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

To study the viscosity of bridgmanite and ferropericlase aggregate, uniaxial compression deformation experiments on pre-synthesized post-spinel phase and bridgmanite two-layered samples were conducted under top lower mantle pressure and 1773 K utilizing DT-Cup apparatus. Up to the strain of 0.25 ± 0.05, the observed comparable strain of the bridgmanite and post-spinel samples suggests the bridgmanite dominates the bulk viscosity of the post-spinel without strain localization in periclase. The microstructures of the deformed post-spinel samples show evidence of a similar strain of periclase with the bulk strain without strain partitioning. Texture analyses of bridgmanite indicate a dominant slip plane (100), with a steady state fabric strength achieved within the strain of 0.12 ± 0.01. The current experiment has provided no evidence about an onset of strain localization of ∼30 vol.% periclase at 0.25 strain. Our observations provide direct experimental verification of bridgmanite controlled rheology under low strain magnitude, which should be considered in geodynamical models which include mantle compositional and rheological evolution in the lower mantle.

DOI： 10.1029/2021JB023586

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

Anelastic measurement by cyclic loading under high pressure has been developed by means of in situ X-ray observation at a synchrotron facility. In this method, the reference material is a key factor to precisely determine attenuation and moduli of unknown materials. We compared the performance of three types of reference materials (dense polycrystalline alumina, alumina single-crystal parallel to c-axis, and flexible graphite) under the pressure of 3 GPa and the temperature range between 1173 and 1373 K. The phase lags of strain between reference materials and samples show that the flexible graphite is less attenuated than dense polycrystalline alumina and alumina single crystal in various periods. The strain ratios show that the flexible graphite is much softer and can produce the measurable strain in the limited displacement. The flexible graphite, as reference material, is more excellent to detect the relatively lower energy dispersion of mantle minerals at high pressure.

DOI： 10.1080/08957959.2021.2013834

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Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

In the lower part of the mantle transition zone, seismic polarization anisotropies, which could be caused by the lattice preferred orientation (LPO) of elastically anisotropic minerals, were observed related with subducted materials. Stishovite, which is one of the dominant minerals in mid-ocean ridge basalt, continental crust and sediment layers, possesses significant anisotropic elasticity and has high potential to contribute to the observed seismic anisotropy. In this study, three types of deformation experiments (uniaxial compression, uniaxial tension and shear) on polycrystalline stishovite were conducted using either a D-DIA apparatus or a D-111 type apparatus with a Kawai-type cell assembly to investigate the LPO of stishovite developed during deformation at pressure of 12 GPa and temperatures of 1600 and 1800 °C. The obtained LPO patterns in all experiments are consistent each other and they suggested the dominant slip is in the [001] direction dispersed on the {110} and {100} planes with [001]{110} slightly more dominant, thus we concluded that the dominant slip system is [001]{hk0}. Based on the present results, the fast vertically and horizontally polarized shear wave anisotropy observed in the lower part of the mantle transition zone could be explained by the LPO of stishovite with vertical and horizontal flow, respectively, related with subducted materials.

DOI： 10.1016/j.pepi.2020.106546

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Publishing type：Research paper (scientific journal)   Publisher：Informa UK Limited  

DOI： 10.1080/08957959.2020.1791107

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Mineralogical Society of America  

<title>Abstract</title>
The pressure dependence of Si diffusion in γ-Fe was investigated at pressures of 5–15 GPa and temperatures of 1473–1673 K using the Kawai-type multi-anvil apparatus to estimate the rate of mass transportation for the chemical homogenization of the Earth's inner core and those of small terrestrial planets and large satellites. The obtained diffusion coefficients D were fitted to the equation D = D0 exp[−(E* + PV*)/(RT)], where D0 is a constant, E* is the activation energy, P is the pressure, V* is the activation volume, R is the gas constant, and T is the absolute temperature. The least-squares analysis yielded D0 = 10-1.17±0.54 m2/s, E* = 336 ± 16 kJ/mol, and V* = 4.3 ± 0.2 cm3/mol. Moreover, the pressure and temperature dependences of diffusion coefficients of Si in γ-Fe can also be expressed well using homologous temperature scaling, which is expressed as D = D0exp{–g[Tm(P)]/T}, where g is a constant, Tm(P) is the melting temperature at pressure P, and D0 and g are 10-1.0±0.3 m2/s and 22.0 ± 0.7, respectively. The present study indicates that even for 1 billion years, the maximum diffusion length of Si under conditions in planetary and satellite cores is less than ∼1.2 km. Additionally, the estimated strain of plastic deformation in the Earth's inner core, caused by the Harper–Dorn creep, reaches more than 103 at a stress level of 103–104 Pa, although the inner core might be slightly deformed by other mechanisms. The chemical heterogeneity of the inner core can be reduced only via plastic deformation by the Harper–Dorn creep.

DOI： 10.2138/am-2020-7197

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Language：English  

Thermochemical heterogeneities detected today in the Earth's mantle could arise from ongoing partial melting in different mantle regions. A major open question, however, is the level of chemical stratification inherited from an early magma-ocean (MO) solidification. Here we show that the MO crystallized homogeneously in the deep mantle, but with chemical fractionation at depths around 1000 km and in the upper mantle. Our arguments are based on accurate measurements of the viscosity of melts with forsterite, enstatite and diopside compositions up to ~30 GPa and more than 3000 K at synchrotron X-ray facilities. Fractional solidification would induce the formation of a bridgmanite-enriched layer at ~1000 km depth. This layer may have resisted to mantle mixing by convection and cause the reported viscosity peak and anomalous dynamic impedance. On the other hand, fractional solidification in the upper mantle would have favored the formation of the first crust.

DOI： 10.1038/s41467-019-14071-8

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Publishing type：Research paper (scientific journal)   Publisher：Informa UK Limited  

DOI： 10.1080/08957959.2019.1689975

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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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Publishing type：Research paper (scientific journal)   Publisher：Japan Association of Mineralogical Sciences  

DOI： 10.2465/gkk.191226

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

The Fe-bearing wadsleyite-ringwoodite phase transition loop under dry conditions in a temperature range of 1473 and 1873 K was determined by in situ X-ray diffraction experiments at the synchrotron facility SPring-8. Pressure at high temperature was precisely determined within a 0.23 GPa error using in situ X-ray diffraction of MgO as a pressure standard. Under dry conditions, assuming an equilibrium chemical composition of wadsleyite and ringwoodite coexisting with garnet in a pyrolite model and an adiabatic temperature gradient with a potential temperature of 1550-1650 K, the phase transition depth and effective width of the seismic discontinuity were found to be 500-514 and 20-22 km, respectively. This effective width, which is three times greater than that of the olivine-wadsleyite phase boundary, can reflect a seismic wave of approximately 0.25 Hz. The wider transition loop between wadsleyite and ringwoodite could create a broad seismic discontinuity. Considering wet and oxidized conditions, the depth of the wadsleyite-ringwoodite phase boundary could be greater than 520 km assuming the small temperature dependency on water and oxygen fugacity effects. Variation in the depth of seismic anomaly may be attributed to water content or oxygen fugacity of the transition zone.

DOI： 10.2138/am-2019-6823

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier B.V.  

Oxygen self-diffusion coefficients (DOx) were measured in single crystals of dry synthetic iron-free olivine (forsterite, Mg2SiO4) at a temperature of 1600 K and under pressures in the range 10−4 to 13 GPa, using a Kawai-type multi-anvil apparatus and an ambient pressure furnace. Diffusion profiles were obtained by secondary ion mass spectrometry operating in depth profiling mode. DOx in forsterite increases with increasing pressure with an activation volume of −3.9 ± 1.2 cm3/mol. Although Mg is the fastest diffusing species in forsterite under low-pressure conditions, O is the fastest diffusing species at pressures greater than ∼10 GPa. Si is the slowest throughout the stable pressure range of forsterite. Based on the observed positive and negative pressure dependence of DOx and DMg (Mg self-diffusion coefficient), respectively, DOx + DMg in forsterite decreases with increasing pressure, and then increases slightly at pressures greater than 10 GPa. This behavior is in agreement with the pressure dependence of ionic conductivity in forsterite based on conductivity measurements (Yoshino et al., 2017), and can be used to explain the conductivity increase from ∼300 km depth to the bottom of the asthenosphere.

DOI： 10.1016/j.pepi.2017.12.005

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

We developed methods to use synthesized boron-doped diamond (BDD) as a heater in a multi-anvil high-pressure apparatus. The synthesized BDD heater could stably generate an ultra-high temperature without the issues (anomalous melt, pressure drop, and instability of heating) arising from oxidation of boron into boron oxide and graphite-diamond conversion. We synthesized BDD blocks and tubes with boron contents of 0.5-3.0 wt.% from a mixture of graphite and amorphous boron at 15 GPa and 2000 degrees C. The electrical conductivity of BDD increased with increasing boron content. The stability of the heater and heating reproducibility were confirmed through repeated cycles of heating and cooling. Temperatures as high as similar to 3700 degrees C were successfully generated at higher than 10 GPa using the BDD heater. The effect of the BDD heater on the pressure-generation efficiency was evaluated using MgO pressure scale by in situ X-ray diffraction study at the SPring-8 synchrotron. The pressure-generation efficiency was lower than that using a graphite-boron composite heater up to 1500 tons. The achievement of stable temperature generation above 3000 degrees C enables melting experiments of silicates and determination of some physical properties (such as viscosity) of silicate melts under the Earth's lower mantle conditions. Published by AIP Publishing.

DOI： 10.1063/1.4993959

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER ASSOC ADVANCEMENT SCIENCE  

An opesn question for solid-earth scientists is the amount of water in Earth's interior. The uppermost mantle and lower mantle contain little water because their dominant minerals, olivine and bridgmanite, have limited water storage capacity. In contrast, the mantle transition zone (MTZ) at a depth of 410 to 660 km is considered to be a potential water reservoir because its dominant minerals, wadsleyite and ringwoodite, can contain large amounts of water [up to 3 weight % (wt %)]. However, the actual amount of water in the MTZ is unknown. Given that water incorporated into mantle minerals can lower their viscosity, we evaluate the water content of the MTZ bymeasuring dislocationmobility, a property that is inversely proportional to viscosity, as a function of temperature and water content in ringwoodite and bridgmanite. We find that dislocation mobility in bridgmanite is faster by two orders of magnitude than in anhydrous ringwoodite but 1.5 orders ofmagnitude slower than inwater-saturated ringwoodite. To fit the observed mantle viscosity profiles, ringwoodite in the MTZ should contain 1 to 2 wt % water. The MTZ should thus be nearly water-saturated globally.

DOI： 10.1126/sciadv.1603024

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

Knowledge of grain growth rate of epsilon-iron can put constraint on estimation of the grain size in the inner core. We determined grain growth rate of epsilon-iron at similar to 55 GPa and 1200-1500 K by means of in-situ X-ray diffraction observation to be G(n) - G(0)(n)= kt, where G (m) is the grain size at time t (s), G(0) (m) is the initial grain size, n is growth exponent (fixed to 2) and k is the growth constant expressed as k = k(0) exp(-H*/RT) with log k(0) (m(n)/s) =-5.8(+/- 2.4) and activation enthalpy H* = 221(+/- 61) kJ/mol, and R is the gas constant and T is the absolute temperature. Extrapolation of the grain growth law of epsilon-iron to the inner core conditions suggests that the grain size in the inner core is in a range from several hundred meters to several kilometers, which is intermediate among the previous estimations, and hence the dominant deformation mechanism is considered to be Harper-Dorn creep rather than diffusion creep as pointed out by the previous work. This indicates the relatively uniform viscosity in the entire inner core. 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2016.11.049

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

Diffusion of Si and 0 in single crystal stishovite was examined at pressures of 14.0-21.5 GPa and temperatures of 1673-2073 K. Self-diffusion coefficients of Si (D-si) and O (D-o) were determined as D-si; [m(2)/s] = 2.4 x 10(-12) exp{-(237 [kJ/mol] + 6.0 [cm(3)/mol] x P)/RT} and D-o [m(2)/s] = 7.2 x 10(-11) exp{-(263 [kJ/mol] + 4.8 [cm(3)/mol] x P)/RT}, respectively, where P is pressure (in GPa), T is absolute temperature (in K) and R is the ideal gas constant. It was revealed that diffusion of Si is approximately one order of magnitude slower than that of 0 and, thus, Si is the rate-controlling element for plastic deformation of stishovite. Si diffusion in stishovite is assessed to be at least three orders of magnitude slower than that in bridgmanite under mid-mantle conditions. Therefore, it is anticipated that highly viscous SiO2-rich components subducted into the lower mantle persist as the seismic reflectors for long term without mixing up with the bridgmanite-dominated surrounding mantle. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2016.11.044

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

We have expanded the pressure ranges at room and high temperatures generated in a Kawai-type multi-anvil apparatus (KMA) using tungsten carbide (WC) anvils with a high hardness of H-v=2700 and a Young's modulus of 660GPa. At room temperature, a pressure of 64GPa, which is the highest pressure generated with KMA using WC anvils in the world, was achieved using 1 degrees-tapered anvils with a 1.5-mm truncation. Pressures of 48-50GPa were generated at high temperatures of 1600-2000K, which are also higher than previously achieved. Tapered anvils make wide anvil gaps enabling efficient X-ray diffraction. The present pressure generation technique can be used for studying the upper part of the Earth's lower mantle down to 1200km depth without sintered diamond anvils.

DOI： 10.1080/08957959.2017.1375491

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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：AMER INST PHYSICS  

To determine the anelastic properties of materials of the Earth's interior, a short-period cyclic loading system was installed for in situ X-ray radiographic observation under high pressure to the multi-anvil deformation DIA press at the bending magnet beam line BL04B1 at SPring-8. The hydraulic system equipped with a piston controlled by a solenoid was designed so as to enable producing smooth sinusoidal stress in a wide range of oscillation period from 0.2 to 100 s and generating variable amplitudes. Time resolved X-ray radiography imaging of the sample and reference material provides their strain as a function of time during cyclic loading. A synchrotron X-ray radiation source allows us to resolve their strain variation with time even at the short period (&lt; 1 s). The minimum resolved strain is as small as 10(-4), and the shortest oscillation period to detect small strain is 0.5 s. Preliminary experimental results exhibited that the new system can resolve attenuation factor Q(-1) at upper mantle conditions. These results are in quantitative agreement with previously reported data obtained at lower pressures. Published by AIP Publishing.

DOI： 10.1063/1.4963747

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

This research shows that small animals, tardigrades (Milnesium tardigradum) in tun (dehydrated) state and Artemia salina cists (dried eggs) can tolerate the very high hydrostatic pressure of 7.5 GPa. It was really surprising that living organisms can survive after exposure to such a high pressure. We extended these studies to the extremely high pressure of 20 GPa by using a Kawai-type octahedral anvil press. After exposure to this pressure for 30 min, the tardigrades were soaked in pure water and investigated under a microscope. Their bodies regained metabolic state and no serious injury could be seen. But they were not alive. A few of Artemia eggs went part of the way to hatching after soaked in sea water, but they never grew any further. Comparing with the case of blue-green alga, these animals are weaker under ultra-high pressure.

DOI： 10.1080/23311940.2016.1167575

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DOI： 10.1016/j.epsl.2015.11.014

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

It was shown in our previous reports that a few spores of moss Venturiella could tolerate the very high pressure of 20 GPa for 30 min and germinated a protonema to the length of 30 inn. However, these spores did not grow any further, and disappeared at around 30 days of incubation after seeded. On the other hand, colonies of blue-green alga Microcystis flos-aquae came to appear about 76 days after the moss spores were seeded. Many of these colonies appeared at the places where the moss spores had disappeared. These colonies were formed by the algae that had adhered to the spore cases of the moss and survived after exposure to the very high pressure of 20 GPa. Though the appearance of the colonies of high pressure exposed algae was delayed by about 50 days compared with that of the control group which was not exposed to high pressure, there seems no difference in their shape and color from those of the control group. The pressure tolerance of blue-green alga is found to be enormously strong, and it can survive after exposure to the high pressure which corresponds to the depth of about 550-600 km from the surface of the Earth, just above the lower mantle. (C) 2014 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jpcs.2014.08.008

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DOI： 10.1080/23311940.2015.1076702

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

Tuite has been suggested as a potential reservoir for trace elements in the deep mantle, but no evidence confirms this supposition. By using a natural apatite as starting material, the trace-element-bearing tuite large crystals were obtained under high-pressure and high-temperature conditions (15 GPa and 1800 K). X-ray diffraction pattern and Micro-Raman spectrum of the run product confirm that tuite was synthesized. The concentrations of trace elements in tuite crystals were analyzed by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). The rare earth element patterns of tuite show enrichment of light rare earth elements relative to heavy rare earth elements. Tuite shows high concentrations of Th and Sr, and negative anomalies of Rb, Nb, and Hf. The results show that tuite can accommodate a large amount of trace elements. Tuite might be an important host to accommodate trace elements if there is much apatite subducted into the deep mantle.

DOI： 10.1007/s11430-014-4980-7

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

The postperovskite phase of ZnGeO3 was confirmed by laser heating experiments of the perovskite phase under 110-130 GPa at high temperature. Ab initio calculations indicated that the phase transition occurs at 133 GPa at 0 K. This postperovskite transition pressure is significantly higher than those reported for other germanates, such as MnGeO3 and MgGeO3. The comparative crystal chemistry of the perovskite-to-postperovskite transition suggests that a relatively elongated b-axis in the low-pressure range resulted in the delay in the transition to the postperovskite phase. Similar to most GdFeO3-type perovskites that transform to the CaIrO3-type postperovskite phase, ZnGeO3 perovskite eventually transformed to the CaIrO3-type postperovskite phase at a critical rotational angle of the GeO6 octahedron. The formation of the postperovskite structure at a very low critical rotational angle for MnGeO3 suggests that relatively large divalent cations likely break down the corner-sharing GeO6 frameworks without a large rotation of GeO6 to form the postperovskite phase.

DOI： 10.1021/ic501958y

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

The electrical conductivity of partially molten peridotite was measured during deformation in simple shear at 1 GPa in a DIA type apparatus with a uniaxial deformation facility. To detect development of electrical anisotropy during deformation of partially molten system, the electrical conductivity was measured simultaneously in two directions of three principal axes: parallel and normal to the shear direction on the shear plane, and perpendicular to the shear plane. Impedance spectroscopy measurement was performed at temperatures of 1523 K for Fe-bearing and 1723 K for Fe-free samples, respectively, in a frequency range from 0.1 Hz to 1 MHz. The electrical conductivity of partially molten peridotite parallel to shear direction increased to more than one order of magnitude higher than those normal to shear direction on the shear plane. This conductivity difference is consistent with the magnitude of the conductivity anisotropy observed in the oceanic asthenosphere near the Eastern Pacific Rise. On the other hand, conductivity perpendicular to the shear plane decreased gradually after the initiation of shear and finally achieved a value close to that of olivine. The magnitude and development style of conductivity anisotropy was almost the same for both Fe-bearing and Fe-free melt-bearing systems, and also independent of shear strain. However, such conductivity anisotropy was not developed in melt-free samples during shear deformation, suggesting that the conductivity anisotropy requires a presence of partial melting under shear stress. Microstructural observations of deformed partially molten peridotite samples demonstrated that conductivity anisotropy was attributed to the elongation of melt pockets parallel to the shear direction. Horizontal electrical conductivity anisotropy revealed by magnetotelluric surveys in the oceanic asthenosphere can be well explained by the realignment of partial melt induced by shear stress. (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2014.08.018

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The electrical conductivity of mantle rocks during phase transformation from ringwoodite to silicate perovskite and ferro-periclase was measured at 25 GPa and various temperatures ranging from 1300 to 1900 K. The electrical conductivity was high at the initial stage of annealing, suggesting that ferro-periclase forms interconnected layers in aggregates of silicate perovskite and ferro-periclase that are representative of lower mantle rock. At 1900 K the electrical conductivity quickly decreased and reached that of silicate perovskite, suggesting the cut-off of the interconnected ferro-periclase because of rounding of crystals. Below 1700 K, the high conductivity values were maintained for experimental duration. The interconnection of ferro-periclase, which has a lower viscosity than silicate perovskite, can be maintained in a cold descending slab over geological time scales (similar to 1 My), indicating that a colder slab is less viscous than the warmer mantle surrounding it. The low-viscosity slab can be prevented from penetrating into the deeper part of the lower mantle by the high viscosities encountered at a depth of similar to 1000 km, referred to as the "viscosity hill", that cause stagnation at this depth as observed by seismic tomography. (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2014.07.017

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

We systematically measured oxygen self-diffusion coefficients (D-O) in forsterite along b crystallographic axis at a pressure of 8GPa and temperatures of 1600-1800K, over a wide range of water content (C-H2O) from &lt;1 up to similar to 800 weight ppm. The experimental results suggest that D-O (C-H2O)(0.050.06)approximate to(C-H2O)(0). Thus, water has no significant effect on oxygen self-diffusion rate in forsterite. Since the C-H2O dependence of silicon self-diffusion rate is also very small, the effect of water on olivine rheology is not significant by assuming the diffusion controlled creep mechanism.
Key Points &lt;list list-type="bulleted" id="jgrb50873-list-0001"&gt;&lt;list-item id="jgrb50873-li-0001"&gt;Water has no effect on oxygen self-diffusion rate in forsterite&lt;list-item id="jgrb50873-li-0002"&gt;Water effect on olivine rheology is much smaller than previously considered

DOI： 10.1002/2014JB011141

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

We determined phase relations in FeCr2O4 at 12-28 GPa and 800-1600 degrees C using a multi-anvil apparatus. At 12-16 GPa, FeCr2O4 spinel (chromite) first dissociates into two phases: a new Fe2Cr2O5 phase + Cr2O3 with the corundum structure. At 17-18 GPa, the two phases combine into CaFe2O4-type and CaTi2O4-type FeCr2O4 below and above 1300 degrees C, respectively. Structure refinements using synchrotron X-ray powder diffraction data confirmed the CaTi2O4-structured FeCr2O4 (Cmcm), and indicated that the Fe2Cr2O5 phase is isostructural to a modified ludwigite-type Mg2Al2O5 (Pbam). In situ high-pressure high-temperature X-ray diffraction experiments showed that CaFe2O4-type FeCr2O4 is unquenchable and is converted into another FeCr2O4 phase on decompression. Structural analysis based on synchrotron X-ray powder diffraction data with transmission electron microscopic observation clarified that the recovered FeCr2O4 phase has a new structure related to CaFe2O4-type. The high-pressure phase relations in FeCr2O4 reveal that natural FeCr2O4-rich phases of CaFe2O4- and CaTi2O4-type structures found in the shocked Suizhou meteorite were formed above about 18 GPa at temperature below and above 1300 degrees C, respectively. The phase relations also suggest that the natural chromitites in the Luobusa ophiolite previously interpreted as formed in the deep-mantle were formed at pressure below 12-16 GPa.

DOI： 10.2138/am.2014.4736

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The growth rate of ringwoodite reaction rims between MgSiO3 perovskite and periclase was investigated at 22.5 GPa and 1,800 A degrees C for 1-24 h using the Kawai-type high-pressure apparatus. The reaction was likely to proceed by a diffusion-controlled mechanism in which the dominant diffusion mechanism was grain-boundary diffusion. The reaction constant (the width of the ringwoodite reaction rim squared divided by time) determined from these experiments was between 1.3 x 10(-15) and 5.6 x 10(-15) m(2)/s. A Pt inert marker experiment indicated that the MgO component migrated faster than the SiO2 component in ringwoodite. Thus, either Mg or O having the slower diffusion rate controlled the reaction. Because previous diffusion studies have shown that diffusion rates of O are slower than those of Mg, O would be a rate-controlling element for ringwoodite formation from MgSiO3 perovskite and periclase. The growth rate appeared to be too fast to explain the observed topographic rise (similar to 10 km) inside mantle plumes at the 660-km discontinuity.

DOI： 10.1007/s00269-014-0669-x

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

The electrical conductivity of brine-bearing quartzite with fluid fractions of 0.19 to 0.30 and salinity of 3 to 17 wt.% was measured at 800 to 1,100 K and 1 GPa. The conductivity of the brine-bearing quartzite increases with salinity and fluid fraction, but is almost independent of temperature. Our results suggest that regions of high conductivity (10(-3) to 10(-2) S/m) in the crust could be explained by the presence of quartzite with fluids of salinity similar to that of seawater. To account for those regions with the highest conductivity of 10(-1) S/m, quartzite with fluid of high salinity (&gt;10 wt.%) is required.

DOI： 10.1186/1880-5981-66-2

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

We generated pressures up to 109.3 GPa in a Kawai-type multianvil apparatus (KMA) equipped with sintered diamond anvils by means of in situ X-ray observation with synchrotron radiation. The unit cell parameters of (Mg0.92Fe0.08)SiO3 perovskite, SiO2 stishovite, and the CaCl2-type polymorph of SiO2 were measured as functions of pressure. We determined the isothermal bulk modulus, K-T0, and its pressure derivative, K'(0), at zero pressure, to be 268 (3) GPa and 3.8 (0.1), respectively, for (Mg0.92Fe0.08)SiO3 Perovskite. Stishovite transforms to the CaCl2-type phase at approximately 54 GPa at 300 K. Compression through stishovite and the CaCl2-type phase can be represented by a single compression curve with K-T0 = 299 (4) GPa and K'(0) = 4.6(0.2). (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2014.01.013

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

We examined the structure of MnO and CoO up to 72 and 88 GPa, respectively, at room temperature by means of in situ X-ray diffraction using the synchrotron radiation at SPring-8. Compression was carried out with the Kawai-type apparatus equipped with sintered diamond anvils. In both MnO and CoO, the cubic B1 lattice starts distorting to the rhombohedral system at 37 and 40 GPa, respectively, which progressively proceeds under increasing pressure. Crystallographic direction of the distortion is opposite; i.e., a contraction along the diagonal [1 1 1] direction of the B1 lattice in MnO and a stretch in CoO. The rhombohedral distortion in 3d transition metal monoxides is discussed. Simultaneously measured electrical resistance of CoO showed characteristic change with pressure; i.e., the pronounced minimum at 14.9 GPa and the maximum at 49 GPa, which serve as good pressure fixed points. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2013.12.009

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The diffusivity of dissolved Mg2SiO4 in wadsleyite saturated KMC melt (K2Mg(CO3)2+25.7wt.% MgSiO3) at 16.5GPa and 1700°C, MgSiO3 diffusivity in perovskite saturated KMCH (K2Mg(CO3)2×2H2O+31.7wt.% MgSiO3) and HM (H2O+75.7wt.% MgSiO3) melts at 24GPa and 1500°C were determined experimentally using a scaled-up version of a Kawai-type multi-anvil apparatus. During a diffusion experiment, silicate saturation was maintained at different levels in the two temperature regions by placing the diffusion cell in the thermal gradient of 20°C/mm. The diffusivity was computed from the total mass of silicate transported from "hot" to the "cold" region during the course of an experiment. At given conditions silicate diffusivities were estimated to be DKMCMg2SiO4=2×10-9m2/s, DKMCHMgSiO3=4×10-9m2/s, and DHMMgSiO3=5×10-8m2/s.Using obtained diffusivities we estimated possible migration rates of dispersed melt inclusion in the deep mantle by means of dissolution-precipitation considering different driving forces. The rates of melt migration driven by the lateral thermal gradient of 1°C/km in the mantle plume range from 4×10-8 to 8×10-7m/year. This means that during plume ascent time of about 50Ma, the melt can be moved by 2-40m. These values clearly demonstrate that the thermal gradient is very weak driving force in terms of melt segregation in the deep mantle. On the other hand, at typical mantle stress of 1MPa and droplet size of 100μm the migration rates of the HM, KMCH and KMC melts are estimated to be 22.5, 0.9 and 0.2m/year, respectively, which are 2-3 orders of magnitude faster than ascent rate of the mantle plume. This implies that all melt droplets on the way of ascending plume would be entrapped by the stressed zone in front of plume and accumulated in the plume head. This mechanism may explain segregation of mantle magmas with the source regions deeper than 150-250km, such as kimberlites. © 2013 Elsevier B.V.

DOI： 10.1016/j.pepi.2013.09.004

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

Tuite, gamma-Ca-3(PO4)(2), is regarded as an important phosphate mineral in the deep mantle playing a crucial role as a host for rare earth elements, large ion lithophile elements, and phosphorus. In this study we report the thermoelastic properties of synthetic gamma-Ca-3(PO4)2 at simultaneously high pressures and temperatures of up to 35.4 GPa and 1300 K, respectively, as determined by means of in situ energy-dispersive X-ray diffraction in a large-volume multi-anvil apparatus. The pressure-volume-temperature data obtained for gamma-Ca-3(PO4)(2) were fitted by the high-temperature Birch-Murnaghan equation of state to yield V-0 = 447.4(4) angstrom(3), K-T0 = 100.8(18) GPa, K-T0' = 5.74(13), (partial derivative K-T/partial derivative T)(p) = -0.020(1) GPa/K, and alpha(T) = 3.26(18) x 10(-5) + 1.76(24) x 10(-8) T. In addition, fitting the present data to the Mie-Gruneisen-Debye equation of state gives gamma(0) = 1.35(6), Theta(0) = 944(136) K, and q = 0.37(29). Based on the thermoelastic properties obtained in our study, the density profiles of gamma-Ca-3(PO4)(2) tuite along typical cold and hot slab geotherms were calculated and are compared with those of the coexisting silicate minerals in subducting mid-ocean ridge basalt.

DOI： 10.2138/am.2013.4403

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

Water has been thought to affect the dynamical processes in the Earth's interior to a great extent. In particular, experimental deformation results(1-4) suggest that even only a few tens of parts per million of water by weight enhances the creep rates in olivine by orders of magnitude. However, those deformation studies have limitations, such as considering only a limited range of water concentrations and very high stresses, which might affect the results. Rock deformation can also be understood as an effect of silicon self-diffusion, because the creep rates of minerals at temperatures as high as those in the Earth's interior are limited by self-diffusion of the slowest species(5,6). Here we experimentally determine the silicon self-diffusion coefficient D-Si in forsterite at 8 GPa and 1,600 K to 1,800 K as a function of water content C-H2O from less than 1 to about 800 parts per million of water by weight, yielding the relationship, D-Si approximate to (C-H2O)(1/3). This exponent is strikingly lower than that obtained by deformation experiments (1.2; ref. 7). The high nominal creep rates in the deformation studies under wet conditions may be caused by excess grain boundary water. We conclude that the effect of water on upper-mantle rheology is very small. Hence, the smooth motion of the Earth's tectonic plates cannot be caused by mineral hydration in the asthenosphere. Also, water cannot cause the viscosity minimum zone in the upper mantle. And finally, the dominant mechanism responsible for hotspot immobility cannot be water content differences between their source and surrounding regions.

DOI： 10.1038/nature12193

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

In our previous studies on the tolerance of living organisms such as planktons and spores of mosses to the high hydrostatic pressure of 7.5 GPa, we showed that all the samples could be borne at this high pressure. These studies have been extended to the extreme high pressure of 20GPa by using a Kawai-type octahedral anvil press. It was found that the average diameter of the spores of Venturiella exposed to 20GPa for 30min was 25.5m, which is 16.5% smaller (40.0% smaller in volume) than that of the control group which was not exposed to high pressure. The inner organisms showed a further extent of plastic deformation. As a result, a gap appeared between the outer cover and the cytoplasm. A relationship has been obtained between the survival ratio and plastic deformation of spores of moss Venturiella caused by the application of ultra high pressure.

DOI： 10.1080/08957959.2013.775281

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

The pyrochlore-type MgZrSi2O7 has been investigated by in situ synchrotron energy-dispersive X-ray diffraction measurements up 24.3GPa at room temperature in a multianvil high pressure apparatus. The pressure has been calculated using an internal gold metal pressure calibrant. No phase transformation was observed in this study. A third-order BirchMurnaghan equation of state was used to fit the pressurevolume data. The fitting gives a volume of V-0=802.8 +/- 0.2 angstrom(3), an isothermal bulk modulus of K-T=249 +/- 12GPa, and first pressure derivative of K-T=3.2 +/- 1.3. If K-T is fixed as 4, K-T is obtained as 241.8 +/- 2.6GPa. Compared with zirconate or titanate pyrochlores, MgZrSi2O7 shows a smaller compressibility due to a larger cation radii ratio (r(Mg, Zr)/r(Si)).

DOI： 10.1080/08957959.2012.750653

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

In order to determine the P-V-T equation of state of epsilon-iron, in situ X-ray observations were carried out at pressures up to 80 GPa and temperatures up to 1900 K using the Kawai-type high pressure apparatus equipped with sintered diamond anvils which was interfaced with synchrotron radiation. The present results indicate the unit cell volume at ambient conditions V-0 = 22.15(5) angstrom(3), the isothermal bulk modulus K-T0 = 202(7) GPa and its pressure derivative K-T0' = 4.5(2), the Debye temperature theta(0) = 1173(62) K, Gruneisen parameter at ambient pressure gamma(0) = 3.2(2), and its logarithmic volume dependence q = 0.8(3). Furthermore, thermal expansion coefficient at ambient pressure was determined to be alpha(0)(K-1) = 3.7(2) x 10(-5) + 7.2(6) x 10(-8)(T-300) and Anderson-Gruneisen parameter delta(T) = 6.2(3). Using these parameters, we have estimated the density of epsilon-iron at the inner core conditions to be similar to 3% denser than the value inferred from seismological observation. This result indicates that certain amount of light elements should be contained in the inner core as well as in the outer core but in definitely smaller amount. Citation: Yamazaki, D., et al. (2012), P-V-T equation of state for epsilon-iron up to 80 GPa and 1900 K using the Kawai-type high pressure apparatus equipped with sintered diamond anvils, Geophys. Res. Lett., 39, L20308, doi: 10.1029/2012GL053540.

DOI： 10.1029/2012GL053540

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

Silicon self-diffusion coefficients (D-Si) in dry synthetic forsterite single crystals were measured at temperatures of 1600 and 1800 K, from ambient pressure up to 13 GPa using an ambient pressure furnace and Kawai-type multi-anvil apparatus. The water contents in the samples were carefully controlled at &lt; 1 mu g/g. Diffusion profiles were obtained by secondary ion mass spectrometry (SIMS) in depth profiling mode. Small negative pressure dependence of D-Si is determined with an activation volume of 1.7 +/- 0.4 cm(3)/mol. The activation energy is found to be 410 +/- 30 kJ/mol. LogD(Si) values (D-Si in m(2)/s) at 1600 and 1800 K at ambient pressure are determined to be -19.7 +/- 0.4 and -18.1 +/- 0.3, respectively. These values are similar to 2.4 orders of magnitude higher than those reported by Jaoul et al. (1981). We speculate that their low D-Si might reflect the effects of a horizontal migration of the isotopically enriched thin films applied on the sample surfaces, which may inhibit diffusion into the substrate during annealing. Our results for D-Si resolve the inconsistency between D-Si measured in diffusion experiments and those deduced from creep rates measured in deformation experiments. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2012.06.044

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The electrical conductivity of olivine and its high-pressure polymorphs with various iron contents [X-Fe = Fe/(Fe + Mg) = 0.1, 0.2, 0.3, 0.5, 0.7 and 1.0] was measured over a wide range of pressure (P) and temperature (T) conditions covering the stability field of olivine, wadsleyite and ringwoodite in a Kawai-type multianvil apparatus. The pressure was determined using in situ X-ray diffraction of MgO as a pressure marker in SPring 8. Molybdenum electrodes were used so that oxygen fugacity is similar to that for the iron-wustite buffer. The transition from low-pressure phase to high-pressure phase led to an increase of conductivity. In the stability field of each phase, the electrical conductivity slightly increased with increasing pressure at a constant temperature, suggesting a negative activation volume. The conductivity increased with increasing total iron content for each phase. All electrical conductivity data fit the formula for electrical conductivity sigma = sigma(0) X(Fe)exp{-[Delta E-0 - alpha X-Fe(1/3) + P(Delta V-0 - beta X-Fe)]/kT}, where sigma(0) is the pre-exponential term, Delta E-0 and Delta V-0 are the activation energy and the activation volume at very low total iron concentration, respectively, and k is the Boltzmann constant. The activation energy decreased with increasing total Fe content in olivine and ringwoodite. Dependence of the activation energy on the total Fe content suggests that the dominant mechanism of charge transport is Fe2+-Fe3+ hopping (small polaron). The activation volume for small polaron conduction in olivine and its high-pressure polymorphs tends to decrease with total Fe content. For olivine with low Fe content, the activation volume for small polaron conduction still is negative and very small. Assuming constant Fe content (X-Fe = 0.1) and oxygen buffer condition, the conductivity will increase with depth mainly due to the increase of the temperature along the mantle adiabat.

DOI： 10.1029/2011JB008774

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The electrical conductivity of fluid-bearing quartzite was determined as function of temperature and fluid fraction at 1 GPa in order to assess the origin of the high conductivity anomalies observed in the middle to lower crustal levels. Dihedral angles of quartz-fluid-quartz determined from recovered samples were below 60, suggesting that fluid forms an interconnected network through the quartz aggregate. The electrical conductivity of quartzite increases with increasing temperature, which can be approximately expressed by Arrhenius equation. The apparent activation enthalpy decreases from 0.70 to 0.25 eV with increasing fluid fraction in volume from 0.00043 to 0.32. The electrical conductivity (sigma) of the fluid-bearing quartzite increased with fluid fraction (phi) proportionally to a power law (sigma proportional to phi(0.56-0.71)) within the temperature range of 900-1000K. The electrical conductivity of the aqueous fluid-bearing quartzite with the maximum fluid fraction (0.32) was found to be about three orders of magnitude higher than that of dry quartzite at 1000 K. However, its electrical conductivity was definitely lower than the geophysically observed values of high-conductivity anomalies, even if the quartzite contained large fluid fractions (0.32). The present results suggest that fluid-bearing quartzite is unable to account for the high-conductivity anomalies in terms of fluid fraction. A significant amount of other ionic species, such as Na, Cl, and Al in aqueous fluid, in addition to silica phases dissolved in fluid, is required to increase conductivity. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2012.03.007

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

Static compression data of (Mg-0.83,Fe-5.17)O and (Mg-0.75,Fe-0.25)O ferropericlases have been measured up to 58 GPa along 300, 700, and 1100 K isotherms, using synchrotron powder X-ray diffraction experiments combined with a Kawai-type, multi-anvil, high-pressure apparatus and sintered diamond anvils. High-temperature and high-pressure equations of state for these two ferropericlases, which have high-spin Fe2+ ions, were developed using measured compression data below 47 GPa, based on the Mie-Gruneisen relation and the Debye thermal model, combined with the 300 K Birch-Murnaghan equation. When the isothermal bulk modulus (K-0T) and the Debye temperature (Theta(0)) are fixed at 160 GPa and 500 K, respectively, the optimized equation-of-state parameters for these two phases are as follows: the pressure derivative of the bulk modulus (K-0T), the Gruneisen constant (gamma(0)), and the q parameter are 4.08 +/- 0.02, 1.53 +/- 0.04, and 0.7 +/- 0.2, respectively, for (Mg-0.83,Fe-0.17)O; and 4.22 +/- 0.03, 1.64 +/- 0.04, and 0.7 +/- 0.2, respectively, for (Mg-0.75,Fe-0.25)O. We found that calculated pressures with these equation-of-state parameters accurately reproduce the measured pressures of each ferropericlase below similar to 50 GPa for the isotherms of 300, 700, and 1100 K. Furthermore, the compression curve indicates that for each ferropericlase at each isothermal compression of 300, 700, and 1100 K, an abrupt volume reduction occurs at similar to 50 GPa. This volume reduction becomes more pronounced with increasing pressure, as a result of the progressive transition from high-spin to low-spin of the Fe2+ ions in each ferropericlase.

DOI： 10.2138/am.2012.3937

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A scaled-up version of a 6-8 Kawai-type multianvil apparatus equipped with 47-mm WC anvils has been developed at the Institute for the Study of the Earth's Interior for operation over pressure ranging up to 19 and 24 GPa using the conventional system with larger compressional volumes between 1.2 and 0.4 cm(3), respectively. This system is used under uniaxial compression along cube diagonal of the Kawai-cell up to the press load of 19 MN. Experiments are performed using octahedral pressure media (PM) made of MgO- and ZrO2-based semi-sintered ceramics and unfired pyrophyllite gaskets. In this study we used "Toshiba-F" grade WC anvils allowing pressure generation up to 24 GPa. We perform pressure calibrations at room and high temperatures, with octahedron/anvil truncation edge-length ratios (a(0)/b, mm) of 12.2/6, 14/6, 14/7, 16/7, 18/7, 18/9, and 18/10. Different configurations show that an increase in edge-length ratio of a(0)/b permits the achievement of higher pressure, which agrees with the results of Frost at al. (Frost, D.J., Poe, B.T., Tronnes, R.G., Liebske, C., Duba, A., Rubie, D.C., 2004. A new large-volume multianvil system. Phys. Earth Planet. Inter. 143, 507). However, it also shifts the pressure maximum to higher press loads, in some cases exceeding the capacity of a press. Our and Frost et al. (2004) data reveal that the 14/6, 18/8, and 18/10 assemblies are the most suitable in generating pressures of up to 19-24 GPa at 19 MN press load limits. The assemblies with a low a(0)/b ratio have a lower upper pressure limit; however, they exhibit a systematically higher efficiency in pressure generation at low press loads. Consequently, assemblages with high and low nab ratios should be used in high and low pressure experiments, respectively. For example, the 18/12 assembly is suitable for 5-11 GPa pressure range (Stoyanov, E., Haussermann, U., Leinenweber, K., 2010. Large-volume multianvil cells designed for chemical synthesis at high pressures. High Pressure Res., 30, 175), whereas the 14/6, 18/8 (Frost et al., 2004), and 18/10 assemblies are suitable for 22-24, 19-23, and 11-19 GPa pressure ranges, respectively. The maximum pressure generation achieved in the present study is 24 GPa, using the 14/6 assembly. This appears to be the maximum pressure level attainable by using WC anvils. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2011.08.001

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The pyrochlore type of MgZrSi2O7 was synthesized at 25 GPa and 1500 degrees C using a Kawai-type, multi-anvil apparatus. Powder X-ray diffraction and Rietveld analysis revealed that the phase assumed the pyrochlore structure (space group Fd (3) over barm, cubic) with the lattice parameter a = 9.2883(1) angstrom and the structural parameter x=0.4295(4). Chemical analysis by the electron probe microanalysis (EPMA) confirmed the stoichiometry of MgZrSi2O7. It was demonstrated that the eight-fold coordinated 16c site is randomly occupied by both Mg2+ and Zr4+ ions in a 1:1 ratio. The high ionic radius ratio R-A/R-B (where A and B denote Mg + Zr and Si, respectively) of 2.22 necessitates a relatively high pressure to stabilize the pyrochlore structure. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.matchemphys.2011.03.017

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

High pressure in situ synchrotron X-ray diffraction experiment of strontium orthophosphate Sr-3(PO4)(2) has been carried out to 20.0 GPa at room temperature using multianvil apparatus. Fitting a third-order Birch-Murnaghan equation of state to the P-V data yields a volume of V (0) = 498.0 +/- A 0.1 (3), an isothermal bulk modulus of K (T) = 89.5 +/- A 1.7 GPa, and first pressure derivative of K (T) &apos; = 6.57 +/- A 0.34. If K (T) &apos; is fixed at 4, K (T) is obtained as 104.4 +/- A 1.2 GPa. Analysis of axial compressible modulus shows that the a-axis (K (a) = 79.6 +/- A 3.2 GPa) is more compressible than the c-axis (K (c) = 116.4 +/- A 4.3 GPa). Based on the high pressure Raman spectroscopic results, the mode Gruneisen parameters are determined and the average mode Gruneisen parameter of PO4 vibrations of Sr-3(PO4)(2) is calculated to be 0.30(2).

DOI： 10.1007/s00269-010-0409-9

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

The pressure-induced electronic spin transition of iron in ferropericlase was investigated as a function of iron content in ferropericlase by in situ electrical conductivity measurement. The electrical conductivity of ferropericlase, (Mg1-x,Fe-x)O (x = 0.07, 0.10, 0.13, 0.17, 0.24), was measured up to 53 GPa and 600 K using the Kawai-type multianvil apparatus equipped with sintered diamond anvils. At pressures up to 25 GPa, the electrical conductivity of ferropericlase generally increases with increasing pressure, and both the activation energy and activation volume of ferropericlase decrease with increasing iron content. For the samples with x = 0.07 and 0.10, the electrical conductivity shows a slight initial decrease and becomes constant between 25 and 40 GPa, upon which it increases slightly as the pressure increases. For the samples with higher iron content, the electrical conductivity constantly increases with pressure over the investigated pressure range. If these changes in the electrical conductivity are due to the isosymmetric high-to low-spin transition of iron in ferropericlase, this conductivity change suggests that the spin transition pressure significantly decreases with decreasing iron content in ferropericlase. Because the amount of iron in ferropericlase that coexists with the Al-bearing perovskite seems to be less than that in the Al-free perovskite, the influence of the iron partitioning between perovskite and ferropericlase by the spin transition appears in a pressure range of about 30-40 GPa in the lower mantle of the Earth.

DOI： 10.1029/2010JB007801

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Si and Mg self-diffusion coefficients were measured simultaneously in single crystals of MgSiO3 perovskite under lower mantle conditions. There is little difference in Si volume diffusivity measured directly using single crystals (this study) and those retrieved from experiments with polycrystals (earlier studies). This agreement between studies establishes the reliability of Si diffusion coefficients measured in perovskite. Within the uncertainties of our measurements, no anisotropy in the diffusion of either Si or Mg could be resolved. Diffusion of Si and Mg in perovskite are described by an Arrhenius equation, D=D0 exp (-H/RT) at 25GPa, with D 0=5.10×10-11m2/s for Si and 4.99×10-11m2/s for Mg, H=308kJ/mol for Si, and 305kJ/mol for Mg. Mg diffusivity in MgSiO3 perovskite is distinctly lower than those measured in olivine, wadsleyite, and ringwoodite. We find that Mg has very similar diffusivity to Si in perovskite. As a consequence, the rheological properties of the lower mantle may be controlled by the coupled motion of Si and Mg. A point defect-based model is discussed that may account for the diffusion behavior of Si and Mg in MgSiO3 perovskite. Our data indicate that, within realistic ranges of temperature, grain size, and state of stress, both diffusion creep as well as dislocation creep may be observed in the lower mantle. Copyright 2011 by the American Geophysical Union.

DOI： 10.1029/2011JB008444

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Other Link： http://orcid.org/0000-0003-0702-0533

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

To determine the phase boundary between the perovskite and post-perovskite structures in MnGeO3, in situ X-ray observations were carried out at pressures of 57-68 GPa and temperatures of 1000-1900 K using the Kawai-type high-pressure apparatus equipped with sintered diamond anvils interfaced with synchrotron radiation. The phase boundary was determined to be P (GPa) = 39.2 + 0.013T (K) based on Tsuchiya's (2003) gold pressure scale. The Clapeyron slope, dP/dT, of 13(+12/-5) MPa/K, determined in the present study is larger that of MgGeO3 and MgSiO3.

DOI： 10.2138/am.2011.3499

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Grain growth rates of majorite and stishovite, in their aggregates with MORB composition, were studied at 18 GPa and temperatures ranging from 1873 to 2223 K. The rates of grain growth were expressed by G(n) - G(0)(n) = k(0)t exp(-H*/RT) where G is the grain size at time t (s), and G(0) is the initial grain size. We determined the grain growth kinetic parameters for majorite, where n = 9.1 +/- 1.3, H-* = 950 +/- 249 kJ/mol, and log k(0) = -32.5 +/- 2.3 m(9.1)/s for the graphite capsule and log k(0) = -31.3 +/- 3.9 m(9.1)/s for the Re capsule. Kinetic parameters for stishovite were determined to be n = 6.6 +/- 0.9, H-* = 599 +/- 226 kJ/mol, and log k(0) = -30.6 +/- 0.9 m(6.6)/s for the graphite capsule and log k(0) = -29.0 +/- 1.1 m(6.6)/s for the Re capsule. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2010.09.009

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The temperature at the 410-km discontinuity is re-evaluated by comparing the depth of the discontinuity with the olivine-wadsleyite transition pressure obtained using in situ X-ray diffraction experiments by Katsura et al. (2004a) and equation of state (EoS) of MgO by Tange et al. (2009) (Tange scale) and Matsui et al. (2000). The newly estimated temperature is 1830 +/- 48 K, 70 K higher than that by our previous estimation. The EoSes of the major mantle minerals (olivine, wadsleyite, ringwoodite and perovskite) are also recalculated using the Tange scale. The adiabatic temperature gradient is calculated using the thermal expansion coefficient obtained from these EoSes. The adiabatic temperature gradient gradually decreases with increasing depth without a phase transition, and abruptly increases in association with phase transitions. The adiabatic temperature gradients are found to be 04-0.5 and 0.3 K/km in the upper and lower parts of the mantle, respectively. The temperatures at a depth of 200 km, the bottom of the mantle transition zone, the top of the lower mantle and a depth of 2700 km are found to be 1720 +/- 40, 2010 +/- 40, 1980 +/- 40, and 2730 +/- 50 K. The mantle potential temperature is found to be 1610 +/- 35 K. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2010.07.001

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

We report on hexagonal aluminum nitride (h-AlN) crystal growth in the Al-N system by means of AlN recrystallization in the field of a temperature gradient at 6 GPa and 1800 degrees C. A special setup for h-AlN growth using a multianvil apparatus has been developed, which allows the growth of colorless transparent h-AlN single crystals. Crystals exhibited two distinct morphological types. The first is short prismatic and platelet-like crystals with smooth faces and a size up to 0.4 mm. The second is skeleton crystals elongated along the [1210] direction and flattened along the (0001) plane with a size of up to 1.0 mm. Crystals have been characterized by scanning electron microscopy, Raman spectroscopy, and electron backscattered diffraction methods. The growth mechanism and main factors determining the crystal habit and growth rate in a high-pressure solution method are discussed. We also discuss the possibility of using the employed technique for cubic aluminum nitride (c-AlN) crystal growth.

DOI： 10.1021/cg901519s

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High pressure generation has been tried by using the Kawai-cell equipped with sintered diamond cubes and the synchrotron radiation at SPring-8. The maximum attainable pressure reached 90.4 GPa at 300 K based on the Anderson et al. (1989) Au scale. Simultaneously, we investigated the perovskite (Pv)-postperovskite (PPv) transformation in MgGeO3 up to ca. 74 GPa and 2200 K by means of in situ X-ray diffraction method. Transformation from Pv to PPv was observed at pressures and temperatures higher than 63 GPa and 1300 K. Both the forward and the reverse reactions were found to be fairly sluggish over the examined temperature range. We determined the phase boundary by passing through the conditions at which either Pv or PPv phase grew and that of coexistence of both the phases, which is expressed by the equation T(K) = 177 P (GPa) - 9677. Our dP/dT slope of 5.6 MPa/K for MgGeO3 is close to the minimum estimate for MgSiO3 and accordingly suggests relatively deeper D '' discontinuity and a high heat flux from the core. We emphasize that the phase boundary completely relies on the pressure scale adopted. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2010.02.023

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

Large single crystals of stishovite were successfully synthesized at 11 GPa from a silica solution in water. The potential of both slow cooling and thermal gradient methods were examined. The thermal gradient method provided crystals of 0.8 x 0.8 x 1.3 min in size grown at 1350 degrees C and a thermal gradient of 50 degrees C/mm using stishovite as a silica source. The use of quartz as a source resulted in the appearance of numerous stishovite crystals in the solution interior resulting in diminished space for the growth of large crystals. This can be explained by a significant difference in the solubility of metastable quartz and stishovite in water, estimated to be 85.3 and 5.6 wt% SiO2 at 1000 degrees C and 11 GPa, respectively. Crystals up to 0.8 x 1.3 x 1.5 mm were grown by the slow cooling method in the system SiO2 + 14.7 wt% H2O as temperature was decreased from 1600 to 1000 degrees C with a cooling rate of 2 degrees C/min. The size of single crystals obtained was large enough to carry out silicon self-diffusion experiments, which were performed at a pressure of 14 GPa and temperatures from 1400 to 1800 degrees C. The lattice diffusion coefficients along the [110] and [001] directions can be expressed as D-[110] (m(2)/s) = 4.10 x 10(-12) exp [-322 (kJ/mol)/RT] and D-[001] (m(2)/s) = 5.62 x 10(-12) exp [-334 (kJ/mol)/RT], respectively, where R is the gas constant and T is the absolute temperature.

DOI： 10.2138/am.2010.3255

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DOI： 10.1029/2009GL039318

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Other Link： http://orcid.org/0000-0002-5422-7396

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

We have synthesized large (0.7-1.0 mm) crystals of anhydrous, water-bearing, and Fe-bearing wadsleyite by means of growth from solution in the thermal gradient field. Nearly anhydrous (&lt;68 +/- 4 wt ppm H2O) Mg2SiO4 crystals were grown using K2Mg(CO3)(2) as a solvent at 16.5 GPa and 1700 degrees C. (Mg0.92Fe0.08)(2)SiO4 crystals containing 84 +/- 17 wt ppm H2O were grown using 92K(2)Mg(CO3)(2)-8FeCl(2) as a solvent. Crystals of Fe-free wadsleyite with 1496 +/- 117 wt ppm H2O were synthesized at 1400 degrees C and 15.5 CiPa by using 2KHCO(3)-Mg(OH)(2) as a solvent.

DOI： 10.2138/am.2009.3150

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

The volume of Mg2SiO4 wadsleyite has been precisely measured at pressures of 11 to 20 GPa and temperatures of 300 to 2100 K by means of in situ X-ray diffraction in a multi-anvil apparatus. The fixed isothermal bulk modulus K-T0 = 169.2 GPa gives its pressure derivative K-T0' = 4.1(1). The fixed Debye temperature theta(0) = 814 K gives a Gruneisen parameter at ambient pressure gamma(0) = 1.64(2) and its logarithmic volume dependence q = 1.5(1). The pressure derivative of the isothermal bulk modulus, Anderson-Gruneisen parameter and thermal expansion coefficient at ambient pressure are found to be (partial derivative K-T/partial derivative(T))(P) =-0.021(1) GPa/K, delta(T) = 5.5(2), alpha(0) = 2.31(3) x 10(-5) + 1.18(3) x 10(-8) (T - 300) K-1. The pressure and volume dependence of thermal expansion coefficient of wadsleyite is the smallest among those of the mantle minerals. The adiabatic temperature gradient in the upper part of the mantle transition zone is 0.34(1) K/km. Citation: Katsura, T., et al. (2009), P-V-T relations of wadsleyite determined by in situ X-ray diffraction in a large-volume high-pressure apparatus, Geophys. Res. Lett., 36, L11307, doi:10.1029/2009GL038107.

DOI： 10.1029/2009GL038107

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

Pore morphology in partially molten peridotites strongly controls many physical properties of the Earth's deep materials. The dihedral angle of the olivine-silicate melt system is a key factor in understanding the physical behavior of the upper mantle. For a limited range of melt compositions, previous studies of wetting behavior have determined dihedral angles of 30-50 degrees. However, the dihedral angle of partially molten peridotites should be variable under a wide range of pressure and temperature conditions, because wetting behavior depends strongly on liquid structure and composition. The dihedral angles of olivine-silicate melt in partially molten peridotite were determined at pressures of 1 to 7 GPa and temperatures between 1473 and 1993 K. The dihedral angle decreased (approaching 0 degrees) with increasing temperature, which corresponds to completely wetted grain boundaries. This angle variation probably depends on a decrease in the solid-melt interfacial energy, which is a product of large change in melt structure. These results suggest that the presence of partial melt would have large influences on the physical properties of the upper mantle even if the melt fraction was very low. if grain boundary diffusion creep dominates in the asthenosphere, the shear strength of partially molten peridotites at asthenospheric pressure (similar to 3 GPa) would be much lower than that predicted from experiments at relatively lower pressure (similar to 0.3 GPa) because of the extremely low grain boundary contiguity. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2009.04.007

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

In order to overcome disadvantages of the DIA type press in squeezing the Kawai-cell, such as uneven compression between the upper and lower anvils and the four surrounding anvils and frictional loss of applied load in the guide block, we have developed a new 6-axis apparatus in which the movements of the six anvils are controlled by a servo mechanism. It is possible to keep the Kawai-cell cubic within an accuracy of +/- 2 mu m during compression and decompression. Pressure generation using sintered diamond cubic anvils with edge length of 14.0 mm and a truncation of 1.5 mm has been carried out up to ca. 60 GPa by measuring electrical resistance of GaP, Zr, and Fe(2)O(3). The results are compared with our previous calibration, carried out using an almost the same sample setup for identical anvils at SPring-8, by means of in situ X-ray observation. It is demonstrated that a significant amount of the applied load is lost by friction when the Kawai-cell is squeezed in the DIA type press. The load loss increases with increasing load, or pressure, and amounts to 45% at ca. 60 GPa. Therefore the 6-axis apparatus is very advantageous to generate higher pressures in the Kawai-cell. However, individual control of the anvils sometimes induces a runaway advancement of the anvils which brings about an abrupt increase of pressure. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2008.11.007

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

Rheology of the lower mantle characterizes the dynamics of the earth&apos;s interior and it is often controlled by the textures of the constituting material which are (Mg,Fe)SiO3 perovskite and ferro-periclase aggregate. We conducted high-pressure experiments to synthesize the (Mg,Fe)SiO3 perovskite and ferro-periclase aggregates and measured two important textures of "grain size" and "dihedral angle". The grain growth rates of perovskite and (ferro-)periclase in two phase aggregates were influenced by the iron content and increased with factors of similar to 1.5 in iron-rich system. This difference in grain growth rates indicates that the viscosity of aggregates of iron-rich system is only a few times greater than that of iron-poor system for likely diffusion creep in the lower mantle. In contrast, the change of the dihedral angle of perovskite - periclase - perovskite at triple grain junction with variation of iron content was not observed systematically, but the dihedral angle decreases from similar to 110 degrees to similar to 105 degrees with an increase of temperature from 1673 to 2273 K. The dihedral angle of 105-110 degrees would imply the interconnected network spatially of ferro-periclase in the aggregates and the connectivity increases with temperature. As a result, at higher temperature, ferro-periclase plays more important role for understanding the rheology of the lower mantle because ferro-periclase is a few order of magnitude softer than (Mg,Fe)SiO3 perovskite. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2008.11.002

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Volumes of forsterite were measured by in situ X-ray diffraction at simultaneously high pressures and high temperatures up to 14 GPa and 1900 K in a Kawai-type multi-anvil apparatus. By fitting the present data to the Mie-Gruneisen-Debye thermal equation of state with the results of the previous reliable studies, we obtained gamma(0) = 1.31(1) and q = 3.2(1). The logarithmic volume dependence of the thermal expansion coefficient was found to be delta(T) = 8.4(2). The average temperature derivative of the isothermal bulk modulus in the investigated pressure-temperature ranges was found to be (partial derivative K-T/partial derivative T)(p) = -0.028(1) GPa/K. The isobaric heat capacity and thermal pressure at high pressure and high temperature were estimated using the present volume data. The adiabatic geotherm at the top and base of the uppermost mantle are 0.60(2) and 0.34(2) K/km. The temperature estimated from the 410-km discontinuity depth and the olivine-wadsleyite transition pressure suggests a mantle potential temperature of 1520 +/- 40 K. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2008.08.002

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

A temperature of 3500 degrees C was generated using a diamond resistance heater in a large-volume Kawai-type high-pressure apparatus. Re and LaCrO(3) have conventionally been used for heaters in high-pressure studies but they cannot generate temperatures higher than 2900 degrees C and make in situ x-ray observations difficult due to their high x-ray absorption. Using a boron-doped diamond heater overcomes these problems and achieves stable temperature generation for pressure over 10 GPa. The heater starting material is a cold-compressed mixture of graphite with boron used to avoid the manufacturing difficulties due to the extreme hardness of diamond. The diamond heater was synthesized in situ from the boron-graphite mixture at temperature of 1600 +/- 100 degrees C and pressure of 20 GPa. By using the proposed technique, we have employed the diamond heater for high-temperature generation in a large-volume high-pressure apparatus. Achievement of temperatures above 3000 degrees C allows us to measure the melting points of the important constituents in earth&apos;s mantle (MgSiO(3), SiO(2), and Al(2)O(3)) and core (Fe and Ni) at extremely high pressures.

DOI： 10.1063/1.3084209

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

Phase equilibria of Fe2O3 have been studied tip to 58 GPa and 1400 K using the Kawai-type multi anvil apparatus equipped with sintered diamond anvils. Identification of phases and pressure determination has been carried out by means of in situ X-ray observation using synchrotron radiation at SPring-8. Hematite (phase I) successively transforms to the Rh2O3(II)-type structure (phase II) and then to an orthorhombic structure (phase III) with increasing pressure. The transformations of hematite into high-pressure phases have been observed only at temperatures higher than 500 K, which is not concordant with previous results obtained by using the diamond anvil cell. Volume changes accompanied by the I-II and II-III transformations are calculated to be 2.8 and -5.0%, respectively. The phase boundary between I and II phases and that between II and III have been proposed to be P (GPa)- 0.015 T(K) + 44.2 and P (GPa) = -0.005 T(K) + 48.7, respectively. Possible correlation between a Mott transition and the phase stabilities may be concealed at room temperature due to Slow reaction kinetics of the structural transformations.

DOI： 10.2138/am.2009.2913

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

High-temperature and high-pressure equations of state (EOSs) of Pt have been developed using measured shock compression data up to 290 GPa and volume thermal expansion data between 100 and nearly 2000 K and 0 GPa. The lattice thermal pressures at high temperatures have been estimated based on the Mie-Gruneisen relation with the Debye thermal model and the Vinet isothermal EOS. The contribution of electronic thermal pressure at high temperatures has also been included here. The optimized EOS parameters of Pt are K-0T = 273 GPa, K'(0T) = 5.20, gamma(0) = 2.70, and q = 1.10 with Theta(0) = 230 K, where the subscript 0 refers to the ambient conditions. The temperature-pressure-volume (T-P-V) data of Pt have also been measured up to 1600 K and 42 GPa, using synchrotron powder x-ray diffraction experiments combined with a Kawai-type multianvil high pressure apparatus and sintered diamond anvils. We find that the newly developed T-P-V EOS of Pt is fully consistent with not only the shock compression data up to 290 GPa and volume thermal expansion data up to near 2000 K, but also the present measured synchrotron T-P-V data and recently measured T-P-V data of Pt up to 1900 K and 80 GPa. Thus we find that there is no need to include a volume dependence of q over a wide pressure range up to more than 300 GPa. The present EOS has been developed without any pressure scale. Such excellent consistency between the EOS and experimental values over wide temperature and pressure ranges shows that the present EOS can be used as a reliable primary pressure standard for static experiments up to 300 GPa and 3000 K. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3054331]

DOI： 10.1063/1.3054331

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

The volume of MgSiO3 perovskite has been precisely measured at pressures of 19 to 53 GPa and temperatures of 300 to 2300 K by means of in situ X-ray diffraction in a multi-anvil apparatus. The present results indicate the isothermal bulk modulus K-T0 = 256(2) GPa and its pressure derivative K-T0' = 3.8(2). The fixed Debye temperature theta(0) = 1030 K gives a Gruneisen parameter at ambient pressure gamma(0) = 2.6(1) and its logarithmic volume dependence q = 1.7(1). The pressure derivative of the isothermal bulk modulus, Anderson-Gruneisen parameter and thermal expansion coefficient at ambient pressure are found to be (partial derivative K-T/partial derivative T)(P) = -0.035(2) GPa/K, delta(T) = 6.5(5), alpha(0) = 2.6(1) x 10(-5) + 1.0(1) x 10(-8) (T - 300)/K. Thus the thermal expansion coefficient largely becomes smaller with increasing pressure. The adiabatic geotherm would be fairly large, such as 0.41 K/km at a 660 km depth, and becoming smaller with increasing depth. The temperature and adiabatic geothermal gradient at the bottom of the D' layer would be 2400 K and 0.14 K/km. The buoyancy-driven mantle convection could be very small in the lower part of the lower mantle. Citation: Katsura, T., et al. (2009), P-V-T relations of MgSiO3 perovskite determined by in situ X-ray diffraction using a large-volume high-pressure apparatus, Geophys. Res. Lett., 36, L01305, doi: 10.1029/2008GL035658.

DOI： 10.1029/2008GL035658

DOI： 10.1029/2008gl035658

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Electrical conductivities of majorite garnet with compositions of pyrolite minus olivine (pyrolite majorite) and mid-ocean ridge basalt (MORB majorite) were measured under physical conditions of the mantle transition zone (18 and 23 GPa and temperatures up to 2000 K) in a Kawai-type multi-anvil apparatus. The samples with MORB composition are mainly composed of majorite, which has higher Fe and Al contents, and contain a small amount of stishovite. The conductivity of the MORB majorite is more than twice higher than those of the pyrolite majorite at the same temperature. The activation energies of these majorites are both 1.4 eV at temperature of 1000-1600 K suggesting that the dominant mechanism of charge transportation is Fe2(+)-Fe3(+) hopping (small polaron) conduction. At higher temperatures (&gt;1600 K), corresponding to temperature conditions of the transition zone. conduction mechanism of the pyrolite majorite would change from small polaron to ionic conduction. The pyrolite majorite has only slightly higher and lower conductivity than dry wadsleyite and ringwoodite, respectively, and will not largely change the conductivity-depth profile predicted for the dry mantle transition zone. The laboratory-based conductivity profile of the mantle transition zone with pyrolitic composition can explain well the current semi-global conductivity-depth profile obtained from electromagnetic study beneath Pacific. On the other hand, the garnetite originating from the oceanic crust has remarkably higher conductivity than the surrounding mantle because the conductivity of MORB majorite is significantly higher than those of wadsleyite and ringwoodite. Conductivity values of MORB majorite agree with those of the stagnant slab beneath the northeastern China. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2008.04.009

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Electrical conductivities of post-spinel, which are thought to be a dominant assembly in the lower mantle, were investigated at the conditions of the uppermost lower mantle (25 GPa and temperatures ranging from 300 to 2000K) in a Kawai-type multi-anvil apparatus. Post-spinel phases with a bulk composition of ((Mg,Fe)(2)SiO4: X-Fe = 0.09) were measured to constrain the bulk conductivity of the lower mantle. To investigate interconnectivity of ferro-periclase in silicate perovskite matrix, a single phase composed of magnesium silicate perovskite ((Mg, Fe)SiO3: X-Fe = 0.1) and ferro-periclase ((Mg, Fe)O: X-Fe = 0.13) were also measured. The conductivity values of the silicate perovskite are distinctly lower than those for the coexisting ferro-pericalse. Both absolute values and change in activation enthalpy for the conductivity of the post-spinel phases are similar to those for the silicate perovskite. These observations suggest that ferro-periclase in post-spinel are isolated in silicate perovskite matrix. Citation: Yoshino, T., D. Yamazaki, E. Ito, and T. Katsura (2008), No interconnection of ferro-periclase in post-spinel phase inferred from conductivity measurement, Geophys. Res. Lett., 35, L22303, doi:10.1029/2008GL035932.

DOI： 10.1029/2008GL035932

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Using in situ strength measurements at pressures up to 10 GPa and at room temperature, 400, 600, and 700 degrees C, we examined rheological properties of olivine, orthopyroxene, and chromian-spinel contained in a mantle-derived xenolith. Mineral strengths were estimated using widths of X-ray diffraction peaks as a function of pressure, temperature, and time. Differential stresses of all minerals increase with increasing pressure, but they decrease with increasing temperature because of elastic strain on compression and stress relaxation during heating. During compression at room temperature, all minerals deform plastically at differential stress of 4-6 GPa. During subsequent heating, thermally induced yielding is observed in olivine at 600 degrees C. Neither orthopyroxene nor spinel shows complete stress relaxation, but both retain some stress even at 700 degrees C. The strength of the minerals decreases in the order of chromian-spinel approximate to orthopyroxene &gt; olivine for these conditions. This order of strength is consistent with the residual pressure of fluid inclusions in mantle xenoliths.

DOI： 10.1007/s00269-008-0218-6

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Large single crystals of MgSiO3 perovskite were successfully synthesized by a thermal gradient method at 24 GPa and 1500 degrees C. This was achieved by an improvement of high-pressure synthesis technique that allowed us to grow single crystals under such ultrahigh-pressure conditions in relatively large volumes (e.g., 10 mm(3)). Since crystal growth is hindered by neighboring crystals, the nucleation density was suppressed by reducing the thermal gradient to 20 degrees C/mm, permitting an increase in free space for large crystal growth. KHCO3-Mg(OH)2 solvent can be used to grow perovskite crystals. However, the carbonate solvent produces melt inclusions. Silicate sources with MgSiO3 composition produce stishovite inclusions, which in turn cause sptitting of perovskite crystals. The formation of these inclusions is avoided by using H2O as a solvent and 85MgSiO(3)-15Mg(2)SiO(4), as a silicate source. The H2O also allows homogeneous crystal growth, probably because of its low viscosity and high silicate solubility. High-quality single crystals larger than I mm were successfully synthesized through these technical developments.

DOI： 10.2138/am.2007.2415

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In situ X-ray observations of the phase transition from ilmenite to perovskite structure in MnGeO3 were carried out in a Kawai-type high-pressure apparatus interfaced with synchrotron radiation. The phase boundary between the ilmenite and perovskite structures in the temperature range of 700-1,400 degrees C was determined to be P (GPa) = 16.5(+/- 0.6) -0.0034(+/- 0.0006)T (degrees C) based on Anderson's gold pressure scale. The Clapeyron slope, dP/dT, determined in this study is consistent with that for the transition boundary between the ilmenite and the perovskite structure in MgSiO3.

DOI： 10.1007/s00269-007-0145-y

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Grain growth kinetics of CaIrO3 perovskite and post-perovskite aggregates was investigated by time-series experiments at pressures of 2 and 3 GPa and temperatures ranging from 1373 to 1773 K in a piston cylinder apparatus. The experiments were conducted in the stability field of both perovskite and post-perovskite. The increase of grain size (G) with time (t) follows a growth law: G(n)-G(0)(n)=k.t (k=k(0) exp(-H*/RT)). The growth exponents (n) for perovskite and post-perovskite are 2.6 +/- 0.5 and 4.5 +/- 0.9, respectively. The activation enthalpy (H*) of post-perovskite grain growth is 251 +/- 35 kJ/mol. Grain growth of post-perovskite is distinctly slower than that of perovskite. Sluggish grain growth of the post-perovskite is caused by its strong anisotropic shape. The phase transition from the perovskite to the post-perovskite at the D" discontinuity would lead to maintenance of small grain size in the D" layer. If diffusion creep is the dominant deformation mechanism of post-perovskite, the phase transformation would induce the significant softening of the D" layer due to slow growth rate of post-perovskite compared with a situation without the phase transition. (c) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2007.01.010

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

Results of experimental studies and theoretical calculations on deformation of D″ layer minerals are reviewed. We conclude that only the results from the experiments under high temperature and modest stress conditions are potentially applicable to the deformation fabrics in the D″ layer. For perovskite and post-perovskite, such experimental data are available only for analog materials. By combining those results with elastic properties, we investigate the nature of seismic anisotropy corresponding to a given deformation geometry. Both azimuthal and polarization anisotropies are expected for all minerals. For horizontal flow, perovskite will produce VSV&gt
VSH anisotropy whereas (Mg,Fe)O shows VSH&gt
VSV anisotropy. VSH/VSV anisotropy caused by post-perovskite depends on the elastic anisotropy and the dominant glide plane, both of which are not well constrained. If we choose (010) as a glide plane, weak VSH&gt
VSV or VSV&gt
VSH anisotropy will develop for shear deformation of post-perovskite depending on the elastic constants. For this glide plane, the magnitude of the anisotropy of (Mg,Fe)O is much larger than that for post-perovskite. For a vertical cylindrical flow expected for upwelling mantle plumes, VSV&gt
VSH anisotropy is expected for both (Mg,Fe)O and post-perovskite but not for perovskite. We conclude that (Mg,Fe)O plays a more important role than post-perovskite for the interpretation of seismic anisotropy in both circum Pacific and the central Pacific D″ layer. In the circum Pacific regions, the seismic anisotropy can be attributed to the deformation-induced lattice-preferred orientation of (Mg,Fe)O and post-perovskite, whereas some additional contribution from aligned melt pocket might be important in the central Pacific.

DOI： 10.1029/174GM07

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Seismic anisotropy is one of the significant features in the D" layer of the Earth and is thought to be derived from the lattice preferred orientation (LPO) of constituent materials or shape preferred orientation (SPO) of heterogeneous materials such as melt and inclusions. Recent experimental and theoretical studies strongly suggest that the D" layer consists mainly of a MgSiO3 Postperovskite phase together with ferro-periclase. To understand the anisotropy in the D" layer, we have conducted a series of simple shear deformation experiments at high temperature and pressure on polycrystalline CaIrO3 as an analogue of MgSiO3 and measured the LPO of the post-perovskite phase. Crystallographic orientation analysis of the deformed post-perovskite phase showed strong LPOs with the dominant slip system being [100](010). Calculation of the elastic wave velocities considering the effect of LPOs of post-perovskite and ferro-periclase showed as azimuthal and polarization anisotropies in the horizontal shear plane where the velocity of horizontally polarized S-wave is considerably faster than that of vertically polarized S-wave. Thus, the seismic anisotropy observed in the D" layer can be reasonably explained by the LPO of the mixture of post-perovskite and ferro-periclase, where the LPO may result from the horizontal shear flow generated by the mantle convection. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2006.10.004

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To obtain higher pressures in a Kawai-type apparatus, we explored and tested high-pressure cell assemblies suitable for experiments using sintered diamond (SD) anvils. As a result, we succeeded in generating pressures exceeding 55 GPa at temperatures of 1000 degrees C in a Kawai-type apparatus (SPEED Mk-II) at SPring-8. Using the optimized cell assembly, we examined the stability field of MnGeO3 perovskite, an analog of MgSiO3 perovskite, which was recently found to transform to a new high-pressure form under the P-T conditions near the core-mantle boundary. From our in situ X-ray observations, MnGeO3 perovskite was found to be stable at pressures up to 56-57 GPa at temperatures of 800-1050 degrees C.

DOI： 10.2138/am.2006.2175

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The phase boundary between wadsleyite and ringwoodite in Mg2SiO4 has been determined in situ using a multi-anvil apparatus and synchrotron X-rays radiation at SPring-8. In spite of the similar X-ray diffraction profiles of these high-pressure phases with closely related structures, we were able to identify the occurrence of the mutual phase transformations based on the change in the difference profile by utilizing a newly introduced press-oscillation system. The boundary was located at similar to 18.9 GPa and 1,400 degrees C when we used Shim's gold pressure scale (Shim et al. in Earth Planet Sci Lett 203:729-739, 2002), which was slightly (similar to 0.8 GPa) lower than the pressure as determined from the quench experiments of Katsura and Ito (J Geophys Res 94:15663-15670, 1989). Although it was difficult to constrain the Clapeyron slope based solely on the present data due to the kinetic problem, the phase boundary [P (GPa)=13.1+4.11x10(-3)xT (K)] calculated by a combination of a P-T position well constrained by the present experiment and the calorimetric data of Akaogi et al. (J Geophys Res 94:15671-15685, 1989) reasonably explains all the present data within the experimental error. When we used Anderson's gold pressure scale (Anderson et al. in J Appl Phys 65:1535-1543, 1989), our phase boundary was located in similar to 18.1 GPa and 1,400 degrees C, and the extrapolation boundary was consistent with that of Kuroda et al. (Phys Chem Miner 27:523-532, 2000), which was determined at high temperature (1,800-2,000 degrees C) using a calibration based on the same pressure scale. Our new phase boundary is marginally consistent with that of Suzuki et al. (Geophys Res Lett 27:803-806, 2000) based on in situ X-ray experiments at lower temperatures (&lt; 1,000 degrees C) using Brown's and Decker's NaCl pressure scales.

DOI： 10.1007/s00269-005-0053-y

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In situ X-ray diffraction measurements of KAlSi3O8-hollandite (K-hollandite) were performed at pressures of 15 - 27 GPa and temperatures of 300-1,800 K using a Kawai-type apparatus. Unit-cell volumes obtained at various pressure and temperature conditions in a series of measurements were fitted to the high-temperature Birch-Murnaghan equation of state and a complete set of thermoelastic parameters was obtained with an assumed K'(300,0) = 4. The determined parameters are V-300,V-0 = 237.6( 2) angstrom(3), K-300,K-0 = 183(3) GPa, (partial derivative K-T,K-0/partial derivative T)(P) = - 0.033( 2) GPa K-1, a(0) = 3.32(5) x 10(-5) K-1, and b(0) = 1.09(1) x 10(-8) K-2, where a(0) and b(0) are coefficients describing the zero-pressure thermal expansion: alpha(T,0) = a(0) + b(0) T. We observed broadening and splitting of diffraction peaks of K-hollandite at pressures of 20 - 23 GPa and temperatures of 300 - 1,000 K. We attribute this to the phase transitions from hollandite to hollandite II that is an unquenchable high-pressure phase recently found. We determined the phase boundary to be P (GPa) = 16.6 + 0.007 T ( K). Using the equation of state parameters of K-hollandite determined in the present study, we calculated a density profile of a hypothetical continental crust (HCC), which consists only of K-hollandite, majorite garnet, and stishovite with 1: 1: 1 ratio in volume. Density of HCC is higher than the surrounding mantle by about 0.2 g cm(-3) in the mantle transition zone while this relation is reversed below 660-km depth and HCC becomes less dense than the surrounding mantle by about 0.15 g cm(-3) in the uppermost lower mantle. Thus the 660-km seismic discontinuity can be a barrier to prevent the transportation of subducted continental crust materials to the lower mantle and the subducted continental crust may reside at the bottom of the mantle transition zone.

DOI： 10.1007/s00269-005-0037-y

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

Thermal equation of state of an Al-rich phase with Na1.13Mg1.51Al4.47Si1.62O12 composition has been derived from in situ X-ray diffraction experiments using synchrotron radiation and a multianvil apparatus at pressures up to 24 GPa and temperatures up to 1,900 K. The Al-rich phase exhibited a hexagonal symmetry throughout the present pressure - temperature conditions and the refined unit-cell parameters at ambient condition were: a = 8.729(1) angstrom, c= 2.7695(5) angstrom, V-0 = 182.77(6) angstrom(3) (Z = 1; formula weight = 420.78 g/mol), yielding the zero-pressure density rho(0) = 3.823(1) g/cm(3). A least-square fitting of the pressure-volume-temperature data based on Anderson&apos;s pressure scale of gold ( Anderson et al. in J Appl Phys 65: 1534 - 543, 1989) to high-temperature Birch-Murnaghan equation of state yielded the isothermal bulk modulus K-0 = 176(2) GPa, its pressure derivative K-0&apos; = 4.9(3), temperature derivative (partial derivative K-T/partial derivative T)(P) = - 0.030(3) GPa K-1 and thermal expansivity alpha(T) = 3.36(6) x 10(-5) + 7.2(1.9) x 10(-9) T, while those values of K-0 = 181.7(4) GPa, (partial derivative K-T/partial derivative T)(P) = -0.020(2) GPa K-1 and alpha(T) = 3.28(7) x 10(-5) + 3.0(9) x 10(-9) T were obtained when K-0&apos; was assumed to be 4.0. The estimated bulk density of subducting MORB becomes denser with increasing depth as compared with earlier estimates ( Ono et al. in Phys Chem Miner 29: 527 - 531 2002; Vanpeteghem et al. in Phys Earth Planet Inter 138: 223 - 230 2003; Guignot and Andrault in Phys Earth Planet Inter 143 44: 107 - 128 2004), although the difference is insignificant (&lt; 0.6%) when the proportions of the hexagonal phase in the MORB compositions ( similar to 20%) are taken into account.

DOI： 10.1007/s00269-005-0029-y

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

Grain growth rates of Mg2SiO4- and (Mg0.9Fe0.1)(2)SiO4-ringwoodites have been studied under the conditions of the mantle transition zone at a pressure of 21 GPa and temperatures ranging from 1473 to 2023 K, using a Kawai-type high-pressure apparatus. The grain growth rates were expressed by G(n) - G(0)(n)=G(0)(n)texp (-H*/RT) where G (m) is grain size at time t (s), and Go is the initial grain size at t=0, with n=4.5 +/- 0.8, and H*=414 kJ/mol and log k(0)=- 20.4 +/- 1.6 m(4.5)/s for (Mg0.9Fe0.1)(2)SiO4-ringwoodite, and H*=456 kJ/mol and logk(0)=-20.2 +/- 1.4 m(4.5)/s for Mg2SiO4-ringwoodite. Using these kinetic parameters for grain growth, we estimated the grain size of ringwoodite in the cold subducting slabs to be less than similar to 100 mu m. This suggests that the dominant deformation mechanism in the subducting slab is diffusion creep. It is also likely that some cold slabs are softer than the warmer surrounding mantle. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2005.06.005

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Fe-Mg interdiffusivities in (Fe,Mg)O magnesiowustite have been measured in experiments conducted at pressures of 7-35 GPa and temperatures of 1573-1973 K using a Kawai-type high-pressure apparatus. The diffusion profiles were measured across the interface between MgO and (Fe(0.5),Mg(0.5))O samples by electron microprobe analysis, and the Fe-Mg interdiffusivities were determined as D(Fe-Mg) = D(0)exp{-E*(1+PV*(Mg)/E*(Mg))/RT}, where D(0) = 4.1((+16.1)(-3.3)) x 10(-7) m(2)/s, E* = (1-C(Mg))E*(Fe) + C(Mg)E*(Mg) (activation energy for the concentration of Mg, where E*(Fe) = 113(+/-74) kJ/mol and E*(Mg) = 226(+/-32) kJ/mol), the activation volume V*(Mg) = 1.8(+/-1.2) x 10(-6) m(3)/mol. By extrapolating these results to the P-T conditions of the core-mantle boundary, we conclude that the interdiffusivity of Fe-Mg in magnesiowustite at the bottom of the lower mantle is at least one order of magnitude larger than that at the top of the lower mantle. (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/S0012-821X(03)00534-X

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Large strain, shear deformation experiments were performed on (Mg(1-x),Fe(x))O (x = 0.25, 1.0), one of the important minerals in Earth&apos;s lower mantle. Deformation experiments were made on coarse-grained (similar to15-20 mum grain-size) hot-pressed aggregates at conditions of T/T(m) similar to 0.46-0.65 (T: temperature, T(m): melting temperature) and sigma/mu similar to 0.4 x 10(-3) to 0.9 x 10(-3) (sigma: differential stress, mu: shear modulus) up to the shear strain of similar to7.8. Under these conditions, deformation occurs by dislocation creep. The microstructural development in (Mg,Fe)O is found to be sluggish and the complete dynamic recrystallization and nearly steady-state fabric (lattice preferred orientation) are achieved only after shear strains of gamma similar to 4. At nearly steady-state, (Mg,Fe)O shows strong fabrics characterized by the (110) axes being parallel to the shear direction and the poles of the {100} planes (and to a lesser extent the poles of the {110} planes) normal to the shear plane. The seismic anisotropy corresponding to the deformation fabrics in (Mg,Fe)O was calculated. The nature of anisotropy corresponding to a given flow geometry changes significantly with strain as a result of fabric evolution. Anisotropy changes also with depth (pressure) due to the large variation of elastic anisotropy of (Mg,Fe)O with depth. Seismic anisotropy caused by the deformation fabric of (Mg,Fe)O is very weak in the shallow lower mantle (&lt;0.1%), but it becomes strong in the deeper portions due to the high elastic anisotropy of (Mg,Fe)O. Near the bottom of the mantle, the steady-state fabric of (Mg,Fe)O corresponding to the horizontal shear will result in similar to 1-2% V(SH) &gt; V(SV) anisotropy (assuming that (Mg,Fe)O occupies similar to20% volume fraction of the lower mantle) and little shear wave splitting of vertically travelling waves, a result that is consistent with the seismological observations in the D" layer of the circum-Pacific regions. Thus, the deformation fabric of (Mg,Fe)O is a vital candidate of the cause of seismic anisotropy in these regions. Anisotropy caused by the lattice preferred orientation of (Mg,Fe)O has a distinct azimuthal anisotropy with a strong 4theta term (theta: azimuth): the direction of propagation of the fastest (slowest) SH (or P) wave is parallel (perpendicular) to the flow direction and the slowest (fastest) SH (or P) wave is at 45degrees from these two directions. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0031-9201(02)00037-7

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

A new apparatus has been developed that allows large-strain plastic deformation experiments under high pressure with a controlled strain rate in simple shear deformation geometry. A modification is made to a Drickamer-type opposed anvil apparatus to allow torsion tests by attaching a rotation actuator composed of a dc servomotor and a gear box. A thin disk of a sample (less than similar to0.8 mm thick and to similar to4 mm diameter) can be sheared between two anvils under pressure by a rotation actuator. Specimens of Fe were sheared to strains exceeding gamma similar to6 at pressures up to similar to 15 GPa. Nearly simple shear deformation was achieved when the initial sample thickness is less than similar to0.4 mm. This apparatus allows studies of plastic flow and deformation microstructures under high pressures. (C) 2001 American Institute of Physics.

DOI： 10.1063/1.1412858

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

We explore the implications of recent mineral physics measurements of diffusion coefficients and melting temperatures of lower mantle materials on the rheological and geothermal structure of Earth's lower mantle. We show that MgSiO3 perovskite is significantly stronger than MgO periclase and therefore the rheology of the lower mantle depends strongly on the geometry of a weaker phase, periclase. We calculate viscosities of the lower mantle for two cases: (1) where periclase occurs as isolated grains and (2) where periclase occurs as continuous films, using mineral physics data and models of two-phase rheology. We find that the effective viscosity for the former is about similar to 10-1000 times higher than the latter. We therefore suggest that the rheology of the lower mantle is structure- and hence strain-dependent. leading to weakening at large strains due to the formation of continuous films of periclase. Overall depth variation of viscosity depends not only on the pressure dependence of creep but also on the geothermal gradient. Both MgSiO3 perovskite and periclase have relatively small activation energies (E-. = gRT(m) with g = 10-14, where R is the gas constant and T-m is melting temperature), and therefore the depth variation of viscosity is rather small, even for a nearly adiabatic temperature gradient. However, the geothermal gradients consistent with the geodynamical inference of nearly depth-independent viscosity are sensitive to the pressure dependence of viscosity which is only poorly understood. A superadiabatic gradient of up to similar to0.6 K/km is also consistent with mineral physics and geodynamical observations.

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Silicon self-diffusion coefficients in MgSiO3 perovskite were measured under lower mantle conditions. The MgSiO3 perovskite was synthesized and diffusion annealing experiments were conducted at pressure of 25 GPa and temperature of 1673-2073 K using a MA8 type high-pressure apparatus. The diffusion profiles were obtained by secondary ion mass spectrometry. The lattice and grain boundary diffusion coefficients (D-1 and D-gb) were determined to be D-1 [m(2)/s] = 2.74 x 10(-10) exg(-336 [kJ/mol]/RT) and delta D-gb [m(3)/s] = 7.12 x 10(-17) exp(-311 [kJ/mol]/RT), respectively, where delta is the width of grain boundary, R is the gas constant and T is the absolute temperature. These diffusion coefficients play a key role for understanding the rheology of the lower mantle, (C) 2000 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0031-9201(00)00135-7

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The earth's lower mantle is mainly composed of (Mg, Fe)SiO3 perovskite and (Mg, Fe)O magnesiowüstite. It is essential to determine the rheological properties of MgSiO3 perovskite and periclase for understanding the rheology of the lower mantle. High pressure and temperature experiments were carried out under lower mantle conditions to determine their rheological properties. The grain growth rates of perovskite and periclase were determined to be G10.6 [ml=1 X 10-57.4t [sec] exp(-320.8 [kJ/mol] IRT) and G10.8 [m] = 1 X10-62.3t [sec] exp(-247.0 [kJ/mol]/RT), respectively, where G is grain size at time t, R is the gas constant and T is the absolute temperature. The lattice diffusion coefficient (D1) and grain boundary diffusion coefficient (Dsb) of silicon in MgSiO3 perovskite were determined at 25 GPa and 1673-2073 K to be D1 [m2/sec]=3.76 X 10-10exp(-338 [kJ/mol] /RT) and δDsb [m3/sec]=1.02 X 10-16 exp(-303 [kJ/mol] /RT), respectively, where δ is the width of the grain boundary. The grain size of perovskite in the lower mantle is estimated to be 1-10 mm, which suggests diffusion creep (Nabarro-Herring creep) as a dominant deformation mechanism in the greater part of the lower mantle. The present results indicate that the subducting slab is much softer than the surrounding lower mantle due to the slow grain growth rate. © 1999, The Japan Society of High Pressure Science and Technology. All rights reserved.

DOI： 10.4131/jshpreview.9.19

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

This is the first report of the direct measurement of alpha-beta transformation kinetics in Mg2SiO4, a major constituent in the Earth's mantle, through in situ X ray diffraction experiments at high pressure. The experiments were conducted using the sintered diamond cubic-anvil apparatus with synchrotron radiation (MAX 80). Although the present work is still preliminary, the kinetic data were analyzed using a nucleation and growth model. The growth rate of beta-phase is determined to be 3.3 (1.6 similar to 4.9) x 10(-10) m/s at 13.0 GPa and 900 degrees C, 7.1 (3.4 similar to 10) x 10(-10) m/s at 14.1 GPa and 885 degrees C, and 1.5 (0.7 similar to 2.3) x 10(-9) m/s at 14.9 GPa and 875 degrees C.

DOI： 10.1029/98GL00224

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In situ X-ray observation has been made on MgsSiO4 forsterite in the pressure ranges over 250–30 GPa and 1250°C, using double stage multianvil system with sintered diamond anvil window and intense X-rays from synchrotm radiation. Forsterite (α-phase) transfomed into spinel (γ-phase) at 28 GPa and 800αC in the frist heating cycles of the two runs. Spinel transformed into the assemblage of perovskite and periclase in the second heating cycless at 26.4 GPa and 1200°C and at 28.5 GPa and 950°C. The results show that α-γ transition can proceed outside the stability field of spinel, and that the blocking temperature, above which the stable assmblage of perovskite and periclase can be formed, has a pressure dependence. © 1998, The Japan Society of High Pressure Science and Technology. All rights reserved.

DOI： 10.4131/jshpreview.7.119

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER ASSOC ADVANCEMENT SCIENCE  

The grain growth rates of MgSiO3 perovskite and periclase in aggregates have been determined at 25 gigapascals and 1573 to 2173 kelvin. The average grain size (G) was fitted to the rate equation, and the grain growth rates of perovskite and periclase were G(10.6) = 1 X 10(-57.4) t exp(-320.8/RT) and G(10.8) = 1 X 10(-62.3) t exp(-247.0/RT), respectively, where t is the time, R is the gas constant, and T is the absolute temperature. These growth rates provide insight into the mechanism for grain growth in minerals relevant to the Earth's lower mantle that will ultimately help define the theology of the lower mantle.

DOI： 10.1126/science.274.5295.2052

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DOI： 10.4294/zisin1948.49.1_39

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

DOI： 10.1029/95jb01688

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An experimental method to study the seismic attenuation factor (Q-1) and anelastic properties of materials at high pressure and high temperature has been established by using the multianvil high-pressure deformation device (D-DIA) and a synchrotron X-ray radiography at SPring8. Time resolved images of the sample and reference material provide their strain as a function of time during cyclic loading. Attenuation is determined as the tangent of the angle of phase lag between the sample and the reference material. A newly installed short period sinusoidal cyclic loading oil pressure system enable us to determine minimal strain of the sample in a wide frequency range from 2 to 0.01 hertz on olivine aggregates at 1 GPa and up to 1673 K. The detectable minimum strain is around 5×10^-5. Several test experiments exhibited resolvable Q^-1 (10^-2) above 1273 K. The results are generally consistent with previously reported data.

DOI： 10.4131/jshpreview.24.126

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We studied the tolerance of living organisms, such as a small animal (Milnesium tardigradum), a small crustacean (Artemia), non-vascular plants or moss (Ptichomitrium and Venturiella), and a vascular plant (Trifolium) to the extremely high hydrostatic pressure of 7.5 GPa. It turned out that most of the high pressure exposed seeds of white clover were alive. Those exposed to 7.5 GPa for up to 1 day and seeded on agar germinated roots. Those exposed for up to 1 hour and seeded on soil germinated stems and leaves. Considering the fact that proteins begins to unfold around 0.3 GPa, it seems difficult to understand that all the living samples which have been investigated can survive after exposure to 7.5 GPa.

DOI： 10.1088/1742-6596/377/1/012053

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Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.67.1.2.0_402_1

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A new carbon-nitride-related material C2N2(CH2) nanopletelet was synthesized by subjecting a precursor C3N4HxOy+Au in a laser-heating diamond anvil cell (LHDAC) to the pressure of 40 GPa and the temperature of 1200-2000 K. The synthesized C2N2(CH2) was accordingly found to be an orthorhombic unit cell of the space group Cmc2(1) with lattice constants a = 7.625 angstrom, b = 4.490 angstrom, and c = 4.047 angstrom. The bulk modulus B-0 was determined to be B-0 = 258 +/- 3.4 GPa, only the 60 % that of the diamond. C2N2(CH2) consists of the tetrahedrally coordinated C with three C-N single bond and the one C-C single bond, and the bridging carbon with the C-CH2-C bond. The C-N single bond length of the tetrahedron ranges from 1.444 to 1.503 angstrom. This bond length is close to the C-N single bond of 1.447 to 1.458 angstrom in the superhard beta-C3N4. The compressibility of the C-N and C-C single bond of C2N2(CH2) ranges from 0.976 to 0.982 with the pressure of 30 GPa. These values are very close to the compressibility of the C-N and C-C single bond of 0.978 to 0.982 in beta-C3N4, cubic-C3N4, and diamond.

DOI： 10.1088/1742-6596/377/1/012028

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A new carbon-nitride- related C2N2(CH2) nanoplatelet was synthesized by subjecting a precursor C3N4HxOy nanoparticle in a laser-heating diamond anvil cell to the pressure of 40 GPa and temperature of 1200-2000 K. The C and N composition of the quenched sample was determined to be C3N2 by using an energy dispersive X-ray spectroscope attached to a transmission electron microscope. The crystal structure and atomic positions of this C3N2 were obtained through Rietveld analysis of the X-ray diffraction pattern measured using synchrotron radiation. The hydrogen composition was difficult to determine experimentally because of the several-hundred-nanometer dimensions of the sample. First-principles calculation was alternatively used to discover the hydrogen composition. The synthesized C2N2(CH2) was accordingly found to be an orthorhombic unit cell of the space group Cmc2(1) with lattice constants a 7.625 angstrom, b 4.490 angstrom, and c 4.047 angstrom. If the CH2 atomic unit is replaced with the CN2 atomic unit and the bonding rearranged, the C2N2(CH2) becomes the expected superhard C3N4. (C) 2011 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.50.095503

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

In this decade, attainable pressure range in a Kawai-type high-pressure apparatus equipped with sintered diamond as second stage anvil is significantly increased and we generated pressure to 97.2 GPa measured by in situ X-ray observation at SPring-8. By using this technique, we measured compressibility of (Fe0.08Mg0.92)SiO3 perovskite up to more than 90 GPa. The bulk modulus and its pressure derivative are determined to be 268 GPa and 3.8, respectively. These values are slightly different from previous results. However, we obtained consistent results with previous study of bulk modulus of 257 GPa and pressure derivative of 4.3 when we fitted the data in the pressure range less than 70 GPa. The change of compressibility may indicate the spin transition in Fe-bearing perovskite around 70 GPa as suggested by previous study, for example, electrical conductivity measurement, X-ray emission method and so on.

DOI： 10.4131/jshpreview.21.272

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Language：English   Publishing type：Rapid communication, short report, research note, etc. (scientific journal)  

DOI： 10.4131/jshpreview.21.148

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DOI： 10.14824/jakoka.2009.0.193.0

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Electrical conductivity of mantle peridotite was measured at 25 GPa and temperature up to 1800 K in a Kawai-type multi-anvil apparatus. The starting material was gel with a composition of fertile spinel lherzolite (KLB1). After the conductivity measurement, mineral phases of run products are composed of magnesium silicate perovskite, ferro-periclase and Ca perovskite. The conductivity value of the peridotite is distinctly higher than those of post-spinel and magnesian silicate perovskite with a composition of (Mg(0.9), Fe(0.1)) SiO(3), but lower than that of ferro-periclase. Both absolute values and change in activation enthalpy for the conductivity of the mantle peridotite are similar to those for the silicate perovskite. A presence of aluminous perovskite with substantial amount of ferric iron in crystal structure would enhance bulk conductivity of the lower mantle.

DOI： 10.1088/1742-6596/215/1/012102

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Phase transformation from perovskite to "post-perovskite" and reserve transition in CaRuO3 was observed by in situ X-ray diffraction at pressure of 20-22 GPa and temperature of 1173-1523 K. These pressure and temperature conditions are 1-2 GPa lower than previous results by quenched method. The axial compressibility is estimated to be a/a(0)&gt;b/b(0)&gt;c/c(0). This result is inconsistent with previous result on CaIrO3.

DOI： 10.1088/1742-6596/215/1/012096

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High pressure generation has been tried by using the Kawai-cell equipped with sintered diamond cubes in conjunction with investigation of the spin transition in Fe2+ of (Mg0.83Fe0.17)O (ferropericlase, Fp). The Kawai-cell was squeezed in the DIA type press SPEED mkII installed at SPring-8. The volumes of the Fp and Au pressure standard were simultaneously determined by in situ X-ray diffraction using the synchrotron radiation. The maximum attainable pressure has reached 90 GPa at 300 K based on Anderson et al.'s Au scale [4]. The P-V data of (Mg0.83Fe0.17)O were acquired at 300 K and 700 K up to 90 GPa. From detailed analysis of the compression data, it is suggested that the spin transition proceeds over pressure ranges from 50 to 70 GPa at 300 K and from 50 to 75 GPa at 700 K.

DOI： 10.1088/1742-6596/215/1/012099

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Language：Japanese   Publishing type：Book review, literature introduction, etc.  

Transformation from perovskite to post-perovskite was observed in MnGeO3 and MgGeO3 in the Kawai-type apparatus equipped with sintered diamond anvils by means of in situ X-ray diffraction method. In MnGeO3, post-perovskite phase was observed at 63.5 GPa and 1233 K. The transition pressure was ∼6 GPa higher than previous report by the laser heated diamond anvil cell experiment. In MgGeO3, we observed the transformation from perovskite to post-perovskite and the reversal transformation under the conditions of 61-64 GPa and 1100-1700 K. The phase boundary was determined to be P (GPa) = 5.2 × 10-3 T (K)+55.2, where P is pressure and T is absolute temperature, which is almost consistent with previous result by diamond anvil experiments. However, reliable pressure standard is needed to determine the boundary precisely.

DOI： 10.4131/jshpreview.18.254

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Language：Japanese   Publishing type：Book review, literature introduction, etc.  

We have developed a new 6-axis apparatus in which movement of the six anvils are controlled by the high-tech servo mechanism. It is possible to keep the Kawai cell cubic within accuracy of ± 2 μm during compression and decompression. Pressures up to ca. 60 GPa have been generated by using sintered diamond cubic anvils with 14 mm edge length and 1.5 mm truncation. Comparison of the results with our previous experiments using the DIA-type press demonstrates that significant amount of applied load is lost by friction in squeezing the Kawai-cell by the DIA-type press. The load loss increases with increasing load, and it amounts to 45% of the applied load when compressed up to ca. 6.2 MN.

DOI： 10.4131/jshpreview.18.208

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Language：Japanese   Publisher：Japan Association of Mineralogical Sciences  

We have measured electrical conductivity of partially molten model peridotite. The model peridotite consists of forsterite with basalt and carbonate without iron. Conductivity was measured using a cubic anvil apparatus with a deformation function and Solartron 1260 impedance analyzer. The measurement conditions are 1600 K and 2 GPa. The shear strain speeds are 6 × 10-7 and 2 × 10-6 /s. We have found that conductivity in the shear direction is one order of magnitude higher than that normal to the shear direction. The magnitude of anisotropy in conductivity is independent of shear velocity. The magnitude of anisotropy is independent of the strain rate. These experimental results suggest that the observed highly anisotropic conductivity is explained by partially molten peridotite under shear conditions.

DOI： 10.14824/jakoka.2008.0.182.0

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We have measured the T-P-V data of Pt at high temperatures between 800 and 1600 K, and high pressures between 21 and 42 GPa, using synchrotron powder X-ray diffraction experiments at Spring-8. Both a Kawai-type multi-anvil high pressure apparatus with sintered diamond anvils and a laser-heated diamond anvil cell were used to measure higher T-P data of Pt. Combining these measured high P and T data with previously reported 300 K volume compression data, and using the Mie-Greuneisen type thermal pressure analysis, we present the T-P-V EOS of Pt, as a reliable pressure calibration standard at high T and P conditions up to 3000 K and more than 150 GPa.

DOI： 10.14824/jakoka.2008.0.193.0

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地球のマントルの代表的な組成と考えられているパイロライトについてマルチアンビル高圧装置と放射光を用いたその場X線回折実験を30-40GPa, 1800℃の領域で行った。その結果これまで報告されている30GPaまでの相関係に変化は見られず、Mg-rich perovskite, Ca-rich perovskite, (Mg,Fe)O ferropericlase が観察された。

DOI： 10.14824/kobutsu.2005.0.14.0

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放射光X線その場観察実験により、パイロライトとMORBの660km地震波不連続面付近の密度変化を明らかにした。密度は高温高圧下における鉱物の格子体積と、回収試料の化学組成分析から、X線密度の定義に従って決定した。パイロライト、MORBともIrifune (1993)、Irifune and Ringwood (1993)の結果と一致した。Irifune (1993)では特に下部マントル領域における密度変化に大きな誤差が生じていた（約±0.1g/cm&lt;SUP&gt;3&lt;/SUP&gt;）。これは、鉱物の化学組成分析、格子定数の誤差と、熱弾性パラメーターの不確定さに起因していた。本研究では、熱弾性パラメーターの誤差が加わらないため、約±0.05 g/cm&lt;SUP&gt;3&lt;/SUP&gt;以下の精度で密度変化を制約することができた。

DOI： 10.14824/kobutsu.2005.0.18.0

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Publisher：Japan Association of Mineralogical Sciences  

The Earth's lower mantle is considered to be composed mainly of (Mg,Fe)SiO3-perovskite and magnesiowüstite, and the iron contents influence their densities and phase relations. Therefore, it is very important to determine the iron contents of these phases in understanding structure and dynamics in the lower mantle. Several workers have studied Fe-Mg partitioning between (Mg,Fe)SiO3-perovskite and magnesiowüstite, but temperature dependence on the partitioning has not been well understood. In this study, we have experimentally determined the partitioning of iron between these two phases and its temperature dependence.We conducted high-pressure experiments using a Kawai type high-pressure apparatus at ~24 GPa, and at 1673-2273K. We used San Carlos olivine with a composition of (Mg0.91Fe0.09)2SiO4 as starting material. After the high presser and temperature runs, the products were examined using SEM, EDS and X-ray diffraction techniques to observe the microstructures, to measure the chemical composition and to identify the phase present, respectively.The partition coefficient defined as KD=(Fe/Mg)Pv/ (Fe/Mg)Mw increased from 0.19 to 0.34, with increasing temperature from 1673-2273K.

DOI： 10.14824/kobutsu.2005.0.16.0

CiNii Article

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Language：Japanese  

J-GLOBAL

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Language：Japanese  

J-GLOBAL

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Language：Japanese  

J-GLOBAL

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Language：Japanese  

J-GLOBAL

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Language：Japanese  

J-GLOBAL

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Language：Japanese  

J-GLOBAL

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Language：Japanese  

CiNii Article

CiNii Books

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Language：Japanese   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2004.abst.0_279_1

CiNii Article

CiNii Books

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Language：Japanese  

J-GLOBAL

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Language：Japanese  

J-GLOBAL

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