Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union (AGU)  

DOI： 10.1029/2022gl100178

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Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2022GL100178

Publishing type：Research paper (scientific journal)   Publisher：American Association for the Advancement of Science (AAAS)  

To understand mantle dynamics, it is important to determine the rheological properties of bridgmanite, the dominant mineral in Earth’s mantle. Nevertheless, experimental data on the viscosity of bridgmanite are quite limited due to experimental difficulties. Here, we report viscosity and deformation mechanism maps of bridgmanite at the uppermost lower mantle conditions obtained through in situ stress-strain measurements of bridgmanite using deformation apparatuses with the Kawai-type cell. Bridgmanite would be the hardest among mantle constituent minerals even under nominally dry conditions in the dislocation creep region, consistent with the observation that the lower mantle is the hardest layer. Deformation mechanism maps of bridgmanite indicate that grain size of bridgmanite and stress conditions at top of the lower mantle would be several millimeters and ~10 ⁵ Pa to realize viscosity of 10 ^21–22 Pa·s, respectively. This grain size of bridgmanite suggests that the main part of the lower mantle is isolated from the convecting mantle as primordial reservoirs.

DOI： 10.1126/sciadv.abm1821

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

<title>Abstract</title>The crystallization of the magma ocean resulted in the present layered structure of the Earth’s mantle. An open question is the electronic spin state of iron in bridgmanite (the most abundant mineral on Earth) crystallized from a deep magma ocean, which has been neglected in the crystallization history of the entire magma ocean. Here, we performed energy-domain synchrotron Mössbauer spectroscopy measurements on two bridgmanite samples synthesized at different pressures using the same starting material (Mg_0.78Fe_0.13Al_0.11Si_0.94O₃). The obtained Mössbauer spectra showed no evidence of low-spin ferric iron (Fe³⁺) from the bridgmanite sample synthesized at relatively low pressure of 25 gigapascals, while that directly synthesized at a higher pressure of 80 gigapascals contained a relatively large amount. This difference ought to derive from the large kinetic barrier of Fe³⁺ rearranging from pseudo-dodecahedral to octahedral sites with the high-spin to low-spin transition in experiments. Our results indicate a certain amount of low-spin Fe³⁺ in the lower mantle bridgmanite crystallized from an ancient magma ocean. We therefore conclude that primordial bridgmanite with low-spin Fe³⁺ dominated the deeper part of an ancient lower mantle, which would contribute to lower mantle heterogeneity preservation and call for modification of the terrestrial mantle thermal evolution scenarios.

DOI： 10.1038/s41598-021-98991-w

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Other Link： https://www.nature.com/articles/s41598-021-98991-w

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

The pressure effect on the electromotive force (EMF) of a Pt13Rh-Pt (type R) thermocouple was examined to determine the temperature measurement accuracy of solid pressure medium apparatuses in high-pressure experiments. Single-wire EMFs were measured up to pressure of 13 GPa and temperature of 1173 K with a Kawai-type multi-anvil apparatus for Pt13Rh and Pt based on the single-wire method. The pressure conditions along the wires were evaluated by in situ X-ray diffraction using synchrotron X-ray radiation. The pressure effect of the Seebeck coefficients of Pt13Rh and Pt were determined by the analysis of the single-wire EMFs and pressure-temperature profiles along the wires and was virtually consistent with those determined in previous studies at lower pressures and temperatures. For type R thermocouple, the difference between the nominal and real temperatures was determined to be as large as -75 K at 13 GPa and 873 K.

DOI： 10.1080/08957959.2019.1705296

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Language：English   Publishing type：Research paper (scientific journal)  

© 2019 Elsevier B.V. Our understanding of the Earth's interior strongly depends on the physical and chemical properties of the Earth's constituent materials, which have been determined using high-pressure/high-temperature experiments involving thermocouples. Thus, knowledge of the pressure effect on the thermocouple electromotive force (EMF) is indispensable for an accurate understanding of the Earth's interior. We have determined the effect of pressure on a W3Re-W25Re thermocouple up to 16 GPa and 1173 K by the single-wire method using a multi-anvil apparatus in conjunction with synchrotron radiation. The difference between the nominal temperature and the real temperature was determined to be −29 K at 16 GPa and 1173 K when using this thermocouple. There have been many debates addressing the discrepancy between the depth of the 660-km seismic discontinuity in the Earth's mantle and the pressure–temperature conditions of the postspinel phase boundary in Mg2SiO4. This discrepancy disappears when the temperature value is corrected. The transport properties (e.g. rheology, element diffusion, electrical conductivity) in the Earth appear to slow down with depth more rapidly than was previously estimated because of the effect of pressure on the thermocouple.

DOI： 10.1016/j.pepi.2019.106348

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of High Pressure Science and Technology  

DOI： 10.4131/jshpreview.30.78

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CiNii Books

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Language：English  

DOI： 10.2138/am-2019-6559

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：FRONTIERS MEDIA SA  

The Earth's core mainly consists of iron, and its thermal transport properties are of vital importance for our understanding of the thermal evolution and the dynamics of the core and the mantle. However, the reported values of thermal conductivity of iron at the core conditions are so far inconclusive. Although hexagonal closed-packed (hcp) iron is often studied as a proxy metal to investigate the physical properties not only of the inner core, but also the outer core, the anisotropy of the thermal conductivity of hcp iron has never been experimentally examined. Here we report the results of texture analyses by means of synchrotron X-ray diffraction experiments and thermal conductivity measurements on polycrystalline hcp iron up to 44.5 GPa and 300 K. These results indicate that the thermal conductivity of single crystal hcp iron along c axis is about 3-4 times higher than that along a axis, which could have partially caused the controversial values of the thermal conductivity of hcp iron at the Earth's core conditions.

DOI： 10.3389/feart.2018.00176

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© 2018 Elsevier B.V. Shear and uniaxial deformation experiments on hexagonal close-packed iron (hcp-Fe) was conducted using a deformation-DIA apparatus at a pressure of 13–17 GPa and a temperature of 723 K to determine its deformation-induced crystallographic-preferred orientation (CPO). Development of the CPO in the deforming sample is determined in-situ based on two-dimensional X-ray diffraction using monochromatic synchrotron X-rays. In the shear deformation geometry, the 〈0001〉 and 〈112¯0〉 axes gradually align to be sub-parallel to the shear plane normal and shear direction, respectively, from the initial random texture. In the uniaxial compression and tensile geometry, the 〈0001〉 and 〈112¯0〉 axes, respectively, gradually align along the direction of the uniaxial deformation axis. These results suggest that basal slip (0001)〈112¯0〉 is the dominant slip system in hcp-Fe under the studied deformation conditions. The P-wave anisotropy for a shear deformed sample was calculated using elastic constants at the inner core condition by recent ab-initio calculations. Strength of the calculated anisotropy was comparable to or higher than axisymmetric anisotropy in Earth's inner core.

DOI： 10.1016/j.epsl.2018.03.029

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN ASSOC MINERALOGICAL SCIENCES  

The morphological stability of hydrous liquid droplets at grain boundaries of eclogite minerals in the basaltic part of a subducting slab were investigated based on experimental constraints for the dihedral angles. We measured the dihedral angles in the eclogite-H2O system at a temperature of 1000 degrees C and at pressures ranging from 4 to 16 GPa. The dihedral angle of hydrous liquid versus garnet-garnet (theta(GG-L)) increased with increasing pressure from 46 degrees at 4 GPa to 66 degrees at 12 GPa, although it showed a weak decreasing trend at pressures higher than 12 GPa. The dihedral angle of hydrous liquid versus clinopyroxene-clinopyroxene (theta(CC-L)) was almost constant with increasing pressure (61 and 59 degrees at 4 and 10 GPa, respectively). The dihedral angle of hydrous liquid versus garnet-clinopyroxene (theta(GC-L)) was 73-76 degrees at 4-10 GPa, and it was always higher than theta(GG-L) and theta(CC-L). By applying the morphological stability criteria for liquid in a system with two solid phases (garnet and clinopyroxene) and bond percolation theory for a three-dimensional lattice of tetracoordination, we found that the hydrous liquid was isolated at the grain edges and corners of eclogite minerals in the cold slab under a wide range of pressure conditions of the upper mantle from 4-14 GPa when the grain size of garnet was equal to that of clinopyroxene. Thus, basaltic crust containing hydrous liquid droplets may carry water to the lowermost upper mantle and the mantle transition zone when the slab is cold.

DOI： 10.2465/jmps.170309

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Creep strength of ringwoodite is important for understanding complicated patterns of the mantle convection in and around the mantle transition zone. To determine the creep strength of ringwoodite, we expanded pressure-temperature conditions of in situ stress-strain measurements in a deformation-DIA apparatus combined with synchrotron X-ray to those of the lower part of the mantle transition zone. The expansion of the pressure-temperature conditions was made by shrinking anvil truncation to 2.0 mm and the development of a cell assembly for in situ deformation experiments up to 1700 K. Utilizing the developed technique, creep-strength measurements on polycrystalline ringwoodite were performed at 16.9-18.0 GPa and 1300-1700 K during axial deformation with strain rates of 1.48-3.59 x 10(-5) s(-1) to strains of 13.2-24.9%. Based on mechanical and microstructural observations, we infer that ringwoodite deformed by exponential dislocation creep through the Peierls mechanism at 1300-1400 K and power law dislocation creep at 1500-1700 K. The creep strength of ringwoodite is apparently lower than that of bridgmanite, wadsleyite and olivine. The present result implies the possibility that the lower mantle transition zone is a low-viscosity layer. Further creep-strength data of these minerals are necessary to be determined above 13.5 GPa and high temperatures to determine viscosity structure in and around the lower mantle transition zone at strain rates relevant to the mantle convection. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2016.08.011

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

Seismic shear wave anisotropy(1-6) is observed in Earth's uppermost lower mantle around several subducted slabs. The anisotropy caused by the deformation-induced crystallographic preferred orientation (CPO) of bridgmanite (perovskite-structured (Mg, Fe) SiO3) is the most plausible explanation for these seismic observations. However, the rheological properties of bridgmanite are largely unknown. Uniaxial deformation experiments(7-9) have been carried out to determine the deformation texture of bridgmanite, but the dominant slip system (the slip direction and plane) has not been determined. Here we report the CPO pattern and dominant slip system of bridgmanite under conditions that correspond to the uppermost lower mantle (25 gigapascals and 1,873 kelvin) obtained through simple shear deformation experiments using the Kawaitype deformation-DIA apparatus(10.) The fabrics obtained are characterized by [100] perpendicular to the shear plane and [001] parallel to the shear direction, implying that the dominant slip system of bridgmanite is [001](100). The observed seismic shear-wave anisotropies near several subducted slabs(1-4) (Tonga-Kermadec, Kurile, Peru and Java) can be explained in terms of the CPO of bridgmanite as induced by mantle flow parallel to the direction of subduction.

DOI： 10.1038/nature19777

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Growth kinetics of forsterite (Fo) reaction rims between periclase (Per) and enstatite (En) were studied experimentally at pressure (P) and temperature (T) conditions of 3.0-11.1 GPa and 1473-1873 K, respectively. Pt markers originally placed at the Per-En interface were always observed at the Per-Fo interface, which indicates that Mg and O are the diffusing species in Fo rim growth (Mg-O coupled diffusion). The presence of some En inclusions in Fo grains and the growth rate of the Fo rim suggests that grain boundary diffusion is dominant rather than lattice diffusion. Considering the very fast grain boundary diffusion of O in olivine, the Mg-O coupled grain boundary diffusion in Fo is deduced to be rate-limited by the diffusivity of Mg. Based on an analysis of data collected under dry conditions, the product of the Mg grain boundary diffusion coefficient (D-gb) and the effective grain boundary width (5) was determined to be delta D-gb = delta D(gb,0)exp[-(E* + PV*)/RT] with delta D-gb,D-0 = 10(-9.68 +/- 1.51) m(3)/s, E* = 379 +/- 44 kJ/mol and V* = -1.9 +/- 1.4 cm(3)/mol. Our results, combined with previously reported data on Mg lattice diffusion in Fo, suggest that for Mg, the significance of grain boundary diffusion increases with depth in the Earth's upper mantle, although lattice diffusion is still dominant for typical mantle grain sizes of 1-10 mm. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2016.06.008

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MINERALOGICAL SOC AMER  

We experimentally explored phase relations in the system FeOOH-TiO2 at pressures of 16 GPa and temperatures of 1000-1600 degrees C, which corresponds to conditions of the Earth's mantle transition zone. Analyses of the recovered samples revealed that, in the studied conditions, there are two stable iron-titanium oxyhydroxide phases whose estimated composition is expressed by (FeH)(1-x)TixO2. One is the Fe-rich solid solution (x &lt; 0.23) with epsilon-FeOOH type crystal structure (orthorhombic, P2(1)nm), and the other is the more Ti-rich solid solution (x &gt; 0.35) with alpha-PbO2 type structure (orthorhombic, Pbcn). The epsilon-FeOOH phase is stable up to similar to 1100 degrees C irrespective of chemical composition, whereas the alpha-PbO2 type phase is stable up to 1500 degrees C for a composition of x = 0.5 and at least to 1600 degrees C for x = 0.75, and thus the alpha-PbO2 type phase is stable at average mantle temperature in the Earth's mantle transition zone. Iron-titanium-rich phases found previously in basalt + H2O system are estimated to be the epsilon-FeOOH and alpha-PbO2 type phases where the phase with iron-rich composition found at relatively low temperature (&lt;1100 degrees C) is epsilon-FeOOH phase and the phase with titanium-rich composition is alpha-PbO2 type phase. The alpha-PbO2 type and epsilon-FeOOH phases may be stable in the subducted basaltic crust at pressures in the mantle transition zone under water-rich conditions.

DOI： 10.2138/am-2016-5517

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

We developed a method to determine the absolute pressure effect on thermocouple electromotive force (EMF), based on a single wire method using Kawai-type multi-anvil apparatus. In this method, pressure conditions along the wires were evaluated based on in situ X-ray diffraction using synchrotron X-ray radiation. The pressure effect of the Seebeck coefficients of chromel and alumel was determined up to 7 GPa and 600 degrees C by the analyses of single wire EMFs and pressure-temperature profiles along the wires. The temperature correction for the type K thermocouple was calculated to be from 0 degrees C to -3 degrees C in the studied conditions. Since the multi-anvil apparatus is capable of achieving much higher pressure and temperature, the method presented in this study promises to reveal absolute temperature correction for thermocouples over a wide range of pressure and temperature conditions.

DOI： 10.1080/08957959.2016.1169275

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MINERALOGICAL SOC AMER  

To understand the origin of observed low velocities in the crustal portion of subducting plates, we performed in situ measurements of elastic wave velocities of anorthite at temperatures up to 1373 K at pressure of similar to 1 GPa and up to 773 K at 2.0-7.0 GPa. A fine-grained polycrystalline anorthite, which was synthesized using a gas pressure apparatus, was used for the measurements. The high-pressure experiments were performed using the multi-anvil apparatus installed on beamline BL04B1 at SPring-8. The elastic wave velocity was measured by the ultrasonic pulse method with synchrotron X-ray radiographic imaging and X-ray diffraction techniques. At similar to 1.0 GPa, elastic wave velocities exhibited a sharp temperature-induced kink at similar to 500 K. Below 500 K, the elastic wave velocities decrease with increasing temperature. In contrast, above 500 K, the elastic wave velocities show an increasing trend in the range of 500-900 K, and then revert back to a decreasing trend at above 900 K. We also found a pressure-induced velocity anomaly of anorthite. At 300-373 K, v(p) is constant up to 4 GPa, but decrease above 4 GPa with increasing pressure, while vs decreases monotonously with increasing pressure. These elastic anomalies are considered to be attributable to the tilting behavior of the corner-sharing TO4 (T = Al, Si) tetrahedra in three-dimensional frameworks of anorthite. Our results suggest the presence of plagioclase feldspar has the potential to causes low-velocity anomaly in the subducting oceanic crust when it survives as a metastable phase in the slab at higher pressure and lower temperature conditions.

DOI： 10.2138/am-2015-5240

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Simple-shear deformation experiments on polycrystalline olivine and olivine single-crystal were conducted at pressures of 1.3-3.8 GPa and temperatures of 1223-1573 K to understand the achievement of steady-state fabric strength and the process of dynamic recrystallization. Development of crystallographic preferred orientation (CPO) of olivine was evaluated from two-dimensional X-ray diffraction patterns, and shear strain was measured from X-ray radiographs. The steady-state fabric strength of the A-type fabric was achieved within total shear strain of gamma = 2. At strains higher than gamma = 1, an increase in concentration of the [010] axes mainly contributes to an increase in fabric strength. At strains higher than gamma = 2, the magnitude of V-SH/V-SV (i.e., ratio of horizontally and vertically polarized shear wave velocities) scarcely increased in most of the runs. The V-SH/V-SV of peridotite (70 vol.% olivine + 30 vol.% minor phases) having the steady-state A-type olivine fabric coincides with that of recent global one-dimensional models under the assumption of horizontal flow, suggesting that the seismic anisotropy observed in the shallow upper mantle is mostly explained by the development of A-type olivine fabric. Experimental results on the deformation of single-crystal olivine showed that the CPO of olivine is influenced by the initial orientation of the starting single crystal because strain is concentrated in the recrystallized areas and the relic of the starting single crystal remains. In the upper mantle, the old CPO of olivine developed in the past may affect the olivine CPO developed in the present. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2015.04.004

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

High-pressure and high-temperature deformation experiments on fine-grained synthetic dunite (forsterite aggregate) were conducted to determine the dominant deformation mechanism in the deep upper mantle. The sintered starting material has 90% forsterite, 10% enstatite, and an average grain size of similar to 1 mu m. Deformation experiments were performed using a deformation-DIA apparatus at pressures of 3.03-5.36 GPa, temperatures of 1473-1573 K, and uniaxial strain rates of 0.91x10(-5) to 18.6x10(-5)s(-1) at dry circumstances &lt; 50H/10(6)Si. The steady state flow stress was determined at each deformation condition. Derived stress-strain rate data is analyzed together with that reported from similar but low-pressure deformation experiments using flow law equations for diffusion creep (stress exponent of n=1, grain-size exponent of p=2) and for dislocation-accommodated grain-boundary sliding (GBS-disl, n=3, p=1). The activation volume for diffusion creep (V*(dif)) and for GBS-disl (V*(GBS)) of dunite is determined to be 8.2 +/- 0.9 and 7.5 +/- 1.0 cm(3)/mol, respectively. Calculations based on these results suggest that both diffusion creep and dislocation creep play an important role for material flow at typical deformation conditions in the Earth's asthenospheric upper mantle whereas the contribution of GBS-disl is very limited, and dislocation creep is the dominant deformation mechanism during the deformation of olivine in sheared peridotite xenolith. Though these conclusions are not definitive, these are the first results on potential deformation mechanisms of forsterite aggregate based on extrapolation in the pressure, temperature, stress, and grain-size space.

DOI： 10.1002/2013JB010473

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DOI： 10.1038/ngeo2074

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The growth rate of MgSiO3 perovskite reaction rims between periclase and stishovite was investigated at 24-50 GPa and 1650-2150 K using a Kawai-type high-pressure apparatus. The textural observations of the recovered samples and rim growth kinetic data revealed that the reaction is controlled by coupled grain boundary diffusion of MgO and grain coarsening in the perovskite reaction layer. Assuming a high diffusivity of O compared with Mg, the grain boundary diffusivity of Mg in the perovskite was determined to be delta D-gb(Mg) [m(3)/s] = 10(-15.1) exp{-[176,000 + (P - 24) x 3.8 x 10(3)]/RT), which is similar to 3-5 gb orders of magnitude faster than that of Si. We found that the bulk diffusivity of Mg in polycrystalline perovskite is affected by the grain boundary when we consider the possible grain sizes and temperatures in the lower mantle. Accordingly, grain boundary diffusion in perovskite may be an effective mechanism for chemical transportation of divalent cations in the lower mantle. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.eps1.2013.06.045

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

In-situ synchrotron X-ray diffraction experiments using a multi-anvil apparatus have been conducted on face-centered cubic iron (gamma-Fe), which is a possible component of metallic cores in planetary bodies. From the pressure-volume-temperature (P-V-T) data collected systematically at 0-24 GPa and 873-1873 K, we have constructed the thermal equation of state (EoS) of gamma-Fe. A fit with a high-temperature BirchMumaghan (HT-BM) EoS yields the unit-cell volume V-0,V- (1273 k)=49.026(25) angstrom(3), isothermal bulk modulus K-1273 k=110.8(18) GPa, pressure derivative of the bulk modulus K'=5.3(2), temperature derivative of the bulk modulus (partial derivative K-T/partial derivative(T))(p)=-0.0288(17) GPa K-1 and thermal expansion coefficient alpha=4.50(36) x 10(-5)+1.81 (30) x 10(-8) T(K) K-1, respectively, at 0 GPa and 1273 K. A fit of the Mie-Gruneisen-Debye BM-EoS yields Vo, 1273 k=49.026(25) K-1273 (k)=111.5(18) GPa, K'=5.2(2), the Gruneisen parameter gamma(0)=2.28(4), and a dimensionless parameter q=-0.21(22), with the fixed Debye temperature theta(0)=340 K. From the present P-V-T data, the spin transformation from mixed- or intermediate-spin to low-spin states is considered to occur with increasing pressure. The successive transition may be subtle, however and its effect on the compression behavior of gamma-Fe is relatively small. The newly determined EoS of gamma-Fe enables us to more precisely estimate the density of the metallic cores of Mercury, Mars and planetary satellites such as the Moon and Ganymede. The estimated densities of cores in those planetary bodies depend strongly on adapted temperatures in the range of those previously proposed. The metallic cores of those planets as well as that of Earth might contain some other elements such as Ni, S, C, Si, O, and H. The core densities determined in this study provide a reference point to discuss the thermal and compositional structures in planetary and satellite cores when their core densities are determined by future surveys. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2013.05.040

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Language：English   Publishing type：Part of collection (book)   Publisher：Wiley Blackwell  

A new method is developed to determine the three-dimensional variation in water content, temperature, and other parameters such as major element chemistry or the melt fraction from anomalies in seismic wave velocities and attenuation. The key to this method is mineral physics observations indicating different sensitivity of seismic wave velocities and attenuation to temperature, water content and other parameters such as major element chemistry, melt fraction or grain-size. Our analysis shows that among these parameters, temperature and water content generally have a more important influence on seismic wave velocities and attenuation than other factors such as major element chemistry, which are important only in limited regions. The method is applied to the upper mantle beneath northern Philippine Sea including the Izu-Bonin subduction zone, where high-resolution velocity and attenuation tomographic models are available down to a depth of ~400 km. We show that the tomographic images of this region can be explained by lateral variations in temperature and water content, with only little influence of major element chemistry. A broad region of high attenuation with modestly low velocities at 300-400 km depth away from the slab in this region is interpreted as region of high water contents. We speculate that this water-rich region may have been formed by the efficient transport of water to deeper mantle by a fast (and cold) subducting slab in this region or water may come from the transition zone.

DOI： 10.1029/168GM17

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Language：English   Publishing type：Research paper (scientific journal)  

Mantle flow in the Earth's mantle transition zone (between 410 and 660km depth) plays a key role to understand the nature of mantle convection, which can be mapped by observed seismic anisotropy combined with crystallographic preferred orientations of mantle minerals. Although wadsleyite is the most important mineral to cause seismic anisotropy observed in the mantle transition zone, there have been limited experimental data on its crystallographic preferred orientation because of experimental limitations. We experimentally evaluated the preferred orientation of wadsleyite developed by shear deformation at pressure-temperature conditions of the mantle transition zone (17.6GPa and 1800-1900K) using a deformation-DIA apparatus. The deformation experiments reveal that the [001] axis and the (010) plane of wadsleyite tend to be subparallel to the shear direction and the shear plane during deformation, respectively. These results demonstrate that polarization seismic anisotropy (velocity contrast between horizontally-polarized and vertically-polarized S-waves, VSH/VSV) observed in the mantle transition zone might be attributed to the preferred orientation of wadsleyite caused by horizontal mantle flow. © 2013 Elsevier B.V.

DOI： 10.1016/j.pepi.2012.12.005

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Si4+ + M2+ &lt;-&gt; 2Al(3+) (M=Mg+Fe+Ca) interdiffusion rates in majoritic garnet have been determined at pressure of 17 GPa and temperatures of 1550-1700 degrees C using a Kawai-type high-pressure apparatus. The diffusion profiles were measured across the interface between pyropic garnet and majoritic garnet samples by an analytical transmission electron microscope, and the rate of the Si4+ + M2+ &lt;-&gt; 2Al(3+) interdiffusion was determined to be a Dsi-Al (m(2) s(-1))=2 x 10(-1) exp [-364 (kJ mol(-1))/RT]. We found that the diffusion rate is low compared to the Si diffusion rate in other silicate minerals relevant to the deep mantle. Slow kinetics of the pyroxene-garnet transformation due to the low diffusion rate indicates that large low-density metastable regions may exist in the slab, greatly contributing to the slab stagnation around the transition region. Stagnant slabs possibly stay in this region over 10(8) yr because of the sluggish pyroxene-garnet transformation, but may eventually fall into the lower mantle after the completion of the transformation. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2012.11.022

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MINERALOGICAL SOC AMER  

Isothermal compression curves of face-centered cubic iron (gamma-Fe) were determined at high temperatures (1273 and 1073 K) up to 27 GPa by in situ X-ray diffraction experiments using synchrotron radiation and the Kawai-type multi-anvil apparatus. Fits of the third-order Birch-Murnaghan equation of state to pressure-volume data yielded V-0 = 48.997 +/- 0.040 angstrom(3), K-T0 = 108.3 +/- 2.4 GPa, and K-T' = 5.8 +/- 0.2 for 1273 K, and V-0 = 48.600 +/- 0.098 angstrom(3), K-T0 = 88.9 +/- 5.1 GPa, and K-T' = 8.9 +/- 0.7 for 1073 K, where V-0, K-T0, and K-T' are unit-cell volume, bulk modulus and its pressure derivative, respectively, at ambient pressure. The relatively large values of K-T' are attributable to successive electronic spin state transitions from mixed-spin at lower pressures to low-spin at higher pressures. When discussing the constituents of Earth's (or other planets') solid inner core in terms of density and equations of state, one must carefully consider the influence of the electronic spin state.

DOI： 10.2138/am.2012.3958

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Deformation experiments on hydrous melt-bearing dunite (olivine+4 vol% orthopyroxene+4 vol% clinopyroxene with less than 2.5 vol% of the melt phase) were conducted at pressures of 1.3-5.7 GPa and temperatures of 1270-1490 K in order to explore the effect of intergranular fluids on the plastic flow of olivine in Earth's upper mantle. The strain rate was proportional to steady-state creep strength to the 2.1 power, and the creep strength markedly increased with increase in grain size. Developments of the crystallographic preferred orientation of olivine and flattening of olivine grains were hardly observed even after 33-55% shortening of the samples. These observations show that grain boundary sliding (GBS) dominated the deformation of olivine (i.e., superplasticity). The creep strength of hydrous melt-bearing dunite was 2-5 times lower than that of melt-free dunite. The dependence of creep rate on melt fraction is known to be expressed empirically as (epsilon) over dot(phi) = (epsilon) over dot(0) exp(alpha phi), where alpha is a constant and phi is the melt fraction. The experimentally obtained value of alpha was in the range of 150-230, corresponding to 5-7 times the reported values for the olivine-basalt system at 0.3 GPa (i.e., creep strength of dunite was efficiently reduced by the hydrous melt). Superplasticity is the dominant creep mechanism of olivine in fluid-bearing fine-grained peridotites under low-temperature and high-stress conditions (i.e., peridotite shear zones in the upper mantle). Superplasticity induced by geological fluids would play an important role in the shear localization (and thus initiation of subduction) in the upper mantle. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2012.04.032

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The effects of water on the crystallographic preferred orientation (CPO) of olivine aggregates were investigated through simple-shear deformation experiments under asthenospheric upper mantle conditions (pressure = 2.1-5.2 GPa, temperature = 1490-1830 K) using a deformation-DIA apparatus. Formation of the A-type olivine fabric (developed by the (010)[100] slip system) was observed under water-depleted conditions (C-OH&lt;650 ppm H/Si in olivine), while B-type fabric (by the (010)[001] slip system) or a B-type-like fabric (by the (010)[hOl] slip system) were predominantly formed under water-rich conditions (&gt;1000 ppm H/Si). In comparison with fabrics of anhydrous olivine (&lt;= 111 ppm H/Si), those of olivine having higher water contents (&gt;= 625 ppm H/Si in olivine) showed stronger anisotropic properties (e.g., P-wave anisotropy, S-wave polarization anisotropy, and the ratio of horizontally and vertically polarized shear waves). The water-induced olivine CPO transition from A-type to B-type(-like) fabric accompanies a change in the alignment of the seismic fast a-axes, resulting in flow-parallel and flow-perpendicular shear wave splitting under water-depleted and water-rich conditions, respectively. The rotation of the fast direction of shear-wave splitting across an arc, which is observed in many subduction zones, is well explained by the likely bimodal water distribution along the mantle wedge (i.e., water-rich in fore-arc and water-depleted in back-arc regions) and the developments of two different types of olivine fabrics (i.e., B-type(-like) fabric in fore-arc and A-type fabric in back-arc regions). (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2011.11.022

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Language：English   Publishing type：Research paper (bulletin of university, research institution)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MINERALOGICAL SOC AMER  

We report on technical improvements in experiments with a deformation-DIA (D-DIA) apparatus, which enable the study of the rheology of solid materials at P-T conditions of the Earth's mantle transition zone. Dimensions of the anvil truncation, pressure medium, and gasket were optimized to achieve deformation experiments above 1:3 GPa with a relatively low press load (&lt;0.7 MN) to minimize the damage of the X-ray transparent second-stage anvils. The adoption of low X-ray absorbing material (e.g., cubic BN anvils, graphite window in a LaCrO3 heater) along the X-ray path enabled quantitative determination of stress and strain of a sample by means of simultaneous in situ X-ray radial diffraction and radiography using synchrotron radiation at SPring-8. Based on the new technique, a uniaxial deformation experiment with a strain rate of 3.88 x 10(-5) s strains up to 25.5% was carried out on wadsleyite at a pressure of 14.5 GPa and a temperature of 1700 K.

DOI： 10.2138/am.2011.3818

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MINERALOGICAL SOC AMER  

To investigate the physical property of Fe7C3, we carried out in situ X-ray diffraction experiments using a Kawai-type multi-anvil apparatus and a diamond anvil cell up to 71.5 GPa and 1973 K. The carbide was found to be stable under these experimental conditions. However, we found anomalous behavior in its isothermal compression and thermal expansivity. These anomalies could be due to the magnetic phase transition in Fe7C3 from a ferromagnetic (fm) to a paramagnetic (pm) phase. The Curie temperature of 523 K at 1 bar (Tsuzuki et al. 1984) decreases with pressure, and the pressure-induced magnetic transition is estimated to occur at 18 GPa and 300 K. The pressure-volume-temperature (P-V-T) data set for the pm-Fe7C3 was fitted by the Mie-Gruneisen-Debye (MGD) equation of state (EOS) and the following parameters were obtained: unit-cell volume V-0 = 184.2 +/- 0.3 angstrom(3), bulk modulus K-0 = 253 +/- 7 GPa, the pressure derivative of bulk modulus K-0 = 3.6 +/- 0.2, Gruneisen parameter gamma(0) = 2.57 +/- 0.05, Debye temperature theta(0) = 920 +/- 140 K, and q = 2.2 +/- 0.5, respectively, at zero pressure. The calculated density for Fe7C3 provides a good explanation for the density of the Earth's inner core obtained from seismological observations.

DOI： 10.2138/am.2011.3703

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Language：Japanese   Publisher：The Japan Society of High Pressure Science and Technology  

&nbsp;&nbsp;Experimental studies on rheology of mantle minerals at pressures higher than 3 GPa and at high temperature have been conducted based on recent experimental techniques in order to address the material transport in the Earth's interior. The high-pressure deformation experiments using deformation-DIA apparatus and rotational Drickamer apparatus have been carried out with <i>in situ</i> stress and strain measurements. The rheological data for olivine, wadsleyite, garnet and periclase at high pressure provide useful information necessary to discuss the rheological structure in the Earth's mantle. Further systematic studies are required to understand the effects of temperature, pressure, stress, chemical composition, water content and microstructure on rheology of deep Earth materials.<br>

DOI： 10.4131/jshpreview.21.137

CiNii Books

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The effects of pressure on crystallographic preferred orientation (CPO) of olivine aggregates were investigated through simple-shear deformation experiments at pressures between 2.1 and 7.6 GPa and temperatures of 1493-1673 K under dry conditions using a deformation-DIA apparatus, and the variations in seismic anisotropy were evaluated under the Earth's upper mantle conditions. We found that the monotonic decrease in seismic anisotropy with depth is caused by the pressure-dependency of the seismic properties of A-type (developed by the (010)[100] slip system) olivine fabric, while the rapid decrease is caused by the fabric transition from A-type to B/C-type (by the (hk0)[001] slip systems) at 7.6 GPa and 1673 K. Moreover, an alternative transition, from A-type fabric to B-type-like fabric (by the (010)[001] slip system), occurs at 7.6 GPa and lower temperature. These two temperature-dependent fabric transitions occurring at 7.6 GPa result in low seismic anisotropy with V-SH/V-SV (the ratio of horizontally and vertically polarized shear waves)&gt; 1 at low temperatures (i.e., old-continental mantle conditions) and V-SH/V-SV &lt; 1 at high temperatures (i.e., oceanic mantle conditions) at greater depths, consistent with seismological observations. Thus, the variations of CPO with pressure and temperature in olivine under dry conditions can explain the seismic anisotropy signatures observed in the upper mantle, without invoking other mechanisms. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2011.01.015

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Technical developments in high-pressure and high-temperature generation have been made, adopting a recently devised multi-anvil 6-6 (MA 6-6) assembly with tungsten carbide (WC) anvils. As a result, the pressure and temperature conditions available in a cubic-anvil DIA type apparatus have been extended to 20GPa and 2000K. Using this assembly operated in a deformation-DIA (D-DIA) apparatus, a deformation experiment to a strain of 15% on a mixture of wadsleyite and ringwoodite was successfully conducted at 16GPa and 1700K and at a strain rate of 6×10-5s-1, demonstrating potential of the present MA 6-6 assembly as an important tool to investigate rheological properties of high-pressure phases under the conditions of the mantle transition zone. © 2010 Elsevier B.V.

DOI： 10.1016/j.pepi.2010.07.004

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Stress relaxation experiments of olivine were conducted under high-pressure and high-temperature conditions up to 10 GPa and 1273 K using a Kawai-type multi-anvil apparatus. A pre-sintered San Carlos olivine sample rod was inserted between two dense Al2O3 pistons to yield high stress at high-pressure within an octahedral pressure medium. Stress was determined from the two-dimensional diffraction pattern taken using monochromatic X-rays and an imaging-plate, and sample length was determined from an X-ray radiograph. In these experiments, pressure was first increased at room temperature, and then the temperature was increased and kept at 673, 873, 1073, and 1273 K. Four relaxation cycles, in total, were carried out in two experimental runs. The magnitude of deviatoric stress was calculated from five diffraction peaks with the following hkls: 02 1, 1 01, 1 30, I 3 1, and 11 2. The calculated deviatoric stress was significantly different depending on which diffraction peak was used (up to a factor of similar to 2) due to plastic deformation within the polycrystalline sample. The deviatoric stress decreased with increasing temperature in all of relaxation cycles. At given temperatures, the final-state value of deviatoric stress increased with increasing pressure. The upper bound for the plastic strain rate in the final-state was determined to be 10(-7) s(-1) based on a comparison between the total sample length determined from the radiograph and the d-spacings along the piston direction determined from X-ray diffraction. Present results suggest a positive activation volume for the low-temperature rheology of olivine. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2010.07.006

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHINA UNIV GEOSCIENCES  

Technical developments for simple shear deformation experiments at high pressures were made. The newly designed cell assembly can be compressed by deformation-DIA apparatuses with the MA 6-6 system, which consists of six second-stage tungsten carbide anvils (with a truncated edge length of 5 mm) and the anvil guide. Deformation of samples was barely observed during the compression process, showing that the shear strain of the deformed samples can be measured by the rotation of a strain marker. Simple shear deformation experiments on anhydrous and hydrous olivine aggregates were conducted under upper mantle conditions (pressures of 5.2-7.6 GPa and temperatures of 1 473-1 573 K), and sample deformation with a shear strain of gamma=0.8-1.2 was successfully achieved at a shear strain rate of 4.0x10(-5)-7.5x10(-5) s(-1). The present study extended the pressure range of simple shear deformation experiments in the deformation-DIA apparatus from 3 GPa in an early study to 7.6 GPa at high temperatures.

DOI： 10.1007/s12583-010-0110-4

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Language：English   Publishing type：Research paper (scientific journal)  

A deformation experiment of ringwoodite with a strain of 9% was achieved at 20 GPa and 1 700 K and at a strain rate of 3×10-5 s-1 using a deformation-DIA (D-DIA) apparatus and a multi-anvil 6-6 (MA 6-6) assembly. The crystallographic orientations of the deformed sample were successfully analyzed by the electron backscatter diffraction (EBSD) method, although any notable lattice-preferred orientation (LPO) was not observed presumably due to the insufficient strain in the present experiment. In this study, the deformation experiment on ringwoodite succeeded at P-T conditions consistent with the lower part of the mantle transition zone and at a controlled strain rate for the first time. The present study extended the pressure range of deformation experiments in the D-DIA apparatus from 16 GPa in our earlier study to 20 GPa at 1 700 K. The successful extension of the pressure range demonstrates potential importance of the D-DIA apparatus in studying rheological properties of minerals under the P-T conditions of the whole mantle transition zone. © 2010 China University of Geosciences and Springer-Verlag Berlin Heidelberg.

DOI： 10.1007/s12583-010-0120-2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MINERALOGICAL SOC AMER  

Density and seismic velocities of the chromitite bodies from the Oman ophiolite were calculated and compared with those of oceanic peridotites. The Oman chromitite is composed of olivine and chromian spinel, and the olivine/spinel volume ratio varies from 20 to 90 vol%. Chromian spinel in the chromitite is enriched in magnesiochromite component, and Fo content of olivine ranges from 94 to 96. Compressibility of a natural chromian spinel [(Mg0.77Fe0.232+)(Cr0.46Al0.50Fe0.043+)O-4] was measured with in situ synchrotron X-ray diffraction experiments, using a diamond anvil cell up to 10 GPa at 300 K. The third-order Birch-Mumaghan equation of state yields the isothermal bulk modulus of K-T = 192(7) GPa, its pressure derivative of K'(T) = 4(1), and the zero-pressure volume of V-0 = 560.6(2) angstrom(3). Based on calculations using present and previous studies, the adiabatic bulk modulus of magnesiochromite component was estimated to be 189 GPa. Using petrological and the mineral physics data, density and seismic velocities (V-phi, V-P, V-S) were calculated. The seismic velocities are higher than those of peridotites in the oceanic upper mantle and decrease with decrease of the spinel/olivine ratio. The contrast between chromitite and oceanic peridotite are 5.0-8.1% for V-phi, 2.7-4.9% for V-S, and 4.1-6.7% for V-P in the Moho transition zone chromitite, and 2.6-6.5% for V-phi, 1.4-3.3% for V-S, and 2.2-5.2% for V-P in the discordant mantle chromitite. This contrast is large enough to be detected by seismological observations and becomes a key to knowing the distributions of chromitite in the oceanic upper mantle.

DOI： 10.2138/am.2010.3498

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

Grain-growth kinetics of (Mg0.85Fe0.15)O ferropericlase was investigated at a temperature of 1873 K up to a pressure of 25 GPa under dry conditions using a Kawai-type multi-anvil apparatus. The grain-growth kinetics of ferropericlase is described by G(n) - G(0)(n) = k(0) exp(-E* +PV*/RT)t where G is the average grain-size at annealing time t; G(0), the initial average grain-size; P, pressure; R, the gas constant; and T, absolute temperature. Least squares fit of this equation for the present data and our previous data on the same material yielded n = 2.8 +/- 0.2, k(0) = 10(-8.4 +/- 1.1) m(2.8)/s, E* = 273 +/- 24 kJ/mol, and V* = 4.5 +/- 0.2 cm(3)/mol. The present results show that at the conditions at the top of the lower mantle (700 km depth), the grain-size of ferropericlase in a single phase system evolves to similar to 1 cm after significant geological time of 1 My. The present results may be applied to regions where single phase ferropericlase aggregates are present, say by deformation-induced phase segregation. In these areas, the grain-growth kinetics is fast so that one expects a large grain-size that will results in strong lattice-preferred orientation causing significant seismic anisotropy. Citation: Tsujino, N., and Y. Nishihara (2010), Effect of pressure on grain-growth kinetics of ferropericlase to lower mantle conditions, Geophys. Res. Lett., 37, L14304, doi: 10.1029/2010GL043491.

DOI： 10.1029/2010GL043491

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

The maximum pressure generated in a cubic anvil apparatus has been extended to approximately 25GPa with the sample volume approximately one order of magnitude larger than that available in the earlier study reporting the highest pressure of 23GPa. The pressure generation experiment was performed using a newly designed multi-anvil 6-6 (MA 6-6) assembly with tungsten carbide anvils possessing truncated edge lengths of 2.5 and 3.0mm, operated in a deformation-DIA-type apparatus. The semiconductor-to-metal transitions in GaP, GaAs, ZnS, and ZnTe at room temperature were used as the pressure references. A cubic anvil apparatus has many advantages in high-pressure experiments over the Kawai (or 6-8)-type apparatus, and the extension of both pressure range and sample volume in the former apparatus should greatly contribute to the advancement of the studies relevant to deformation, measurement of physical properties, synthesis, and crystal structure analysis of materials under high pressures and temperatures.

DOI： 10.1080/08957950903503912

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP PUBLISHING LTD  

We have demonstrated the feasibility of a two-dimensional angle-dispersive x-ray diffraction (2D-ADXD) measurement system using a Kawai-type multianvil press at SPring-8. By taking advantage of the x-ray-transparent anvil and energy-dispersive x-ray diffraction (EDXD) techniques, high-pressure 2D-ADXD measurements of KCl were performed up to 9.9 GPa. Entire Debye-Scherrer rings were obtained, and the B1-B2 phase change of KCl was clearly observed at 2.3 GPa. The developed 2D-ADXD measurement system enabled us to obtain enough high-quality diffraction data to precisely determine and refine the structure of KCl at high-pressure.

DOI： 10.1088/1742-6596/215/1/012027

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

A system for stress measurement under high pressure has been developed at beamline BL04B1, SPring-8, Japan. A Kawai-type multi-anvil apparatus, SPEED-1500, was used to pressurize polycrystalline KCl to 9.9 GPa in a mechanically anisotropic cell assembly with the KCl sample sandwiched between dense Al2O3 pistons. The variation of deviatoric stress was determined from the lattice distortion measured using two-dimensional X-ray diffraction with monochromatic synchrotron X-rays. The low-pressure B1 phase transformed to the high-pressure polymorph B2 during compression. The deviatoric stress increased with increasing pressure in both the B1 and B2 phases except for the two-phase-coexisting region at a pressure of 2-3 GPa. This new system provides one of the technical foundations for conducting precise rheological measurements at conditions of the Earth's lower mantle.

DOI： 10.1107/S0909049509034955

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Grain-growth kinetics Of (Mg(0.85)Fe(0.15))O ferropericlase was investigated at pressures of 5 and 10GPa and temperatures of 1673-1873 K using a Kawai-type multi-anvil apparatus. Presintered ferropericlase aggregate with an average grain size of 4.0 mu m was used as starting material of grain-growth annealing experiments. The grain-growth kinetics of ferropericlase is described by G(n) - G(0)(n) = k(0) t exp[-(E* + PV*)/RT], where G is the average grain size at annealing time t, Go the initial average grain size, P the pressure, R the gas constant and T is the absolute temperature, with n = 2.6 +/- 0.4, log(10) k(0) = -7.5 +/- 1.7 m(2.6)/s. E* = 262 +/- 30 kJ/mol, V* = 4.7 +/- 0.7 cm(3)/mol. Compared at same pressure and temperature, grain-growth rate of ferropericlase is similar to olivine and faster than those of wadsleyite and ringwoodite. The present results show that, at the top of the lower mantle (P = 25 GPa and T = 1773 10 grain size of ferropericlase in single phase system evolves to similar to 2 x 10(-2) m after significant geological time (10 My) while a previous study predicts that grain size of MgO in two-phase system is as small as similar to 8 x 10(-6) in at same condition. (C) 2008 Elsevier B.V. All rights reserved

DOI： 10.1016/j.pepi.2008.04.002

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

High-pressure and high-temperature X-ray diffraction experiments on FeHx up to 20 GPa and 1598 K were performed using a Kawai-type multi-anvil apparatus, SPEED-MkII, installed at BL04B1 beam line of SPring-8 synchrotron facility. Iron powder was packed in a container made of NaCl, a very efficient sealing material for hydrogen under high pressure, together with a hydrogen source, LiAlH4. The temperature of hydrogenation, transition of iron hydride phases, and melting of gamma-FeHx were all determined in situ in the pressure range between 10 and 20 GPa. Hydrogen concentration in both epsilon'- and gamma-FeHx phases reached x = 1.0 above 10 GPa. Melting temperatures of gamma-FeH were determined to be 1473, 1448 +/- 25, 1538 +/- 15, 1548 +/- 25 and 1585 +/- 13 K at 10, 11.5,15,18 and 20 GPa, respectively. These temperatures are nearly 700 K lower than that of pure iron under the corresponding pressures. The Clapeyron-slope (dT/dP slope) of the melting curve of gamma-FeH is 13 K/GPa, which is significantly smaller than those of other possible core constituents (Fe, FeO, FeS). By extrapolating the epsilon'-gamma phase boundary linearly and the melting curve of gamma-FeH based on Lindemann's melting law, the triple point of epsilon'- and gamma-FeH and iron hydride melt is located at P = 60 GPa and T = 2000 K. Beyond the triple point, an attempt to construct a melting curve of epsilon'-FeH by the Lindemann's law using estimated thermal equation of state of epsilon'-FeH was unsuccessful. Therefore, we decided, instead, to extrapolate the melting curve of gamma-FeH beyond the triple point to 135 GPa yielding the melting temperature of FeH similar to 2600 K at core mantle boundary (CMB). Based on these results, we propose that the temperature of the Earth's outer core could be much lower than current estimates, if the Earth's outer core incorporated significant amounts of hydrogen. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2008.05.017

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

In the upper mantle, the X discontinuity at the depths of 240 to 340 km is observed in many localities, but its origin is under debate. The phase transformation of (Mg, Fe) SiO3 from orthopyroxene to high-pressure clinopyroxene has been proposed to cause this discontinuity. In this study, in situ X-ray diffraction experiments were performed, and the orthoenstatite/high-pressure clinoenstatite (C-2/c) phase boundary in the MgSiO3 system was determined. All the experiments were carried out using a Kawai-type multianvil apparatus installed at BL04B1 in SPring-8, Hyogo, Japan. Two types of experiments were carried out: (1) "phase observation experiments" at varying pressures and temperatures and (2) "quench experiments" at fixed pressure and temperature. The phase boundary, determined precisely by integrating the results of both sets of experiments, was found to be P (GPa) = 0.0035T (degrees C) + 3.7, using a recent MgO pressure scale. The orthoenstatite/high-pressure clinoenstatite phase boundary at 1400 degrees C determined here is 0.7-1.0 GPa lower than previous reports based on quench experiments. The phase transformation of orthopyroxene is expected to occur at 260 km depth along a typical mantle geotherm, and the shallower part of the observed X discontinuity can be explained by this phase transformation.

DOI： 10.1029/2008JB005894

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

In order to determine an accurate and reliable high-pressure and high-temperature equation of state (EOS) of MgO, unified analyses were carried out for various pressure-scale-free experimental data sets measured at 1 atm to 196 GPa and 300-3700 K, which are zero-pressure thermal expansion data, zero-pressure and high-temperature adiabatic bulk modulus (K-S) data, room temperature and high-pressure KS data, and shock compression data. After testing several EOS models based on the Mie-Gruneisen-Debye description for the thermal pressures with the Vinet and the third-order Birch-Murnaghan equations for the 300-K isothermal compression, we determined the K'(T0) and gamma(V) using a new functional form gamma = gamma(0){1 + a[(V/V-0)(b)-1]} to express the volume dependence of the Gruneisen parameter. Through least squares analyses with prerequisite zero-pressure and room temperature properties of V-0, K-S0, alpha(0), and C-P0, we simultaneously optimized a set of parameters of K'(T0), gamma(0), alpha, and b required to represent the P-V-T EOS. Determined new EOS models of MgO successfully reproduced all the analyzed P-V-T-K-S data up to 196 GPa and 3700 K within the uncertainties, and the total residuals between calculated and observed pressures were found to be 0.8 GPa in root mean squares. These EOS models, even though very simple, are able to reproduce available data quite accurately in the wide pressure-temperature range and completely independent from other pressure scales. We propose these models for primary pressure calibration standards applicable to quantitative high-pressure and high-temperature experiments.

DOI： 10.1029/2008JB005813

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

Phase relations in the system MgO-FeO-SiO2 were investigated between 22 and 47 GPa at 1500 degrees C and 2000 degrees C using multianvil apparatus with sintered diamond anvils. Synthesized samples were analyzed with electron microprobe, analytic transmission electron microscopy, and X-ray diffraction using synchrotron radiation. Univariant compositions of (Mg,Fe)SiO3 perovskite and (Mg,Fe)O magnesiowustite coexisting with SiO2 stishovite were determined as functions of pressure and temperature. The maximum iron solubility in perovskite corresponding to the univariant composition gradually increases with increasing pressure and temperature to be more than 30 mol % at 2000 degrees C and pressures above 40 GPa, and a significant pressure effect was found in Fe-Mg partitioning between perovskite and magnesiowustite in pressures between 22 and 35 GPa. The iron content of magnesiowustite dramatically increases from 50 to greater than 90 mol % with increasing pressure, and the Fe-Mg distribution coefficients between perovskite and magnesiowustite, K-D = (X-Fe(Pv)/X-Mg(Pv))/(X-Fe(Mw)/X-Mg(Mw)), decrease to less than 0.05. This significant pressure effect in Fe-Mg partitioning causes strong concentration of ferrous iron in magnesiowustite with increasing depth in the lower mantle.

DOI： 10.1029/2008JB005891

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Large-strain plastic deformation experiments of wadsleyite and olivine were conducted using a rotational Drickamer apparatus (RDA) up to pressure and temperature conditions corresponding to the Earth's mantle transition zone. Sintered ring-shaped (Mg,Fe)(2)SiO4 wadsleyite and olivine samples were deformed at P similar to 16 GPa and T=1600 and 1800 K, and P similar to 11 GPa and T=1800 K, respectively, with equivalent strain rate of epsilon(over dot)(E) similar to 6 x 10(-5) s(-1). In situ observations of deforming samples were carried out using the synchrotron radiation facility at Brookhaven National Laboratory, NSLS, X17B2. Stress was measured by X-ray diffraction at six different angles with respect to the compression axis. The stress estimated by X-ray diffraction was in good agreement with the stress estimated from dislocation density (for olivine). Strain was determined using X-ray radiographs of a strain marker (Re or Mo foil). Deformation of samples with a RDA involves both uniaxial compression and simple shear. A new formulation is developed to analyze both components to determine the theological properties of a sample. Stress-strain curves show strain-hardening up to the equivalent strain of epsilon(E) similar to 0.2 followed by the quasi-steady state deformation. Wadsleyite is found to be stronger than olivine compared at similar conditions and the creep strength of olivine at P similar to 11 GPa is much higher than those at lower pressures. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2008.03.003

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

Pressure-volume-temperature relations have been measured to 20.6 GPa and 1273 K for Fe-and Al-bearing phase D (Mg0.99Fe0.12Al0.09Si1.75H2.51O6) using synchrotron X-ray diffraction with SPEED-MkII multianvil press at SPring-8 facility. The analysis of room temperature data fitted to a third-order Birch-Murnaghan equation of state (EOS) yields V-0 = 85.32 +/- 0.02 angstrom(3); K-0 = 141.5 +/- 3 GPa and K' = 6.2 +/- 0.4. The pressure was calibrated using the Au EOS by Anderson et al. (1989). Fixing K' to 4.0, gives K-0 = 155.3 +/- 0.8 GPa. These values are consistent with thermal EOS analysis as well as previous estimations for Fe-Al-bearing and Fe-Al-free phase D. A fit to high-temperature P-V-T data using Birch-Murnaghan EOS yields V-0 = 85.32 +/- 0.02 angstrom(3); K-0 = 139.6 +/- 3.0 GPa; K' = 6.6 +/- 0.4; (partial derivative K-T/partial derivative T)(P) = -0.023 (8) GPa K-1 and zero-pressure thermal expansion alpha = a(0) + a(1)T with a(0) = 3.4 (2) x 10(-5) K-1 and a(1) = 0.4 (6) x 10(-8) K-1. The estimated Anderson-Gruneisen parameter is partial derivative(T) = 4.9. Lattice dynamical approach using the Mie-Gruneisen-Debye EOS yields Gruneisen parameter gamma(0) = 1.09 +/- 0.09 and q = 0.42 +/- 0.97, if Debye temperature theta(0) fixed at 920 K, as calculated from sound velocities. The EOS from this study enables the accurate estimation of the density of phase D in a pyrolitic composition under deep mantle conditions. The density reduction of hydrated subducting slab (similar to 1 wt.% H2O) in the lower mantle due to the presence of similar to 7% of phase D would be 1.0%.

DOI： 10.1029/2007JB004937

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MINERALOGICAL SOC AMER  

The effect of chemical environment on the hydrogen-related defect chemistry in wadsleyite was investigated using Fourier-transform infrared (FTIR) spectroscopy. Samples were annealed at P = 14-16 GPa and T = 1230-1973 K using Kawai-type multi-anvil apparatus. The effect of oxygen fugacity (f(O2)) was investigated using three metal-oxide buffers (Mo-MoO2, Ni-NiO, and Re-ReO2)The effect of water fugacity (f(H2O)) was studied using two different capsule assemblies ("nominally dry" and "dry" assemblies). A range of total OH concentration (C-OH,(Total)) of studied wadslyeites varies between &lt;50 H/10(6)Si (&lt;3 wt ppm H2O) and 23 000 H/10(6)Si (1400 wt ppm H2O). The observed FTIR spectra were classified into four different classes, i.e., peaks at 3620 ("3620"), 3480 ("3480"), and 3205 cm(-1) ("3205") and the others (Group O), where the Group O includes peaks at 3270, 3330, and 3580 cm(-1). The variation in OH concentration corresponding to each peak was analyzed separately. The OH concentrations correspond to "3620," "3480," and "3205" were found to be highly dependent on both f(H2O) and f(O2). Assuming C-OH,(Group) (O) = 2[(2H)(M)(x)] (C-OH,(Group) (O) is OH concentration of Group O), present data were analyzed by using thermodynamic model for concentration of hydrogen-related defects. Based on analytical results, OH concentration of "3620" and "3480" was found to be reasonably explained by q = 1/2 and r = 1/12 (q and r are f(H2O) and f(O2) exponents, respectively), whereas that of "3205" was consistent with q = 1/2 and r = -1/12. These results suggest that "3620" and "3480" correspond to H whereas "3205" corresponds to H center dot, respectively, under the charge neutrality condition of [Fe-M(')] = 2[V-M(")].

DOI： 10.2138/am.2008.2653

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Language：Japanese  

In this article, recent technical developments in high-pressure deformation experiments especially in the field of Earth science are reviewed. The diamond anvil cell has an advantage in performing deformation experiments at very high pressures (up to 160 GPa) compared to other large-volume apparatuses. However, diamond anvil cell has severe limitation in quantitative strain measurements, deformation at high temperatures and deformation with large strain. On the other hand, quantitative rheological measurements at relatively high pressures (up to 10-20 GPa) and high temperatures (up to 1000-2000 K) are possible by using recently developed large-volume deformation apparatuses, rotational Drickamer apparatus, deformation-DIA and "big D-DIA". Synchrotron X-ray is a powerful tool for in-situ strain and stress measurements in high-pressure deformation experiments using these apparatuses.

DOI： 10.4131/jshpreview.18.223

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Pressure-volume-temperature relations have been measured to 27 GPa and 1373 K for superhydrous phase B (Mg10Si3O14(OH)(4)) using synchrotron X-ray diffraction with a multi-anvil apparatus at the SPring-8 facility. The analysis of room-temperature data fitted to a third-order Birch-Murnaghan equation of state (EOS) yields V-0 = 623.38 +/- 0.39 angstrom(3); K-0 = 138.7 +/- 3.0 GPa and K' = 4.9 +/- 0.3, when pressure was calibrated using the An EOS of Anderson et al. [Anderson, O.L., Issak, D.G., Yamamoto, S., 1989. Anharmonicity and the equation of state for gold. J. Appl. Pbys. 65, 1534-1543]. These values are consistent with subsequent thermal EOS analysis and previous estimations for superhydrous phase B. A fit of P-V-T data to high-temperature Birch-Murnaghan EOS yields V-0 = 623.47 +/- 0.37 angstrom(3); K-0 = 135.8 +/- 2.6 GPa; K' = 5.3 +/- 0.2; (partial derivative K-T/partial derivative T)(P) = -0.026 +/- 0.003 GPa/K and zero-pressure thermal expansion alpha = a(0) + a(1) T with a(0) = 3.2 (1) x 10(-5) K-1 and a(1) = 1.2 (4) x 10(-8) K-1. The Anderson-Gruneisen parameter is estimated to be delta(T) = 5.4. A fit to the thermal pressure EOS gives V-0 = 623.50 +/- 0.36 angstrom(3); K-0 = 135.3 +/- 2.3 GPa; K'= 5.3 +/- 0.2; (partial derivative K-T/partial derivative T)v = -0.002 (2) GPa/K and alpha(0) = 3.8 (2) x 10(-5) K-1. The lattice dynamical approach using a Mie-Gruneisen-Debye EOS yields Gruneisen parameter gamma(0) = 1.33 +/- 0.05 and q = 2.03 +/- 0.35, if the Debye temperature theta(0) is fixed at 860 K, as calculated from sound velocities. The analysis of axial compressibility and thermal expansivity indicates that the a-axis is more compressible (K-Ta = 126 +/- 13 GPa) than the b-axis (K-Tb = 137 +/- 1 GPa) and c-axis (K-Tc = 143 +/- 1 GPa). The temperature dependence of K-T is stronger for the b-axis, (partial derivative K-T/partial derivative T)(Pb) = -0.033 (3) GPa/K, than for the a-axis (partial derivative K-T/partial derivative T)(Pa) = -0.028 (7) GPa/K and c-axis (partial derivative K-T/partial derivative T)(Pc) = -0.017 (3) GPa/K. The present EOS enables us to accurately estimate the density of superhydrous phase B in a pyrolitic composition under deep mantle conditions. The density reduction of hydrated subducting slab (similar to 1 wt.% H2O) at the top of the lower mantle due to the presence of similar to 18% of superhydrous phase B would be 1.9-2.1 %. Accordingly, a model slab that is homogeneously hydrated may be buoyant relative to the surrounding mantle rocks and would not penetrate to the deep lower mantle. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2007.06.003

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Many physical properties of liquid-bearing rocks in the deep Earth's interior are strongly controlled by its wetting behavior. We report experimental results on the variation of dihedral angle and micro structures in the forsterite-H2O system at 1200 degrees C and pressures ranging from I to 13 GPa. The dihedral angle of the system decreases systematically with pressure and above the mantle transition zone (similar to 400 km depth) it becomes approximately 0 degrees, corresponding to completely wetted grain boundaries. This condition is probably reached because of a decrease in the solid-liquid interfacial energy with pressure due to the dramatically increased solubility of silicates in the liquid. These results suggest that the presence of partial melt would have drastic influences on physical properties of upper mantle around the transition zone even if the melt fraction is very low. Low velocity regions just above the mantle transition zone may result from the presence of hydrous melt. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2007.02.002

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Grain-growth kinetics in wadsleyite was investigated using a multianvil high-pressure apparatus. Fine-grained wadsleyite aggregates gates were synthesized by isostatic hot-pressing and were subsequently annealed under high pressure and temperature in a controlled chemical environment. Wadsleyite samples show normal grain-growth characterized by a log-normal grain-size distribution following the relation, L-n - L-0(n) = kt where it is a constant, L the grain-size at time t, L-0 the grain-size at time t = 0 and k is a rate constant that depends on temperature T and chemical environments (f(O2): oxygen fugacity in Pa, C-OH: water content in H/10(6)Si) as:
k=A'(D)f(O2)'(D) exp (-H-D*/RT) + A'wf'(w)(O2) C-OH(q) exp (-H-w*/RT)
with A'(-4.9 +/- 6.1(-8.0 +/- 7.4))(D) (m(n) s(-1) Pa-rD), r(D) = 0.12 +/- 0.11 (0.20 +/- 0.14), h(D)* = 410 +/- 230(500 +/- 270) U/mol, A'(w)= 10(-18.2 +/- 1.4(-24.0 +/- 1.7)) (m(n) s(-1) Pa-rw), r(W), = 0.14 +/- 0.05(0.22 +/- 0.06), q = 1.7 +/- 0.3(2.2 +/- 0.3) and H-W* = 120 +/- 60(160 +/- 70) KJ/mol with assumed value of n = 2(3) (values in parentheses denote parameters for it = 3). Both water and oxygen fugacities significantly enhance grain-growth kinetics. The large value of the parameter describing the water fugacity dependence, q similar to 1.5-2.5, cannot be explained solely by a simple model in which grain-growth is controlled by diffusion of atoms (defects) across the grain-boundaries The interaction of grain-boundaries with charged defects or the density of hydrated ledges may be important factors that control the grain-growth kinetics of wadsleyite. When compared at similar thermo-chemical conditions, grain-growth of wadsleyite is found to be more sluggish than grain-growth of olivine. The present results show that a small wadsleyite grain-size (&lt; 1 mm) in subducting slabs can be maintained for a significant geological time (similar to 1 My) under "dry" (&lt; 200 H/10(6)Si) conditions when the temperature is lower than 1500 K, whereas when a large amount of water (&gt; 100,000 H/10(6)Si) is present, a small grain-size (&lt; 1 mm) can only be maintained for a significant time at low temperatures (&lt; 600 K). (c) 2005 Elsevier B.V All rights reserved.

DOI： 10.1016/j.pepi.2005.08.002

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MINERALOGICAL SOC AMER  

Metallic coils (in most cases Cu coils) are often used in high-pressure experiments to protect thermocouple wires. In this paper we show that these coils have important influences on thermocouple EMF and therefore on the temperature measurements. We tested this effect by measuring EMF from Cu coiled single wires of chromel and alumel, and, further, we conducted experiments to compare the EMF from W5Re-W26Re thermocouples with and without Cu coils attached to them. The results show systematic differences in thermocouple readings; the EMFs from W-Re thermocouples with Cu coils give systematically lower values than EMFs from thermocouples without Cu coils. The results were analyzed using a simple model. The difference in thermocouple EMFs between thermocouples with and without protection coils is given by
Delta E-TC = E-2 - E1+/1 + R-2/R-1+ - E-2 - E1-/1 + R-2/R1-
where E-i and R-i are the EMF and the electrical resistance of metal i in the portion of the Cu coil, and the subscripts 1+, 1-, and 2 indicate positive thermocouple metal, negative thermocouple metal, and coil metal, respectively. The addition of a coil with different metal has a large effect - the Delta E-TC will be close to -(E1+ - E1-) &lt; 0 when the resistance of the coil is significantly smaller than that of a thermocouple wire. For a Cu coil and W-Re thermocouple, R-1+,R- 1- &gt;&gt; R-2 and therefore thermocouple readings with a Cu coil will lead to underestimation of the real temperature. Under common experimental conditions with a multi-anvil apparatus, the error in the temperature estimate caused by Cu protection coils is similar to 100-150 K for a peak temperature of 1600-2000 K.

DOI： 10.2138/am.2006.1883

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Language：English   Publishing type：Part of collection (book)   Publisher：Blackwell Publishing Ltd  

A new method is developed to determine the three-dimensional variation in water content, temperature, and other parameters such as major element chemistry or the melt fraction from anomalies in seismic wave velocities and attenuation. The key to this method is mineral physics observations indicating different sensitivity of seismic wave velocities and attenuation to temperature, water content and other parameters such as major element chemistry, melt fraction or grain-size. Our analysis shows that among these parameters, temperature and water content generally have a more important influence on seismic wave velocities and attenuation than other factors such as major element chemistry, which are important only in limited regions. The method is applied to the upper mantle beneath northern Philippine Sea including the Izu-Bonin subduction zone, where high-resolution velocity and attenuation tomographic models are available down to a depth of ~400 km. We show that the tomographic images of this region can be explained by lateral variations in temperature and water content, with only little influence of major element chemistry. A broad region of high attenuation with modestly low velocities at 300-400 km depth away from the slab in this region is interpreted as region of high water contents. We speculate that this water-rich region may have been formed by the efficient transport of water to deeper mantle by a fast (and cold) subducting slab in this region or water may come from the transition zone.

DOI： 10.1029/168GM17

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

In-situ synchrotron X-ray diffraction experiments were conducted using the SPEED-1500 multi-anvil press of SPring-8 on stishovite SiO2 and pressure-volume-temperature data were collected at up to 22.5 GPa and 1,073 K, which corresponds to the pressure conditions of the base of the mantle transition zone. The analysis of room-temperature data yielded V-0=46.56(1) Angstrom(3), K-T0=296(5) GPa and K'(T)=4.2(4), and these properties were consistent with the subsequent thermal equation of state (EOS) analyses. A fit of the present data to high-temperature Birch-Murnaghan EOS yielded(partial derivativeK(T)/partial derivativeT)(P)=-0.046(5) GPa K-1 and alpha=a+bT with values of a=1.26(11)x10 K-5(1) and b=1.29(17)x10 K-8(2). A fit to the thermal pressure EOS gives alpha(0)=1.62(9)x10(-5) K-1, (partial derivativeK(T) /partial derivativeT)(V)=-0.027(4) GPa K-1 and (partial derivative(2)P/partial derivativeT(2))(V)=27(5)x10(7) GPa K-1. The lattice dynamical approach by Mie-Gruneisen-Debye EOS yielded gamma(0)=1.33(6), q=6.1(8)and theta(0)=1160(120) K. The strong volume dependence of the thermal pressure of stishovite was revealed by the analysis of present data, which was not detectable by the previous high-temperature data at lower pressures, and this yields (partial derivativeK(T) /partial derivativeT) (V)not equal0 and qnot equal1. The analyses for the fictive volume for a and c axes show that relative stiffness of c axis to a axis is similar both on compression and thermal expansion. Present EOS enables the accurate estimate of density of SiO2 in the deep mantle conditions.

DOI： 10.1007/s00269-004-0426-7

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

In situ synchrotron X-ray diffraction experiments were conducted using the SPEED-1500 multi-anvil press at SPring-8 on majoritic garnet synthesized from natural mid-ocean ridge basalt (MORB), whose chemical composition is close to the average of oceanic crust, at 19 GPa and 2200 K. Pressure-volume-temperature data were collected using a newly developed high-pressure cell assembly to 21 GPa and 1273 K. Data were fit to the high-temperature Birch-Murnaghan equation of state, with fixed values for the ambient cell volume (V-0 = 1574.14(4)Angstrom(3)) and the pressure derivative of the isothermal bulk modulus (K-T' = 4). This yielded an isothermal bulk modulus of K-T0 = 173(1) GPa, a temperature derivative of the bulk modulus (deltaK(T)/deltaT)(P) = -0.022(5) GPa K-1, and a volumetric coefficient of thermal expansivity alpha = a + bT with values of a = 2.0(3) x 10(-5) K-1 and b = 1.0(5) x 10(-8) K-2. The derived thermoelastic parameters are very similar to those of pyrope. The density of subducted oceanic crust compared to pyrolitic mantle at the conditions in Earth's transition zone (410-660 km depth) was calculated using these results and previously reported thermoelastic parameters for MORB and pyrolite mineral assembledges. These calculations show that oceanic crust is denser than pyrolitic mantle throughout the mantle transition zone along a normal geotherm, and the density difference is insensitive to temperature at the pressures in lower part of the transition zone. (C) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2004.08.003

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DOI： 10.1029/2004JB003504

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DOI： 10.1016/B978-044451979-5.50010-7

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

In situ synchrotron X-ray diffraction (XRD) experiments were conducted using the SPEED-1500 multi-anvil press of SPring-8 on (Mg0.91Fe0.09)(2)SiO4 ringwoodite (Rw), whose composition is similar to that expected in the Earth's mantle transition zone. Pressure-volume-temperature data were collected using a NaCl or MgO capsule up to 21 GPa and 1273 K. A fit to high-temperature Birch-Murnaghan (HTBM) equation of state (EOS) with fixed values of ambient cell volume V-0 = 527.83(7) Angstrom(3) and isothermal bulk modulus K-T0 = 187 GPa yielded a pressure derivative of isothermal bulk modulus K'(T) = 4.41(1), a temperature derivative of bulk modulus (partial derivative(KT)/partial derivativeT)(P) = -0.028(5)GPaK(-1), and a volumetric thermal expansivity alpha = a + bT with values of a = 1.9(2) x 10(-5) K-1 and b = 1.2(4) x 10(-8) K-2. These properties are consistent with the analysis using the thermal pressure (Th-P) EOS. The derived K'(T) and (partial derivativeK(T)/partial derivativeY)(P) are consistent with previous studies on Mg2SiO4 ringwoodite. However, consistent with measurements at 0 GPa, the present equation of state yields significantly higher thermal expansivity than derived by diamond anvil experiments on Mg2SiO4 ringwoodite to 30 GPa and 700 K. On the basis of the equation of state, the density jump around 660 km depth expected for pyrolitic homogeneous mantle (caused by ringwoodite --&gt; Mg-perovskite (MgPv) + magnesiowustite (Mw) and garnet(GRT) --&gt; MgPv transitions) was estimated. The density jump calculated for pyrolite (9.2%) is significantly larger than that across the 660 km discontinuity derived by recent seismolocrical studies (4-6%). One possible explanation for this is that the recent seismic data reflect only the sharp transition concerned with the Rw --&gt; MgPv + Mw transition. (C) 2004, Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2003.02.001

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MINERALOGICAL SOC AMER  

In-situ synchrotron X-ray diffraction experiments were conducted using the MAX-III multianvil press of KEK on an omphacite (Di(63)Jd(37)), for which Di = Ca(Mg,Fe)Si2O6 and Jd = NaAlSi2O6. Pressure-volume-temperature data were collected at up to 10 GPa and 1000 K. A fit to the high-temperature Birch-Murnaghan equation of state yielded an isothermal bulk modulus K-70 = 126(1) GPa, an assumed pressure derivative of the bulk modulus K-T' = 4.0, a temperature derivative of the bulk modulus (partial derivativeK(T)/partial derivativeT)(p) = -0.015(4) GPa/K, and a volumetric thermal expansivity alpha = 2.2(1) x 10(-5) K-1, when the equation of state of NaCl by Brown (1999) is adopted for the pressure scale. The derived K-T0 value is consistent with the linear interpolations from K-T0 values for diopside and jadeite in the literature.

DOI： 10.2138/am-2003-0110

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To determine the reaction boundary dolomite = aragonite + magnesite, in situ X-ray experiments on dolomite decomposition and synthesis were carried out in the temperature range 900 to 1300 K. Dolomite decomposition experiments were conducted with increasing pressure at constant temperature, and the boundary was determined to be 5.3-5.9 GPa in the temperature range 800-1200 K and 5.9-6.3 GPa at 1300 K. Dolomite synthesis experiments were carried out with decreasing pressure at constant temperature or with increasing temperature at constant press load. The dolomite synthesis boundary was determined to be 6.7-6.9 GPa at 1300 K, 3.7-4.4 GPa at I 100 K, and 2-3 GPa at 800 K. Except at 1300K, the synthesis boundary is much lower in pressure and has a steeper dP/dT slope than the decomposition boundary. The difference in the reaction boundary reflects the different kinetics between decomposition and synthesis reactions, and the former may be closer to the equilibrium phase boundary. The experimental results show that the phase boundary between dolomite and aragonite + magnesite is located at similar to6.4 GPa at 1300 K and has a dP/dTslope of 0.001 +/- 0.001 GPa/ K in the temperature range 900 to 1200 K.

DOI： 10.2138/am-2002-0715

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Knowledge of the mineralogical constituents of the Earth's mantle depends heavily on high-P experiments of pyrolite composition. In order to understand the planetary interior better, phase relations and mineral physics properties of compositions other than pyrolite may also be important. High-P and high-T experiments were conducted on an Al-depleted komatiite which can be regarded as a kind of piclogite composition. Fourteen experiments were carried out along a model geotherm between 5 and 23 GPa and 1100 and 1600 degreesC with a multi-anvil apparatus. Analyses of quenched run products showed that, in the studied komatiite, the fractions of olivine and its high-P polymorphs (wadsleyite and ringwoodite) are 40-50 vol%, pyroxene-garnet phase transition occurs at 13-17 GPa (while the respective values for pyrolite are similar to 60 vol% and 12-15 GPa). The density and seismic velocity profiles of komatiite mantle were calculated using thermoelastic parameters of related minerals, and they showed quite good agreements with those of seismic observations around the transition zone as well as those for pyrolite. (C) 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0012-821X(01)00378-8

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Language：Japanese   Publisher：Japan Association of Mineralogical Sciences  

Deformation experiments on hydrous melt-bearing dunite were conducted under upper mantle conditions, in order to explore the effect of intergranular fluids on the plastic flow of olivine in Earth's upper mantle. The creep strength of hydrous melt-bearing dunite was about 2 times lower than the dislocation creep strength of hydrous olivine under these experimental conditions. The strain rate was proportional to differential stress to the 2.1 power, and the differential stress markedly increased with increase in grain size. These observations show that grain boundary sliding dominated the deformation of olivine (i.e., superplasticity). Superplasticity is the dominant creep mechanism of olivine in fluid-bearing fine-grained peridotites under low-temperature and high-stress conditions

DOI： 10.14824/jakoka.2011.0.45.0

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In order to clarify the dominant deformation mechanism in the upper mantle, we have conducted deformation experiments at pressure and temperature conditions of 3.0–5.3 GPa and 1473–1573 K, respectively, using fine-grained (grain size of &sim;1 um) forsterite aggregate. The analysis of stress-strain rate data taken at dry conditions using a flow law equation yielded the activation volumes of &sim;7 and &sim;11 cm3/mol for diffusion creep and dislocation creep accommodated grain-boundary sliding, respectively. The present results implies that the diffusion creep is the predominant deformation mechanism at the most conditions of pressure, temperature and strain-rate in the upper mantle.

DOI： 10.14824/jakoka.2011.0.47.0

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Language：English   Publisher：AMER GEOPHYSICAL UNION  

DOI： 10.1029/2010JB007959

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Language：English   Publishing type：Research paper, summary (international conference)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

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Language：English   Publishing type：Book review, literature introduction, etc.   Publisher：AMER GEOPHYSICAL UNION  

[1] Chemical differentiation from pyrolite to harzburgite due to partial melting and melt extraction process causes the chemical heterogeneity in Earth's upper mantle that can be detected by seismological observations. The variation in major element chemistry in natural samples reflects complicated processes that include not only partial melting but also other various magmatic processes. On the basis of a comparison of chemical and mineralogical compositions of natural peridotites with those from melting experiment, density and seismic velocities of various peridotites are calculated for the range of pressure and temperature in the upper mantle using the latest data on mineral thermoelasticity. We conclude that the seismic velocities of shallow oceanic peridotites is characterized by a single parameter such as Mg # ( molar ratio Mg/( Mg + Fe)), whereas the characterization of the deep continental peridotites requires two parameters, Mg # and Opx # ( volume fraction of orthopyroxene). In agreement with previous studies, we find that in spinel stability field, the seismic velocities have positive correlation with Mg # from pyrolite to residual harzburgite, while in garnet stability field, seismic velocities of residual harzburgite are indistinguishable from those of pyrolite. The seismic velocities of the deep continental peridotites are lower than those of pyrolite and residual harzburgite because of the high concentration of orthopyroxene with low seismic velocities and have large pressure dependence. A jump of seismic velocity will occur at 300 km in orthopyroxene-rich continental harzburgite due to the orthorhombic to high-pressure monoclinic phase transition in ( Mg, Fe) SiO3 pyroxene. This phase transition may correspond to the X discontinuity.

DOI： 10.1029/2004JB003504

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