query: the boundary that separates the crust from the mantle is the

pos: Mohorovičić discontinuity Mohorovičić discontinuity The Mohorovičić discontinuity (), usually referred to as the Moho, is the boundary between the Earth's crust and the mantle. Named after the pioneering Croatian seismologist Andrija Mohorovičić, the Moho separates both the oceanic crust and continental crust from underlying mantle.The Mohorovičić discontinuity was first identified in 1909 by Mohorovičić, when he observed that seismograms from shallow-focus earthquakes had two sets of P-waves and S-waves, one that followed a direct path near the Earth's surface and the other refracted by a high-velocity medium. The Moho lies almost entirely within the lithosphere; only beneath mid-ocean ridges does it define

pos: Mohorovičić discontinuity Mohorovičić discontinuity The Mohorovičić discontinuity (), usually referred to as the Moho, is the boundary between the Earth's crust and the mantle. Named after the pioneering Croatian seismologist Andrija Mohorovičić, the Moho separates both the oceanic crust and continental crust from underlying mantle.The Mohorovičić discontinuity was first identified in 1909 by Mohorovičić, when he observed that seismograms from shallow-focus earthquakes had two sets of P-waves and S-waves, one that followed a direct path near the Earth's surface and the other refracted by a high-velocity medium. The Moho lies almost entirely within the lithosphere; only beneath mid-ocean ridges does it define

pos: Mohorovičić discontinuity an initial bore hole to a depth of approximately 1.5 kilometres. The attempt did not even reach 1.3 km, but researchers hope to further their investigations at a later date. Mohorovičić discontinuity The Mohorovičić discontinuity (), usually referred to as the Moho, is the boundary between the Earth's crust and the mantle. Named after the pioneering Croatian seismologist Andrija Mohorovičić, the Moho separates both the oceanic crust and continental crust from underlying mantle.The Mohorovičić discontinuity was first identified in 1909 by Mohorovičić, when he observed that seismograms from shallow-focus earthquakes had two sets of P-waves and S-waves, one that followed

pos: Crust (geology) the crust. The boundary between the crust and mantle is conventionally placed at the Mohorovičić discontinuity, a boundary defined by a contrast in seismic velocity. The crust of the Earth is of two distinctive types: Because both continental and oceanic crust are less dense than the mantle below, both types of crust "float" on the mantle. This is isostasy, and it's also one of the reasons continental crust is higher than oceanic: continental is less dense and so "floats" higher. As a result, water pools in above the oceanic crust, forming the oceans. The temperature of the crust increases with

pos: Structure of the Earth discontinuity (a second order discontinuity). The uppermost mantle together with the crust constitutes the lithosphere. The crust-mantle boundary occurs as two physically different events. First, there is a discontinuity in the seismic velocity, which is most commonly known as the Mohorovičić discontinuity or Moho. The cause of the Moho is thought to be a change in rock composition from rocks containing plagioclase feldspar (above) to rocks that contain no feldspars (below). Second, in oceanic crust, there is a chemical discontinuity between ultramafic cumulates and tectonized harzburgites, which has been observed from deep parts of the oceanic crust that have been

pos: Ivrea zone the terrane was uplifted during the formation of the Alps, the upper crust was eroded off so that these rocks are now at the surface. Geophysical research shows the mantle is relatively close under the surface at the Ivrea zone. Some geologists think the boundary between pyroxenites and lherzolites, that is also found in outcrops in the Ivrea zone, represents the Mohorovičić discontinuity (the Moho). The Moho is seismologically defined as the boundary between the crust and mantle. Ivrea zone The Ivrea zone is a tectonic terrane in the Italian Alps, that consists of a steeply dipping piece of the

pos: London-Brabant Massif much carbon dioxide. It is now best viewed as a block of dense crust floating deeply sunk into the mantle and overlain with less dense superficial rocks. It depresses the boundary of the crust and the mantle (Mohorovičić discontinuity, commonly Moho) to depths greater than 40 kilometres as against a figure at the top of the continental shelf of about thirty and less than fifteen below oceanic depths. The map shows that there is some tendency for such seismic activity as there is in the region, to occur around the margin of the massif. It was into this pattern that

pos: Shatsky Rise Earth. It covers an area that has been estimated to (roughly the size of California or Sumatra) and a volume of . Beneath Shatsky rise, however, the Mohorovičić discontinuity (Moho, the mantle-crust boundary) disappears at a depth of whereas it is normally observed at a depth of . Furthermore, the crustal thickness between the massifs of the Shatsky Rise is almost twice that of normal crust thickness. This considered, the area covered by the rise, assuming the crust was also formed by the Shatsky Rise volcanism, has been estimated to and the volume to . After its formation Shatsky Rise

pos: Mantle (geology) overlying crust make up tectonic plates, which move over the asthenosphere. The Earth's mantle is divided into three major layers defined by sudden changes in seismic velocity: The lower ~200 km of the lower mantle constitutes the D" (D-double-prime) layer, a region with anomalous seismic properties. This region also contains LLSVPs and ULVZs. 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

pos: Andrija Mohorovičić of material, they are reflected and refracted, just as light is when striking a prism, and that when earthquakes occur, two waves—longitudinal and transverse—propagate through the soil with different velocities. By analyzing data from more observation posts, Mohorovičić concluded that the Earth has several layers above a core. He was the first to establish, based on the evidence from seismic waves, the discontinuity that separates the Earth's crust from its mantle. This is now called the Mohorovičić discontinuity or (because of the complexity of that name) "Moho". According to Mohorovičić, a layered structure would explain the observation of depths where

pos: Earth chlorine, sulfur, and fluorine are the important exceptions to this and their total amount in any rock is usually much less than 1%. Over 99% of the crust is composed of 11 oxides, principally silica, alumina, iron oxides, lime, magnesia, potash, and soda. Earth's interior, like that of the other terrestrial planets, is divided into layers by their chemical or physical (rheological) properties. The outer layer is a chemically distinct silicate solid crust, which is underlain by a highly viscous solid mantle. The crust is separated from the mantle by the Mohorovičić discontinuity. The thickness of the crust varies from

neg: Mantle (geology) are also sampled as xenoliths within basalts or kimberlites. Most estimates of the mantle composition are based on rocks that sample only the uppermost mantle. There is debate as to whether the rest of the mantle, especially the lower mantle, has the same bulk composition. The mantle's composition has changed through the Earth's history due to the extraction of magma that solidified to form oceanic crust and continental crust. In the mantle, temperatures range from approximately at the upper boundary with the crust to approximately at the core-mantle boundary. The geothermal gradient of the mantle increases rapidly in the thermal

neg: Opening of the North Atlantic Ocean The final major phase of breakup occurred in the early Cenozoic, as Laurentia separated from Eurasia. As the two plates broke free from each other, the Atlantic Ocean continued to expand. The Iceland plume is a mantle plume under Iceland that carries hot material from the deep within Earth's mantle upwards to the crust. The rising hot material weakens the lithosphere, making the separation of plates easier. The flow of hot plume material creates volcanism under the continental lithosphere. Iceland extends across the Mid-Atlantic Ridge. The Mid-Atlantic Ridge is a divergent plate boundary, and it separates the Eurasian and North

neg: Convergent boundary in the mantle. Convection cells are the result of heat generated by radioactive decay of elements in the mantle escaping to the surface and the return of cool materials from the surface to the mantle. These convection cells bring hot mantle material to the surface along spreading centers creating new crust. As this new crust is pushed away from the spreading center by formation of newer crust, it cools, thins, and becomes denser. Subduction initiates when this dense crust converges with less dense crust. The force of gravity helps drive the subducting slab into the mantle. Evidence supports that the

neg: Structure of the Earth obducted onto the continental crust and preserved as ophiolite sequences. Many rocks now making up Earth's crust formed less than 100 million (1) years ago; however, the oldest known mineral grains are about 4.4 billion (4.4) years old, indicating that Earth has had a solid crust for at least 4.4 billion years. Earth's mantle extends to a depth of 2,890 km, making it the thickest layer of Earth. The mantle is divided into upper and lower mantle. The upper and lower mantle are separated by the transition zone. The lowest part of the mantle next to the core-mantle boundary is

neg: Mantle (geology) a thickness of making up about 84% of Earth's volume. It is predominantly solid but in geological time it behaves as a viscous fluid. Partial melting of the mantle at mid-ocean ridges produces oceanic crust, and partial melting of the mantle at subduction zones produces continental crust. The Earth's mantle is divided into two major rheological layers: the rigid lithosphere comprising the uppermost mantle, and the less viscous asthenosphere, separated by the lithosphere-asthenosphere boundary. Lithosphere underlying ocean crust has a thickness of around 100 km, whereas lithosphere underlying continental crust generally has a thickness of 150-200 km. The lithosphere and

neg: Igneous rock can occur because of the upward intrusion of magma from the mantle. Temperatures can also exceed the solidus of a crustal rock in continental crust thickened by compression at a plate boundary. The plate boundary between the Indian and Asian continental masses provides a well-studied example, as the Tibetan Plateau just north of the boundary has crust about 80 kilometers thick, roughly twice the thickness of normal continental crust. Studies of electrical resistivity deduced from magnetotelluric data have detected a layer that appears to contain silicate melt and that stretches for at least 1,000 kilometers within the middle crust along

neg: Core–mantle boundary Variations in the thermal properties of the core-mantle boundary may affect how the outer core's iron-rich fluids flow, which are ultimately responsible for Earth's magnetic field. The approx. 200 km thick layer of the lower mantle directly above the boundary is referred to as the D″ region ("D double-prime" or "D prime prime") and is sometimes included in discussions regarding the core–mantle boundary zone. The D″ name originates from mathematician Keith Bullen's designations for the Earth's layers. His system was to label each layer alphabetically, A through G, with the crust as 'A' and the inner core as 'G'. In

neg: Agulhas Passage the Agulhas Passage the boundary between the Earth's crust and the mantle (the Moho) ascend from over which is normal for a continent-ocean boundary. The crustal thickness under the Agulhas Passage varies from which is equally normal for oceanic crust. It is possible, however, that volcanic flows from the Agulhas Plateau large igneous province (LIP) added crustal material to the Agulhas Passage (which is 160-120 Ma) during the LIP formation (100-80 Ma) and that the crust under the passage was originally thinner. The sedimentary layers are very thin in the western Agulhas Passage, in places only . In the central

neg: Mantle plume in the oceanic slab (the water-soluble elements are added to the crust in island arc volcanoes). Seismic tomography shows that subducted oceanic slabs sink as far as the bottom of the mantle transition zone at 650 km depth. Subduction to greater depths is less certain, but there is evidence that they may sink to mid-lower-mantle depths at about 1,500 km depth. The source of mantle plumes is postulated to be the core-mantle boundary at 3,000 km depth. Because there is little material transport across the core-mantle boundary, heat transfer must occur by conduction, with adiabatic gradients above and below this

neg: Crust (geology) depth, reaching values typically in the range from about to at the boundary with the underlying mantle. The temperature increases by as much as for every kilometer locally in the upper part of the crust, but the geothermal gradient is smaller in deeper crust. The continental crust has an average composition similar to that of andesite. The most abundant minerals in Earth's continental crust are feldspars, which make up about 41% of the crust by weight, followed by quartz at 12%, and pyroxenes at 11%. Continental crust is enriched in incompatible elements compared to the basaltic ocean crust and much

neg: Earth about under the oceans to for the continents. The crust and the cold, rigid, top of the upper mantle are collectively known as the lithosphere, and it is of the lithosphere that the tectonic plates are composed. Beneath the lithosphere is the asthenosphere, a relatively low-viscosity layer on which the lithosphere rides. Important changes in crystal structure within the mantle occur at below the surface, spanning a transition zone that separates the upper and lower mantle. Beneath the mantle, an extremely low viscosity liquid outer core lies above a solid inner core. The Earth's inner core might rotate at a

neg: Opening of the North Atlantic Ocean force doming of the crust. This causes thinning of the crust and lithosphere, then melting and underplating occur. Finally, there is rifting at the crest of the domed crust and volcanism occurs. In passive rifting, driven by plate tectonics, the crust and lithosphere extend as a result of plate boundary forces such as slab pull. Far field stresses thin the crust and lithospheric mantle, and hot asthenospheric mantle passively enters the thinned area. The upwelling of asthenosphere is not involved in the actual rifting process. The upward flow of the asthenosphere results in decompression melting, magmatic underplating and some volcanism

neg: Geothermal gradient atomic radii such as magnesium (Mg), titanium (Ti), and calcium (Ca). The geothermal gradient is steeper in the lithosphere than in the mantle because the mantle transports heat primarily by convection, leading to a geothermal gradient that is determined by the mantle adiabat, rather than by the conductive heat transfer processes that predominate in the lithosphere, which acts as a thermal boundary layer of the convecting mantle. Heat flows constantly from its sources within the Earth to the surface. Total heat loss from the Earth is estimated at 44.2 TW (). Mean heat flow is 65 mW/m over continental crust

neg: Primitive mantle this is the so-called D"-layer at the core-mantle boundary. The "Late veneer hypothesis" suggests that specific materials were added at the surface from extra external sources. There are arguments against this hypothesis Primitive mantle The primitive mantle is, in geochemistry, a hypothetical reservoir with the composition of the Earth's crust and mantle taken together. The currently accepted scientific hypothesis is that the Earth was formed by accretion of material with a chondritic composition. Still during the accretionary phase planetary differentiation started, giving rise to the Earth's core, where heavy metallic siderophile elements accumulated. Around it was a (in this stage)

neg: Gakkel Ridge from the mantle, below the crust, which is very unusual for a mid-ocean ridge . It confirms that the mantle and crust of Gakkel ridge, like some segments of the Southwest Indian Ridge, are very cold. Gakkel Ridge The Gakkel Ridge (formerly known as the Nansen Cordillera and Arctic Mid-Ocean Ridge) is a mid-oceanic ridge, a divergent tectonic plate boundary between the North American Plate and the Eurasian Plate. It is located in the Eurasian Basin of the Arctic Ocean, between Greenland and Siberia, and has a length of about 1,800 kilometers. Geologically, it connects the northern end of the

neg: Gravity of Mars by porosity and geochemistry of the rock. Relevant information could be obtained from Martian meteorites and in-situ analysis. Since Bouguer gravity anomalies have strong link with depth of crust-mantle boundary, one with positive Bouguer anomalies may mean that it has a thinner crust composed of lower density material and is influenced more strongly by the denser mantle, and vice versa. However, it could also be contributed by the difference in density of the erupted volcanic load and sedimentary load, as well as subsurface intrusion and removal of material. Many of these anomalies are associated with either geological or topographic features.

neg: Non-volcanic passive margins the material below the surface. Large amplitude magnetic anomalies are associated with high magnetic susceptibility (~0.06 emu) igneous rocks of VPM. In contrast, NVPM exhibit only small amplitude anomalies associated with the edge effect at the boundary between the exhumed mantle (~0.003 emu) at the transition zone, and the true oceanic crust basalt (~0.05 emu). This anomaly can be used to locate the boundary between transitional crust and oceanic crust. The absence of large amplitude anomalies is a very strong indication that a margin is non-volcanic. Passive rifting, unlike active rifting, occurs principally by extensional tectonic forces as opposed to

neg: Mantle plume mantle source. There are two competing interpretations for this. In the context of mantle plumes, the near-surface material is postulated to have been transported down to the core-mantle boundary by subducting slabs, and to have been transported back up to the surface by plumes. In the context of the Plate hypothesis, subducted material is mostly re-circulated in the shallow mantle and tapped from there by volcanoes. The processing of oceanic crust, lithosphere, and sediment through a subduction zone decouples the water-soluble trace elements (e.g., K, Rb, Th) from the immobile trace elements (e.g., Ti, Nb, Ta), concentrating the immobile elements

neg: Lithosphere 50–140 km thick (but beneath the mid-ocean ridges is no thicker than the crust), while continental lithosphere has a range in thickness from about 40 km to perhaps 280 km; the upper ~30 to ~50 km of typical continental lithosphere is crust. The mantle part of the lithosphere consists largely of peridotite. The crust is distinguished from the upper mantle by the change in chemical composition that takes place at the Moho discontinuity. Oceanic lithosphere consists mainly of mafic crust and ultramafic mantle (peridotite) and is denser than continental lithosphere, for which the mantle is associated with crust made of

neg: Tectonic subsidence (which creates horsts and grabens) or by a system of listric faults. These fault systems allow the region to stretch, while also decreasing its thickness. A thinner crust subsides relative to thicker, undeformed crust. Lithospheric stretching/thinning during rifting results in regional necking of the lithosphere (the elevation of the upper surface decreases while the lower boundary rises). The underlying asthenosphere passively rises to replace the thinned mantle lithosphere. Subsequently, after the rifting/stretching period ends, this shallow asthenosphere gradually cools back into mantle lithosphere over a period of many tens of millions of years. Because mantle lithosphere is denser than asthenospheric

neg: Seismic tomography Larger scale features that can be imaged with tomography include the high velocities beneath continental shields and low velocities under ocean spreading centers. The mantle plume hypothesis proposes that areas of volcanism not readily explained by plate tectonics, called hotspots, are a result of thermal upwelling from as deep as the core-mantle boundary that become diapirs in the crust. This is an actively contested theory, although tomographic images suggest there are anomalies beneath some hotspots. The best imaged of these are large low-shear-velocity provinces, or superplumes, visible on S-wave models of the lower mantle and believed to reflect both thermal

neg: Mantle plume becoming a diapir in the Earth's crust. In particular, the concept that mantle plumes are fixed relative to one another, and anchored at the core-mantle boundary, would provide a natural explanation for the time-progressive chains of older volcanoes seen extending out from some such hot spots, such as the Hawaiian–Emperor seamount chain. Two largely independent convective processes are proposed: The plume hypothesis was studied using laboratory experiments conducted in small fluid-filled tanks in the early 1970s. Thermal or compositional fluid-dynamical plumes produced in that way were presented as models for the much larger postulated mantle plumes. On the basis of

neg: Geodynamics of Venus The breakdown of mantle layering and consequent mantle overturns would lead to dramatic episodes of volcanism, formation of large amounts of crust, and tectonic activity on the planet's surface, as has been inferred to have happened on Venus around 500 Ma from the surface morphology and cratering. Catastrophic resurfacing and widespread volcanism can be caused periodically by an increase in mantle temperature due to a change in surface boundary conditions from mobile to stagnant lid. Despite their categorical separation, all of the models display some sort of conceptual overlap that applies to the others. Solomatov and Moresi (1996) suggested that

neg: Geothermal energy earth, and "θερμος (thermos)", meaning hot. Earth's internal heat is thermal energy generated from radioactive decay and continual heat loss from Earth's formation. Temperatures at the core–mantle boundary may reach over 4000 °C (7,200 °F). The high temperature and pressure in Earth's interior cause some rock to melt and solid mantle to behave plastically, resulting in portions of the mantle convecting upward since it is lighter than the surrounding rock. Rock and water is heated in the crust, sometimes up to 370 °C (700 °F). With water from hot springs, geothermal energy has been used for bathing since Paleolithic times

neg: Gravity of Mars flow. Combination studies on geophysics and geochemistry suggested that average crustal thickness could be down to 50 + 12 km. Measurement of gravity field by different orbiters allows higher-resolution global Bouguer potential model to be produced. With local shallow density anomalies and effect of core flattening eliminated, the residual Bouguer potential is produced, as indicated by the following equation, formula_24 The residual Bouguer potential is contributed by the mantle. The undulation of the crust-mantle boundary, or the Moho surface, with mass of terrain corrected, should have resulted in varying residual anomaly. In turn, if undulating boundary is observed, there should

neg: Olympic-Wallowa Lineament and 17 million years), suggestions that the ur-OWL arises from deep in the crust, and evidence that the OWL is not (contrary to expectations) itself a boundary between oceanic and continental crust. The lack of results so far suggests that the broader context of the OWL should be considered. Following are some elements of that broader context, which may – or may not – relate in some way to the OWL. The broadest and fullest context of the OWL is the global system of plate tectonics, driven by convective flows in the Earth's mantle. The primary story on the western

neg: Delamination (geology) buoyancy of the lower continental crust and mantle lithosphere drive delamination. Delamination occurs when the lower continental crust and mantle lithosphere break away from the upper continental crust. There are two conditions that need to be met in order for delamination to proceed: The metamorphic transition from mafic granulite facies to the denser eclogite facies in the lower portion of the crust is the main mechanism responsible for creating negative buoyancy of the lower lithosphere. The lower crust undergoes a density inversion, causing it to break off of the upper crust and sink into the mantle. Density inversions are more

neg: Mesosphere (mantle) The base of the lower mantle is at about 2700 km. "Mesosphere" (not to be confused with mesosphere, a layer of the atmosphere) is derived from “mesospheric shell”, coined by Reginald Aldworth Daly, a Harvard University geology professor. In the pre-plate tectonics era, Daly (1940) inferred that the outer Earth consisted of three spherical layers: lithosphere (including the crust), asthenosphere, and mesospheric shell. Daly’s hypothetical depths to the lithosphere–asthenosphere boundary ranged from , and the top of the mesospheric shell (base of the asthenosphere) were from . Thus, Daly’s asthenosphere was inferred to be thick. According to Daly, the base

neg: Pelotas Basin Pelotas Basin is underlain by an extremely deformed (highly stretched, thinned and faulted) continental crust, covered by grabens that can achieve thicknesses of more than . The nature of the lower crust below the Pelotas Basin remains uncertain, but by analogy with the Namibian conjugate margin, it may correspond to a high-density igneous crust-mantle interface intruded by the Tristan da Cunha plume. The central onshore boundary of the basin is formed by the Neoproterozoic Pelotas Batholith. The stratigraphy of the Pelotas Basin and the Punta del Este Basin to the south had a different history due to the Polônio paleohigh

neg: Northern Cordilleran Volcanic Province Columbia, mantle xenoliths record the maximum temperature of , as well as the maximum temperature range from . The minimum xenolith temperatures indicate that the boundary between the Earth's crust and mantle is shallowest beneath the northern portion of the Northern Cordilleran Volcanic Province. Therefore, the temperature ranges for the northernmost xenolith series is about one-half the temperature range found in xenoliths at the southern portion of the volcanic province. Megacrysts, crystals or grains that are considerably larger than the encircling matrix, are commonly found in lava flows throughout the Northern Cordilleran Volcanic Province. They consist of three different groups,

neg: Crust (geology) only planet in our Solar System with plate tectonics. The crust is a thin shell on the outside of the 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 denser than

neg: Lower oceanic crust occur at depth, where temperatures are higher, the formed cumulates are then “dragged” up by mantle flow to form the lower oceanic crust. Today, a model intermediate between these two has become popular. This model is referred to as a “plum pudding”, where the lower oceanic crust is constructed from a number of nested plutons that crystallize within the mantle or crust. Schwartz et al. (2005) describes another variant. He postulates that the lower crust is constructed both from the nested shallow-level plutons and from the products of deeper-seated crystallization Lower oceanic crust The lower oceanic crust is the lower

neg: Deep crustal hot zone will have the chemical signatures of both crustal and mantle material. Because the melt consists of reworked mantle material and remolten crustal material, it will be more evolved than the mantle material that intruded. The material that will migrate upwards is expected to be mostly rhyolitic. Deep crustal hot zone The Deep Crustal Hot Zone (DCHZ) is a zone in the lower crust where hot mantle material intrudes. In a volcanic arc setting, hot, molten material from the mantle may intrude the lower crust. This hot material generates a new, more evolved melt in this area of the crust, which

neg: Earth's internal heat budget primordial heat, respectively. The structure of the Earth is a rigid outer crust that is composed of thicker continental crust and thinner oceanic crust, solid but plastically flowing mantle, a liquid outer core, and a solid inner core. The fluidity of a material is proportional to temperature; thus, the solid mantle can still flow on long time scales, as a function of its temperature and therefore as a function of the flow of Earth's internal heat. The mantle convects in response to heat escaping from Earth's interior, with hotter and more buoyant mantle rising and cooler, and therefore denser, mantle

neg: Lithosphere-Asthenosphere boundary 100 km deep. Lithosphere-Asthenosphere boundary The Lithosphere-Asthenosphere boundary (LAB) represents a mechanical difference between layers in Earth’s inner structure. Earth’s inner structure can be described both chemically (crust, mantle, core) and mechanically. The Lithosphere-Asthenosphere boundary (referred to as the LAB by geophysicists) lies between Earth's cooler, rigid lithosphere and the warmer, ductile asthenosphere. The actual depth of the boundary is still a topic of debate and study, although it is known to vary according to the environment. The LAB is determined from the differences in the lithosphere and asthenosphere including, but not limited to, differences in grain size, chemical composition,

neg: Lithosphere-Asthenosphere boundary Lithosphere-Asthenosphere boundary The Lithosphere-Asthenosphere boundary (LAB) represents a mechanical difference between layers in Earth’s inner structure. Earth’s inner structure can be described both chemically (crust, mantle, core) and mechanically. The Lithosphere-Asthenosphere boundary (referred to as the LAB by geophysicists) lies between Earth's cooler, rigid lithosphere and the warmer, ductile asthenosphere. The actual depth of the boundary is still a topic of debate and study, although it is known to vary according to the environment. The LAB is determined from the differences in the lithosphere and asthenosphere including, but not limited to, differences in grain size, chemical composition, thermal properties, and

neg: Subcontinental lithospheric mantle the depleted Archean subcontinental lithosphere. For more information, see Archean subduction. The mechanism of arc subduction is well understood to be the location where new continental crust is formed and is presumably also the site of subcontinental mantle genesis. Firstly, hydrated oceanic crust slabs begin subducting which releases fluids (subduction zone metamorphism) to the mantle wedge above. Continued subduction of the slab leads to further hydration of the mantle which causes partial melting in the mantle wedge. It is expected then that the modern subcontinental mantle is a former, melt-depleted mantle wedge. If the connection between continental crust and the

neg: Lau Basin mantle source for CLSC/ELSC. The source of mantle melt to the Lau Basin is centered west of the spreading centers at shallow depth. This source may have directly supplied the western part of Lau Basin. The MORB-type basalt filled the grabens that were originally formed by extension in western Lau Basin. Asymmetric melt supply gave rise to the asymmetric thickness of crust at different sections of the basin. This melt supply may still be continuing today as indicated by a low-velocity anomaly in the upper mantle beneath the western Lau Basin. At the subduction boundary between Pacific plate and Tonga-Kermadec

neg: Primitive mantle Primitive mantle The primitive mantle is, in geochemistry, a hypothetical reservoir with the composition of the Earth's crust and mantle taken together. The currently accepted scientific hypothesis is that the Earth was formed by accretion of material with a chondritic composition. Still during the accretionary phase planetary differentiation started, giving rise to the Earth's core, where heavy metallic siderophile elements accumulated. Around it was a (in this stage) undifferentiated mantle, the primitive mantle. 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

neg: Afar Triple Junction both the lithosphere and crust (note that the crust is a part of the lithosphere). This is a product of what is referred to as mantle upwelling where hotter asthenosphere rises up into colder lithosphere. This rise is associated with thinning and stretching of the lithosphere. Rifting is said to have begun in the Late Cretaceous epoch to Paleogene period. At that time the African plate was experiencing far-field stresses caused by portions of the northern boundary of the African plate subducting under the Eurasian plate. Today, the Arabian plate is experiencing a crustal down pull, or slab pull, that

neg: African Plate rifts such as the Anza Trough where the crust was pulled apart, and the resulting depression filled with more modern sediment. The African Plate is rifting in the eastern interior of the African continent along the East African Rift. This rift zone separates the African Plate to the west from the Somali Plate to the east. One hypothesis proposes the existence of a mantle plume beneath the Afar region, whereas an opposing hypothesis asserts that the rifting is merely a zone of maximum weakness where the African Plate is deforming as plates to its east are moving rapidly northward. The

neg: Moon atop. The final liquids to crystallise would have been initially sandwiched between the crust and mantle, with a high abundance of incompatible and heat-producing elements. Consistent with this perspective, geochemical mapping made from orbit suggests the crust of mostly anorthosite. The Moon rock samples of the flood lavas that erupted onto the surface from partial melting in the mantle confirm the mafic mantle composition, which is more iron-rich than that of Earth. The crust is on average about thick. The Moon is the second-densest satellite in the Solar System, after Io. However, the inner core of the Moon is small,

neg: Plate tectonics Earth and Venus, and there is evidence for ice on its surface and in its crust. In the 1990s, it was proposed that Martian Crustal Dichotomy was created by plate tectonic processes. Scientists today disagree, and think that it was created either by upwelling within the Martian mantle that thickened the crust of the Southern Highlands and formed Tharsis or by a giant impact that excavated the Northern Lowlands. Valles Marineris may be a tectonic boundary. Observations made of the magnetic field of Mars by the "Mars Global Surveyor" spacecraft in 1999 showed patterns of magnetic striping discovered on this

neg: Rhenium–osmium dating 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. This is thought to evidence of subducted ancient high Re/Os basaltic crust that is being recycled back into the mantle. This combination of radiogenic (Os that was created by decay of Re) and nonradiogenic melts helps to support the theory of

neg: Plate tectonics convection; that is, the slow creeping motion of Earth's solid mantle. Plate movement is thought to be driven by a combination of the motion of the seafloor away from spreading ridges due to variations in topography (the ridge is a topographic high) and density changes in the crust (density increases as newly formed crust cools and moves away from the ridge). At subduction zones the relatively cold, dense crust is "pulled" or sinks down into the mantle over the downward convecting limb of a mantle cell. Another explanation lies in the different forces generated by tidal forces of the Sun

neg: Low-velocity zone the core-mantle boundary. These LVZs may have important implications for plate tectonics and the origin of the Earth's crust. The LVZ has been interpreted to indicate the presence of a significant degree of partial melting, and alternatively as a natural consequence of a thermal boundary layer and the effects of pressure and temperature on the elastic wave velocity of mantle components in the solid state. In any event, a very limited amount of melt (about 1%) is needed to produce these effects. Water in this layer can lower the melting point, and may play an important part in its composition.

neg: Divergent double subduction "divergent" is used to describe one oceanic plate subducting in different directions on two opposite sides. It should not be confused with use of the same term in 'divergent plate boundary' which refers to a spreading center that separates two plates moving away from each other. The complete evolution of a divergent double subduction system can be divided into four major stages. As the central oceanic plate subducts on both sides into the two overriding plates, the subducting oceanic slab brings fluids down and the fluids are released in the mantle wedge. This initiates the partial melting of the mantle

neg: Geology of the Pacific Northwest locked in the minerals of solid rock to escape. The water vapor rises into the pliable mantle above the subducting plate, causing some of the mantle to melt. This newly formed magma rises toward the Earth's surface to erupt, forming a chain of volcanoes (the Cascade Volcanic Arc) above the subduction zone. A close-up look at the Cascades reveals a more complicated picture than a simple subduction zone. Not far off the coast of the North Pacific lies a spreading ridge; a divergent plate boundary made up of a series of breaks in the oceanic crust where new ocean crust

neg: Subduction 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. The subduction of cold oceanic crust into the mantle depresses the local geothermal gradient and causes a larger portion of Earth to deform in a more brittle fashion than

neg: Convergent boundary pulled into mantle and help drive mantle convection. In collisions between two oceanic plates, the cooler, more dense oceanic lithosphere sinks beneath warmer, less dense oceanic lithosphere. As the slab sinks deeper into the mantle, it releases water from dehydration of hydrous minerals in the oceanic crust. This water reduces the melting temperature of rocks in the asthenosphere and causes partial melting. Partial melt will travel up through the asthenosphere, eventually reach the surface, and form volcanic island arcs. When oceanic lithosphere and continental lithosphere collide, the dense oceanic lithosphere slides beneath the less dense continental lithosphere. An accretionary wedge

neg: Crust (geology) centers, where partial-melting of the underlying mantle yields basaltic magmas and new ocean crust forms. This "ridge push" is one of the driving forces of plate tectonics, and it is constantly creating new ocean crust. That means that old crust must be destroyed somewhere, so, opposite a spreading center, there is usually a subduction zone: a trench where an ocean plate is being shoved back into the mantle. This constant process of creating new ocean crust and destroying old ocean crust means that the oldest ocean crust on Earth today is only about 200 million years old. In contrast, the

neg: Rarotonga hotspot boundary and spread out when they rise, forming a large "head" that causes intense volcanic activity once it hits the crust. This volcanism is responsible for the formation of the oceanic plateaus. Later, the remnant "tail" of the plume is still rising and induces the formation of volcano chains as the crust moves over the plume tail, thus forming the linear chains. A number of hotspots are or were active in the Pacific Ocean and some of these may be the product of mantle plumes. Other hotspots such as Rarotonga appear to have been active only for short time periods;

neg: Deep crustal hot zone Deep crustal hot zone The Deep Crustal Hot Zone (DCHZ) is a zone in the lower crust where hot mantle material intrudes. In a volcanic arc setting, hot, molten material from the mantle may intrude the lower crust. This hot material generates a new, more evolved melt in this area of the crust, which may collect and migrate upwards towards the upper crust. Here, it would collect in a magma chamber and later erupt. The upper crust consists mainly of evolved, intermediate to silicic magmatic rocks. These rocks may form from either differentiation of primary, mantle-derived magma, or from partial

neg: Plate tectonics 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). The relative movement of the plates typically ranges from zero to 100 mm annually. Tectonic plates are composed of oceanic lithosphere and thicker continental lithosphere, each topped by its own kind of crust. Along convergent boundaries,

neg: Earth's internal heat budget Earth's internal heat loss at the surface is by conduction through the crust, and mantle convection is the dominant control on heat transport from deep within the Earth. Most of the heat flow from the thicker continental crust is attributed to internal radiogenic sources, in contrast the thinner oceanic crust has only 2% internal radiogenic heat. The remaining heat flow at the surface would be due to basal heating of the crust from mantle convection. Heat fluxes are negatively correlated with rock age, with the highest heat fluxes from the youngest rock at mid-ocean ridge spreading centers (zones of mantle

neg: Climate across Cretaceous–Paleogene boundary This concludes that global firestorms may have resulted from the initial incendiary blast. If global, widespread fires occurred, carbon dioxide content would have increased in the atmosphere, causing a temporary greenhouse effect once the dust cloud settled. The Deccan Trap eruptions were associated with a deep mantle plume. The theory suggests that about 66 million years ago, the mantle plume at the Réunion hotspot burned through the Earth's crust and flooded western India with basaltic lava. The basaltic lava covered over 1,609,344 square kilometers of India under successive lava flow. Volcanic gases, mostly sulfur dioxide, were released during the massive

neg: Andesite the subducted oceanic crust is submitted to increasing pressure and temperature, leading to metamorphism. Hydrous minerals such as amphibole, zeolites, chlorite etc. (which are present in the oceanic lithosphere) dehydrate as they change to more stable, anhydrous forms, releasing water and soluble elements into the overlying wedge of mantle. Fluxing water into the wedge lowers the solidus of the mantle material and causes partial melting. Due to the lower density of the partially molten material, it rises through the wedge until it reaches the lower boundary of the overriding plate. Melts generated in the mantle wedge are of basaltic composition,

neg: Receiver function Receiver function A receiver function technique is a way to model the boundary layers and structure of the Earth by using the information from teleseismic earthquakes recorded at a three component seismograph. A teleseismic P-wave will generate P to S conversions at boundaries, such as the Moho (crust-mantle boundary), beneath the seismograph. The difference in travel time between the generated S-wave and P-wave contains information about the distance to the boundary and if further reverberations are included more detailed structure can be resolved. This is done by deconvolution of the incoming vertical and longitudinal components of the seismogram which removes

neg: Geochemistry of carbon subduction from the crust. This includes the major carbon containing sediments such as limestone, or coal. Each year 2×10 kg of CO is transferred from the crust to the mantle by subduction. (1700 tons of carbon per second). Upwelling mantle material can add to the crust at mid oceanic ridges. Fluids can extract carbon from the mantle and erupt in volcanoes. At 330 km deep a liquid consisting of carbon dioxide and water can form. It is highly corrosive, and dissolves incompatible elements from the solid mantle. These elements include uranium, thorium, potassium, helium and argon. The fluids can then

neg: Tectonics of Mars have caused substantial melting and crustal production above a single rising mantle plume in the southern hemisphere, resulting in a thickened crust. It has also been suggested that the formation of a highly viscous melt layer beneath the thickened crust in the southern hemisphere could lead to lithospheric rotation. This may have resulted in the migration of volcanically active areas toward the dichotomy boundary, and the subsequent placement and formation of the Tharsis plateau. The single plume hypothesis is also used to explain the presence of magnetic anomalies in the southern hemisphere, and the lack thereof in the northern hemisphere.

neg: Intraplate deformation Intraplate deformation Intraplate deformation is the folding, breaking, or flow of the Earth's crust within plates instead of at their margins. 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. The theory of plate tectonics states that the Earth's crust is made up of rigid plates that "float" on top of the mantle and move relative to one another. As the plates move, the crust deforms dominantly along the plate margins. Intraplate deformation differs from that respect by the observation

neg: Continental arc magmas and felsic or silica crust meltings. The mixing of existing continental crust, lower part of lithosphere or lithospheric mantle under the continental crust, the subducting oceanic crust and sediments, the mantle wedge and the underplates materials together is the main source of continental arc rocks. The dehydration of the downgoing slab and the partial melting of asthenosphere together generate the primary magma of continental arcs. Primary magma is composed of olivine tholeiitic basalt because of mixture of peridotites from the mantle wedge and large ion lithophile enriched (LIL-enriched) fluids from the dehydrating subducting plate. Because the larger thickness and

neg: Abyssal plain typically in the abyssal zone, at depths from 3000 to 6000 metres. The table below illustrates the classification of oceanic zones: 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

neg: Ridge push plates apart. Ridge push is the result of gravitational forces acting on the young, raised oceanic lithosphere around mid-ocean ridges, causing it to slide down the similarly raised but weaker asthenosphere and push on lithospheric material farther from the ridges. Mid-ocean ridges are long underwater mountain chains that occur at divergent plate boundaries in the ocean, where new oceanic crust is formed by upwelling mantle material as a result of tectonic plate spreading and relatively shallow (above ~60 km) decompression melting. The upwelling mantle and fresh crust are hotter and less dense than the surrounding crust and mantle, but cool

neg: North American Plate creating the Gulf of California. However, it is as yet unclear whether the oceanic crust east of the Rise and west of the mainland coast of Mexico is actually a new plate beginning to converge with the North American Plate, consistent with the standard model of rift zone spreading centers generally. 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

neg: Tonga Trench Pacific Plate due to its bending. The Pacific crust that descends into the trench is old, 100–140 Ma, and relatively cold and it can therefore store a lot of elastic energy. As it reaches deep into the mantle, more than , and encounters barriers, it is being contorted, which produces deep mantle earthquakes. Oceanic trenches are important sites for the formation of what will become continental crust and for recycling of material back into the mantle. Along the Tonga Trench mantle-derived melts are transferred to the island arc systems, and abyssal oceanic sediments and fragments of oceanic crust are collected.

neg: Lower oceanic crust Lower oceanic crust The lower oceanic crust is the lower part of the oceanic crust and represents the major part of it (volumetrically biggest part). It is generally located 4–8 km below the ocean floor and the major lithologies are mafic (ultramafic and gabbroic rocks) which derive from melts rising from the earth's mantle. This part of the oceanic crust is an important zone for processes such as melt accumulation and melt modification (fractional crystallisation and crustal assimilation). And the recycling of this part of the oceanic crust, together with the upper mantle has been suggested as a significant source

neg: Archean subduction Earth being 200 K hotter in the Archean than it is today. Assuming seafloor spreading generated oceanic lithosphere in the Archean, higher temperatures led to greater melting of mantle material rising at oceanic spreading centres. This in turn produced thicker oceanic crust and thicker regions of underlying depleted lithospheric mantle. As such, the density of the lithosphere was reduced due to both differentiation of the crust from the mantle and the ensuing relative depletion of the residual mantle in Fe and Al. These expected properties have led to suggestions that oceanic lithosphere was so light that it subducted very shallowly

neg: Haddington Island (British Columbia) Plate to its west subducted under the North American Plate at the Cascadia subduction zone. As the ocean crust of the Juan de Fuca and the Explorer Plate melts, it creates magma that penetrates the crust, causing periodic eruptions of the volcanoes. The western end of the Alert Bay Volcanic Belt is now approximately northeast of the Nootka Fault, which separates the Explorer and Juan de Fuca plates. However, at the time of its formation Haddington Island may have been coincident with the subducted plate boundary. Also, the timing of volcanism corresponds to shifts of plate motion and changes in

neg: Composition of Mars ways. First, Martian meteorite analysis suggests that the planet's mantle is about twice as rich in iron as the Earth's mantle. Second, its core is richer in sulphur. Third, the Martian mantle is richer in potassium and phosphorus than Earth's and fourth, the Martian crust contains a higher percentage of volatile elements such as sulphur and chlorine than the Earth's crust does. Many of these conclusions are supported by "in situ" analyses of rocks and soils on the Martian surface. Mars is fundamentally an igneous planet. Rocks on the surface and in the crust consist predominantly of minerals that crystallize

neg: Geophysics S-waves in the outer core. This indicates that the outer core is liquid, because liquids cannot support shear. The outer core is liquid, and the motion of this highly conductive fluid generates the Earth's field. The inner core, however, is solid because of the enormous pressure. 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

neg: Internal structure of the Moon a mafic mantle and a plagioclase-rich crust. Geochemical mapping from orbit implies that the crust of the Moon is largely anorthositic in composition, consistent with the magma ocean hypothesis. In terms of elements, the lunar crust is composed primarily of oxygen, silicon, magnesium, iron, calcium, and aluminium, but important minor and trace elements such as titanium, uranium, thorium, potassium, and hydrogen are present as well. Based on geophysical techniques, the crust is estimated to be on average about 50 km thick. Partial melting within the mantle of the Moon gave rise to the eruption of mare basalts on the lunar

neg: Iceland glaciers cover 14.3% of its surface; only 23% is vegetated. The largest lakes are Þórisvatn reservoir: and Þingvallavatn: ; other important lakes include Lagarfljót and Mývatn. Jökulsárlón is the deepest lake, at . Geologically, Iceland is part of the Mid-Atlantic Ridge, a ridge along which the oceanic crust spreads and forms new oceanic crust. This part of the mid-ocean ridge is located above a mantle plume, causing Iceland to be subaerial (above the surface of the sea). The ridge marks the boundary between the Eurasian and North American Plates, and Iceland was created by rifting and accretion through volcanism along

neg: Crust (geology) Crust (geology) In geology, the crust is the outermost solid shell of a rocky planet, dwarf planet, or natural satellite. It is usually distinguished from the underlying mantle by its chemical makeup; however, in the case of icy satellites, it may be distinguished based on its phase (solid crust vs. liquid mantle). The crusts of Earth, Moon, Mercury, Venus, Mars, Io, and other planetary bodies formed via igneous processes, and were later modified by erosion, impact cratering, volcanism, and sedimentation. Most terrestrial planets have fairly uniform crusts. Earth, however, has two distinct types: continental crust and oceanic crust. These two

neg: Oceanic crust 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. As the mantle rises it cools and melts, as the pressure decreases and it crosses the solidus. The amount of melt produced depends only on the temperature of the mantle as it rises. Hence most oceanic crust is the same thickness

neg: Abyssal plain mantle is partially melted into magma as it moves upwards under mid-ocean ridges. This upwelling magma then cools and solidifies by conduction and convection of heat to form new oceanic crust. Accretion occurs as mantle is added to the growing edges of a tectonic plate, usually associated with seafloor spreading. The age of oceanic crust is therefore a function of distance from the mid-ocean ridge. The youngest oceanic crust is at the mid-ocean ridges, and it becomes progressively older, cooler and denser as it migrates outwards from the mid-ocean ridges as part of the process called mantle convection. The lithosphere,

neg: Geology of the United States 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

neg: Oceanic crust Oceanic crust Oceanic crust is the uppermost layer of the oceanic portion of a tectonic plate. It is composed of the upper oceanic crust, with pillow lavas and a dike complex, and the lower oceanic crust, composed of troctolite, gabbro and ultramafic cumulates. The crust overlies the solidified and uppermost layer of the mantle. The crust and the solid mantle layer together constitute oceanic lithosphere. Oceanic crust is primarily composed of mafic rocks, or sima, which is rich in iron and magnesium. It is thinner than continental crust, or sial, generally less than 10 kilometers thick; however it is denser,

neg: Receiver function the common part of the components - namely, the source and travel path information. The resulting waveform is the receiver function. Similarly, a teleseismic S-wave will generate an S to P conversion beneath the seismic station. Receiver function A receiver function technique is a way to model the boundary layers and structure of the Earth by using the information from teleseismic earthquakes recorded at a three component seismograph. A teleseismic P-wave will generate P to S conversions at boundaries, such as the Moho (crust-mantle boundary), beneath the seismograph. The difference in travel time between the generated S-wave and P-wave contains

neg: Earth's crustal evolution the lithosphere enough to rupture it, such plumes would have been present in the hot Archean mantle. Pre-tectonic subduction can also be inferred from the internal volcanism on Venus. Artemis Corona is a large plume formed by the upwelling of mantle derived magma and is on a scale potentially comparable to that in the Archean mantle. Models using its known characteristics showed that continued magmatism from conductive heat through the plume caused gravitational collapse. The weight of collapse caused the spreading of the surrounding crust outwards and subsequent subduction around the margins. The anhydrous nature of the crust on Venus

neg: Cima volcanic field been estimated for the lava erupted by the Black Tank cone. The magma erupted in the field ultimately appears to originate from the lithospheric or asthenospheric mantle with little contribution of crustal components, unlike earlier felsic volcanism. Upwelling of asthenosphere material appears to be responsible for the volcanism at the end, possibly associated with the change in the tectonics of the region from subduction-dominated to tectonics of a transform boundary. Fractional crystallization, magma ponding in the crust, differences in the mantle sources and partial melting processes have been invoked to explain certain compositional differences in the erupted rocks. The climate

neg: Venus volcanism. Whereas Earth's crust is in continuous motion, Venus is thought to be unable to sustain such a process. Without plate tectonics to dissipate heat from its mantle, Venus instead undergoes a cyclical process in which mantle temperatures rise until they reach a critical level that weakens the crust. Then, over a period of about 100 million years, subduction occurs on an enormous scale, completely recycling the crust. Venusian craters range from in diameter. No craters are smaller than 3 km, because of the effects of the dense atmosphere on incoming objects. Objects with less than a certain kinetic energy

neg: Silverthrone Caldera subduction related. The Cascadia subduction zone is a long convergent plate boundary that separates the Juan de Fuca, Explorer, Gorda and North American Plates. Here, the oceanic crust of the Pacific Ocean sinks beneath North America at a rate of per year. Hot magma upwelling above the descending oceanic plate creates volcanoes, each of which erupts for a few million years. It is estimated that the subduction zone has existed for at least 37 million years; in that time it has created a line of volcanoes, called the Cascade Volcanic Arc, that stretches over along the subduction zone from Northern

neg: Provenance (geology) Variation of Nd/Nd is caused by decay of Sm. Now Sm/Nd rato of the mantle is higher than that of the crust and Nd/Nd ratio is also higher than in the mantle than in the crust. Nd/Nd ratio is expressed in εNd notation (DePaolo and Wasserbur 1976). formula_1. CHUR refer to Chondritic Uniform Reservoir. So ϵNd is a function of T (time). Nd isotope evolution in mantle and crust in shown in the figure to the right. The upper plot (a), bold line shows the evolution of the bulk earth or CHUR(chondritic uniform reservoir). The lower plot (b) shows evolution

neg: Oceanic crust crust with laboratory determinations of seismic velocities in known rock types, and samples recovered from the ocean floor by submersibles, dredging (especially from ridge crests and fracture zones) and drilling. Oceanic crust is significantly simpler than continental crust and generally can be divided in three layers. According to mineral physics experiments, at lower mantle pressures, oceanic crust becomes denser than the surrounding mantle. The most voluminous volcanic rocks of the ocean floor are the mid-oceanic ridge basalts, which are derived from low-potassium tholeiitic magmas. These rocks have low concentrations of large ion lithophile elements (LILE), light rare earth elements (LREE),

neg: Delamination (geology) likely to occur where there are high mantle temperatures. This limits this phenomenon to arc environments, volcanic rifted margins and continental areas undergoing extension. The asthenosphere rises until it comes into contact with the base of the lower crust, causing the lower crust and lithospheric mantle to start to peel away. Slumping, cracking, or plume erosion facilitates the intrusion of underlying asthenosphere. Potential energy that drives the delamination is released as the low density, hot asthenosphere rises and replaces the higher density, cold lithosphere. Separation of lowermost crust and lithospheric mantle is controlled by the effective viscosity of the upper

neg: Crust (geology) formed almost immediately after formation of the Moon. Magmatism continued after the period of intense meteorite impacts ended about 3.9 billion years ago, but igneous rocks younger than 3.9 billion years make up only a minor part of the crust. Crust (geology) In geology, the crust is the outermost solid shell of a rocky planet, dwarf planet, or natural satellite. It is usually distinguished from the underlying mantle by its chemical makeup; however, in the case of icy satellites, it may be distinguished based on its phase (solid crust vs. liquid mantle). The crusts of Earth, Moon, Mercury, Venus, Mars,

neg: Mantle plume deep (1000 km) mantle is at the core-mantle boundary. Mantle plumes were originally postulated to rise from this layer because the "hot spots" that are assumed to be their surface expression were thought to be fixed relative to one another. This required that plumes were sourced from beneath the shallow asthenosphere that is thought to be flowing rapidly in response to motion of the overlying tectonic plates. There is no other known major thermal boundary layer in the deep Earth, and so the core-mantle boundary was the only candidate. The base of the mantle is known as the D″ layer,

neg: Columbia Plateau its present course by the northwesterly advancing lava. The lava, as it flowed over the area, first filled the stream valleys, forming dams that in turn caused impoundments or lakes. 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

neg: Agulhas Plateau in 1964 (i.e. part of what would become the Heezen-Tharp map of the world's ocean floor finally published in 1977), but its crustal composition, paleoposition, and geological origin remained enigmatic for decades. The boundary between the Earth's crust and the mantle (the Moho) rises from between the Agulhas Bank (south of South Africa) and the Agulhas passage (south of the bank), typical for a continent-ocean transition. The Agulhas Passage consists of 120-160 Ma-old oceanic crust, whereas the 100-80 Ma-old Agulhas Plateau rises above the surrounding ocean floor while the Moho dips to between below it. The morphology of the basement