Japan.
|
|
H. D. Holland and K. K. Turekian), Elsevier-Pergamon, Oxford. in a discussion of the possible importance of the mineral as a significant reservoir of water in the Earth's mantle. Titanium is a minor constituent of clinohumite in most such occurrences. Clinohumite is stable throughout the upper mantle to depths of at least and is a potential host phase for H (water) in this region of the Earth's interior.
|
|
Further differentiation would take place later, creating the different chemical reservoirs of crust and mantle, with incompatible elements accumulating in the crust. Today differentiation still continues in the upper mantle. Reservoirs depleted in lithophile elements are called depleted, "fresh" undifferentiated parts of the mantle are called enriched or primitive. The last name is confusing but derives from the fact that such reservoirs are comparable in composition to the primitive mantle.
|
|
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.
|
|
The Anahim hotspot has been imaged through seismic tomography and is estimated to be wide. Recent high-resolution local tomography indicates a possible lower- mantle plume and a pond of plume material is evidenced by a large low-velocity zone in the upper mantle. These low seismic velocity zones often indicate hotter and more buoyant mantle material. The low-velocity zone is flanked on both sides by high-velocity anomalies of variable amplitude.
|
|
He has recently begun work on the Oman Ophiolite complex which provides access to rocks which once made up the Oceanic crust and upper mantle. He has published in journals including Nature, Tectonics, Terra Nova, and Earth and Planetary Science Letters and has received funding from the National Science Foundation for his research. His work in western Canada has been influential in both understanding magmatic arcs and the paleogeography of North America.
|
|
She performed refraction measurements to study the seismic anisotropy in the upper mantle, showing that the maximum and minimum velocity was consistent with seafloor spreading. Alongside extensive studies of the Atlantic and Pacific Ocean, Keen used biostratigraphic and metamorphic data to analyse the exploratory wells around Labrador. She showed that the subsidence of basement followed similar depth-age curves to the oceanic lithosphere. Keen developed thermal-mechanical models and applied them to rifted continental margins.
|
|
Atekwana also uses geophysics to investigate tectonic processes. Her geophysical studies reveal crust and upper mantle structures that inform the geodynamic processes associated with incipient rifting of continental crust. For example, Atekwana and colleagues show how geophysically imaged pre-existing basement structures in Malawi and Botswana influenced strain localization during early rifting. Another case study from the nascent Okavango rift in northwest Botswana provides evidence that pre-existing basement structures control rifting.
|
|
Archean lithosphere is strongly depleted in fertile melt indicators such as CaO and Al2O3. This depletion in major-elements should then be consequence of the Archean lithosphere's formation. Trace-elements are abundant in Archean lithosphere relative to MORB (which samples modern upper mantle) and have been sampled by Re-Os isotope dating of peridotites and ophiolites. The trace element composition of these xenoliths suggest mixing between the two different layers of subcontinental mantle.
|
|
The Trans-Mexican Volcanic Belt in Mexico A volcanic belt is a large volcanically active region. Other terms are used for smaller areas of activity, such as volcanic fields. Volcanic belts are found above zones of unusually high temperature (700-1400 °C) where magma is created by partial melting of solid material in the Earth's crust and upper mantle. These areas usually form along tectonic plate boundaries at depths of 10–50 km.
|
|
Manning's current projects include high-pressure experiments investigating how minerals dissolve in water in the lower crust and upper mantle, studies of metamorphism of oceanic gabbros from the East Pacific Rise to understand the timing an temperatures of fluid-rock interactions in the lower crust of mid-ocean ridges, and finally investigations into the links between fluid flow, mineral reaction, and permeability in the Spanish Peaks fossil hydrothermal system of south-central Colorado.
|
|
The lithosphere, which is the rigid outermost shell of a planet (the crust and upper mantle), is broken into tectonic plates. The Earth's lithosphere is composed of seven or eight major plates (depending on how they are defined) and many minor plates. Where the plates meet, their relative motion determines the type of boundary: convergent, divergent, or transform. Earthquakes, volcanic activity, mountain-building, and oceanic trench formation occur along these plate boundaries (or faults).
|
|
Mooney is considered a world leader in geophysical studies of the Earth's crust and upper mantle. In 1995, he was awarded the Geological Society of America's (GSA) George P. Woollard Award. This award is given annually to recognize a person who has made outstanding contributions to geology using geophysical methods. as well as being a Fellow of the American Geophysical Union (AGU), the Royal Astronomical Society and the Geological Society of London.
|
|
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.
|
|
Reconstruction of seismic reflections in the deep interior indicate some major discontinuities in seismic velocities that demarcate the major zones of the Earth: inner core, outer core, mantle, lithosphere and crust. The mantle itself is divided into the upper mantle, transition zone, lower mantle and D′′ layer. Between the crust and the mantle is the Mohorovičić discontinuity. The seismic model of the Earth does not by itself determine the composition of the layers.
|
|
Cross section of the Earth, showing the paths of earthquake waves. The paths curve because the different rock types found at different depths change the speed at which the waves travel. S waves do not travel through the core The boundary between the upper mantle and the lower mantle is a discontinuity. Earthquakes at shallow depths are a result of strike-slip faulting; however, below about the hot, high pressure conditions inhibit further seismicity.
|
|
Ordovician ophiolite in Gros Morne National Park, Newfoundland An ophiolite is a section of Earth's oceanic crust and the underlying upper mantle that has been uplifted and exposed above sea level and often emplaced onto continental crustal rocks. The Greek word ὄφις, ophis (snake) is found in the name of ophiolites, because of the superficial texture of some of them. Serpentinite especially evokes a snakeskin. The suffix lite from the Greek lithos means "stone".
|
|
Parallel to geological and geophysical measures (e.g. isotope ratios and seismic velocities) it is constructive to test hypotheses on computer based geodynamical models. A 3D numerical geodynamical model of the plume-crust coupling was capable of reproducing the lateral asymmetry of the EAR around the Tanzania craton. Numerical modeling of plume-induced continental break-up shows two distinct stages, crustal rifting followed by lithospheric breakup, and the upwelling between stages of an upper mantle plume.
|
|
Other sources consider the volcano late Holocene in age, or even as active during historical time. Hot springs are found southeast of Balagan-Tas. They reach temperatures of , which together with the other activity indicates a hot upper mantle. If reports of activity of the supposed Indighirsky volcano in the 1770s refer to Balagan-Tas, this volcano may have had historical activity, one of the few outside of Kamchatka in continental Asia.
|
|
This produces anomalous thermal, chemical and physical effects in the mantle that can dramatically change the over-riding plate by interrupting the established tectonic and magmatic regimes. In general, the data used to identify possible slab windows comes from seismic tomography and heat flow studies.van Wijk, J.W., Govers, R., Furlong, K.P., 2001, Three-dimensional thermal modeling of the California upper mantle: a slab window vs. stalled slab, Earth and Planetary Letters, v.
|
|
The importance of shear zones lies in the fact that they are major zones of weakness in the Earth's crust, sometimes extending into the upper mantle. They can be very long-lived features and commonly show evidence of several overprinting stages of activity. Material can be transported upwards or downwards in them, the most important one being water circulating dissolved ions. This can bring about metasomatism in the host rocks and even re-fertilise mantle material.
|
|
Another hypothesis is that the Anahim hotspot is supplied by a miniplume. These mantle plumes have their roots in the upper mantle but they may later originate from the lower mantle. Arguments for an Anahim miniplume are centred on the existence of two small dike swarms at the western (hence oldest) end of the Anahim Volcanic Belt. This assumption is in turn based on the notion that giant dike swarms mark the arrival of deep-seated mantle plumes.
|
|
Deep-focus earthquakes give rise to minimal surface waves. Their focal depth causes the earthquakes to be less likely to produce seismic wave motion with energy concentrated at the surface. The path of deep-focus earthquake seismic waves from focus to recording station goes through the heterogeneous upper mantle and highly variable crust only once. Therefore, the body waves undergo less attenuation and reverberation than seismic waves from shallow earthquakes, resulting in sharp body wave peaks.
|
|
A sample of serpentinite rock, partially made up of chrysotile, from Slovakia A rock of serpentinite from the Maurienne valley, Savoie, French Alps Sample of serpentinite from the Golden Gate National Recreation Area, California, United States Chromitic serpentinite (7.9 cm across), Styria Province, Austria. Protolith was a Proterozoic-Early Paleozoic upper mantle dunite peridotite that has been multiply metamorphosed during the Devonian, Permian, and Mesozoic. Tightly folded serpentinite from the Tux Alps, Austria. Closeup view about 30cm × 20cm.
|
|
The plate tectonics rock cycle is an evolutionary process. Magma generation, both in the spreading ridge environment and within the wedge above a subduction zone, favors the eruption of the more silicic and volatile rich fraction of the crustal or upper mantle material. This lower density material tends to stay within the crust and not be subducted back into the mantle. The magmatic aspects of plate tectonics tends to gradual segregation within or between the mantle and crust.
|
|
Second, radioactive heat production is concentrated within the crust of the Earth, and particularly within the upper part of the crust, as concentrations of uranium, thorium, and potassium are highest there: these three elements are the main producers of radioactive heat within the Earth. Thus, the geothermal gradient within the bulk of Earth's mantle is of the order of 0.5 kelvin per kilometer, and is determined by the adiabatic gradient associated with mantle material (peridotite in the upper mantle).
|
|
Recycling of existing primordial crust contributes to the production of secondary crust. Partial melting of the existing crust increases the mafic content of the melt producing basaltic secondary crust. A further method of formation due to the decay of radioactive elements within the Earth releasing heat energy and eventually causing the partial melting of upper mantle, also producing basaltic lavas. As a result, most secondary crust on Earth is formed at mid ocean ridges forming the oceanic crust.
|
|
Gradually through the upper mantle, pyroxenes become less stable and transforms into majoritic garnet. Experiments on olivines and pyroxenes show that these minerals change structure as pressure increases at greater depth, and this explains why the density curves are not perfectly smooth. When there is a conversion to a more dense mineral structure, the seismic velocity rises abruptly and creates a discontinuity. At the top of the transition zone, olivine undergoes isochemical phase transitions to wadsleyite and ringwoodite.
|
|
The fact that the Moon is less dense than the Earth is advanced as support for it to be hollow. The moon's mean density is 3.3 g/cm3 whereas the Earth's is 5.5 g/cm3. One explanation of this discrepancy is that the moon may have been formed by a giant impact which ejected some of the early Earth's upper crust into its orbit. The Earth's upper mantle and crust are less dense than its core.
|
|
The observed continental drift is a complicated relationship between the forces causing oceanic lithosphere to sink and the movements within Earth's mantle. Although there is a tendency to larger viscosity at greater depth, this relation is far from linear and shows layers with dramatically decreased viscosity, in particular in the upper mantle and at the boundary with the core.Walzer, Uwe; Hendel, Roland and Baumgardner, John. Mantle Viscosity and the Thickness of the Convective Downwellings. igw.uni-jena.
|
|
Partial melting of the upper mantle as a result of the spreading centre will leave mantle material depleted in some compounds. It has low Sr and Pb isotope ratios and high Nd ratios. DGM is found in the central islands of the Galapagos such as Santiago, Santa Cruz, San Cristobal and Santa Fe. It fills in the centre of the horseshoe formed by the PLUME lavas to the west, north and south. FLO – (Floreana), characteristic of that island's lavas.
|
|
Ringwoodite is polymorphous with forsterite, Mg2SiO4, and has a spinel structure. Spinel group minerals crystallize in the isometric system with an octahedral habit. Olivine is most abundant in the upper mantle, above about ; the olivine polymorphs wadsleyite and ringwoodite are thought to dominate the transition zone of the mantle, a zone present from about 410 to 660 km depth. Ringwoodite is thought to be the most abundant mineral phase in the lower part of Earth’s transition zone.
|
|
The Yellowstone Geodynamic Project sought to image the plume beneath the hotspot. They found a strong low-velocity body from ~30 to 250 km depth beneath Yellowstone and a weaker anomaly from 250 to 650 km depth which dipped 60° west-northwest. The authors attribute these features to the mantle plume beneath the hotspot being deflected eastward by flow in the upper mantle seen in S-wave models. The Hawaii hotspot produced the Hawaiian–Emperor seamount chain.
|
|
Thus, the term depleted MORB mantle (DMM) is often used to describe the upper mantle that sources mid-ocean ridge volcanism. Ocean island basalts also sample geochemically depleted mantle domains. In fact, most ocean island basalts are geochemically depleted, and <10% of ocean island basalts have lavas that extend to geochemically enriched (i.e., 143Nd/144Nd lower than the Earth’s building blocks) compositions. There are two geochemically enriched domains, named enriched mantle 1 (EM1), and enriched mantle 2 (EM2).
|
|
Former alum and sulfur mines east of Ciomadul were abandoned due to the dangers from toxic gases. At depths of , a magma chamber has been identified beneath Ciomadul, based on magnetotelluric data, and several of magma may still be stored underneath Ciomadul. A deeper basaltic melt zone may also exist. Further, a zone of low seismic velocity has been identified with geophysical and seismic modelling in the lower crust and upper mantle beneath Ciomadul, down to depths of or .
|
|
The Negriales rocks are the richest in silicon dioxide, and their trace element composition sharply diverges as well. The Negriales rocks may originate from parental magmas that are different from the main Lastarria magmas. The petrogenesis of Lastarria rocks, like those of other volcanoes in the Central Volcanic Zone, involves the prolonged interaction with crustal rocks in magma chambers as well as the fractionation of certain minerals. Enriched lower crust and upper mantle might also contribute.
|
|
Wu, P. & van der Wal, W. Postglacial sealevels on a spherical, self-gravitating viscoelastic earth: effects of lateral viscosity variations in the upper mantle on the inference of viscosity contrasts in the lower mantle. Earth and Planetary Science Letters, Volume 211, Issues 1–2, June 15, 2003, Pages 57–68.Colwell, J. E., Esposito, L. W. & M. Sremcevic. Self-gravity wakes in Saturn’s A ring measured by stellar occultations from Cassini. Geophysical Research Letters, volume 33, April 1, 2006.
|
|
The Abyssinian crimsonwing is a small, shy greyish olive finch with bright crimson wings, mantle, back and rump. It is sexually dimorphic. In the males the head and upper mantle are greyish olive apart from the blackish lores, while the rest of the upper parts, except for the short, rounded, black tail, are deep crimson. The chin is dull yellow and the rest of the underparts are greyish- olive, with some flank feathers having red tips.
|
|
Hotspots are formed when magma from the lower mantle upwells to the crust of Earth and breaks through the surface crust, whether that be oceanic crust or continental. This movement of magma breaks through the upper mantle, or the lithosphere, and creates a volcanic spot. This does not mean that all volcanoes are hotspots; some are created through interactions at plate boundaries. Tectonic plates move over hotspots creating a chain of volcanically-formed mountains over time.
|
|
Though the power law creep rate increases with increasing water content due to weakening, reducing activation energy of diffusion and thus increasing the NH creep rate, NH is generally still not large enough to dominate. Nevertheless, diffusional creep can dominate in very cold or deep parts of the upper mantle. Additional deformation in the mantle can be attributed to transformation enhanced ductility. Below 400 km, the olivine undergoes a pressure-induced phase transformation, which can cause more deformation due to the increased ductility.
|
|
A geological theory known as "Earth Crust Displacement" forms the basis of their work. The Atlantis Blueprint uses both scientific and pseudoscientific (such as mere speculation and assumptions) means to back up the theory. Charles Hapgood came up with the "Earth Crustal Displacement theory". Hapgood's theory suggests that Earth's outer crust is able to move upon the upper mantle layer rapidly up to a distance of 2,000 miles, placing Atlantis in Antarctica, when considering the movements of the crust in the past.
|
|
He examined the crustal structures of many locations in China and investigated sources of seismic waves. He studied the geodynamics of the extensional basins in North China and their connection to the 1976 Tangshan earthquake. In the 1990s, Zeng organized the first Sino- American joint project to investigate the crust and upper mantle of the Tibetan Plateau and the collision process of the Indian Plate with the Eurasian Plate. He was conferred the State Science and Technology Progress Award (Third Class) in 1997.
|
|
The upper parts of the Yunnan nuthatch are blue-grey, including the calotte, despite being separated from the upper mantle by a paler area. It has a thin white eyebrow, which extends to the front of the bird and is above the black eye line. Each eye has a fine white circle around it, and it has a white cheek and throat. The lower parts are pale and unified, and the grey-black beak is sharp and pointed with a yellowish base.
|
|
These layers most commonly have been interpreted as products of reaction between ascending magmas and peridotite of the upper mantle. The layers typically are a few centimeters to a meter or so in thickness. Pyroxenites that occur as xenoliths in basalt and in kimberlite have been interpreted as fragments of such layers. Although some mantle pyroxenites contain garnet, they are not eclogites, as clinopyroxene in them is less sodic than omphacite and the pyroxenite compositions typically are unlike that of basalt.
|
|
The Mid-Atlantic Ridge spreading center pulls the lithosphere apart, creating normal faults which expose sub-surface rocks to seawater. Olivine, the mineral responsible for Lost City's serpentinization. The Atlantis Massif is described as an ultramafic oceanic core complex of the Mid- Atlantic Ridge, with upper mantle rock being exposed to seawater through faulting from tectonic extension associated with oceanic spreading centers. The spreading half-rate is approximated to about 12 mm/yr, classifying it as a slow-spreading ridge.
|
|
The subspecies became extinct following the habitat destruction brought about by settlement and construction activity in the 1930s. It differed from the typical P. v. varius in having a broad chestnut-coloured band on the upper mantle, olive-green (not dark grey) lower mantle, and orangey (not white) sides to the head (Harrap & Quinn 1996, del Hoyo et al. 2007). Like many bird taxa from the Okinawa region, the scientific name is named after the veteran specimen collector Hyojiri Orii.
|
|
Vesuvius was formed as a result of the collision of two tectonic plates, the African and the Eurasian. The former was subducted beneath the latter, deeper into the earth. As the water-saturated sediments of the oceanic African plate were pushed to hotter depths inside the planet, the water boiled off and lowered the melting point of the upper mantle enough to partially melt the rocks. Because magma is less dense than the solid rock around it, it was pushed upward.
|
|
Conventional scientific wisdom is that the entire mantle is largely made up of olivine-dominated peridotite, some of it primordial material. Anderson, on the other hand, showed that the mid-mantle is composed of piclogite, a pyroxene and garnet- rick rock. Counter to prevailing scientific views, Anderson argued that the deeper layers of the mantle are dense and refractory and unable to rise to the surface or to produce basalts. Anderson suggested that all basalts are produced in the upper mantle.
|
|
Anderson, on the other hand, accepted the classical view that the Earth's interior is cooling and that volcanoes simply tap a layer of melted rock that exists in the upper mantle, or outer shell of the Earth. It is through the movement of the plates that the magma is allowed to reach the surface through fracture zones, rifts, volcanoes and so-called hot spots. Anderson also considered that plate tectonics is a natural result of a planet being cooled from above.Harding, Stephan.
|
|
In 1968, she began working at the Department of Geophysics at Leningrad State University. In 1986, she became a full professor at Saint Petersburg State University. Her areas of research include computer modelling of the propagation of surface waves and of tsunamis and determining variations in cross-sections of the earth's crust and upper mantle based on seismic data. She served on the editorial boards for the Russian journal Izvestiya, Physics of the Solid Earth and for the Chinese Journal of Geophysics.
|
|
All continental crust is ultimately derived from mantle-derived melts (mainly basalt) through fractional differentiation of basaltic melt and the assimilation (remelting) of pre-existing continental crust. The relative contributions of these two processes in creating continental crust are debated, but fractional differentiation is thought to play the dominant role. These processes occur primarily at magmatic arcs associated with subduction. There is little evidence of continental crust prior to 3.5 Ga.Hart, P. J., Earth's Crust and Upper Mantle, American Geophysical Union, 1969, pp.
|
|
The cometary and asteroidal delivery of water to accreting Earth and Mars has significant caveats, even though it is favored by D/H isotopic ratios. Key issues include: # The higher D/H ratios in Martian meteorites could be a consequence of biased sampling since Mars may have never had an effective crustal recycling process # Earth's Primitive upper mantle estimate of the 187Os/188Os isotopic ratio exceeds 0.129, significantly greater than that of carbonaceous chondrites, but similar to anhydrous ordinary chondrites.
|
|
PLUME lavas are also found in the lavas from the Galapagos Spreading Centre due to convection and mixing of all of these lavas. In the upper mantle convection currents bring in mantle material at shallow angles from the south of the Galapagos Spreading Centre. These convection current will draw in some PLUME type magma to the spreading centre where it is then erupted. DGM – (Depleted Galapagos Mantle), this has similar characteristics to ocean ridge basalts throughout the Pacific and the Galapagos Spreading Centre.
|
|
The wavelength and amplitude of this flexure can be used to constrain the state of stress across the plate boundary. The width of the outer rise is directly related to the flexural rigidity of the lithosphere. The thickness of the elastic lithosphere varies between 20 and 30 km for most trench profiles. Faulting related to plate bending and stair-stepping of the descending slab into the trench may allow seawater to infiltrate deep into the crust and perhaps upper mantle.
|
|
244x244pxThe equilibrium reaction involving diamond is424x424px Mg_2Si_2O_6+2MgCO_3\rightleftharpoons2Mg_2SiO_4+2C(Diamond)+2O_2. Examining the oxygen fugacity of the upper mantle and transition enables us to compare it with the conditions (equilibrium reaction shown above) required for diamond formation. The results show that the logfO_2 is usually 2 units lower than the carbonate-carbon reaction which means favoring the formation of diamond at transition zone conditions. It has also been reported that pH decrease would also facilitate the formation of diamond in Mantle conditions.
|
|
Folding in soft sediments along the Dauki fault reveals the compression direction. Directional compressional tectonism has been expressed through lateral movements along the Dauki Fault as well as other faults and folds just south of the Haflong Thrust. It has been observed from the studies that the Dauki fault zone and the areas in Bangladesh show various tectonic features, which are mostly controlled by vertical movements. The occurrence of several deep earthquakes (> 100 km) indicate deep tectonic activities in the upper mantle.
|
|
The geophysical method of seismic tomography is a suitable tool to investigate Earth's subsurface structures deeper than the crust. It is an inverse problem technique that models which are the velocities of the inner Earth that reproduce the seismographic data recorded all around the world. Recent improvements of tomographic Earth models of P-wave and S-wave velocities suggest that a superplume upwelling from the lower mantle at the northeastern EAR feeds plumes of smaller scale into the upper mantle.
|
|
A very light grey form from western dry region of India named by Walter Koelz as kathiawarensis is also considered merely as a variant. In southern India and Sri Lanka, subspecies caniceps, is marked by the rufous restricted to the rump, light crown and the pure grey on the back. Biswamoy Biswas supported the view that nigriceps (having upper mantle grey and lower mantle rufous) was a hybrid of tricolor and erythronotus. Subspecies longicaudatus has a greyer crown and is found in Thailand and Burma.
|
|
UHP terrains vary greatly in size, from the >30,000 km2 giant UHP terrains in Norway and China, to small kilometer-scale bodies.Ernst, W. G., Hacker, B. R., and Liou, J. G., 2007, Petrotectonics of ultrahigh- pressure crustal and upper-mantle rocks: Implications for Phanerozoic collisional orogens: Geological Society of America Special Paper, v. 433, p. 27-49. The giant UHP terrains have a metamorphic history spanning tens of millions of years, whereas the small UHP terrains have a metamorphic history spanning millions of years.
|
|
PREM has been widely used as the basis for seismic tomography and related global geophysical models. It incorporates anelastic dispersion and anisotropy and therefore it is frequency-dependent and transversely isotropic for the upper mantle. PREM was developed by Adam M. Dziewonski and Don L. Anderson in response to guidelines of a "Standard Earth Model Committee" of the International Association of Geodesy (IAG) and the International Association of Seismology and Physics of the Earth's Interior (IASPEI) Other Earth reference models include iasp91 and ak135.
|
|
The Gorringe Bank was eventually renamed Gorringe Ridge owing to its extensive length and the determination that it is the result of two tectonic plates which are sliding into and past each other. The plate boundaries here are converging at 4 mm/y, as well as sliding past each other. upper mantle and oceanic crust are exposed along this ridge. Ferrogabbro dated at 77 Mya has been intruded, Also at 66 Mya the Canary hotspot mantle plume passed by and caused alkaline magma to intrude.
|
|
Her primary research interests are the mechanics and kinematics of deformation in the Earth's lithosphere, rheology of the crust and upper mantle, strain localisation, rock mechanics, tectonic geomorphology, Quaternary geochronology, quantifying slip rates and earthquake hazards. Her research methodology combines field, analytical and experimental techniques to improve understanding of deformation at active and ancient plate margins. She has made contributions toward understanding the link between deformation of slow ductile flow and rapid seismogenic movements of brittle lithosphere. This helped improve understanding of seismic hazard potential.
|
|
UNESCO records the Lord Howe Island Group as a World Heritage Site of global natural significance. Most of the island is virtually untouched forest, with many of the plants and animals found nowhere else in the world. Other natural attractions include the diversity of the landscapes, the variety of upper mantle and oceanic basalts, the world's southernmost barrier coral reef, nesting seabirds, and the rich historical and cultural heritage. The Lord Howe Island Act 1981 established a "Permanent Park Preserve" (covering about 70% of the island).
|
|
In addition, the area is large, exposed, and there are areas that have experienced relatively low deformation and alteration to the original rock sequences. The Isua Greenstone is divided into a northern and a southern section by the Ivinnguit Fault, shown on the map below right. The northern area of the Isua Greenstone Belt is mainly composed of amphibolite rocks, volcanic rocks, upper mantle peridotite, and layered gabbros; a suite which suggests crustal shortening. Scientists have used different methods to determine how the Isua Greenstone Belt formed.
|
|
It analyzed wave propagation in layered complex media. Prior to Anderson's work, seismologists had assumed that the Earth's interior behaved like glass, and was isotropic. After completing his Ph.D. in 1962, Anderson joined the faculty at Caltech and moved on to other areas of study, writing papers on the composition, physical state, and origin of the Earth as well as other planets. Much later in his career, he returned to the effects of anisotropy and partial melting and the presence of fluids in the upper mantle.
|
|
The upper mantle causes the tectonic plates to move. Crust and mantle are distinguished by composition while the lithosphere and asthenosphere are defined by a change in mechanical properties. The top of the mantle is defined by a sudden increase in the speed of seismic waves, which was first noted by Andrija Mohorovičić in 1909; this boundary is now referred to as the Mohorovičić discontinuity or "Moho". The Moho defines the base of the crust and varies from to below the surface of the Earth.
|
|
From 2014 he has been a member of the board of curators of this faculty. A foreign member of the Finnish Academy of Sciences, he was a member of the steering committee of the NATO Science for Peace program The scientific activity of Marek Grad is seismology, especially structural seismology. He studies the Earth's crust and the upper mantle using the methods of explosive seismology (mainly the so-called deep seismic sounding). He participated in research in Finland, Spitsbergen and West Antarctica, among others .
|
|
This causes high ratios of Re/Os in oceanic crust (which is derived from partial melting of mantle) and low ratios of Re/Os in the lower mantle. In this regard, the Re–Os system to study the geochemical evolution of mantle rocks and in defining the chronology of mantle differentiation is extremely helpful. Peridotite xenoliths which are thought to sample the upper mantle sometimes contain supra-chondritic Os-isotopic ratios.Bizimis, M., Griselin, M., Lassiter, J. C., Salters, V. J. M. & Sen, G.(2007).
|
|
Sawamoto et al (1984) firstly measured the P-wave velocity (Vp) and S-wave velocity (Vs) of Mg-endmember of wadsleyite at ambient condition by the Brillouin spectroscopy. Their data suggested that olivine-wadsleyite phase transition would cause Vp jump of ~13% and Vs jump of ~14%. Therefore, the olivine- wadsleyite phase transition is widely believed to be the main cause for the 410 km seismic discontinuity at the boundary between the Upper Mantle and the Mantle Transition Zone in Earth (Sawamoto et al., 1984).
|
|
One cause for forebulge formation is loading of the continental lithosphere by ice sheets during continental glaciations. Because of the removal of the ice sheets, the formerly-glaciated areas are currently rising in a phenomenon known as post-glacial rebound. Because of the coupling of the mantle with the plates, data from post-glacial rebound are used as a direct probe of the viscosity of the upper mantle. As the ice melts and the land under it rises by isostatic recovery, the forebulge also subsides.
|
|
Xenoliths have been found in some meteorites. To be considered a true xenolith, the included rock must be identifiably different from the rock in which it is enveloped; an included rock of similar type is called an autolith or a cognate inclusion. Xenoliths and xenocrysts provide important information about the composition of the otherwise inaccessible mantle. Basalts, kimberlites, lamproites and lamprophyres, which have their source in the upper mantle, often contain fragments and crystals assumed to be a part of the originating mantle mineralogy.
|
|
MT measurements can investigate depths from about 300 m down to hundreds of kilometers, though investigations in the range of 500 m to 10,000 m are typical. Greater depth requires measuring lower frequencies, which in turn requires longer recording times. Very deep, very long-period measurements (mid-crust through upper mantle depths), may require recordings of several days to weeks or more to obtain satisfactory data quality. Horizontal resolution of MT mainly depends on the distance between sounding locations- closer sounding locations increase the horizontal resolution.
|
|
Scientific drilling into the Earth is a way for scientists to probe the Earth's sediments, crust, and upper mantle. In addition to rock samples, drilling technology can unearth samples of connate fluids and of the subsurface biosphere, mostly microbial life, preserved in drilled samples. Most of the technology used for drilling come from advances in the oil and gas industry. Scientific drilling is carried out on land by the International Continental Scientific Drilling Program (ICDP) and at sea by the Integrated Ocean Drilling Program (IODP).
|
|
It is estimated that the amount of water in the upper mantle of Mars, represented by hydroxyl ions contained within the minerals of Mars's geology, is equal to or greater than that of Earth at 50–300 parts per million of water, which is enough to cover the entire planet to a depth of . In 2005, radar data revealed the presence of large quantities of water ice at the poles and at mid-latitudes. The Mars rover Spirit sampled chemical compounds containing water molecules in March 2007.
|
|
The crust in conjunction with the upper mantle comprises the lithosphere. The base of the lithosphere beneath the Basin and Range is estimated to be about 60 – 70 km. Opinions vary regarding the total extension of the region; however, the median estimate is about 100% total lateral extension. Total lateral displacement in the Basin and Range varies from 60 – 300 km since the onset of extension in the Early Miocene with the southern portion of the province representing a greater degree of displacement than the north.
|
|
Deep seafloor deposition is the largest long-term sink of the marine silica cycle (6.3 ± 3.6 Tmol Si year−1), and is roughly balanced by the sources of silica to the ocean. The silica deposited in the deep ocean is primarily in the form of siliceous ooze, which is eventually subducted under the crust and metamorphosed in the upper mantle. Under the mantle, silicate minerals are formed in oozes and eventually uplifted to the surface. At the surface, silica can enter the cycle again through weathering.
|
|
CoRoT-7b artist view. The uncertainty in CoRoT-7b mass does not allow precise modelling of the planet structure. Nevertheless, educated guesses could still be put forth. Assuming a 5-Earth-masses planet, the planet was modeled to have convection in the mantle with a small core with no more than 15% the mass of the planet, or 0.75 M⊕. The lower mantle above the core-mantle boundary has more sluggish convection than the upper mantle because the greater pressure causes fluids to become more viscous.
|
|
The ultramafic xenoliths of the field are composed roughly of 80% spinel lherzolites, with lesser harzburgites, dunites, and pyroxenites. There is a high abundance of clinopyroxenes, about 35% by volume. Granulite xenoliths, interpreted as being derived from the lower crust, and peridotite xenoliths, interpreted as derived from the upper mantle, are particularly abundant in the Woodford, Media Luna, and Basu cones. The site exhibits strong deformation textures, which may have recorded plastic deformation that occurred with the diapiric rise of mantle through the low- velocity zone.
|
|
Pegmatite dyke offset by a steeply-dipping dextral shear zone, Cap de Creus dolomites of the Noonday Formation in Mosaic Canyon, Death Valley A shear zone is a very important structural discontinuity surface in the Earth's crust and upper mantle. It forms as a response to inhomogeneous deformation partitioning strain into planar or curviplanar high-strain zones. Intervening (crustal) blocks stay relatively unaffected by the deformation. Due to the shearing motion of the surrounding more rigid medium, a rotational, non co- axial component can be induced in the shear zone.
|
|
A few hotspots are thought to exist below the North American Plate. The most notable hotspots are the Yellowstone (Wyoming), Jemez Lineament (New Mexico), and Anahim (British Columbia) hotspots. These are thought to be caused by a narrow stream of hot mantle convecting up from the Earth's core–mantle boundary called a mantle plume, although some geologists think that upper mantle convection is a more likely cause. The Yellowstone and Anahim hotspots are thought to have first arrived during the Miocene period and are still geologically active, creating earthquakes and volcanoes.
|
|
Whole-mantle convection Mantle convection is the very slow creeping motion of Earth's solid silicate mantle caused by convection currents carrying heat from the interior to the planet's surface. Physics Department, University of Winnipeg The Earth's surface lithosphere rides atop the asthenosphere and the two form the components of the upper mantle. The lithosphere is divided into a number of tectonic plates that are continuously being created or consumed at plate boundaries. Accretion occurs as mantle is added to the growing edges of a plate, associated with seafloor spreading.
|
|
Peridot ( or ) (sometimes called chrysolite) is gem-quality olivine and a silicate mineral with the formula of (Mg, Fe)2SiO4. As peridot is a magnesium- rich variety of olivine (forsterite), the formula approaches Mg2SiO4. Its green color is dependent on the iron contents within the structure of the gem. Peridot occurs in silica-deficient rocks such a volcanic basalt as well as in pallasitic meteorites. Peridot is one of only two gems observed to be formed not in the Earth’s crust, but in molten rock of the upper mantle.
|
|
Lehmann was significantly hampered in her work and maintaining international contacts during the German occupation of Denmark in World War II. She served as the Chair of the Danish Geophysical Society in 1940 and 1944 respectively. In 1952, Lehmann was considered for a professorship in geophysics at Copenhagen University, but was not appointed. In 1953, she retired from her position at the Geodetic Institute. She moved to the US for several years and collaborated with Maurice Ewing and Frank Press on investigations of Earth's crust and upper mantle.
|
|
If spreading continues past the incipient stage described above, two of the rift arms will open while the third arm stops opening and becomes a 'failed rift' or aulacogen. As the two active rifts continue to open, eventually the continental crust is attenuated as far as it will stretch. At this point basaltic oceanic crust and upper mantle lithosphere begins to form between the separating continental fragments. When one of the rifts opens into the existing ocean, the rift system is flooded with seawater and becomes a new sea.
|
|
At the Mid-Atlantic Ridge (and in other mid-ocean ridges), material from the upper mantle rises through the faults between oceanic plates to form new crust as the plates move away from each other, a phenomenon first observed as continental drift. When Alfred Wegener first presented a hypothesis of continental drift in 1912, he suggested that continents plowed through the ocean crust. This was impossible: oceanic crust is both more dense and more rigid than continental crust. Accordingly, Wegener's theory wasn't taken very seriously, especially in the United States.
|
|
The asthenosphere is a part of the upper mantle just below the lithosphere that is involved in plate tectonic movement and isostatic adjustments. The lithosphere-asthenosphere boundary is conventionally taken at the 1300 °C isotherm. Below this temperature (closer to the surface) the mantle behaves in a rigid way; above this temperature (deeper below the surface) it acts in a ductile fashion. Seismic waves pass relatively slowly through the asthenosphere compared to the overlying lithospheric mantle, thus it has been called the low-velocity zone (LVZ), although the two are not exactly the same.
|
|
The Earth's layered structure. (1) inner core; (2) outer core; (3) lower mantle; (4) upper mantle; (5) lithosphere; (6) crust (part of the lithosphere) Earth layered structure. Typical wave paths from earthquakes like these gave early seismologists insights into the layered structure of the Earth Advances in seismology, computer modeling, and mineralogy and crystallography at high temperatures and pressures give insights into the internal composition and structure of the Earth. Seismologists can use the arrival times of seismic waves in reverse to image the interior of the Earth.
|
|
Sketch showing the multi-scale nature of mantle plumes, which involves the creation of the lower-mantle superplume from the D layer and generation of the upper-mantle plumes from the low-viscosity layer below . Tectonic plates generally focus deformation and volcanism at plate boundaries. However, the Anahim hotspot is about from the nearest plate boundary. While studying the Anahim Volcanic Belt in 1979, Canadian geologists Mary Bevier, Richard Armstrong and Jack Souther used the hotspot theory to explain this zone of volcanism so far from regular conditions.
|
|
The existence of olivine, orthopyroxene and spinel xenocrysts in Level Mountain basalt suggest that volcanism at the complex originated from the upper mantle. Hiatuses of up to a million years or more can be expected between periods of volcanic activity at Level Mountain. Geologic map of Level Mountain showing eruptive products and eruptive centres Like several other volcanoes in northern British Columbia, Level Mountain was volcanically active during past glacial periods. Its involvement with glaciation resulted in several interactions between magma and ice, affording multiple examples of glaciovolcanic processes.
|
|
Abyssal plains cover more than 33% of the ocean floor (about 23% of Earth's surface), but they are poorly preserved in the sedimentary record because they tend to be consumed by the subduction process. The abyssal plain is formed when the lower oceanic crust is melted and forced upwards by the asthenosphere layer of the upper mantle. As this basaltic material reaches the surface at mid-ocean ridges, it forms new oceanic crust. Abyssal plains result from the blanketing of an originally uneven surface of oceanic crust by fine-grained sediments, mainly clay and silt.
|
|
The mantle is composed of silicate rocks that are rich in iron and magnesium relative to the overlying crust. Although solid, the high temperatures within the mantle cause the silicate material to be sufficiently ductile that it can flow on very long timescales. Convection of the mantle is expressed at the surface through the motions of tectonic plates. As there is intense and increasing pressure as one travels deeper into the mantle, the lower part of the mantle flows less easily than does the upper mantle (chemical changes within the mantle may also be important).
|
|
The rupture may have affected the crust and the upper mantle according to the kinematic source inversion. The rupture was caused by ductile shear heating instability which is different from frictional failure and operates between , which corresponds to about the depths of . The serpentinization of oceanic lithosphere can lead to a low friction coefficient, but the reaction is possible only up to , which corresponds to the depth of about . A single dynamic weakening mechanism which can work over the whole range of slip of this earthquake is still to be identified.
|
|
The newest lavas are on the eastern and southern sides as well as within the caldera. Lava flows from Wolf are unusual for a mid-ocean island and also differ from the two volcanoes next to it, Ecuador and Darwin, and other volcanoes closer to the centre of the plume. The lavas from Wolf are similar to those erupted from the Galapagos Spreading Center, a mid-ocean ridge over 200 km away, which may be due to interaction between the plume, which is centred on Fernandina, and the upper mantle.
|
|
Mooney has also been a visiting professor of geophysics in many different universities over the years including, Stanford University (1984–2008; 2014–present), Pierre et Marie Curie University, France (1998) and University of Kiel, Germany (1985). With Claus Prodehl of Universität Karlsuhe, Germany, Mooney wrote Exploring the Earth's Crust - History and Results of Controlled-Source Seismology). Since 2011, he has been collaborating with the Saudi Geological Survey in a study of the crustal and upper mantle structure beneath western Saudi Arabia using data from the SGS broadband seismic network.
|
|
Examples of mascon basins on Mars include the Argyre, Isidis, and Utopia basins. Theoretical considerations imply that a topographic low in isostatic equilibrium would exhibit a slight negative gravitational anomaly. Thus, the positive gravitational anomalies associated with these impact basins indicate that some form of positive density anomaly must exist within the crust or upper mantle that is currently supported by the lithosphere. One possibility is that these anomalies are due to dense mare basaltic lavas, which might reach up to 6 kilometers in thickness for the Moon.
|
|
Temperatures range from approximately at the upper boundary with the crust to approximately at the core-mantle boundary. The highest temperature of the upper mantle is Although the high temperature far exceeds the melting points of the mantle rocks at the surface the mantle is almost exclusively solid. The enormous lithostatic pressure exerted on the mantle prevents melting, because the temperature at which melting begins (the solidus) increases with pressure. Pressure increases as depth increases, since the material beneath has to support the weight of all the material above it.
|
|
These regions have high enough pressure and temperature to allow diamonds to form and they are not convecting, so diamonds can be stored for billions of years until a kimberlite eruption samples them. Host rocks in a mantle keel include harzburgite and lherzolite, two type of peridotite. The most dominant rock type in the upper mantle, peridotite is an igneous rock consisting mostly of the minerals olivine and pyroxene; it is low in silica and high in magnesium. However, diamonds in peridotite rarely survive the trip to the surface.
|
|
The Romanche Fracture Zone offsets the Mid- Atlantic ridge by , making it the largest equatorial fracture zone in the Atlantic. According to the normal scenario for the opening of the South Atlantic, it is spreading at a rate of and began forming about . North of and parallel to the fracture zone is a transverse ridge which is particularly prominent over hundreds of kilometres east and west of the MAB of the South Atlantic. The western part of the transverse ridge consists of fragments of uplifted oceanic crust and upper mantle.
|
|
The first theories for seafloor spreading in the early and mid twentieth century explained the elevations of the mid-ocean ridges as upwellings above convection currents in Earth's mantle. The next idea connected seafloor spreading and continental drift in a model of plate tectonics. In 1969, the elevations of ridges was explained as thermal expansion of a lithospheric plate at the spreading center. This 'cooling plate model' was followed in 1974 by noting that elevations of ridges could be modeled by cooling of the whole upper mantle including any plate.
|
|
Using newly implemented telemetric seismographic stations, they were able to record both P-wave and S-wave arrivals from earthquakes up to 260 km beneath the volcanic area. The depths of these earthquakes make this area ideal for studying the structure of the upper mantle. They noted the arrivals of two distinct shear waves with different polarizations (N-S, fast and E-W, slow) approximately 0.7 seconds apart. It was concluded that the splitting was not caused by the earthquake source but by the travel path of the waves on the way to the seismometers.
|
|
Much of the mantle consists of olivine and its high-pressure polymorphs. At the top of the transition zone, it undergoes a phase transition to wadsleyite, and at about 520 km depth, wadsleyite transforms into ringwoodite, which has the spinel structure. At the top of the lower mantle, ringwoodite decomposes into bridgmanite and ferropericlase. The most common mineral in the upper mantle is olivine. For a depth of 410 km, an early estimate of 0.13 percentage of water by weight (wt%) was revised upwards to 0.4 wt% and then to 1 wt%.
|
|
Its face, upper throat, and upper mantle are grey, and its back, upperwing, and tail are grey-black. It has a white rump and underparts with a black thumbmark on underwing and black narrow leading and trailing edges on the wing and black wing tips. Its bill is pale grey-green with a pale yellow upper ridge, and a bright yellow tip on the upper mandible, and a dark spot on the tip of the lower mandible. The juveniles have more extensive grey areas and a blue-grey bill with black tips on both mandibles.
|
|
The external force are the long term movements of tectonic plates or the liquid rock currents within the upper mantle, which is a continuous force applied eventually the plate will snap back or fracture relieving stress on the system to flipping it to a stable state, i.e. an earthquake. Volcanoes are similar in that the build-up of magma pressure underneath will eventually overcome the layer of dry rock on top causing an eruption. Such models can be used to predict the occurrence of earthquakes and volcanoes in active regions and predict aftershocks which are common after a large events.
|
|
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.
|
|
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.
|
|
Primitive arc systems are those built on oceanic lithosphere, such as the Izu-Bonin-Mariana, Tonga-Kermadec, and Scotia (South Sandwich) arc systems. The inner trench slope of these convergent margins exposes the crust of the forearc, including basalt, gabbro, and serpentinized mantle peridotite. These exposures allow easy access to study the lower oceanic crust and upper mantle in place and provide a unique opportunity to study the magmatic products associated with the initiation of subduction zones. Most ophiolites probably originate in a forearc environment during the initiation of subduction, and this setting favors ophiolite emplacement during collision with blocks of thickened crust.
|
|
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.
|
|
Studies have been done on the phenomenon of magmatic underplating in various areas around the world. In northern Italy, the effects of magmatic underplating were studied along a traverse through the Strona-Ceneri Zone and the Ivrea Verbano Zone. The studies included a thermal modeling method which split the cross section up into three different sections: the upper crust, the lower crust, and the upper mantle. The model displayed multiple magmatic intrusions spreading over time, which resulted in the heating up of the lower crust causing metamorphism and anatexis, and even managed to moderately heat up the top of the lower crust.
|
|
Harzburgite is the most commonly found variety of peridotite in ophiolites, which are fragments of oceanic crust and the underlying oceanic mantle obducted and exposed during collision with continental crust. Examples of ophiolites with extensive harzburgite include the Troodos Ophiolite in Cyprus, the Semail Ophiolite in Oman, the Coast Range ophiolites of California, and the Bay of Islands Ophiolite in Newfoundland. Harzburgite may also be found in some Alpine peridotite massifs that consist mostly of lherzolite. Alpine or orogenic lherzolites represent subcontinental mantle lithosphere (the upper mantle below continental crust) exposed during the plate tectonic collision of continental plates.
|
|
Figure 1: Arabian Plate map with Semail Ophiolite location on the eastern corner of the Arabian Peninsula Close-up view of a section of the ophiolite. The Semail Ophiolite of the Hajar Mountains of Oman and the United Arab Emirates is a large slab of oceanic crust, made of volcanic rocks and ultramafic rocks from the Earth's upper mantle, that was overthrust onto continental crust as an ophiolite. It is located on the eastern corner of the Arabian Peninsula and covers an area of approximately 100,000 km2. Based on uranium-lead dating techniques, the Semail Ophiolite formed in the Late Cretaceous.
|
|
Current studies of Earth's rare trace elements seek to quantify and examine the chemical composition of elements in the Earth's crust. There are still uncertainties in the understanding of the lower crust and upper mantle region of Earth's interior. In addition, numerous studies have focused on looking at the partition coefficients of certain elements in the basaltic magma to characterize the composition of oceanic crust. By having a way to measure the composition of elements in the crust and mantle given a mineral sample, compatibility allows relative concentrations of a particular trace element to be determined.
|
|
In 2005 he moved to a position at Cornell University where he was a member of the Institute for the Study of the Continents, and a member of the faculty in the Department of Earth and Atmospheric Sciences and the American Indian Program. In 2012, Andronicos accepted a position as an associate professor at Purdue University in the Department of Earth, Atmospheric, and Planetary Sciences. His research is focused on understanding high temperature deformation in the deep crust and upper mantle. He has focused his work on continental orogenic belts in the southwestern United States, western Canada, and the Tibetan plateau.
|
|
Violet Rosemary Strachan Hutton FInstP FRSE FRAS (22 October 1925 – 1 April 2004), known to her peers as Rosemary, was a Scottish geophysicist and pioneer of magnetotellurics. Her research focused on the use of electromagnetic methods to determine the electrical conductivity and structure of the Earth's crust, lithosphere and upper mantle, with a particular focus on the African continent and Scotland. She spent over two decades at the University of Edinburgh School of GeoSciences as a researcher and lecturer and was a Fellow of many societies including the American Geophysical Union and The Royal Society of Edinburgh.
|
|
Earth cutaway from core to crust, the lithosphere comprising the crust and lithospheric mantle (detail not to scale) The subcontinental lithospheric mantle (SCLM) is the uppermost solid part of Earth's mantle associated with the continental lithosphere. The modern understanding of the Earth's upper mantle is that there are two distinct components - the lithospheric part and the asthenosphere. The lithosphere, which includes the continental plates, acts as a brittle solid whereas the asthenosphere is hotter and weaker due to mantle convection. The boundary between these two layers is rheologically based and is not necessarily a strict function of depth.
|
|
Plates in the crust of Earth Earth's crust is a thin shell on the outside of Earth, accounting for less than 1% of Earth's volume. It is the top component of lithosphere: a division of Earth's layers that includes the crust and the upper part of the mantle. The lithosphere is broken into tectonic plates that move, allowing heat to escape from the interior of the Earth into space. The crust lies on top of the mantle, a configuration that is stable because the upper mantle is made of peridotite and so is significantly more dense than the crust.
|
|
But more recently some geologists, such as Gillian Foulger view upper-mantle convection as a cause. This in turn has re-raised the antipodal pair impact hypothesis, the idea that pairs of opposite hot spots may result from the impact of a large meteor. Geologists have identified some 40-50 such hotspots around the globe, with Hawaii, Réunion, Yellowstone, Galápagos, and Iceland overlying the most currently active. An example of a hotspot volcanic belt is the Anahim Volcanic Belt in British Columbia, Canada, which was formed as a result of the North American Plate sliding westward over the Anahim hotspot.
|
|
Within the Basin and Range Province, the Earth's crust (and upper mantle) has been stretched up to 100% of its original width. The entire region has been subjected to extension that thinned and cracked the crust as it was pulled apart, creating large faults. Along these roughly north–south-trending faults mountains were uplifted and valleys down-dropped, producing the distinctive alternating pattern of linear mountain ranges and valleys of the Basin and Range province. Although there are other types of faults in the Basin and Range province, the extension and crustal stretching that have shaped the present landscape produce mostly normal faults.
|
|
The crystal system of post-perovskite is orthorhombic, its space group is Cmcm, and its structure is a stacked SiO6-octahedral sheet along the b axis. The name "post-perovskite" derives from silicate perovskite, the stable phase of MgSiO3 throughout most of Earth's mantle, which has the perovskite structure. The prefix "post-" refers to the fact that it occurs after perovskite structured MgSiO3 as pressure increases (and historically, the progression of high pressure mineral physics). At upper mantle pressures, nearest Earth's surface, MgSiO3 persists as the silicate mineral enstatite, a pyroxene rock forming mineral found in igneous and metamorphic rocks of the crust.
|
|
On the sides of the neck and the upper mantle were iridescent display feathers that have variously been described as being a bright bronze, violet or golden-green, depending on the angle of the light. The upper back and wings were a pale or slate gray tinged with olive brown, that turned into grayish-brown on the lower wings. The lower back and rump were a dark blue- gray that became grayish-brown on the upper tail-covert feathers. The greater and median wing-covert feathers were pale gray, with a small number of irregular black spots near the end.
|
|
Unlike nominally anhydrous olivine, these high-pressure olivine polymorphs have a large capacity to store water in their crystal structure. This has led to the hypothesis that the transition zone may host a large quantity of water. In Earth's interior, olivine occurs in the upper mantle at depths less than about 410 km, and ringwoodite is inferred to be present within the transition zone from about 520 to 670 km depth. Seismic activity discontinuities at about 410 km, 520 km, and at 670 km depth have been attributed to phase changes involving olivine and its polymorphs.
|
|
He was a visiting researcher in 1980 at Macquarie University in Sydney and in 1984 at the Max Planck Institute for Chemistry in Mainz. Watson's research deals (mostly but not exclusively) with the geochemistry of the deep Earth inaccessible to drilling or other direct observation. He studies the chemical composition and materials present in these deep regions and their changes over geologic time. The geochemistry of Earth's deep crust and upper mantle (down to depths of about 150 kilometers) are studied in his laboratory through the design and execution of experiments involving high temperatures and high pressures.
|
|
It is generally accepted that basin and range topography is the result of extension and thinning of the lithosphere, which is composed of crust and upper mantle. Extensional environments like the Basin and Range are characterized by listric normal faulting, or faults that level out with depth. Opposing normal faults link at depth producing a horst and graben geometry, where horst refers to the upthrown fault block and graben to the down dropped fault block. The average crustal thickness of the Basin and Range Province is approximately 30 – 35 km and is comparable to extended continental crust around the world.
|
|
Crustal material at the western edge of the Pacific Plate is some of the oldest oceanic crust on earth (up to 170 million years old), and is, therefore, cooler and denser; hence its great height difference relative to the higher-riding (and younger) Mariana Plate. The deepest area at the plate boundary is the Mariana Trench proper. The movement of the Pacific and Mariana plates is also indirectly responsible for the formation of the Mariana Islands. These volcanic islands are caused by flux melting of the upper mantle due to the release of water that is trapped in minerals of the subducted portion of the Pacific Plate.
|
|
Some subducted slabs seem to have difficulty penetrating the major discontinuity that marks the boundary between upper mantle and lower mantle at a depth of about 670 kilometers. Other subducted oceanic plates have sunk all the way to the core-mantle boundary at 2890 km depth. Generally slabs decelerate during their descent into the mantle, from typically several cm/yr (up to ~10 cm/yr in some cases) at the subduction zone and in the uppermost mantle, to ~1 cm/yr in the lower mantle. This leads to either folding or stacking of slabs at those depths, visible as thickened slabs in Seismic tomography.
|
|
The dull-mantled antbird is long and weighs around . Overall, these birds look essentially blackish grey in the front half and dark reddish brown in the hind part, with a black wing-patch with white spots right where the two main colors meet. But in the dusky forest understory, the birds may appear all-black, with only the white spotting standing out.Zimmer & Isler (2003a) The plumage of the male is blackish grey on the head, neck, upper mantle and on the underside up to the upper belly, and reddish brown on most of the remaining upperparts and underparts; remiges and rectrices are somewhat darker, with dark reddish brown edges.
|
|
In May 2011, 615–1410 ppm water in melt inclusions in lunar sample 74220 was reported, the famous high-titanium "orange glass soil" of volcanic origin collected during the Apollo 17 mission in 1972. The inclusions were formed during explosive eruptions on the Moon approximately 3.7 billion years ago. This concentration is comparable with that of magma in Earth's upper mantle. Although of considerable selenological interest, this announcement affords little comfort to would-be lunar colonists – the sample originated many kilometers below the surface, and the inclusions are so difficult to access that it took 39 years to find them with a state-of-the-art ion microprobe instrument.
|
|
Further, some hotspots such as the Hawaii hotspot show evidence of movement but the Arago hotspot appears to be static. The Arago and other hotspots probably are not deep mantle plumes but rather more shallow structures that are also influenced by the lithosphere; in the case of the Arago hotspot the absence of an oceanic plateau that could have been formed by the head of the mantle plume supports such a shallow origin. The upper mantle might be the source of the Arago hotspot. Data on the presence of seismic velocity anomalies and whether they are positive (higher) or negative (lower) beneath Arago are contradictory.
|
|
At the base of the lithosphere (the layer of crust and upper mantle that forms Earth's moving tectonic plates). In an effort to figure out why this area, far from a plate boundary, had such an enormous outpouring of lava, scientists established hardening dates for many of the individual lava flows. They found that the youngest volcanic rocks were clustered near the Yellowstone Plateau, and that the farther west they went, the older the lavas. Although scientists are still gathering evidence, a probable explanation is that a hot spot, an extremely hot plume of deep mantle material, is rising to the surface beneath the Columbia Plateau Province.
|
|
The creation of the abyssal plain is the result of the spreading of the seafloor (plate tectonics) and the melting of the lower oceanic crust. Magma rises from above the asthenosphere (a layer of the upper mantle), and as this basaltic material reaches the surface at mid-ocean ridges, it forms new oceanic crust, which is constantly pulled sideways by spreading of the seafloor. Abyssal plains result from the blanketing of an originally uneven surface of oceanic crust by fine- grained sediments, mainly clay and silt. Much of this sediment is deposited by turbidity currents that have been channelled from the continental margins along submarine canyons into deeper water.
|
|
The passage of the MTJ causes mantle material to flow into the region vacated by the Gorda plate. Once this hot mantle material is south of the triple junction, it will cool, stiffen, and accrete to adjacent lithosphere, eventually welding to it and moving along with it, analogous to the motion of a conveyor belt. Lower crust-upper mantle viscous coupling plays a dominant role in converting accretionary margin materials into continent-like crust. Researchers were able to demonstrate that in this ‘conveyor belt’ mechanism, the crust is first thickened north of the triple junction, and after passage, the crust is thinned south of the triple junction.
|
|
There are many challenges involved with trying to differentiate a nuclear explosion from other natural and man- made phenomena, such as earthquakes, mining explosions, and construction. Nuclear explosions exceeding 150 kilotons generate pressure waves that primarily travel through the Earth's core and mantle. These types of explosions are straightforward to identify because the mixture of rock the signals pass through is fairly homogeneous and the signals generated are free from noise. Smaller nuclear explosions are more difficult to identify because pressure waves primarily travel through the Earth's upper mantle and crust, leading to signal distortion due to the heterogeneity of rocks at this depth.
|
|
The transition zone is located between the upper mantle and the lower mantle between a depth of and This is thought to occur as a result of rearrangement of grains in olivine to form a denser crystal structure as a result of the increase in pressure with increasing depth. Below a depth of , due to pressure changes ringwoodite minerals change into two new denser phases, bridgmanite and periclase. This can be seen using body waves from earthquakes, which are converted, reflected or refracted at the boundary, and predicted from mineral physics, as the phase changes are temperature and density-dependent and hence depth dependent.
|
|
The Hawaii hotspot has been imaged through seismic tomography, and is estimated to be wide. Tomographic images show a thin low-velocity zone extending to a depth of , connecting with a large low-velocity zone extending from a depth of to the core-mantle boundary. These low seismic velocity zones often indicate hotter and more buoyant mantle material, consistent with a plume originating in the lower mantle and a pond of plume material in the upper mantle. The low-velocity zone associated with the source of the plume is north of Hawaii, showing that the plume is tilted to a certain degree, deflected toward the south by mantle flow.
|
|
In 1964, Henry Menard proposed that this was a superswell raised by volcanism during the Cretaceous (120-80 mya).For an illustration of Menard's model of the evolution of the Darwin Rise see A problem with this conjecture is that this region actually has a sea floor at a normal depth that happens to possess an abundance of sea mounts. Instead this feature may have formed from diapirs or plumes rising from the Earth's upper mantle, which results in chains of sea mounts along the direction of the plate motion. However, this idea remains in dispute and an alternate hypothesis involving multiple "plumelets" has been proposed.
|
|
Entities found in these lake beds include fossil leaf impressions, petrified wood, fossil insects, and bones of vertebrate animals. Evidence suggests that some concentrated heat source is melting rock beneath the Columbia Plateau Province at the base of the lithosphere (the layer of crust and upper mantle that forms Earth's moving tectonic plates). In an effort to figure out why this area, far from a plate boundary, had such an enormous outpouring of lava, scientists established hardening dates for many of the individual lava flows. They found that the youngest volcanic rocks were clustered near the Yellowstone Plateau, and that the farther west they went, the older the lavas.
|
|
Several hypotheses have been proposed to explain the volcanism of the Canary Islands.Vonlanthen, P., Kunze, K., Burlini, L. and Grobety, B. (2006) Seismic properties of the upper mantle beneath Lanzarote (Canary Islands): Model predictions based on texture measurements by EBSD, Tectonophysics, volume 428, pages 65-85, doi:10.1016/j.tecto.2006.09.005 Two hypotheses have received the most attention from geologists: (1) the volcanism is related to crustal fractures extending from the Atlas Mountains of Morocco, and (2) the volcanism is caused by the African Plate moving slowly over a hotspot in the Earth's mantle. Currently, a hotspot is the explanation accepted by most geologists who study the Canary Islands.
|
|
In values of weight percent oxide, the pure magnesian variety of wadsleyite would be 42.7% SiO2 and 57.3% MgO by mass. An analysis of trace elements in wadsleyite suggests that there are a number of elements included in it. Results demonstrate traces of rubidium (Rb), strontium (Sr), barium (Ba), titanium (Ti), zirconium (Zr), niobium (Nb), hafnium (Hf), tantalum (Ta), thorium (Th), and uranium (U) in wadsleyite and suggest that the concentrations of these elements could be larger than what has been supposed in the transition zone of Earth's upper mantle. Moreover, these results help in understanding chemical differentiation and magmatism inside the Earth (Mibe et al. 2006).
|
|
Subduction beside the northern portion of the Western Cordillera deceased between 43 and 40 million years ago. This finally caused the formation of a slab window under the northern portion of the Western Cordillera 10 million years ago, supporting an entrance to relatively undepleted upper mantle. A switch in relative plate motions at the Queen Charlotte Fault 10 million years ago produced consequent strain throughout the northern portion of the Western Cordillera, resulting in crustal thinning and decompression melting of oceanic island basalt-like mantle to create alkaline volcanism. Several plate motion models indicate a rebound to net compression throughout the Queen Charlotte Fault sometime after four million years ago.
|
|
This, and other observations, have been interpreted as indicating that the distinct geochemical signature of ocean island basalts results from inclusion of a component of subducted slab material. This must have been recycled in the mantle, then re-melted and incorporated in the lavas erupted. In the context of the plume hypothesis, subducted slabs are postulated to have been subducted down as far as the core-mantle boundary, and transported back up to the surface in rising plumes. In the plate hypothesis, the slabs are postulated to have been recycled at shallower depths – in the upper few hundred kilometers that make up the upper mantle.
|
|
The males in breeding plumage have a very variable distribution of the black on the upperparts and can be confused with Marshall's iora, however, the latter always has white tips to the tail. The nominate subspecies is found along the Himalayas and males of this population are very similar to females or have only a small amount of black on the crown. In northwestern India, septentrionalis is brighter yellow than others and in the northern plains of India humei males in breeding plumage have a black cap and olive on the upper mantle. In southwestern India and Sri Lanka multicolor has the breeding males with a jet black cap and mantle.
|
|
Likewise, percolation requires the dihedral angle between melt and crystals to be less than 60 degrees to maintain connectivity. However, measurements at the surface suggest that the dihedral angle is frequently greater than 60 degrees, thereby limiting the occurrence of percolation, although it is uncertain whether it may be less than 60 degrees in the lower mantle. Traces of iron have not been observed in the upper mantle, which would be expected had percolation dominated there. Another argument against percolation as a dominant mechanism of iron migration is that it requires temperature to stay within a narrow margin, above the iron solidus but below rock solidus.
|
|
Although the last eruption occurred around 10,000 years ago, the presence of escaping volcanic gases in the region indicates that it is still active, if only weakly. A seismic anomaly has been observed in the upper mantle beneath the Eifel volcanic area and interpreted as indicating the presence of a mantle plume. Several predictions of the plume hypothesis are not fulfilled, however, and it has been proposed that the volcanic activity in this area is a result of passive melting due to lithospheric/crustal extension and shallow convective processes related to the ongoing subduction of the Eurasian plate as part of the Alpine orogeny.
|
|
The Aspen anomaly is a seismic velocity anomaly in the mantle beneath central Colorado (in the region of Aspen, Colorado), which appears to reach down into the upper mantle. Helium with isotope ratios indicative of mantle origin emanates from the terrain above the anomaly. The Aspen anomaly coincides with the highest region of the Rocky Mountains (such as the San Juan Mountains and the Sawatch Range) and divergent drainages (Arkansas River, Colorado River and Gunnison River) which have cut deep gorges. This region underwent significant uplift during the Cenozoic starting from 10-5 million years ago and was subsequently eroded by the Colorado River.
|
|
14García Senz, 2002, p.31 At the end of formation of the back-arc basin, around 95 Ma, high temperature metamorphism developed as a result of crustal thinning synchronously or immediately after the Albian to Cenomanian basin formation. Lower crustal granulitic rocks, as well as ultramafic upper mantle rocks (lherzolites) were emplaced along the prominent North Pyrenean Fault (NPF) crustal feature. The North Pyrenean Fault developed during the sinistral (left-lateral) displacement of the Iberian Plate, which age is determined by the age of flysch pull-apart basins formed synchronously with the strike-slip movement along the NPF from Middle Albian to Early Cenomanian.
|
|
The International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) is a learned society that focuses on research in volcanology, efforts to mitigate volcanic disasters, and research into closely related disciplines, such as igneous geochemistry and petrology, geochronology, volcanogenic mineral deposits, and the physics of the generation and ascent of magmas in the upper mantle and crust. It is one of eight constituent associations of the International Union of Geodesy and Geophysics (IUGG). IAVCEI is run by an Executive Committee whose membership changes every four years. The Executive determines policies for the Association, enacting them through a series of commissions and task groups.
|
|
Ultramafic rocks such as peridotite and dunite can be residues left after extraction of magmas, and typically they are more enriched in olivine after extraction of partial melts. Olivine and high pressure structural variants constitute over 50% of the Earth's upper mantle, and olivine is one of the Earth's most common minerals by volume. The metamorphism of impure dolomite or other sedimentary rocks with high magnesium and low silica content also produces Mg-rich olivine, or forsterite. Fe-rich olivine fayalite is relatively much less common, but it occurs in igneous rocks in small amounts in rare granites and rhyolites, and extremely Fe-rich olivine can exist stably with quartz and tridymite.
|
|
Due to the flow in the lower mantle causing slab suction, changes in viscosity will have a much different effect than how it would apply to the upper mantle. In the lower mantle if you have a decrease in viscosity the flow will become much more rapid and increase the effect of slab suction and if viscosity in the lower mantle increases the effects of slab suction will decrease. Associated with the slab suction force is the idea of trench roll- back. As a slab of oceanic crust subducts into the mantle, the hinge of the plate (the point where the plate begins to subduct) tends to regress away from the trench.
|
|
The oval-shaped ridge was made many millions of years ago when volcanic material from the Earth's upper mantle moved upwards and then sideways.Compton, K., Mindat: Prospect, New South Wales Slow erosion of the overlying layers of sedimentary rock by the flow of rainwater have eventually laid bare the edges of the volcanic and metamorphic rocks of the intrusion.Conybeare Morrison, Prospect Hill Conservation Management Plan, Holroyd City Council, 2005 The Gap, an ocean cliff on the South Head peninsula in Watsons Bay, was laid as sediment more than 200 million years ago in the Triassic period. During the Jurassic era, a cataclysmic event resulted in an enormous crack forming within the strata.
|
|
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.
|
|
One of the most noteworthy aspects of Newfoundland geology is a result of the constant movement of tectonic plates. Approximately 500 million years ago the action of these plates forced parts of the oceanic crust beneath the Iapetus Ocean up and over the eastern margin of the North American plate. Sections of oceanic crust which overlie continental crust are known as ophiolites. Gros Morne National Park was designated a UNESCO World Heritage Site because it is one of the best places in the world to see the effects of plate tectonics and one of the few places where rocks formed at the Mohorovicic Discontinuity between the crust and the upper mantle of the Earth can be seen.
|
|
Rayleigh waves, also called ground roll, are surface waves that travel as ripples with motions that are similar to those of waves on the surface of water (note, however, that the associated particle motion at shallow depths is retrograde, and that the restoring force in Rayleigh and in other seismic waves is elastic, not gravitational as for water waves). The existence of these waves was predicted by John William Strutt, Lord Rayleigh, in 1885. They are slower than body waves, roughly 90% of the velocity of S waves for typical homogeneous elastic media. In a layered medium (like the crust and upper mantle) the velocity of the Rayleigh waves depends on their frequency and wavelength.
|
|
John Tuzo Wilson (October 24, 1908 – April 15, 1993) was a Canadian geophysicist and geologist who achieved worldwide acclaim for his contributions to the theory of plate tectonics. Plate tectonics is the idea that the rigid outer layers of the Earth (crust and part of the upper mantle), the lithosphere, is broken up into around 13 pieces or "plates" that move independently over the weaker asthenosphere. Wilson maintained that the Hawaiian Islands were created as a tectonic plate (extending across much of the Pacific Ocean) shifted to the northwest over a fixed hotspot, spawning a long series of volcanoes. He also conceived of the transform fault, a major plate boundary where two plates move past each other horizontally (e.g.
|
|
However, the focus of volcanism at Yellowstone in the Columbia Plateau Province is far inland from the subduction zone that lies along the Oregon and Washington coast. Evidence suggests that some concentrated heat source is melting rock beneath the Columbia Plateau Province, at the base of the lithosphere (the layer of crust and upper mantle that forms Earth's moving tectonic plates). In an effort to figure out why this area, far from a plate boundary, had such an enormous outpouring of lava, scientists established hardening dates for many of the individual lava flows. They found that the youngest volcanic rocks were clustered near the Yellowstone Plateau, and that the farther west they went, the older the lavas.
|
|
Garnet lherzolite is a major constituent of the Earth's upper mantle (extending to ~300 km depth). Lherzolite is known from the lower ultramafic part of ophiolite complexes (although harzburgite is more common in this setting), from alpine-type peridotite massifs, from fracture zones adjacent to mid-oceanic ridges, and as xenoliths in kimberlite pipes and alkali basalts. Partial melting of spinel lherzolite is one of the primary sources of basaltic magma. The name is derived from its type locality, the Lherz Massif (an alpine peridotite complex, also known as orogenic lherzolite complex), at Étang de Lers, near Massat in the French Pyrenees; Étang de Lherz is the archaic spelling of this location.
|
|
Degassing of underlying volatile-rich alkali basalt may have transported enough alkali elements into the Amalia magma chamber to change the magma to a peralkaline composition. Fractional crystallization took place at an intermediate level of the crust before the final magma body formed at a relatively shallow level. Miocene lavas from the same region did not assimilate significant crust nor mix with primitive basalts, suggesting that these processes required large magma chambers fed by large flows of basaltic magma from the upper mantle. The Miocene magmas may reflect a time when the flow of basaltic magma had diminished or extensive faulting allowed the magma to erupt before it could pool in the subsurface.
|
|
Geologists think one of the reasons that volcanoes on Mars are able to grow so large is because Mars lacks plate tectonics. The Martian lithosphere does not slide over the upper mantle (asthenosphere) as on Earth, so lava from a stationary hot spot is able to accumulate at one location on the surface for a billion years or longer. On 17 October 2012, the Curiosity rover on the planet Mars at "Rocknest" performed the first X-ray diffraction analysis of Martian soil. The results from the rover's CheMin analyzer revealed the presence of several minerals, including feldspar, pyroxenes and olivine, and suggested that the Martian soil in the sample was similar to the "weathered basaltic soils" of Hawaiian volcanoes.
|
|
However, not much of a noticeable evidence linking the production of magma in the upper mantle to a possible tectonic system has been stated. The existence of a fault next to the western flank of the Mount Edziza volcanic complex is normally considered to be the prime structural evidence for continental rifting in the Northern Cordilleran Volcanic Province. However, more recent mapping and seismic studies in the Coast Mountains have documented the presence of brittle rift-related faults southwest of the small community of Stewart in northwestern British Columbia. But these faults were in a matter of dispute in 1997 by geologists, stating these faults were last active between 20 and five million years ago.
|
|
Although extensive rifting has not yet been recognized in the Northern Cordilleran Volcanic Province, volcanism throughout the past 1.6 million years is possibly due to repetitive upper mantle upwelling and adjacent transtension throughout the Queen Charlotte Fault, accommodated partly by numerous east-west trending fault zones that extend all through the Northern Cordilleran Volcanic Province. The volcanics comprising the Northern Cordilleran Volcanic Province are consistent with the rifting environment. Alkaline basalt, lesser hawaiite and basanite magmas from effusive eruptions create the massive shield volcanoes and small cinder cones throughout the volcanic province, several of which comprise lherzolite magma. Felsic magmas from more viscous eruptions create the massive central volcanoes and largely consist of trachyte, pantellerite and comendite lavas.
|
|
Understanding that the differences between Earth's layers are not just rheological, but chemical, is essential to understanding how we can track the movement of crustal material even after it has been subducted. After a rock has moved to the surface of the earth from beneath the crust, that rock can be sampled for its stable isotopic composition. It can then be compared to known crustal and mantle isotopic compositions, as well as that of chondrites, which are understood to represent original material from the formation of the solar system in a largely unaltered state. One group of researchers was able to estimate that between 5 and 10% of the upper mantle is composed of recycled crustal material.
|
|
Only 1% of the surface of the far side is covered by maria, compared to 31.2% on the near side. According to research analyzed by NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission, the reason for the difference is because the Moon's crust is thinner on the near side compared to the far side.Universe Today The dark splotches that make up the large lunar maria are lava-filled impact basins that were created by asteroid impacts about four billion years ago. Though both sides of the Moon were bombarded by similarly large impactors, the near side hemisphere crust and upper mantle was hotter than that of the far side, resulting in the larger impact craters.
|
|
Current research indicates that complex convection within the Earth's mantle allows material to rise to the base of the lithosphere beneath each divergent plate boundary. This supplies the area with vast amounts of heat and a reduction in pressure that melts rock from the asthenosphere (or upper mantle) beneath the rift area, forming large flood basalt or lava flows. Each eruption occurs in only a part of the plate boundary at any one time, but when it does occur, it fills in the opening gap as the two opposing plates move away from each other. Over millions of years, tectonic plates may move many hundreds of kilometers away from both sides of a divergent plate boundary.
|
|
The tectonic plates of the lithosphere on Earth Earth cutaway from center to surface, the lithosphere comprising the crust and lithospheric mantle (detail not to scale) A lithosphere ( [lithos] for "rocky", and [sphaira] for "sphere") is the rigid,Skinner, B.J. & Porter, S.C.: Physical Geology, page 17, chapt. The Earth: Inside and Out, 1987, John Wiley & Sons, outermost shell of a terrestrial-type planet, or natural satellite, that is defined by its rigid mechanical properties. On Earth, it is composed of the crust and the portion of the upper mantle that behaves elastically on time scales of thousands of years or greater. The outermost shell of a rocky planet, the crust, is defined on the basis of its chemistry and mineralogy.
|
|
While most volcanoes are created by geological activity at tectonic plate boundaries, the Anahim hotspot is located hundreds of kilometres away from the nearest plate boundary. This hotspot's existence was first proposed in the 1970s by three scientists who used John Tuzo Wilson's classic hotspot theory. This theory proposes that a single, fixed mantle plume builds volcanoes that then, cut off from their source by the movement of the North American Plate, become increasingly inactive and eventually erode over millions of years. A more recent theory, published in 2001 by the Geological Society of America, suggests that the Anahim hotspot might be supplied by a mantle plume from the upper mantle rather than a deep-seated plume proposed by Wilson.
|
|
The multi-anvil press is a type of device designed to produce extremely high pressures in a relatively small volume. This type of anvil press is used in materials science and geology for the synthesis and study of solid phase materials under extreme pressure, as well as for the industrial production of valuable minerals, especially synthetic diamonds. These instruments allow the simultaneous compression and heating of millimeter size solid phase samples such as rocks, minerals, ceramics, glasses, composite materials, or metal alloys and are capable of reaching pressures above 25 GPa and temperatures exceeding 2500 °C. This allows mineral physicists and petrologists studying the Earth’s interior to experimentally reproduce the conditions found throughout the lithosphere and upper mantle, to a depth of 700 km (citation, figure 1,2).
|
|
In the case of raising the temperature, mantle melting will only occur if the mantle is heated past the normal geotherm. It is believed that heat flux from the core and lower mantle is responsible for increasing the temperature of the upper mantle. Local perturbations of the geothermal gradient, such as hotspots, are not well understood but are considered to be a likely heat source for the mantle.The decay of radioactive elements, though considered to be one of the simplest ways of generating heat in the mantle, is not realistically responsible for mantle melting, as it would take over 10 million years for the radioactive decay of K, U and Th to increase the temperature of peridotite by 1 degree Celsius.
|
|
In meteorites, ringwoodite occurs in the veinlets of quenched shock-melt cutting the matrix and replacing olivine probably produced during shock metamorphism. In Earth's interior, olivine occurs in the upper mantle at depths less than about 410 km, and ringwoodite is inferred to be present within the transition zone from about 520 to 660 km depth. Seismic activity discontinuities at about 410 km, 520 km, and at 660 km depth have been attributed to phase changes involving olivine and its polymorphs. The 520-km depth discontinuity is generally believed to be caused by the transition of the olivine polymorph wadsleyite (beta-phase) to ringwoodite (gamma-phase), while the 660-km depth discontinuity by the phase transformation of ringwoodite (gamma-phase) to a silicate perovskite plus magnesiowüstite.
|
|
The age-progressive distribution of the Hawaiian-Emperor seamount chain has been explained as a result of a fixed, deep-mantle plume rising into the upper mantle, partly melting, and causing a volcanic chain to form as the plate moves overhead relative to the fixed plume source. Other "hot spots" with time-progressive volcanic chains behind them include Réunion, the Chagos-Laccadive Ridge, the Louisville Ridge, the Ninety East Ridge and Kerguelen, Tristan, and Yellowstone. An intrinsic aspect of the plume hypothesis is that the "hot spots" and their volcanic trails have been fixed relative to one another throughout geological time. Whereas there is evidence that the chains listed above are time-progressive, it has, however, been shown that they are not fixed relative to one another.
|
|
The use of reflection seismology in studies of tectonics and the Earth's crust was pioneered in the 1970s by groups such as the Consortium for Continental Reflection Profiling (COCORP), who inspired deep seismic exploration in other countries such as BIRPS in Great Britain and ECORS in France. The British Institutions Reflection Profiling Syndicate (BIRPS) was started up as a result of oil hydrocarbon exploration in the North Sea. It became clear that there was a lack of understanding of the tectonic processes that had formed the geological structures and sedimentary basins which were being explored. The effort produced some significant results and showed that it is possible to profile features such as thrust faults that penetrate through the crust to the upper mantle with marine seismic surveys.
|
|
In the upper mantle, heat and pressure dehydrates these minerals, releasing much of it to the overlying mantle wedge, triggering the melting of rock that rises to form volcanic arcs. However, some of the "nominally anhydrous minerals" that are stable deeper in the mantle can store small concentrations of water in the form of hydroxyl (OH−), and because they occupy large volumes of the Earth, they are capable of storing at least as much as the world's oceans. The conventional view of the ocean's origin is that it was filled by outgassing from the mantle in the early Archean and the mantle has remained dehydrated ever since. However, subduction carries water down at a rate that would empty the ocean in 1–2 billion years.
|
|
Oceanic crust is formed at a mid-ocean ridge, while the lithosphere is subducted back into the asthenosphere at oceanic trenches Age of oceanic crust (red is youngest, and blue is oldest) Oceanic crust, which forms the bedrock of abyssal plains, is continuously being created at mid- ocean ridges (a type of divergent boundary) by a process known as decompression melting. Plume-related decompression melting of solid mantle is responsible for creating ocean islands like the Hawaiian islands, as well as the ocean crust at mid-ocean ridges. This phenomenon is also the most common explanation for flood basalts and oceanic plateaus (two types of large igneous provinces). Decompression melting occurs when the upper mantle is partially melted into magma as it moves upwards under mid-ocean ridges.
|
|
Episodic behavior of Venus model showing strong mantle layering at 675 Ma, followed by a break in the basalt barrier at 750 Ma, the mantle overturns at 810 Ma and layering is reestablished again at 1000 Ma.Turcotte (1993) suggested that Venus has episodic tectonics, whereby short periods of rapid tectonics are separated by periods of surface inactivity lasting on the order of 500 Ma. During periods of inactivity, the lithosphere cools conductively and thickens to over 300 km. The active mode of plate tectonics occurs when the thick lithosphere detaches and founders into the interior of the planet. Large scale lithosphere recycling is thus invoked to explain resurfacing events. Episodic large scale overturns can occur due to a compositionally stratified mantle where there is competition between the compositional and thermal buoyancy of the upper mantle.
|
|
Since the downgoing slab is partly anchored in the viscous layers of the mantle, and therefore its lateral movement is significantly slower than the surface plate, then any motion of the overriding plate will cause extensional or compressional stress in the back-arc region depending on the direction of motion. In addition, mantle convection in the upper mantle wedge caused by the downward movement of the subducted slab causes stress in the upper plate and the high heat flow that characterizes back-arcs. The pulling effect of the slab as it goes down into the mantle causes a rollback motion of the trench, which also applies stress on the back- arc region of the upper plate. However, this last process has less of an impact on deformation compared to upper plate motion.
|
|
Peridotites have two primary modes of origin, as mantle rocks formed during the accretion and differentiation of the Earth, or as cumulate rocks formed by precipitation of olivine ± pyroxenes from basaltic or ultramafic magmas; these magmas are ultimately derived from the upper mantle by partial melting of mantle peridotites. Mantle peridotites are sampled as alpine-type massifs in collisional mountain ranges or as xenoliths in basalt or kimberlite or as abyssal peridotites (sampled from ocean floor). In all cases these rocks are pyrometamorphic (that is, metamorphosed in the presence of molten rock) and represent either fertile mantle (lherzolite) or partially depleted mantle (harzburgite, dunite). Alpine peridotites may be either of the ophiolite association and representing the uppermost mantle below ocean basins, or masses of subcontinental mantle emplaced along thrust faults in mountain belts.
|
|
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.
|
|
The onset of Cordilleran orogenesis began in the Middle Jurassic time, as a result of the breakup of Pangea and North American plate motion toward subduction zones at the western margin. Most of the Canadian Cordillera today consists of numerous tectonostratigraphic terranes that were accreted to the stable margin of North America from the Jurassic to Early Tertiary as a result of eastward and northward drifting island arcs that collided with the continental lithosphere of North America. These terranes were accreted due to upper-crustal rocks being detached from the denser lower-crustal and proto-Pacific upper mantle lithosphere that was subducted under the North American craton. The allochthonous upper crustal terranes were juxtaposed over top of each other and over the western margin of the North American craton along a system of interconnected, northeast and southwest verging major thrust faults.
|
|
In particular, xenon is useful for calculations of water loss over time. Not only is it a noble gas (and therefore is not removed from the atmosphere through chemical reactions with other elements), but comparisons between abundances of its nine stable isotopes in the modern atmosphere reveal that the Earth lost at least one ocean of water early in its history, between the Hadean and Archean eras. Any water on Earth during the later part of its accretion would have been disrupted by the Moon-forming impact (~4.5 billion years ago), which likely vaporized much of Earth's crust and upper mantle and created a rock-vapor atmosphere around the young planet. The rock vapor would have condensed within two thousand years, leaving behind hot volatiles which probably resulted in a majority carbon dioxide atmosphere with hydrogen and water vapor.
|
|
There is a general agreement that the axial trough of the Red Sea originated by seafloor spreading, and therefore is underlain by oceanic crust, the nature of the crust beneath the main trough and coastal plains of the Red Sea is still controversial, leading to the development of a few theories. One theory suggests that the entire Red Sea basin is underlain by oceanic crust, while another theory claims that the main trough is underlain only in part by oceanic crust. A third theory suggests that outside the axial trough, the crust has a continental composition, with the presence of basaltic dykes, while another hypothesis suggests that the lower crust in the rift consists of rift meta-sediments, in direct contact with the upper mantle. All geophysical data from the axial trough reveal seismic velocities typical for oceanic crust.
|
|
Minor and major volcanoes of the Northern Cordilleran Volcanic Province, including the Queen Charlotte, Denali and Tintina fault zones A range of more heavily alkaline rock types not commonly found in the Western Cordillera are regionally widespread in the Northern Cordilleran Volcanic Province. These include nephelinite, basanite and peralkaline phonolite, trachyte, and comendite lavas. The most magnesium oxide-rich nephelinites, basanites and alkaline basalts all through the Northern Cordilleran Volcanic Province display trace element abundances and isotopic compositions that are logical with an asthenospheric source like those for average oceanic island basalt and for alkaline basalts younger than five million years in the rift-related Basin and Range Province of southwestern United States and northwestern Mexico. One hypothesized explanation for oceanic island basalt in the Earth's upper mantle under the Northern Cordilleran Volcanic Province is the existence of a slab window.
|
|
A multi-anvil press, or anvil press is a type of device related to a machine press that is used to create extraordinarily high pressures within a small volume. They are used in materials science and geology for the synthesis and study the different phases of materials under extreme pressure, as well as for the industrial production of valuable minerals, especially synthetic diamonds, as they mimic the pressures and temperatures that exist deep in the Earth. These instruments allow the simultaneous compression and heating of millimeter size solid phase samples such as rocks, minerals, ceramics, glasses, composite materials, or metals and are capable of reaching pressures above 25 GPa and temperatures exceeding 2,500 °C. This allows mineral physicists and petrologists studying the Earth's interior to experimentally reproduce the conditions found throughout the lithosphere and upper mantle, a region that spans the near surface to a depth of 700 km.
|
|
In north Italy the dip of this interface is 30° to 40° at a depth of 80–90 km.. The strike of the Apennine subduction zone forms a long, irregular arc with centers of curvature in the Tyrrhenian Sea following the hanging wall over which the mountains have been raised; i.e., the eastern wall of the mountains. It runs from near the base of the Ligurian Apennines in the Po Valley along the margin of the mountains to the Adriatic, along the coastal deeps of the Adriatic shore, strikes inland at Monte Gargano cutting off Apulia, out to sea again through the Gulf of Taranto, widely around the rest of Italy and Sicily and across inland north Africa. The upper mantle above deep is broken into the "Northern Apennines Arc" and the "Calabrian Arc", with compressional forces acting in different directions radially toward the arcs' centers of curvature.
|
|
A major feature of the Hawaiian trail is a sudden 60° bend at a 40- to 50-million-year-old section of its length, and according to Wilson's theory, this is evidence of a major change in plate direction, one that would have initiated subduction along much of the Pacific Plate's western boundary. This part of the theory has recently been challenged, and the bend might be attributed to the movement of the hotspot itself. Geophysicists believe that hotspots originate at one of two major boundaries deep in the Earth, either a shallow interface in the lower mantle between an upper mantle convecting layer and a lower non-convecting layer, or a deeper D ("D double-prime") layer, approximately thick and immediately above the core-mantle boundary. A mantle plume would initiate at the interface when the warmer lower layer heats a portion of the cooler upper layer.
|
|
In 1862, the physicist William Thomson, 1st Baron Kelvin published calculations that fixed the age of Earth at between 20 million and 400 million years. Dalrymple (1994) pp. 14–17, 38 He assumed that Earth had formed as a completely molten object, and determined the amount of time it would take for the near-surface temperature gradient to decrease to its present value. His calculations did not account for heat produced via radioactive decay (a then unknown process) or, more significantly, convection inside the Earth, which allows the temperature in the upper mantle to remain high much longer, maintaining a high thermal gradient in the crust much longer. Even more constraining were Kelvin's estimates of the age of the Sun, which were based on estimates of its thermal output and a theory that the Sun obtains its energy from gravitational collapse; Kelvin estimated that the Sun is about 20 million years old.
|
|
These ideas evolved from the integration of geochemistry, petrology, seismology, and thermodynamics, while standard models are based only on one or two of these disciplines and many assumptions. Anderson also challenged traditional scientific views on how volcanoes are formed, particularly, the theory of convective mantle plumes in the Earth, as proposed by W. Jason Morgan, Anderson argued that the so-called mantle plume hypothesis is invalid and that hotspots and oceanic islands such as Hawaii or Iceland are, instead, the normal products of plate tectonics. While many geochemists believe that volcanoes stem from narrow plumes coming up from just above the Earth's core, Anderson showed that they can be explained entirely by chemical and mineralogical anomalies in the upper mantle. Moreover, Anderson pointed out that all demonstrations of the mantle plume hypothesis violate the basic laws of thermodynamics because they rely on a constant supply of heat coming from the deep Earth or even from outside the Earth.
|
|
As an oceanic plate descends into the upper mantle, its minerals tend to lose water. How much water is lost and when depends on the pressure, temperature and mineralogy. Water is carried by a variety of minerals that combine various proportions of magnesium oxide (MgO), silicon dioxide (SiO2), and water. At low pressures (below 5 GPa), these include antigorite, a form of serpentine, and clinochlore (both carrying 13 wt% water); talc (4.8 wt%) and some other minerals with a lower capacity. At moderate pressure (5–7 GPa) the minerals include phlogopite (4.8 wt%), the 10Å phase (a high pressure product of talc and water, 10–13 wt%) and lawsonite (11.5 wt%). At pressures above 7 GPa, there is topaz-OH (Al2SiO4(OH)2, 10 wt%), phase Egg (AlSiO3(OH), 11–18 wt%) and a collection of dense hydrous magnesium silicate (DHMS) or "alphabet" phases such as phase A (12 wt%), D (10 wt%) and E (11 wt%).
|
|
In 1983, G. Poupinet and others observed that the travel time of PKIKP waves (P-waves that travel through the inner core) was about 2 seconds less for straight north-south paths than straight paths on the equatorial plane. Even taking into account the flattening of the Earth at the poles (about 0.33% for the whole Earth, 0.25% for the inner core) and crust and upper mantle heterogeneities, this difference implied that P waves (of a broad range of wavelengths) travel through the inner core about 1% faster in the north-south direction than along directions perpendicular to that. This P-wave speed anisotropy has been confirmed by later studies, including more seismic data and study of the free oscillations of the whole Earth. Some authors have claimed higher values for the difference, up to 4.8%; however, in 2017 D. Frost and B. Romanowicz confirmed that the value is between 0.5% and 1.5%.
|
|
This experiment was designed to explore the deep structure of the North American continent, but also formed the starting point for the development of novel methods of seismological investigation: with Winston Chan, Martha Savage, and other colleagues, Silver elaborated on earlier workSilver, P. G., Chan, W. W. (1988): Implications for continental structure and evolution from seismic anisotropy. Nature 335, 34–39 Link to paper (access restricted) and deduced from the measurements the splitting of shear waves, a type of seismic anisotropy, for areas of the size of tectonic plates in order to determine the patterns of convection in the upper mantle and the deformation history of the continental and subcontinental lithosphere that record how the continent grew and evolved.Silver, P. G., Chan, W. W. (1991): Shear wave splitting and subcontinental mantle deformation. J. Geophys. Res. 96(B10), 16429–16454 Link to paper (access restricted) This approach has been developed ever since and is now in widespread use to study the patterns of convective flow in the Earth’s interior and the processes by which the continents were assembled.
|
|
Stanley (1999) One perspective of how the cratonization process might have first begun in the Archean is given by Warren B. Hamilton: > Very thick sections of mostly submarine mafic, and subordinate ultramafic, > volcanic rocks, and mostly younger subaerial and submarine felsic volcanic > rocks and sediments were oppressed into complex synforms between rising > young domiform felsic batholiths mobilized by hydrous partial melting in the > lower crust. Upper-crust granite-and-greenstone terrains underwent moderate > regional shortening, decoupled from the lower crust, during compositional > inversion accompanying doming, but cratonization soon followed. Tonalitic > basement is preserved beneath some greenstone sections but supracrustal > rocks commonly give way downward to correlative or younger plutonic rocks... > Mantle plumes probably did not yet exist, and developing continents were > concentrated in cool regions. Hot-region upper mantle was partly molten, and > voluminous magmas, mostly ultramafic, erupted through many ephemeral > submarine vents and rifts focussed at the thinnest crust.... Surviving > Archean crust is from regions of cooler, and more depleted, mantle, wherein > greater stability permitted uncommonly thick volcanic accumulations from > which voluminous partial-melt, low-density felsic rocks could be > generated.
|
|
According to some geologists, there is evidence that a mantle plume has existed in the region for about 140 million years, first remaining in roughly the same position while the African plate rotated above it, and then remaining stationary under the Oku area since around 66 million years ago. In this theory, the abnormal heat rising in a mantle plume would lead to melting of the upper mantle, which raises, thins and weakens the crust and facilitates rifting. This may have been repeated several times in the Benue Trough between 140 Ma and 49 Ma. One plume-related hypothesis for the later development of the Cameroon Line around 30 Ma is that it coincides with development of a shallow mantle convection system centered on the mantle plume, and is related to thinning and extension of the crust along the Cameroon line as pressures relaxed in the now stationary plate. The mantle plume hypothesis is disputed by scientists who point out that features of the region are quite different from what is predicted by that hypothesis, and that a source in a lithospheric fracture is more likely to be the explanation.
|
|