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Akihiro Yamada - One of the best experts on this subject based on the ideXlab platform.
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sound velocity of casio 3 perovskite suggests the presence of basaltic crust in the earth s lower Mantle
Nature, 2019Co-Authors: Tetsuo Irifune, Steeve Greaux, Yuji Higo, Yoshinori Tange, Takeshi Arimoto, Akihiro YamadaAbstract:Laboratory measurements of sound velocities of high-pressure minerals provide crucial information on the composition and constitution of the deep Mantle via comparisons with observed seismic velocities. Calcium silicate (CaSiO3) perovskite (CaPv) is a high-pressure phase that occurs at depths greater than about 560 kilometres in the Mantle1 and in the subducting oceanic crust2. However, measurements of the sound velocity of CaPv under the pressure and temperature conditions that are present at such depths have not previously been performed, because this phase is unquenchable (that is, it cannot be physically recovered to room conditions) at atmospheric pressure and adequate samples for such measurements are unavailable. Here we report in situ X-ray diffraction and ultrasonic-interferometry sound-velocity measurements at pressures of up to 23 gigapascals and temperatures of up to 1,700 kelvin (similar to the conditions at the bottom of the Mantle transition region) using sintered polycrystalline samples of cubic CaPv converted from bulk glass and a multianvil apparatus. We find that cubic CaPv has a shear modulus of 126 ± 1 gigapascals (uncertainty of one standard deviation), which is about 26 per cent lower than theoretical predictions3,4 (about 171 gigapascals). This value leads to substantially lower sound velocities of basaltic compositions than those predicted for the pressure and temperature conditions at depths between 660 and 770 kilometres. This suggests accumulation of basaltic crust in the uppermost lower Mantle, which is consistent with the observation of low-seismic-velocity signatures below 660 kilometres5,6 and the discovery of CaPv in natural diamond of super-deep origin7. These results could contribute to our understanding of the existence and behaviour of subducted crust materials in the deep Mantle. In situ high-pressure and high-temperature measurements of the sound velocity of CaSiO3 perovskite suggest accumulation of basaltic crust in the Earth’s uppermost lower Mantle.
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sound velocity of casio 3 perovskite suggests the presence of basaltic crust in the earth s lower Mantle
Nature, 2019Co-Authors: Tetsuo Irifune, Steeve Greaux, Yuji Higo, Yoshinori Tange, Takeshi Arimoto, Akihiro Yamada, Zhaodong LiuAbstract:Laboratory measurements of sound velocities of high-pressure minerals provide crucial information on the composition and constitution of the deep Mantle via comparisons with observed seismic velocities. Calcium silicate (CaSiO3) perovskite (CaPv) is a high-pressure phase that occurs at depths greater than about 560 kilometres in the Mantle1 and in the subducting oceanic crust2. However, measurements of the sound velocity of CaPv under the pressure and temperature conditions that are present at such depths have not previously been performed, because this phase is unquenchable (that is, it cannot be physically recovered to room conditions) at atmospheric pressure and adequate samples for such measurements are unavailable. Here we report in situ X-ray diffraction and ultrasonic-interferometry sound-velocity measurements at pressures of up to 23 gigapascals and temperatures of up to 1,700 kelvin (similar to the conditions at the bottom of the Mantle transition region) using sintered polycrystalline samples of cubic CaPv converted from bulk glass and a multianvil apparatus. We find that cubic CaPv has a shear modulus of 126 ± 1 gigapascals (uncertainty of one standard deviation), which is about 26 per cent lower than theoretical predictions3,4 (about 171 gigapascals). This value leads to substantially lower sound velocities of basaltic compositions than those predicted for the pressure and temperature conditions at depths between 660 and 770 kilometres. This suggests accumulation of basaltic crust in the uppermost lower Mantle, which is consistent with the observation of low-seismic-velocity signatures below 660 kilometres5,6 and the discovery of CaPv in natural diamond of super-deep origin7. These results could contribute to our understanding of the existence and behaviour of subducted crust materials in the deep Mantle.
Tetsuo Irifune - One of the best experts on this subject based on the ideXlab platform.
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sound velocity of casio 3 perovskite suggests the presence of basaltic crust in the earth s lower Mantle
Nature, 2019Co-Authors: Tetsuo Irifune, Steeve Greaux, Yuji Higo, Yoshinori Tange, Takeshi Arimoto, Akihiro Yamada, Zhaodong LiuAbstract:Laboratory measurements of sound velocities of high-pressure minerals provide crucial information on the composition and constitution of the deep Mantle via comparisons with observed seismic velocities. Calcium silicate (CaSiO3) perovskite (CaPv) is a high-pressure phase that occurs at depths greater than about 560 kilometres in the Mantle1 and in the subducting oceanic crust2. However, measurements of the sound velocity of CaPv under the pressure and temperature conditions that are present at such depths have not previously been performed, because this phase is unquenchable (that is, it cannot be physically recovered to room conditions) at atmospheric pressure and adequate samples for such measurements are unavailable. Here we report in situ X-ray diffraction and ultrasonic-interferometry sound-velocity measurements at pressures of up to 23 gigapascals and temperatures of up to 1,700 kelvin (similar to the conditions at the bottom of the Mantle transition region) using sintered polycrystalline samples of cubic CaPv converted from bulk glass and a multianvil apparatus. We find that cubic CaPv has a shear modulus of 126 ± 1 gigapascals (uncertainty of one standard deviation), which is about 26 per cent lower than theoretical predictions3,4 (about 171 gigapascals). This value leads to substantially lower sound velocities of basaltic compositions than those predicted for the pressure and temperature conditions at depths between 660 and 770 kilometres. This suggests accumulation of basaltic crust in the uppermost lower Mantle, which is consistent with the observation of low-seismic-velocity signatures below 660 kilometres5,6 and the discovery of CaPv in natural diamond of super-deep origin7. These results could contribute to our understanding of the existence and behaviour of subducted crust materials in the deep Mantle.
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sound velocity of casio 3 perovskite suggests the presence of basaltic crust in the earth s lower Mantle
Nature, 2019Co-Authors: Tetsuo Irifune, Steeve Greaux, Yuji Higo, Yoshinori Tange, Takeshi Arimoto, Akihiro YamadaAbstract:Laboratory measurements of sound velocities of high-pressure minerals provide crucial information on the composition and constitution of the deep Mantle via comparisons with observed seismic velocities. Calcium silicate (CaSiO3) perovskite (CaPv) is a high-pressure phase that occurs at depths greater than about 560 kilometres in the Mantle1 and in the subducting oceanic crust2. However, measurements of the sound velocity of CaPv under the pressure and temperature conditions that are present at such depths have not previously been performed, because this phase is unquenchable (that is, it cannot be physically recovered to room conditions) at atmospheric pressure and adequate samples for such measurements are unavailable. Here we report in situ X-ray diffraction and ultrasonic-interferometry sound-velocity measurements at pressures of up to 23 gigapascals and temperatures of up to 1,700 kelvin (similar to the conditions at the bottom of the Mantle transition region) using sintered polycrystalline samples of cubic CaPv converted from bulk glass and a multianvil apparatus. We find that cubic CaPv has a shear modulus of 126 ± 1 gigapascals (uncertainty of one standard deviation), which is about 26 per cent lower than theoretical predictions3,4 (about 171 gigapascals). This value leads to substantially lower sound velocities of basaltic compositions than those predicted for the pressure and temperature conditions at depths between 660 and 770 kilometres. This suggests accumulation of basaltic crust in the uppermost lower Mantle, which is consistent with the observation of low-seismic-velocity signatures below 660 kilometres5,6 and the discovery of CaPv in natural diamond of super-deep origin7. These results could contribute to our understanding of the existence and behaviour of subducted crust materials in the deep Mantle. In situ high-pressure and high-temperature measurements of the sound velocity of CaSiO3 perovskite suggest accumulation of basaltic crust in the Earth’s uppermost lower Mantle.
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absence of an aluminous phase in the upper part of the earth s lower Mantle
Nature, 1994Co-Authors: Tetsuo IrifuneAbstract:RECENT high-pressure experiments1–3 suggest that the Earth's lower Mantle is composed of MgSiO3 and CaSiO3 perovskites, (Mg, Fe)O magnesiowiistite, and a minor but significant amount of aluminous phases, such as majorite garnet or an unidentified Al-rich phase. The stability of majorite garnet and the nature of any such aluminous phase, however, are controversial issues rele-vant to the mineralogy of the lower Mantle4–7. Here I report an experimental study of the phase transformations that occur in a pyrolite Mantle composition with increasing pressure from 23 to 28 GPa (equivalent to ∼650–770 km depth in the Mantle). The results demonstrate that majorite garnet completely transforms to perovskite structures at pressures above 26 GPa (>720 km depth). A12O3 is accommodated mainly in MgSiO3 perovskite, and no separate aluminous phase was observed at higher pressures, leading to the conclusion that the upper part of the Earth's lower Mantle is composed only of two perovskites and magnesiowustite.
Steeve Greaux - One of the best experts on this subject based on the ideXlab platform.
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sound velocity of casio 3 perovskite suggests the presence of basaltic crust in the earth s lower Mantle
Nature, 2019Co-Authors: Tetsuo Irifune, Steeve Greaux, Yuji Higo, Yoshinori Tange, Takeshi Arimoto, Akihiro YamadaAbstract:Laboratory measurements of sound velocities of high-pressure minerals provide crucial information on the composition and constitution of the deep Mantle via comparisons with observed seismic velocities. Calcium silicate (CaSiO3) perovskite (CaPv) is a high-pressure phase that occurs at depths greater than about 560 kilometres in the Mantle1 and in the subducting oceanic crust2. However, measurements of the sound velocity of CaPv under the pressure and temperature conditions that are present at such depths have not previously been performed, because this phase is unquenchable (that is, it cannot be physically recovered to room conditions) at atmospheric pressure and adequate samples for such measurements are unavailable. Here we report in situ X-ray diffraction and ultrasonic-interferometry sound-velocity measurements at pressures of up to 23 gigapascals and temperatures of up to 1,700 kelvin (similar to the conditions at the bottom of the Mantle transition region) using sintered polycrystalline samples of cubic CaPv converted from bulk glass and a multianvil apparatus. We find that cubic CaPv has a shear modulus of 126 ± 1 gigapascals (uncertainty of one standard deviation), which is about 26 per cent lower than theoretical predictions3,4 (about 171 gigapascals). This value leads to substantially lower sound velocities of basaltic compositions than those predicted for the pressure and temperature conditions at depths between 660 and 770 kilometres. This suggests accumulation of basaltic crust in the uppermost lower Mantle, which is consistent with the observation of low-seismic-velocity signatures below 660 kilometres5,6 and the discovery of CaPv in natural diamond of super-deep origin7. These results could contribute to our understanding of the existence and behaviour of subducted crust materials in the deep Mantle. In situ high-pressure and high-temperature measurements of the sound velocity of CaSiO3 perovskite suggest accumulation of basaltic crust in the Earth’s uppermost lower Mantle.
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sound velocity of casio 3 perovskite suggests the presence of basaltic crust in the earth s lower Mantle
Nature, 2019Co-Authors: Tetsuo Irifune, Steeve Greaux, Yuji Higo, Yoshinori Tange, Takeshi Arimoto, Akihiro Yamada, Zhaodong LiuAbstract:Laboratory measurements of sound velocities of high-pressure minerals provide crucial information on the composition and constitution of the deep Mantle via comparisons with observed seismic velocities. Calcium silicate (CaSiO3) perovskite (CaPv) is a high-pressure phase that occurs at depths greater than about 560 kilometres in the Mantle1 and in the subducting oceanic crust2. However, measurements of the sound velocity of CaPv under the pressure and temperature conditions that are present at such depths have not previously been performed, because this phase is unquenchable (that is, it cannot be physically recovered to room conditions) at atmospheric pressure and adequate samples for such measurements are unavailable. Here we report in situ X-ray diffraction and ultrasonic-interferometry sound-velocity measurements at pressures of up to 23 gigapascals and temperatures of up to 1,700 kelvin (similar to the conditions at the bottom of the Mantle transition region) using sintered polycrystalline samples of cubic CaPv converted from bulk glass and a multianvil apparatus. We find that cubic CaPv has a shear modulus of 126 ± 1 gigapascals (uncertainty of one standard deviation), which is about 26 per cent lower than theoretical predictions3,4 (about 171 gigapascals). This value leads to substantially lower sound velocities of basaltic compositions than those predicted for the pressure and temperature conditions at depths between 660 and 770 kilometres. This suggests accumulation of basaltic crust in the uppermost lower Mantle, which is consistent with the observation of low-seismic-velocity signatures below 660 kilometres5,6 and the discovery of CaPv in natural diamond of super-deep origin7. These results could contribute to our understanding of the existence and behaviour of subducted crust materials in the deep Mantle.
Daniel J Frost - One of the best experts on this subject based on the ideXlab platform.
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accretion and differentiation of the terrestrial planets with implications for the compositions of early formed solar system bodies and accretion of water
Icarus, 2015Co-Authors: David C Rubie, Seth A Jacobson, Alessandro Morbidelli, D P Obrien, Edward D Young, J De Vries, F Nimmo, H Palme, Daniel J FrostAbstract:Abstract In order to test accretion simulations as well as planetary differentiation scenarios, we have integrated a multistage core–Mantle differentiation model with N-body accretion simulations. Impacts between embryos and planetesimals are considered to result in magma ocean formation and episodes of core formation. The core formation model combines rigorous chemical mass balance with metal–silicate element partitioning data and requires that the bulk compositions of all starting embryos and planetesimals are defined as a function of their heliocentric distances of origin. To do this, we assume that non-volatile elements are present in Solar System (CI) relative abundances in all bodies and that oxygen and H2O contents are the main compositional variables. The primary constraint on the combined model is the composition of the Earth’s primitive Mantle. In addition, we aim to reproduce the composition of the martian Mantle and the mass fractions of the metallic cores of Earth and Mars. The model is refined by least squares minimization with up to five fitting parameters that consist of the metal–silicate equilibration pressure and 1–4 parameters that define the starting compositions of primitive bodies. This integrated model has been applied to six Grand Tack N-body accretion simulations. Investigations of a broad parameter space indicate that: (1) accretion of Earth was heterogeneous, (2) metal–silicate equilibration pressures increase as accretion progresses and are, on average, 60–70% of core–Mantle boundary pressures at the time of each impact, and (3) a large fraction (70–100%) of the metal of impactor cores equilibrates with a small fraction of the silicate Mantles of proto-planets during each core formation event. Results are highly sensitive to the compositional model for the primitive starting bodies and several accretion/core-formation models can thus be excluded. Acceptable fits to the Earth’s Mantle composition are obtained only when bodies that originated close to the Sun, at
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isotopic evidence for internal oxidation of the earth s Mantle during accretion
Earth and Planetary Science Letters, 2012Co-Authors: Daniel J Frost, Helen M Williams, Bernard J Wood, Jon Wade, J TuffAbstract:Abstract The Earth's Mantle is currently oxidised and out of chemical equilibrium with the core. The reasons for this and for the relatively oxidised state of Earth's Mantle relative to the Mantles of other terrestrial planets are unclear. It has been proposed that the oxidised nature and high ferric iron (Fe 3 + ) content of Earth's Mantle was produced internally by disproportionation of ferrous iron (Fe 2 + ) into Fe 3 + and metallic iron by perovskite crystallisation during accretion. Here we show that there is substantial Fe isotope fractionation between experimentally equilibrated metal and Fe 3 + -bearing perovskite (≥ 0.45‰/amu), which can account for the heavy Fe isotope compositions of terrestrial basalts relative to equivalent samples derived from Mars and Vesta as the latter bodies are too small to stabilise significant perovskite. Mass balance calculations indicate that all of the Mantle's Fe 3 + could readily have been generated from a single disproportionation event, consistent with dissolution of perovskite in the lower Mantle during a process such as the Moon-forming giant impact. The similar Fe isotope compositions of primitive terrestrial and low-titanium lunar basalts is consistent with models of equilibration between the Mantles of the Earth and Moon in the aftermath of the giant impact and suggests that the heavy Fe isotope composition of the Earth's Mantle was established prior to, or during the giant impact. The oxidation state and ferric iron content of the Earth's Mantle was therefore plausibly set by the end of accretion, and may be decoupled from later volatile additions and the rise of oxygen in the Earth's atmosphere at 2.45 Ga.
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pressure sensitivity of olivine slip systems and seismic anisotropy of earth s upper Mantle
Nature, 2005Co-Authors: David Mainprice, Helene Couvy, Andrea Tommasi, Patrick Cordier, Daniel J FrostAbstract:The mineral olivine dominates the composition of the Earth's upper Mantle and hence controls its mechanical behaviour and seismic anisotropy. Experiments at high temperature and moderate pressure, and extensive data on naturally deformed Mantle rocks, have led to the conclusion that olivine at upper-Mantle conditions deforms essentially by dislocation creep with dominant [100] slip. The resulting crystal preferred orientation has been used extensively to explain the strong seismic anisotropy observed down to 250 km depth1,2,3,4. The rapid decrease of anisotropy below this depth has been interpreted as marking the transition from dislocation to diffusion creep in the upper Mantle5. But new high-pressure experiments suggest that dislocation creep also dominates in the lower part of the upper Mantle, but with a different slip direction. Here we show that this high-pressure dislocation creep produces crystal preferred orientations resulting in extremely low seismic anisotropy, consistent with seismological observations below 250 km depth. These results raise new questions about the mechanical state of the lower part of the upper Mantle and its coupling with layers both above and below.
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partitioning of oxygen during core formation on the earth and mars
Nature, 2004Co-Authors: David C Rubie, Christine K Gessmann, Daniel J FrostAbstract:Core formation on the Earth and Mars involved the physical separation of metal and silicate, most probably in deep magma oceans. Although core-formation models explain many aspects of Mantle geochemistry, they have not accounted for the large differences observed between the compositions of the Mantles of the Earth (approximately 8 wt% FeO) and Mars (approximately 18 wt% FeO) or the smaller mass fraction of the martian core. Here we explain these differences as a consequence of the solubility of oxygen in liquid iron-alloy increasing with increasing temperature. We assume that the Earth and Mars both accreted from oxidized chondritic material. In a terrestrial magma ocean, 1,200-2,000 km deep, high temperatures resulted in the extraction of FeO from the silicate magma ocean owing to high solubility of oxygen in the metal. Lower temperatures of a martian magma ocean resulted in little or no extraction of FeO from the Mantle, which thus remains FeO-rich. The FeO extracted from the Earth's magma ocean may have contributed to chemical heterogeneities in the lowermost Mantle, a FeO-rich D" layer and the light element budget of the core.
John R. Baumgardner - One of the best experts on this subject based on the ideXlab platform.
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Effects of depth-dependent viscosity and plate motions on maintaining a relatively uniform mid-ocean ridge basalt reservoir in whole Mantle flow
Journal of Geophysical Research, 2002Co-Authors: David Robert Stegman, Mark A Richards, John R. BaumgardnerAbstract:[1] Mid-ocean ridge basalts (MORBs) exhibit relatively uniform and depleted rare earth element concentrations compared with ocean island basalts (OIBs). Previous researchers have focused on long-term (billion-year timescale) preservation of an enriched and heterogeneous OIB reservoir within the convecting Mantle. Such studies commonly conclude that the OIB reservoir must exist in an area which remains isolated from convection, i.e., D″. Here we investigate the maintenance of MORB reservoir homogeneity over shorter timescales in the face of vigorous upper/lower Mantle mass exchange (deep subduction), which may be due to two effects: (1) a high-viscosity lower Mantle and/or (2) chaotic mixing due to toroidal flow generated by surface plate motions. We explore this conceptual model using three-dimensional spherical numerical models that include surface plate motions, radial viscosity variation, and a geophysically plausible model of Mantle density contrasts. A correlation dimension method is used to characterize mixing of passive tracers. For a uniform viscosity Mantle the upper and lower Mantles mix on essentially the same timescales. A factor of 100 viscosity contrast results in a relative mixing time for the lower Mantle only ∼30–60% longer than that of the upper Mantle. Therefore neither a strong viscosity contrast nor toroidal mixing significantly affects the relative mixing times of the upper and lower Mantle. We conclude that return flow from the lower Mantle is of similar (depleted) composition and that the depleted MORB source reservoir constitutes most of the Mantle, except for a convectively isolated OIB source region at the base of the Mantle.
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effect of depth dependent viscosity on the planform of Mantle convection
Nature, 1996Co-Authors: Hanspeter Bunge, Mark A Richards, John R. BaumgardnerAbstract:LITHOSPHERIC plate motions at the Earth's surface result from thermal convection in the Mantle1. Understanding Mantle convection is made difficult by variations in the material properties of rocks as pressure and temperature increase from the surface to the core. The plates themselves result from high rock strength and brittle failure at low temperature near the surface. In the deeper Mantle, elevated pressure may increase the effective viscosity by orders of magnitude2–5. The influence of depth-dependent viscosity on convection has been explored in two-dimensional numerical experiments6–8, but planforms must be studied in three dimensions. Although three-dimensional plan-forms can be elucidated by laboratory fluid dynamic experiments9,10, such experiments cannot simulate depth-dependent rheology. Here we use a three-dimensional spherical convection model11,12 to show that a modest increase in Mantle viscosity with depth has a marked effect on the planform of convection, resulting in long, linear downwellings from the upper surface boundary layer and a surprisingly 'red' thermal heterogeneity spectrum, as observed for the Earth's Mantle13. These effects of depth-dependent viscosity may be comparable to the effects of the plates themselves.
