掲載種別：研究論文（学術雑誌）   出版者・発行元：Springer Science and Business Media LLC  

DOI： 10.1038/s41561-023-01169-4

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その他リンク： https://www.nature.com/articles/s41561-023-01169-4

担当区分：最終著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Wiley  

DOI： 10.1002/pssb.202300079

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掲載種別：研究論文（学術雑誌）   出版者・発行元：American Geophysical Union (AGU)  

DOI： 10.1029/2022gl101769

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担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier BV  

DOI： 10.1016/j.lithos.2022.106817

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担当区分：最終著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Frontiers Media SA  

DOI： 10.3389/feart.2022.1030793

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掲載種別：研究論文（学術雑誌）   出版者・発行元：American Association for the Advancement of Science (AAAS)  

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

DOI： 10.1126/sciadv.abm1821

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier BV  

DOI： 10.1016/j.gsf.2021.101342

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Geophysical Union (AGU)  

DOI： 10.1029/2021jb022977

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その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2021JB022977

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Informa UK Limited  

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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担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Springer Science and Business Media LLC  

<title>Abstract</title>The compositional difference between subducting slabs and their surrounding lower-mantle can yield the difference in incorporation mechanism of Fe and Al into bridgmanite between both regions, which should cause heterogeneity in physical properties and rheology of the lower mantle. However, the precise cation-distribution has not been examined in bridgmanites with Fe- and Al-contents expected in a mid-ocean ridge basalt component of subducting slabs. Here we report on Mg_0.662Fe_0.338Si_0.662Al_0.338O₃ bridgmanite single-crystal characterized by a combination of single-crystal X-ray diffraction, synchrotron ⁵⁷Fe-Mössbauer spectroscopy and electron probe microanalysis. We find that the charge-coupled substitution ^AMg²⁺  + ^BSi⁴⁺  ↔ ^AFe³⁺(high-spin) + ^BAl³⁺ is predominant in the incorporation of Fe and Al into the practically eightfold-coordinated A-site and the sixfold-coordinated B-site in bridgmanite structure. The incorporation of both cations via this substitution enhances the structural distortion due to the tilting of BO₆ octahedra, yielding the unusual expansion of mean &lt;A–O&gt; bond-length due to flexibility of A–O bonds for the structural distortion, in contrast to mean &lt;B–O&gt; bond-length depending reasonably on the ionic radius effect. Moreover, we imply the phase-transition behavior and the elasticity of bridgmanite in slabs subducting into deeper parts of the lower mantle, in terms of the relative compressibility of AO₁₂ (practically AO₈) and BO₆ polyhedra.

DOI： 10.1038/s41598-021-00403-6

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その他リンク： https://www.nature.com/articles/s41598-021-00403-6

掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier BV  

DOI： 10.1016/j.pepi.2021.106824

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担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

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担当区分：最終著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Mineralogical Society of America  

<title>Abstract</title>
Electrical conductivities of diaspore (α-AlOOH), δ-AlOOH, and ε-FeOOH were measured by impedance spectroscopy with a frequency range from 10–1 to 106 Hz at pressures from 8 to 20 GPa and temperatures from 500 to 1200 K, well below the dehydration temperatures of these phases at the relevant pressures. For diaspore, the relationship between electrical conductivity and reciprocal temperature can be well fitted by the Arrhenius formula:


σ = σ 0 exp ⁡ [ − ( Δ E + P Δ V ) k T ] ,


where σ0 is the pre-exponential factor, ∆E is the activation energy, and ∆V is activation volume of 56.0 ± 1.2 S/m, 0.55 ± 0.02 eV, and 1.68 ± 0.12 cm3/mol, respectively. The electrical conductivity of diaspore decreases with increasing pressure ranging from 8 to 12 GPa by a half order of magnitude, whereas the conductivity becomes almost constant in a pressure range above 12 GPa. δ-AlOOH and ε-FeOOH show one and two orders of magnitude higher electrical conductivity than diaspore. Electrical conductivities of δ-AlOOH and ε-FeOOH, which have isostructural CaCl2-type hydroxide structure, show the nearly identical activation enthalpies (0.38 ± 0.01, 0.33 ± 0.05 eV), which are relatively lower than that of diaspore. The dominant conduction mechanism of AlOOH phases can be regarded as proton conduction. The conductivity difference between diaspore and δ-AlOOH attributes to result in the different O1H bond lengths of each phase. The reduction of O1H bond length with increasing pressure could enhance the proton migration by reducing the potential barrier, thereby raising the electrical conductivity. Small polaron conduction may contribute to the conductivity of ε-FeOOH to generate higher conductivity than δ-AlOOH. Furthermore, hydrogen bond symmetrization will also play an important role in the conductivity discrepancy of these hydrous minerals with CaCl2-type hydroxide structure. For subducted sedimentary rocks, polymorphs of AlOOH and FeOOH are representative hydrous phases. Al-rich sediments show conductivity reduction with increasing depth until phase transformation occurs because diaspore represents negative pressure dependence of conductivity. After transformation to δ-AlOOH, the conductivity will jump up around 18 GPa. If ε-FeOOH is stable above 5 GPa in an iron-rich lithology, such as banded iron formation (BIF), a high conductivity zone with positive pressure dependence could be observed to the deep lower mantle.

DOI： 10.2138/am-2021-7605

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier BV  

Classical view has interpreted deuterons in nominally anhydrous minerals (NAMs) diffuse slightly slower than protons by the Knudsen limit of root 2, whereas here we report deuteron diffusion is about 3 similar to 7 times faster than proton one in Mg2SiO4 wadsleyite based on the H-D interdiffusion couple experiments using a pair of wadsleyite single crystal at 16 GPa and 900-1300 K. Our results indicate hydrogen diffusion in wadsleyite is affected by multiple diffusion mechanisms, of which, proton (deuteron) migrating along interstitial defects is particularly efficient to separate hydrogen isotopes in crystalline network probably owing to a quantum sieving effect. The resulting diffusion-driven H/D fractionation can explain common observations of deuterium depletion of NAMs in mantle xenoliths, suggesting that MORE inclusions hosted in xenoliths are more reliable for indicating the hydrogen isotope composition of the mantle rather than the xenolithic NAMs. (C) 2021 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2021.116815

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Oxford University Press (OUP)  

<title>Abstract</title>
Magmatic liquids, including silicate and carbonate melts, are principal agents of mass and heat transfer in Earth and terrestrial planets, and they play a crucial role in various geodynamic processes and Earth's evolution. Electrical conductivity data of these melts elucidate the cause of electrical anomalies in Earth's interior and shed light on the melt structure. With the improvement on high-pressure experimental techniques and theoretical simulations, major progresses have been made on this front in the past several decades. This review aims to summarize recent advances in experimental and theoretical studies on the electrical conductivity of silicate and carbonate melts of different compositions and volatile contents under high temperature and pressure. The electrical conductivity of silicate melt depends strongly on temperature, pressure, water content, and the ratio of non-bridging oxygens to tetrahedral cations (NBO/T). By contrast, the electrical conductivity of carbonate melts exhibits a weak dependence on temperature and pressure due to their fully depolymerized structure. The electrical conductivity of carbonate melts is higher than that of silicate melts by at least two orders of magnitude. Water can increase electrical conductivity significantly and reduce the activation energy of silicate melts. Conversely, this effect is weak for carbonate melts. In addition, the replacement of alkali-earth elements (Ca2+ or Mg2+) with alkali elements causes a significant decrease in the electrical conductivity of carbonate melts. A distinct compensation trend is revealed for the electrical conductivity of silicate and carbonate melts under anhydrous and hydrous conditions. Several important applications of laboratory-based melt conductivity are introduced to understand the origin of high-conductivity anomalies in the Earth's mantle. Perspectives for future studies are also provided.

DOI： 10.1093/nsr/nwab064

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier BV  

DOI： 10.1016/j.icarus.2021.114367

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担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier BV  

DOI： 10.1016/j.epsl.2020.116672

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier BV  

DOI： 10.1016/j.epsl.2020.116380

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Springer Science and Business Media {LLC}  

DOI： 10.1007/s00410-020-1667-2

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掲載種別：研究論文（学術雑誌）   出版者・発行元：AIP Publishing  

DOI： 10.1063/1.5143525

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担当区分：最終著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：AIP Publishing  

DOI： 10.1063/1.5112045

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.epsl.2019.115887

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.epsl.2019.04.048

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その他リンク： http://orcid.org/0000-0002-5422-7396

記述言語：英語   掲載種別：研究論文（学術雑誌）  

©2019. American Geophysical Union. All Rights Reserved. Knowledge of water content and distribution in the Earth's mantle is critical to understanding the geochemical evolution and geodynamic processes of the Earth, since water can incorporate into nominally anhydrous minerals at high pressure and dramatically affect the chemical and physical properties of mantle minerals. Hydrogen diffusion controls the transport of water and electrical conductivity in the deep Earth but is not fully understood for olivine, the most abundant mineral in the upper mantle. Here we present new hydrogen self-diffusion coefficients determined from interdiffusion in H- and D-doped olivine single-crystal couples at the upper mantle conditions (3–13 GPa and 1,000–1,300 K). Present activation enthalpy for hydrogen migration is significant smaller than previous work determined within a limited measured temperature range. Parallel interdiffusion experiments with diversified water concentrations demonstrated that hydrogen diffusivity strongly accelerated by the water content in olivine. The geometric average diffusion coefficient on olivine is showed as a function of temperature and water content: (Formula presented.). Combined with the Nernst-Einstein relation, the present results can constrain the contribution of water to the electrical conductivity on olivine. It suggests that in situ conductivity measurements on hydrous olivine at low temperatures (<1,000 K) produced too low activation enthalpy to extrapolate to the higher temperatures. Comparison with previous results by conductivity measurements on single-crystal olivine suggests that the literature data except for Dai and Karato (2014) might overestimate water effect on conductivity because of heterogeneity of synthetic single crystals. Because of a change of dominant hydrogen diffusion mechanism at high temperature, this study suggests that the modeling of mantle conductivity with a high activation enthalpy from diffusion data is more trustworthy. Considering a reevaluated activation enthalpy on hydrogen diffusion and water solubility in olivine, comparisons between present conductivity model and geophysical observations suggest that hydration of olivine cannot account for extremely high conductive values (10−2–10−1 S/m) observed in the oceanic asthenosphere.

DOI： 10.1029/2019JB017576

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.2138/am-2019-6823

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その他リンク： http://orcid.org/0000-0002-5422-7396

DOI： 10.1016/j.crte.2018.06.013

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その他リンク： http://orcid.org/0000-0002-5422-7396

DOI： 10.1016/j.lithos.2019.01.004

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その他リンク： http://orcid.org/0000-0002-5422-7396

DOI： 10.1029/2018JB016415

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その他リンク： http://orcid.org/0000-0002-5422-7396

掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.crte.2018.07.004

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その他リンク： http://orcid.org/0000-0002-5422-7396

© 2018, Springer Science+Business Media, LLC, part of Springer Nature. We used in situ measurements of X-ray diffraction patterns in a cubic multi-anvil press at pressures up to 3 GPa and at 500–1300 K to examine thermal expansion and its pressure dependence in (Mg0.73Fe0.27)(Cr0.56Al1.44)O4 spinel separated from a mantle-derived xenolith. Thermal expansion of mantle minerals is considerably important to examine thermodynamic properties of mantle. Nevertheless, no report of the relevant literature describes a study investigating the thermal expansion of natural mantle spinel under the P–T conditions presented above. Cell volume of the natural spinel increased concomitantly with increasing temperature, enabling us to estimate thermal expansion coefficients. The relation between the cell volume and pressure at 700 K is distinct in slope from those of adjacent temperature, perhaps because of the transition of spinel from order to disorder. Pressure dependence of thermal expansion coefficients was not identified. Reports of some earlier studies have described various values of thermal expansion coefficients of MgAl2O4: αmean = 1.70–2.94 × 10−5 K−1. The obtained mean thermal expansion coefficient (2.66 × 10−5) is slightly higher than the reported values. This slight difference might be inferred as reflecting the effects of the presence of Fe and Cr, respectively, at sites A and B.

DOI： 10.1007/s10853-018-2848-5

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その他リンク： http://orcid.org/0000-0002-5422-7396

DOI： 10.1016/j.epsl.2018.10.009

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その他リンク： http://orcid.org/0000-0002-5422-7396

記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier B.V.  

The electrical conductivity of Na, Mg-bearing carbonate melts was measured in a Kawai-type multi-anvil apparatus as a function of pressure. The carbonate samples were mixtures of MgCO3 and Na2CO3 or Mg5(CO3)4(OH)2·4(H2O) and Na2CO3. High-pressure experiments on the carbonate systems were performed up to 1800 K in a wide pressure range from 3.4 to 10.9 GPa. The sample conductivity abruptly changed at the eutectic temperature, which increased with increasing pressure. The hydrous carbonate yielded a lower eutectic temperature than the anhydrous carbonate and showed weaker pressure dependence. The molten state carbonates showed very high electrical conductivity with temperature dependence following the Arrhenius law. As the pressure increased, the conductivity decreased. The negative pressure dependence of the electrical conductivity of the hydrous carbonate melt was larger than that of the anhydrous one. The activation volumes were ΔV = 1.81 and 3.61 cm mol−1 for the anhydrous and hydrous carbonate melts, respectively. The high electrical conductivity observed in the mantle beneath the Slave and Brazilian cratons can be explained by the process of lithospheric rejuvenation due to a small amount of hydrous carbonated melt released from the crystallization of the kimberlitic magma at the base of the continental mantle lithosphere.

DOI： 10.1016/j.pepi.2018.05.003

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その他リンク： http://orcid.org/0000-0002-5422-7396

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.2138/am-2018-6295

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その他リンク： http://orcid.org/0000-0002-5422-7396

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Blackwell Publishing Ltd  

We measured the electrical resistivity of iron, Fe99C1, Fe3C, and Fe7C3 up to ~80 GPa using the van der Pauw method in a diamond anvil cell. The electrical resistivity of disordered Fe99C1 at high pressure shows a strong impurity resistivity of carbon. The ferromagnetic-paramagnetic transition in Fe3C and Fe7C3 is associated with the flattening of the resistivity pressure gradient at ~6 GPa. Fe7C3 exhibits the highest electrical resistivity among all iron-light element alloys, and Fe3C and Fe7C3 disobey the Matthiessen's rule by showing a lower electrical resistivity than a disordered iron-carbon alloy because of chemical ordering. A comparison of the impurity resistivity between silicon, sulfur, nickel, and carbon shows that carbon has an exceedingly stronger alloying effect than other elements. If the chemical ordering observed in Fe-Si system is held true for the Fe-C system, the chemical ordering in Fe7C3 possibly increases the thermal conductivity of the inner core and enlarges the thermal and electrical conductivity gap at the inner-core boundary. Models of the thermal conductivity of liquid Fe70C30 with 8.4 wt % carbon show a low thermal conductivity of 38 Wm−1 K−1 at the pressure-temperature conditions of the topmost outer core. The corresponding heat flow of 6 TW at the core-mantle boundary is notably lower than previous electrical resistivity results on Fe and Fe alloys. The alloying effect of carbon on the electrical and thermal conductivity of iron can thus play a significant role in understanding the heat flux at the core-mantle boundary and the thermal evolution of the core.

DOI： 10.1029/2017JB015260

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier B.V.  

Knowledge of the distribution of water in the Earth's mantle is key to understanding the mantle convection and geochemical evolution of the Earth. As wadsleyite and ringwoodite can incorporate large amounts of water in their crystal structures, proton conduction has been invoked to account for the widespread conductive anomalies observed in the mantle wedge, where descending slab stagnates at the transition zone. However, there is a lot of controversy on whether proton conduction by itself is able to explain such anomalies, because of large discrepancy in the extent of the water effect deduced from previous electrical conductivity measurements on hydrous polycrystalline wadsleyite and ringwoodite. Here we report the hydrogen self-diffusion coefficient obtained from H–D interdiffusion experiments in wadsleyite single-crystal couples. Our results demonstrate that the effect of water on the electrical conductivity of wadsleyite is limited and hydrous wadsleyite by itself is unable to explain conductive anomalies in the transition zone. In contrast, the expected hydrogen effective diffusion does not allow the wide propagation of water between the stagnant slab and surrounding mantle, probably leading to persistence of local water saturation and continuous release of supercritical fluids at the stagnant slab roof on geological time scales. This phenomenon provides an alternative explanation for both the high-conductivity and seismic-velocity anomalies observed in the mantle wedge at the transition-zone depth.

DOI： 10.1016/j.epsl.2017.12.032

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その他リンク： http://orcid.org/0000-0002-5422-7396

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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その他リンク： http://orcid.org/0000-0002-5422-7396

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Geological Society of America  

Phengite is a critical carrier of water and potassium (K) in sediment as well as in the basaltic layers of subducted slabs. However, although phengite dehydration can potentially be used to interpret high conductivity in the mantle overlying such slabs at depths between 250 km and 300 km, no experimental constraints on the electrical conductivity of this mineral have so far been performed. We investigated the electrical conductivity of natural phengite before and after dehydration at pressures (P) as high as 12 GPa and at temperatures (T) as high as 1200 K. The results of this study confirm positive T and negative P effects on the electrical conductivity of phengite before its breakdown
subsequently, at 12 GPa and 850 K, electrical conductivity dramatically increased from 10-4 S/m to 100.5 S/m. Characteristic impedance spectra, as well as postexperimental textural observations and sample chemical analyses, show that these abrupt conductivity changes are due to K-rich fluids released by phengite dehydration. These high conductivities of K-rich fluids are in close agreement with geophysical observations at depths of between 250 km and 300 km in backarcs beneath the North Philippine Sea and central Argentina. Comparisons between the geotherms of these areas and the stability field of phengite defined by phase equilibrium experiments suggest that the descending crust is almost completely dehydrated and should not cause further K-metasomatism subsequent to the breakdown of phengite at depths of ~300 km.

DOI： 10.1130/G39716.1

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その他リンク： http://orcid.org/0000-0002-5422-7396

記述言語：英語   出版者・発行元：ELSEVIER SCIENCE BV  

We review the currently available results of laboratory experiments, geochemistry and MT observations and attempt to explain the conductivity structures in the oceanic asthenosphere by constructing mineral-physics models for the depleted mid-oceanic ridge basalt (MORB) mantle (DMM) and volatile-enriched plume mantle (EM) along the normal and plume geotherms. The hopping and ionic conductivity of olivine has a large temperature dependence, whereas the proton conductivity has a smaller dependence. The contribution of proton conduction is small in DMM. Melt conductivity is enhanced by the H2O and CO2 components. The effects of incipient melts with high volatile components on bulk conductivity are significant. The low solidus temperatures of the hydrous carbonated peridotite produce incipient melts in the asthenosphere, which strongly increase conductivity around 100 km depth under older plates. DMM has a conductivity of 10(-1.2-1.5) S/m at 100-300 km depth, regardless of the plate age. Plume mantle should have much higher conductivity than normal mantle, due to its high volatile content and high temperatures. The MT observations of the oceanic asthenosphere show a relatively uniform conductivity at 200-300 km depth, consistent with the mineral-physics model. On the other hand, the MT observations show large lateral variations in shallow parts of the asthenosphere despite similar tectonic settings and close locations. Such variations are difficult to explain with the mineral-physics model. High conductivity layers (HCL), which are associated with anisotropy in the direction of the plate motion, have only been observed in the asthenosphere under infant or young plates, but they are not ubiquitous in the oceanic asthenosphere. Although the general features of HCL imply their high-temperature melting origin, the mineral-physics model cannot explain them quantitatively. Much lower conductivity under hotspots, compared with the model plume-mantle conductivity suggests the extraction of volatiles from the plume mantle by the ocean island basalt (OIB) magmatism. (C) 2017 Published by Elsevier B.V.

DOI： 10.1016/j.tecto.2017.07.001

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その他リンク： http://orcid.org/0000-0002-5422-7396

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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その他リンク： http://orcid.org/0000-0002-5422-7396

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER GEOPHYSICAL UNION  

We investigated Fe-free and Fe-bearing CF phases using nuclear forward scattering and X-ray diffraction coupled with diamond anvil cells up to 80GPa at room temperature. Octahedral Fe3+ ions in the Fe-bearing CF phase undergo a high-spin to low-spin transition at 25-35GPa, accompanied by a volume reduction of similar to 2.0% and a softening of bulk sound velocity up to 17.6%. Based on the results of this study and our previous studies, both the NAL and CF phases, which account for 10-30 vol % of subducted MORB in the lower mantle, are predicted to undergo a spin transition of octahedral Fe3+ at lower mantle pressures. Spin transitions in these two aluminous phases result in an increase of density of 0.24% and a pronounced softening of bulk sound velocity up to 2.3% for subducted MORB at 25-60GPa and 300K. The anomalous elasticity region expands and moves to 30-75GPa at 1200K and the maximum of the V reduction decreases to similar to 1.8%. This anomalous elastic behavior of Fe-bearing aluminous phases across spin transition zones may be relevant in understanding the observed seismic signatures in the lower mantle.

DOI： 10.1002/2017JB014095

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We investigated transverse acoustic (TA) phonons in iron-bearing magnesium oxide (ferropericlase) up to 56 GPa using inelastic x-ray scattering (IXS). The results show that the energy of the TA phonon far from the Brillouin zone center suddenly increases with increasing pressure above the spin transition pressure of ferropericlase. Ab initio calculations revealed that the TA phonon energy far from the Brillouin zone center is higher in the low-spin state than in the high spin state; that the TA phonon energy depend weakly on pressure; and that the energy gap between the TA and the lowest-energy-optic phonons is much narrower in the low-spin state than in the high-spin state. This allows us to conclude that the anomalous behavior of the TA mode in the present experiments is the result of gap narrowing due to the spin transition and explains contradictory results in previous experimental studies.

DOI： 10.1088/1361-648X/aa7026

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER GEOPHYSICAL UNION  

The iron spin transition directly affects properties of lower mantle minerals and can thus alter geophysical and geochemical characteristics of the deep Earth. While the spin transition in ferropericlase has been documented at P similar to 60GPa and 300K, experimental evidence for spin transitions in other rock-forming minerals, such as bridgmanite and post-perovskite, remains controversial. Multiple valence, spin, and coordination states of iron in bridgmanite and post-perovskite are difficult to resolve with conventional spin probing techniques. Optical spectroscopy, on the other hand, can discriminate between high and low spin and between ferrous and ferric iron at different sites. Here we establish the optical signature of low spin Fe3+O6, a plausible low spin unit in bridgmanite and post-perovskite, by optical absorption experiments in diamond anvil cells. We show that the optical absorption of Fe3+O6 in new aluminous phase (NAL) is very sensitive to the iron spin state and may represent a model behavior of bridgmanite and post-perovskite across the spin transition. Specifically, an absorption band centered at similar to 19,000cm(-1) is characteristic of the (T2gT1g)-T-2-T-2 ((2)A(2g)) transition in low spin Fe3+ in NAL at 40GPa, constraining the crystal field splitting energy of low spin Fe3+ to similar to 22,200cm(-1), which we independently confirm by first-principles calculations. Together with available information on the electronic structure of Fe3+O6 compounds, we show that the spin-pairing energy of Fe3+ in an octahedral field is similar to 20,000-23,000cm(-1). This implies that octahedrally coordinated Fe3+ in bridgmanite is low spin at P&gt;similar to 40GPa.

DOI： 10.1002/2017JB014134

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その他リンク： http://orcid.org/0000-0002-5422-7396

記述言語：英語   掲載種別：研究論文（学術雑誌）  

© 2016 Elsevier B.V. Knowledge of grain growth rate of ε-iron can put constraint on estimation of the grain size in the inner core. We determined grain growth rate of ε-iron at ∼55 GPa and 1200–1500 K by means of in-situ X-ray diffraction observation to be Gn−G0n=kt, where G (m) is the grain size at time t (s), G0(m) is the initial grain size, n is growth exponent (fixed to 2) and k is the growth constant expressed as k=k0exp⁡(−H⁎/RT) with log k0(mn/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 ε-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.

DOI： 10.1016/j.epsl.2016.11.049

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER GEOPHYSICAL UNION  

Graphite is considered as one of candidate to explain the high-conductivity anomalies revealed through magnetotelluric (MT) observations. To investigate the effect of interfacial energy on the interconnection of graphite in olivine matrix, we measured the electrical conductivity of polycrystalline San Carlos olivine mixed with 0.8 vol % graphite on the grain boundaries via impedance spectroscopy at 1 GPa and 300-1700 K in a cubic multianvil apparatus. The olivine-graphite dihedral angle of the recovered sample was also measured to determine interfacial energy between graphite and olivine. The bulk electrical conductivities and large activation enthalpy (approximate to 1.32 eV) of the carbon-bearing sample were consistent with those of dry polycrystalline olivine. This behavior implies that graphite cannot be interconnected on olivine grain boundaries, which is also supported by the large dihedral angle (98 degrees) of the olivine/graphite system. Impedance spectroscopy measurements were performed at 3 GPa and a temperature of up to 1700 K for carbon-coated olivine bicrystal samples to investigate the stability of graphite films on the grain boundaries of silicate minerals under upper-mantle conditions. The conductivities rapidly or slowly dropped as a function of time and graphite film thickness during annealing at the target temperature. This phenomenon exhibits that graphite film on the olivine grain boundary is readily destroyed under upper-mantle conditions as supported by microstructural observations on the recovered carbon-coated olivine bicrystal samples. Higher interfacial energy and larger dihedral angle (approximate to 98 degrees) between graphite and olivine would not allow the maintenance of graphite film on olivine grain boundaries. The activation enthalpy for the apparent disconnection rate of a graphite film on olivine grain boundaries is close to that of carbon diffusion in olivine grain boundaries, which suggests that the disconnection of the graphite film is likely to be controlled by carbon grain boundary diffusion. Therefore, graphite is an unlikely candidate to explain the high-conductivity anomalies revealed by MT surveys in the upper mantle.

DOI： 10.1002/2016GC006530

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER GEOPHYSICAL UNION  

Electrical conductivity of dry forsterite has been measured in muli-anvil apparatus to investigate the pressure dependence of ionic conduction in forsterite. The starting materials for the conductivity experiments were a synthetic forsterite single crystal and a sintered forsterite aggregate synthesized from oxide mixture. Electrical conductivities were measured at 3.5, 6.7, 9.6, 12.1, and 14.9GPa between 1300 and 2100K. In the measured temperature range, the conductivity of single crystal forsterite decreases in the order of [001], [010], and [100]. In all cases, the conductivity decreases with increasing pressure and then becomes nearly constant for [100] and [001] and slightly increases above 7GPa for [010] orientations and a polycrystalline forsterite sample. Pressure dependence of forsterite conductivity was considered as a change of the dominant conduction mechanism composed of migration of both magnesium and oxygen vacancies in forsterite. The activation energy (E) and activation volume (V) for ionic conduction due to migration of Mg vacancy were 1.8-2.7eV and 5-19cm(3)/mol, respectively, and for that due to O vacancy were 2.2-3.1eV and -1.1 to 0.3cm(3)/mol, respectively. The olivine conductivity model combined with small polaron conduction suggests that the most part of the upper mantle is controlled by ionic conduction rather than small polaron conduction. The previously observed negative pressure dependence of the conductivity of olivine with low iron content (Fo(90)) can be explained by ionic conduction due to migration of Mg vacancies, which has a large positive activation volume.

DOI： 10.1002/2016JB013555

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掲載種別：研究論文（学術雑誌）  

© 2017 by Walter de Gruyter Berlin/Boston. We report here new experimental kinetic data on the structural evolution of carbonaceous material (CM) to graphite during heating at various temperatures (1000 to 1450 °C) for various durations (10 min to 115 h) under a pressure of 1 GPa. Natural CMs extracted from sedimentary rocks in the Shimanto accretionary complex and the Hidaka metamorphic belt of Japan transformed in morphology and crystallinity with increasing temperature and annealing duration to become fully ordered graphite (d002spacing ~3.36 Å). Transmission electron microscopy showed that both samples have undergone microstructural evolution from amorphous carbon to platy graphitic carbon. These changes match the evolution of the samples&#039; X-ray diffraction (XRD) patterns and micro-Raman spectra. The time-temperature relations of crystal parameters obtained by XRD and micro-Raman spectroscopy demonstrated a sigmoidal transformation curve from an amorphous to a graphitic structure, suggesting complexity of these successive and/or parallel chemical reactions are responsible for graphitization. To assess these complex chemical processes, we adopted three different approaches for formulating the graphitization kinetics using a power rate model, a Johnson-Mehl-Avrami (JMA) model and a superposition method. Irrespective of the models employed, the effective activation energies were estimated to lie between 259 and 339 kJ/mol, which are much lower than those reported previously for graphitization. Summarizing the previous studies and our results between 0.1 and 1000 MPa, we found that the effective activation energies systematically decrease as a function of pressure. Based on the experimental results in this study, the sigmoid functions obtained from the time-temperature relations can be extrapolated to low-temperature conditions at 1 GPa. Our kinetic model using unit-cell height c predicts that CM undergoing metamorphism for about 1 m.y. will begin to crystallize at ~410 °C, and will transform to fully ordered graphite at over ~520 °C. Thus, natural graphitization undergoes a much faster transformation than reported in previous studies at 1 atm and could be explored in laboratory experiments using natural precursor materials under pressure conditions and time spans that reflect natural conditions in the Earth&#039;s crust.

DOI： 10.2138/am-2017-5733

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER GEOPHYSICAL UNION  

We have investigated phase relations and melting behavior of Fe3C and Fe7C3 using X-ray diffraction in a laser-heated diamond cell up to 185 GPa and 5200 K. Our results show that the starting Fe3C sample decomposes into a mixture of solid orthorhombic Fe7C3 and hcp-Fe at above 145 GPa upon laser heating and then transforms into Fe-C liquid and solid Fe7C3 at temperatures above 3400 K. Using the intensity of the diffuse scattering as a primary criteria for detecting melting, the experimentally derived liquidus for a bulk composition of Fe3C fitted with the Simon-Glatzel equation is T-m(K) = 1800 x [1 + (P-m = 5.7)/15.10 +/- 2.55](1/2.41) (+/- 0.17) at 24-185 GPa, which is similar to 500 K higher than the melting curve of iron reported by Anzellini et al. (2013) at Earth's core pressures. The higher melting point and relative stability of Fe7C3 in Fe-rich Fe-C system at Earth's core conditions indicate that Fe7C3 could solidify out of the early Earth's molten core to become a constituent of the innermost inner core.

DOI： 10.1002/2016GL071353

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：SPRINGER  

The electrical conductivity of (Mg1-x, Fe-x) SiO3 orthopyroxene with various iron contents [X-Fe = Fe/(Fe + Mg) = 0, 0.1, 0.3, 0.5, 0.7 and 1.0] was measured in a Kawai-type multianvil apparatus by impedance spectroscopy over a wide range of pressure (P) and temperature (T) covering the stability field of orthopyroxene. Impedance spectroscopy measurements indicated that the electrical conductivity of orthopyroxene systematically increased with increasing total iron content. The conductivity slightly decreased with increasing pressure at a constant temperature. For samples with lower Fe content, two conduction mechanisms were identified from the Arrhenius behavior. A change in the activation enthalpy indicated that the dominant conduction mechanism changed from small polaron to ionic conduction with increasing temperature. At temperature below 1373 K, relatively low activation enthalpies and small positive activation volumes suggest that the dominant mechanism of charge transport is Fe2+-Fe3+ hopping (small polaron). At higher temperatures above 1473 K, ionic conduction (via Mg vacancy mobility) dominates, with higher activation enthalpy exceeding 2 eV and larger positive activation volume. All electrical conductivity data fit the formula for electrical conductivity
sigma = sigma(i)(0) exp[-(Delta E-0(i) + P Delta V-0(i))/k(B)T] + sigma(p)(0) X-Fe
exp {-[Delta E-0(p) - alpha X-Fe(1/3) + P(Delta V-0(p) - beta X-Fe)]/k(B)T}.
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, k(B) is the Boltzmann constant, T is the absolute temperature, and superscripts i and p denote the ionic and small polaron conductions, respectively. Electrical conductivity of Al-free orthopyroxene with X-Fe = 0.1 is distinctly lower than that of olivine with X-Fe = 0.1. Above 3 GPa Al content in orthopyroxene becomes smaller in association with garnet formation. Unless iron content in orthopyroxene is considerably high (X-Fe &gt; 0.2), orthopyroxene has little influence on the electrical structure of the upper mantle.

DOI： 10.1007/s00410-016-1315-z

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

© 2016 Elsevier B.V. The CaCO3–Fe0 system, as a model for redox reactions between carbonates and reduced lithologies at the slab-mantle interface during subduction or at core-mantle boundary, was investigated systematically at temperatures from 650 to 1400 °C and pressures from 4 to 16 GPa using multianvil apparatus. CaCO3 reduction via reaction: 3 CaCO3 (aragonite) + 13 Fe0 (metal) = Fe7C3 (carbide) + 3 CaFe2O3 (Ca-wüstite) was observed. The thickness of the reaction-product layer (Δx) increases linearly with the square root of time in the time-series experiments (t), indicating diffusion-controlled process. The reaction rate constant (k = Δx2/2t) is log-linear relative to 1/T. Its temperature dependences was determined to be k [m2/s] = 2.1 × 10−7exp(−162[kJ/mol]/RT) at 4–6 GPa and k [m2/s] = 2.6 × 10−11exp(−65[kJ/mol]/RT) at 16 GPa. The sluggish kinetics of established CaCO3–Fe0 interaction suggests that significant amount of carbonates could survive during subduction from metal saturation boundary near 250 km depth down to the transition zone and presumably to the lower mantle if melting of carbonates is not involved.

DOI： 10.1016/j.pepi.2016.08.008

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER GEOPHYSICAL UNION  

Hydrous magnesium silicate phase D plays a key role in the transport of water from the upper to the lower mantle via subducted slabs. Here we report pressure dependence hyperfine and lattice parameters of FeAl-bearing phase D up to megabar pressures using synchrotron nuclear forward scattering and X-ray diffraction in a diamond anvil cell at room temperature. FeAl-bearing phase D undergoes a two-stage high-spin to low-spin transition of iron for Fe2+ at 37-41GPa and for Fe3+ at 64-68GPa. These transitions are accompanied by an increase in density and a significant softening in the bulk modulus and bulk velocity at their respective pressure range. The occurrence of the dense low-spin FeAl-bearing phase D with relatively high velocity anisotropies in deep-subducted slabs can potentially contribute to small-scale seismic heterogeneities in the middle-lower mantle beneath the circum-Pacific area.

DOI： 10.1002/2016JB013209

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER GEOPHYSICAL UNION  

The new hexagonal aluminous phase, named the NAL phase, is expected to be stable at depths of &lt;1200km in subducted slabs and believed to constitute 10 similar to 30wt% of subducted mid-ocean ridge basalt together with the CaFe2O4-type aluminous phase. Here elasticity of the single-crystal NAL phase is investigated using Brillouin light scattering coupled with diamond anvil cells up to 20GPa at room temperature. Analysis of the results shows that the substitution of iron lowers the shear modulus of the NAL phase by similar to 5% (similar to 6GPa) but does not significantly affect the adiabatic bulk modulus. The NAL phase exhibits high-velocity anisotropies with AV(P)=14.7% and AV(S)=15.12% for the Fe-bearing phase at ambient conditions. The high AV(S) of the NAL phase mainly results from the high anisotropy of the faster V-S1 (13.9 similar to 15.8%), while the slower V-S2 appears almost isotropic (0.1 similar to 2.8%) at ambient and high pressures. The AV(P) and AV(S) of the NAL phase decrease with increasing pressure but still have large values with AV(P)=11.4% and AV(S)=14.12% for the Fe-bearing sample at 20.4GPa. The extrapolated AV(P) and AV(S) of the Fe-free and Fe-bearing NAL phases at 40GPa are larger than those of bridgmanite at the same pressure. Together with its spin transition of iron and structural transition to the CF phase, the presence of the NAL phase with high-velocity anisotropies may contribute to the observed seismic anisotropy around subducted slabs in the uppermost lower mantle.

DOI： 10.1002/2016JB013136

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

The electrical conductivity of San Carlos clinopyroxene aggregates with various water contents were measured under Ni-NiO buffer at 1.5 GPa and 600-1200 K in a DIA-type apparatus. The conductivity increases with increasing water content in clinopyroxene. Hidden conduction mechanism was detected because of the much smaller iron content in clinopyroxene, which was usually covered by small polaron conduction in other nominally anhydrous minerals. The identified activation enthalpies ranged from 0.70-0.75 eV to 1.23-1.37 eV. Our result reveals that the dominant charge-carrying species in electrical conductivity could change with temperature and water content. At high temperatures relevant to asthenospheric condition, activation enthalpy for the conductivity agrees well with that for the hydrogen self-diffusion. The dominant charge carrier therefore might be M site vacancy. However, contrary to previous view that all hydrogens contribute to increasing conductivity equally, our result shows that only a limited amount (20%-40%) of hydrogen acts as effective charge carrier in clinopyroxene. On the other hand, the activation enthalpy for the conductivity at low temperatures is significantly lower than that for the hydrogen self-diffusion, similar to what has been observed in olivine and orthopyroxene. This type of conduction is probably caused by fast diffusion of specific hydrogen or fast hydrogen grain boundary diffusion. At low temperatures, the proton conduction of clinopyroxene is nearly one order and two orders of magnitude lower than those of olivine and orthopyroxene, respectively, and tends to converge at high temperatures. Using the present data combined with conductivity of olivine and orthopyroxene, a laboratory-based conductivity-depth profile in the uppermost mantle shows that hydrous clinopyroxene cannot account for the high conductive regions observed beneath the ocean floor near Eastern Pacific Rise. The presence of partial melt would be unavoidable. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2016.04.028

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：SPRINGER  

The Accessible Silicate Earth (ASE) has a higher Nd-142/Nd-144 ratio than most chondrites. Thus, if the Earth is assumed to have formed from these chondrites, a complement low-Nd-142/Nd-144 reservoir is needed. Such a low-Nd-142/Nd-144 reservoir is believed to have been derived from a melt in the early Earth and is called the Early Enriched Reservoir (EER). Although the major element composition of the EER is crucial for estimating its chemical and physical properties (e.g., density) and is also essential for understanding the origin and fate of the EER, which are both major factors that determine the present composition of the Earth, it has not yet been robustly established. In order to determine the major element composition of the EER, we estimated the age and pressure-temperature conditions to form the EER that would best explain its Nd isotopic characteristics, based on Sm-Nd partitioning and its dependence on pressure, temperature, and melting phase relations. Our estimate indicates that the EER formed within 33.5 Myr of Solar System formation and at near-solidus temperatures and shallow upper-mantle pressures. We then performed high-pressure melting experiments on primitive peridotite to determine the major element composition of the EER at estimated temperature at 7 GPa and calculated the density of the EER. The result of our experiments indicates that the near-solidus melt is iron-rich komatiite. The estimated density of the near-solidus melt is lower than that of the primitive peridotite, suggesting that the EER melt would have ascended in the mantle to form an early crust. Given that high mantle potential temperatures are assumed to have existed in the Hadean, it follows that the EER melt was generated at high pressure and, therefore, its composition would have been picritic to komatiitic. As the formation age of the EER estimated in our study precedes the last giant, lunar-forming impact, the picritic to komatiitic crust (EER) would most likely have been ejected from the Earth by the last giant impact or preceding impacts. Thus, the EER has been lost, leaving the Earth more depleted than its original composition.

DOI： 10.1186/s40645-016-0099-0

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

Al-rich phases (NAL: new hexagonal aluminous phase and CF: calcium-ferrite phase) are believed to constitute 10 similar to 30 wt% of subducted mid-ocean ridge basalt (MORB) in the Earth's lower mantle. In order to understand the effects of iron on compressibility and elastic properties of the NAL phase, we have studied two single-crystal samples (Fe-free Na1.14Mg1.83Al4.74Si1.23O12 and Fe-bearing Na0.71Mg2.05Al4.62Si1.16Fe0.092+Fe0.173+O12) using synchrotron nuclear forward scattering (NFS) and X-ray diffraction (XRD) combined with diamond anvil cells up to 86 GPa at room temperature. A pressure induced high-spin (HS) to low-spin (LS) transition of the octahedral Fe3+ in the Fe-bearing NAL is observed at approximately 30 GPa by NFS. Compared to the Fe-free NAL, the Fe-bearing NAL undergoes a volume reduction of 1.0% (similar to 1.2 angstrom(3)) at 33 similar to 47 GPa as supported by XRD, which is associated with the spin transition of the octahedral Fe3+. The fits of Birch-Murnaghan equation of state (B-M EoS) to P-V data yield unit-cell volume at zero pressure V-0 = 183.1(1) angstrom(3) and isothermal bulk modulus K-T0 = 233(6) GPa with a pressure derivative K-T0' = 3.7(2) for the Fe-free NAL; V0-HS = 184.76(6) angstrom(3) and KT0-HS = 238(1) GPa with KT0-HS' = 4 (fixed) for the Fe-bearing NAL. The bulk sound velocities (V-Phi) of the Fe-free and Fe-bearing NAL phase are approximately 6% larger than those of Al, Fe-bearing bridgmanite and calcium silicate perovskite in the lower mantle, except for the spin transition region where a notable softening of V-Phi with a maximum reduction of 9.4% occurs in the Fe-bearing NAL at 41 GPa. Considering the high volume proportion of the NAL phase in subducted MORB, the distinct elastic properties of the Fe-bearing NAL phase across the spin transition reported here may provide an alternative plausible explanation for the observed seismic heterogeneities of subducted slabs in the lower mantle at depths below 1200 km. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2015.11.011

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

Electrical conductivity measurements of bridgmanite with various Al contents and a constant Mg# of 90 were performed at temperatures ranging from room temperature up to 2000 K at pressures of 26-28 GPa in a Kawai-type multianvil apparatus by impedance spectroscopy analysis. The incorporation of Al into bridgmanite raises its electrical conductivity significantly, but it is a small conductivity variation with respect to the quantity of Al. Synchrotron Mossbauer spectroscopy of recovered samples showed significant amounts of ferric iron in aluminous bridgmanite. The mobility of the charge carriers in bridgmanite was calculated based on the conductivity and the Fe3+/Sigma Fe ratio. The relationship between the logarithm of the electrical conductivity and the reciprocal temperature is consistent with Fe2+-Fe3+ electron hopping (small polarons) as the dominant conduction mechanism at low temperatures (&lt;1400 K) and ionic conduction at higher temperatures (&gt;1600 K). By taking various conduction mechanisms into account, we develop an electrical conductivity model for aluminous bridgmanite as a function of the Al and Fe contents. The small polaron conduction model indicates that the electrical conductivity of aluminous bridgmanite has a maximum at around 0.06 Al atoms per formula unit, and any further increase in the Al content in bridgmanite reduces the conductivity. In contrast, the ionic conduction model indicates that the electrical conductivity simply increases with increasing Al content. The resulting conductivity of Al-bearing bridgmanite first increases up to 0.06 Al atoms per formula unit and then remains constant or increases with increasing Al content at higher temperatures. The increase in conductivity observed in the uppermost part of the lower mantle by electromagnetic studies can be explained by the gradual decomposition of majorite garnet. The deeper lower mantle conductivity would be controlled by small polaron conduction because of the large positive activation volume required for ionic conduction. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2015.11.032

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：TAYLOR & FRANCIS LTD  

We have investigated the performance of a graphite-boron composite (GBC) with 3 wt % boron as a precursor for a boron-doped diamond heater in a Kawai-type apparatus at 15 GPa. We first tested a machinable cylinder of GBC sintered at 1000 degrees C in Ar/H-2 gas (99:1 molar ratio). Boron oxide (B2O3) formed during sintering frequently hindered the GBC heater from stable operation at temperatures higher than 1400 degrees C by producing melt throughout the heater together with oxide and/or silicates. We then rinsed the GBC heater in hydrochloric acid to remove B2O3. After rinsing, we succeeded in stably generating temperatures higher than 2000 degrees C. We also improved a molding process of different-sized GBC tubes for convenient use and tested the molded GBC heater. It was free from the B2O3 problem. The electromotive force of the W/Re thermocouple was successfully monitored up to 2400 degrees C.

DOI： 10.1080/08957959.2016.1164151

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER GEOPHYSICAL UNION  

Hydrogen lattice diffusion in Fe-bearing ringwoodite was investigated through hydrogen and deuterium interdiffusing in a pair of synthesized single crystals at various temperatures (1000-1300 K) at 21 GPa. Diffusion profiles were investigated by secondary ion mass spectrometer to determine the hydrogen self-diffusivity in ringwoodite. Temperature dependences of hydrogen diffusion in ringwoodite were determined to be D-H=10(-7.29(+/- 0.46)) exp[-101(+/- 10) kJ mol(-1)/RT] m(2)/s in ringwoodite at 21GPa. The proton conductivities of ringwoodite estimated from the present diffusion coefficients are similar to those of Yoshino et al. [2008] at the transition zone condition at low water content (&lt;1000 ppm by weight (ppmw)) but lower at higher water content range (&gt;1000 ppmw). If the proton-vacancy mechanism is assumed to be a main controlling mechanism, contribution of water to the electrical conductivity of ringwoodite is insignificant due to large contribution of hopping conduction at the transition zone condition, and global average water concentration in the lower part of transition zone is less than 1000 ppmw.

DOI： 10.1002/2015GL064486

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD  

We have examined the stabilities of different polycyclic aromatic hydrocarbons (PAHs) at 7 GPa and 773-973 K and at 16 GPa and 300 K. Experiments were performed using a large-volume multi-anvil apparatus. Quenched products were analyzed by matrix-assisted laser desorption/ionization (MALDI) and Raman spectroscopy. The MALDI measurements revealed the considerable oligomerization of PAHs at 7 GPa and 773-873 K and insignificant PAH oligomerization at 16 GPa and 300K. At 7 GPa and 773 K, oligomers with molecular weight up to 3400 Da were found, while only a small number of dimers of the starting PAHs were detected at 16 GPa and 300K. PAH decomposition at 7 GPa occurred from 873 to 973 K, and the decomposition products consisted of nanocrystalline graphite. The determined decomposition temperatures of the PAHs (873-973 K) are much lower than Earth's geotherms and the subduction slab P-T profiles at 7 GPa; therefore, PAH inclusions in mantle-derived minerals, which can be crystallized at 6-7 GPa and 1600-1700 K, should be secondary phases and could be formed by the successive polycondensation of simple hydrocarbon molecules under natural catalysts during eruption processes at sub-ambient pressures and temperatures. (C) 2014 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.carbon.2014.12.011

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

The electrical conductivities of albite-water, albite-quartz-water and albite-water-NaCl systems have been measured in terms of impedance spectroscopy at 1 GPa and 400-1000 K. The relationship between electrical conductivity and temperature in the albite-(quartz)-water system cannot be expressed by the Arrhenian formula, whereas that in the brine-bearing system follow the Arrhenian law showing small temperature dependence. The electrical conductivity of the albite-(quartz)-water samples decreased with decreasing temperature from 1000 to 800 K, then increased rapidly upon further cooling from 800 to around 550 K. The bulk conductivities of the albite-(quartz)-water system are consistent with variation of the total concentration of the dissolved electric charge carriers of H+, OH-, Na+, AlO2- and HSiO3- in aqueous fluid with temperature based on the thermal dynamic calibration. There is a small negative dependence of bulk conductivity on aqueous fluid fraction. Electrical conductivity of the albite-water-NaCl samples is higher than that of the albite-(quartz)-water samples, which shows the following features: (1) small dependence of conductivity on the temperature; (2) increase of electrical conductivity with the fluid fraction and the salinity. Our results suggest that the high conductivity anomalies of 10(-1) S/m typically observed in the continental crust can be explained by the presence of albite and quartz with fluid fraction as low as 0.014 at temperatures lower than 650 K. In the case that the geotherm is higher than 650 K, the observed value of 10(-1) S/m can be explained by the brine-bearing albite with a fluid fraction of 1 vol% if the salinity is similar to the seawater. (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2014.12.021

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER GEOPHYSICAL UNION  

Thermal conductivity and diffusivity for three pyroxenes, omphacite, jadeite, and diopside, were determined up to 14 GPa and 1000 K in the Kawai-type multianvil apparatus via the pulse heating method. Measurements for omphacite are characterized by much lower thermal conductivity and thermal diffusivity than those of its two end-members of jadeite and diopside, presumably because of the complex substitution of four cations (Na+1, Ca+2, Al+3, and Mg+2) in omphacite. Therefore, simple arithmetic averaging is unsuitable for estimating thermal conductivity and diffusivity of the jadeite-diopside solid solution system. The thermal property of eclogite was estimated from those of garnet and omphacite. The thermal conductivity of eclogite is much smaller than that of harzburgite, which is assumed to compose of 80% olivine and 20% enstatite, implying that subducted oceanic crust impedes thermal conduction from the hotter wedge mantle to the subducting slab. Thermal structure simulation results show that temperature of the subduction zone is about 50 degrees C decreased when the effect of oceanic crust is included.

DOI： 10.1002/2014JB011208

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：SPRINGER  

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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記述言語：英語   出版者・発行元：ELSEVIER SCIENCE BV  

DOI： 10.1016/j.epsl.2014.02.016

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

Carbon isotope fractionation between graphite and carbonated silicate melt was determined at 5 GPa and in the temperature range between 1400 and 1900 degrees C. High pressure experiments were carried out in the carbon-saturated model harzbergite system (Enstatite-Magnesite-Olivine-Graphite), where carbonated silicate melt and graphite were the two stable carbon-bearing phases in the run products. Carbonated silicate melting resulted in an isotopic fractionation between graphite and carbon in the silicate melt, where the carbon in the melt is C-13 enriched than co-existing graphite. 13C enrichment in carbonate melt when compared to graphite was further confirmed in experiments where redox melting between olivine and graphite produced carbonate melt as well as carbonate reduction experiments to form graphite. Although a quantitative estimate of fractionation between carbonate melt and graphite could not be obtained, our results indicate that mantle melting in the presence of graphite can result in progressive C-13 carbon isotope enrichment in carbonate melt and depletion in graphite, which can be an alternate explanation for the carbon isotopic heterogeneity observed in the mantle derived carbon. (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2014.02.006

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

Ilmenite-type FeGeO3was prepared by high-pressure synthesis technique using a Kawai-type multi-anvil apparatus at 23.5 GPa and 500 °C. The effects of post annealing on the high-pressure synthesized samples were investigated by XRD analysis, Mössbauer spectroscopy and SQUID-magnetization measurements. The subsequent annealing after the high-pressure synthesis was effective to improve the crystallinity and increased the crystallite size of the ilmenite-type FeGeO3. The room temperature Mössbauer spectrum was composed of sharp paramagnetic doublets assigned to Fe2+. The well-crystallized ilmenite-type FeGeO3showed typical antiferromagnetic behavior with the Néel temperature of 79 K, while the as-prepared sample without annealing demonstrated the superparamagnetic characteristics with larger magnetization. © 2014 Springer International Publishing Switzerland.

DOI： 10.1007/s10751-014-1014-y

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER GEOPHYSICAL UNION  

The electrical conductivity of single-crystal brucite was measured as a function of pressure and temperature (P-T) using impedance spectroscopy (IS). IS measurements demonstrated that electrical conductivity perpendicular to the c axis is nearly half order of magnitude higher than that parallel to the c axis under the same P-T conditions. Electrical conductivity increased by 2 orders of magnitude during compression from 3.7 to 11GPa, irrespective of crystallographic direction. However, the conductivity increase with pressure became less significant upon further compression from 11 to 13GPa. The pressure effect is closely related to the interactions between neighboring hydroxyls. The ratio of free protons to total hydrogen increases from 2% to 33% when pressure increases from 3.7 to 13GPa at 950K. This indicates that most of the protons are bound within the crystal structure at low pressures, whereas more protons become free and mobile at higher pressures.
Key Points
&lt;list list-type="bulleted" id="grl51358-list-0001"&gt; &lt;list-item id="grl51358-li-0001"&gt;Electrical conductivity of brucite is measured under high P-T conditions &lt;list-item id="grl51358-li-0002"&gt;Electrical conductivity of brucite is greatly enhanced by compression &lt;list-item id="grl51358-li-0003"&gt;More protons become mobile at higher pressure

DOI： 10.1002/2013GL058627

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

The electrical conductivity of stishovite with various Al2O3 and H2O contents was measured at 12 GPa of pressure (P) and temperatures (T) up to 1900 K in a Kawai-type multi-anvil apparatus. Starting materials were pre-synthesized at 12 GPa and 1673 K from various mixtures of SiO2, Al2O3 and Al(OH)(3). The synthesized stishovite aggregates contained various H2O concentrations up to 0.25 wt.%. The conductivity of relatively dry stishovite was almost constant independently of Al content, whereas the conductivity significantly increased with increasing H2O content in stishovite. All electrical conductivity data fit the formula for electrical conductivity sigma = sigma C-0(W) exp{-[Delta H-0 - alpha C-W(1/3)]/kT}, where sigma(0) is the pre-exponential term, C-W is the H2O concentration, Delta H-0 is the activation enthalpy at very low H2O concentration, and k is the Boltzmann constant. The activation enthalpy decreased from 1.22 to 0.90 eV with increasing H2O content from 0.01 to 0.22 wt.%. A nearly linear correlation of the conductivity values on the H2O content suggests that the dominant mechanism of charge transport in stishovite is proton conduction. Although electrical conductivity of hydrous stishovite is higher than that of garnet in the subducted oceanic crust, small amount of hydrous stishovite is insufficient to raise conductivity. On the other hand, hydrous stishovite can contribute to the high conductivity occasionally observed at the mantle transition zone, if the subducted Archean continental crusts with tonalite-trondhjemite-granodiorite (TTG) composition were accumulated above the 660 km seismic discontinuity. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2013.12.003

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

We have determined the pressure and temperature dependencies of Si volume diffusion rates in a single crystal of Pyp(75)Alm(15)Gr(10) garnet at 6-25 GPa and 1400-1800 degrees C by the Si-29 tracer diffusion method. High-pressure experiments were conducted using the Kawai-type multi-anvil high-pressure apparatus. Diffusion profiles were obtained using secondary ion mass spectrometry in the depth-profiling mode. The Si diffusion coefficient in garnet (D-gt) is expressed by the Arrhenius equation: D-gt = D-0 exp(-(E* +- PV*)/RT), with log(10)D(0) = -7.1 +/- 1.7 m(2)/s, E* = 345 +/- 56 kJ/mol, and V* = 4.7 +/- 0.5 cm(3)/mol. Si diffusion seems to be the slowest in the major constituent elements in a pyrope-rich garnet and control rates of plastic deformation. The comparison between Si diffusion rates in garnet and wadsleyite/ringwoodite suggests that garnet has similar or slightly lower strength (at most similar to 2 times) compared with wadsleyite, and has similar or slightly higher strength (at most similar to 3 times) compared with ringwoodite at temperatures ranging from 900 to 1300 degrees C. Thus, strength contrast between subducted oceanic crust and underlying peridotite layer may be small at the mantle transition zone conditions. This result suggests that the separation of subducted oceanic crust from an underlying peridotite layer may not occur. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2013.11.002

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Proton diffusion in brucite was investigated by conducting hydrogen-deuterium (H-D) exchange experiments using multi-anvil high-pressure apparatuses at pressures from 3 to 15 GPa and temperatures in the range of 750-1050 K. The diffusion couple was composed of a natural proton-dominated brucite single crystal surrounded by synthesized D-doped brucite polycrystals. Micro-Raman spectroscopy was used to determine the diffusion profiles of the samples. The D/H diffusion profile across the boundary between single crystal and polycrystalline D-doped brucite showed an asymmetric pattern characterized by faster diffusion in aggregates. The D/H interdiffusion rate determined from the analysis of the single crystal side indicates that the interdiffusion rate increases with increasing H/D ratio. The H-D interdiffusion rate in the direction perpendicular to the c-axis is about 0.5 orders of magnitude higher than that in the direction parallel to the c-axis. At 3 GPa, the H-D interdiffusion coefficients [D(m2/s)] along and perpendicular to the c-axis of brucite at compositions of CnormOD = 0.2 in the single-crystal region were determined to be 3.30(±1.77) × 10 -11exp[-48.2(±5.8) (kJ/mol)/RT] and 1.43(±1.33) × 10-9exp[-67.5(±23.2) (kJ/mol)/RT], respectively. The H-D interdiffusion rate perpendicular to and along the c-axis increased about one order of magnitude by compression from 3 to 10 GPa, but the pressure enhancement became weaker above 10 GPa. From 10 to 15 GPa, there is almost no pressure dependence of proton diffusion for both directions. As pressure increases up to 10 GPa, enhancement of the proton migration is strongly correlated with the activation of the atomic interaction and decrease of O· · ·O' distance induced by compression. The positive pressure effect on the proton diffusion in brucite suggests that proton diffusion in higher-pressure hydrous phase becomes faster because of the shorter O· · ·O' distance.

DOI： 10.2138/am.2013.4550

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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その他リンク： http://orcid.org/0000-0002-5422-7396

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

Electrical conductivities of dense hydrous magnesium silicates (DHMS), phase A, super-hydrous phase B (SuB) and phase D, were measured by means of impedance spectroscopy in the frequency range of 10(-1)-10(6) Hz at temperatures up to 775, 700 and 700 K and pressures of 10, 18 and 22 GPa, respectively. For all phases, the increase in electrical conductivity (sigma) with temperature follows the Arrhenian formula: sigma = sigma(0)exp(-(Delta H/kT)). The pre-exponential factors (sigma(0)) and activation enthalpies (Delta H) of phase A, SuB and phase D yield values of 7.28 +/- 0.82 S/m and 0.77 +/- 0.01 eV, 292 +/- 48 S/m and 0.83 +/- 0.01 eV and 1342 +/- 154 and 0.75 +/- 0.01 eV, respectively. Higher pressure DHMS phases show higher conductivity values. The electrical conductivities of phase D and super hydrous phase B are about two and one orders of magnitude higher than that of phase A in the same temperature range, respectively. Although the proton conduction is considered to be a dominant mechanism, there is no clear relationship between water content and conductivity. Rather the conductivity of DHMS phase is closely related to the O center dot center dot center dot O distance. The conductivity-depth profiles for a cold subduction zone were constructed based on the phase proportion predicted in the descending slab. The results show distinctly lower conductivity values than those geophysically observed beneath the northeastern China and the Philippine Sea, where the cold slab stagnates in the mantle transition zone. Consequently, the DHMS phases themselves cannot be a main contributor to enhance the conductivity in the stagnant slab. Dehydration of the stagnant slab would strongly enhance the conductivities in the transition zone beneath northeastern China and Philippine Sea. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2013.03.026

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その他リンク： http://orcid.org/0000-0002-5422-7396

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

DOI： 10.1016/j.epsl.2013.02.032

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ACADEMIC PRESS INC ELSEVIER SCIENCE  

We synthesized well-crystallized ilmenite-type FeGeO3 to investigate its structural and magnetic properties. Ilmenite-type FeGeO3 were synthesized by high-pressure synthesis technique using a Kawai-type multi-anvil apparatus. Their structural and magnetic properties were examined by XRD analysis with Rietveld refinement, transmission electron microscopy, Mossbauer spectroscopy and SQUID-magnetization measurements. The subsequent annealing after the high-pressure synthesis was effective to improve the crystallinity of the ilmenite-type FeGeO3. The primary particle size of ilmenitetype FeGeO3 was similar to 15 nm. Some particles seemed to be covered with non- or poorly crystalline phase even after the annealing, and others showed a lamellar microstructure parallel to the (0 0 1) plane. Theilmenite-type FeGeO3 showed typical antiferromagnetic behavior with the Neel temperature of 79 K. (c) 2012 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.jssc.2012.11.020

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：WILEY-V C H VERLAG GMBH  

Magnesium silicide (Mg2Si) is a promising as an environmental friendly thermoelectric material. It is difficult to synthesize high-purity Mg2Si because of the boiling of Mg and the oxidation of Mg. In order to avoid the disagreement of stoichiometric ratio and the oxidation, we have performed high-pressure synthesis. And also the high-pressure X-ray diffraction by the synchrotron radiation source was carried out to find synthetic condition under pressure, and we have found that Mg2Si was synthesized at 1.0 GPa beyond 573 K. Because high synthetic temperature causes the oxidation of Mg, the high-pressure synthesis by means of a piston cylinder apparatus performed at 673 K. The synthesized compounds were evaluated by XRD analysis and thermoelectric measurement. Because the size of compounds synthesized under pressure is small, we also developed and evaluated the new equipment of the thermoelectric measurement for such as small sample. (c) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

DOI： 10.1002/pssc.201300404

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記述言語：英語   掲載種別：論文集(書籍)内論文   出版者・発行元：ANNUAL REVIEWS  

The electrical conductivity of Earth's mantle has recently become an interesting topic across diverse Earth science communities. Many electrical conductivity data of mantle phases have been accumulated through the development of high-pressure experiments. These data will provide information on valence states, water concentration, Fe concentration, oxygen fugacity, and the connectivity of the conductive phase in geological materials such as minerals, melts, and rocks. Although several groups have measured the electrical conductivity of mantle materials at high pressure, they have provided inconsistent results, especially with regard to the effect of water. Thus, it is timely to review the problems underlying experimental techniques. We discuss the current understanding of the effect of water on the electrical conductivity of nominally anhydrous mantle minerals, with some speculation on the form of volatile components in Earth's interior. Finally, we consider the role of water in major conductivity anomalies observed in the upper mantle and transition zone.

DOI： 10.1146/annurev-earth-050212-124022

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.epsl.2012.10.020

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

The relationship between structure and properties of the Na2O center dot 3SiO(2) melt was investigated using molecular dynamics (MD) simulations and electrical conductivity measurements under high pressure. The inter-atomic potential was newly developed using energy surfaces derived by quantum chemical calculations. In MD simulations, changes of the structure and properties were observed as a function of pressure. An increase in self-diffusion coefficients of network forming atoms is closely related to the distortion of the -Si-O- network and the changes in distributions of poly-membered rings which forms the -Si-O- network. In the electrical conductivity measurements, we found a negative pressure dependence at least up to 3 GPa. This suggests that electric conductivity in Na2O center dot 3SiO(2) melt is controlled by ionic conduction of sodium atoms. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jnoncrysol.2012.08.027

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その他リンク： http://orcid.org/0000-0002-5422-7396

記述言語：英語   出版者・発行元：ELSEVIER SCIENCE BV  

DOI： 10.1016/j.epsl.2012.10.020

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

The electrical conductivity of Ca-free aluminous enstatite with various water contents has been determined at a pressure of 3 GPa in a Kawai-type multi-anvil apparatus. Impedance spectroscopy was performed for both hydrogen-doped and -undoped samples in a frequency range from 0.1 Hz to 1 MHz to examine the effect of water on conductivity. Two conduction mechanisms were identified for hydrogen-undoped samples at temperature of 1000-1723 K and for hydrogen-doped samples at relatively lower temperature range of 500-900 K to minimize dehydration of samples. For the hydrogen-undoped samples, the activation enthalpy is around 1.9 eV at the higher temperatures range ( &gt; 1300 K) suggesting that the dominant charge transfer mechanism is Fe2+ -Fe3+ hopping (small polaron) conduction. For the hydrogen-doped samples measured below 900 K, the activation enthalpy decreases from 1.11 to 0.70 eV, and the conductivity values systematically increase with increasing water content, suggesting that proton conduction is the dominant conduction mechanism. Taking hopping conduction and water content dependence of activation enthalpy for proton conduction into account, all electrical conductivity data were fitted to the formula o-=o-ohexp( HhIkT)+ sigma(op)C(w)exp[-(H-p(o)-alpha C-w(1/3))/kT], where sigma(0) is pre-exponential factor, C-w is the water content in weight percent, H is the activation enthalpy. H-p(o), is the activation enthalpy for proton conduction at very low water concentration, alpha is the geometrical factor, k is the Boltzmann constant, T is absolution temperature and subscripts h and p represent hopping and proton conductions, respectively. Using the present results, a laboratory-based conductivity-depth profile in the Earth's upper mantle has been constructed as a function of water content. Comparison of our model with the currently available geophysical observations beneath the Eastern Pacific Rise indicates that hydrous aluminous enstatite cannot account for the high conductivity anomaly at the top of the asthenosphere as well as hydrous olivine. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2012.09.020

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER GEOPHYSICAL UNION  

Electrical conductivity of serpentinite with various amounts of magnetite was measured during shear deformation at high pressure and temperatures (P = 1.0 GPa, T = 750 K) corresponding to mantle wedge conditions to evaluate the contribution of aligned magnetite to the bulk conductivity of serpentinite. Under hydrostatic conditions, the sample conductivity considerably increases when the magnetite volume fraction exceeds 25% in volume, suggesting the presence of the percolation threshold for magnetite interconnection. During shear deformation, the conductivity for the samples with less than 25 vol.% magnetite increased by an order of magnitude or higher with increasing shear strain up to 9, which is likely a result of the clustering or realignment of magnetite grains in the serpentinites. However, activation enthalpy was nearly constant before and after deformation experiments, suggesting that shear deformation is unlikely to enhance establishment of interconnection of magnetite. Consequently, more than 25 vol.% magnetite is needed to establish connectivity of magnetite in serpentinite. On the other hand, the conductivity of serpentinite with low volume fraction of magnetite (5%), which is typical concentration of natural serpentinites, is almost similar to that of magnetite-free serpentinites. The present results show that the interconnection of magnetite in serpentinites by shear deformation is not expected as an origin of the high conductivity anomaly occasionally observed at the slab interface in the mantle wedge. The origin of high conductivity, therefore, indicates the presence of aqueous fluid with high salinity rather than the magnetite interconnection. Citation: Kawano, S., T. Yoshino, and I. Katayama (2012), Electrical conductivity of magnetite-bearing serpentinite during shear deformation, Geophys. Res. Lett., 39, L20313, doi:10.1029/2012GL053652.

DOI： 10.1029/2012GL053652

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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その他リンク： http://orcid.org/0000-0002-5422-7396

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER GEOPHYSICAL UNION  

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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

Recent laboratory electrical conductivity measurements of the main mantle constituent minerals have represented considerable efforts to determine the effects of water content on electrical conductivity. However, there are large discrepancies between the results of Yoshino et al. (2008a) and those of Dai and Karato (2009a) on hopping conduction and the effects of water on the electrical conductivity of wadsleyite. To investigate the cause of these discrepancies, the electrical conductivity of anhydrous and hydrous wadsleyite were newly measured under low and high temperature conditions by impedance spectroscopy. The conductivity values of dry wadsleyite aggregates with less than 2 ppm H2O by weight were similar to those for hopping conduction reported by Yoshino et al. (2008a) and distinctly higher than those of Dai and Karat (2009a). For hydrous wadsleyite, at temperatures below 1000 K, the electrical conductivity in an Arrhenius plot was repeatable along the heating-cooling paths and was similar to the results of Yoshino et al. (2008a). The impedance spectrum in the complex impedance plane of hydrous wadsleyite showed a semicircular shape, and the infrared spectrum did not show any shape change after the conductivity measurements. In contrast, when the temperature exceeds 1000 K, the electrical conductivity in an Arrhenius plot showed higher activation enthalpy. The impedance spectra were greatly distorted and the impedance arc contained at least two relaxation processes. This shape is similar to those reported by Dai and Karato (2009a) who measured the conductivity above 1000 K. The infrared spectra showed a large contribution from molecular water after conductivity measurements, suggesting significant dehydration during the conductivity measurements. In summary, the results obtained from conductivity measurements at higher temperatures ( &gt; 1000 K) do not represent the proton conduction in the grain interior. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2012.05.023

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

In order to investigate the effect of carbonate-content in partial melt on bulk conductivity under high pressure, electrical conductivity measurements were performed on carbonate melt-bearing peridotites using a Kawai-type multi-anvil apparatus. The starting materials were composed of spinet Iherzolite (KLB1) with small amounts of dolomite (1 and 3 wt.%). To obtain various melt fractions, annealing experiments were performed at different temperatures above 1400 K at 3 GPa. At low temperatures (&lt;= 1500 K), the conductivity was distinctly higher than that of carbonate-free peridotite and close to that of the carbonatite melt-bearing olivine aggregates. Although the sample conductivity increased with increasing temperature, the rate at which the conductivity increases was small and the conductivity approached that of silicate melt-bearing peridotite. CO2 concentration in the partial melt decreased with increasing annealing temperature. Thus, the small increase of the conductivity with annealing temperature is attributed to a decrease of the melt conductivity due to a decrease in carbonate content in the partial melt. As the carbonate concentration in the melt decreases, the estimated melt conductivity approaches that of the basaltic melt. Therefore, conductivity enhancement by the carbonate-bearing melt is very effective at temperature just above that of the carbonate peridotite solidus. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2012.01.005

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

We report here new experimental data on equilibrium carbon isotope fractionation between graphite/diamond and iron carbide melt at 5 and 10 GPa and in the temperature range between 1200 and 2000 degrees C. Carbon isotope equilibrium was tested using morphological features of graphite and also by performing a longer duration experiment, both of which suggested that equilibrium carbon isotope fractionation is present. The results suggest that iron carbide melt will preferentially accumulate C-12 rather than C-13. An equilibrium temperature dependent fractionation between iron carbide melt and graphite/diamond is proposed based on the relation
Delta C-13((gr/dia - iron carbide melt)) = 8.85{10(6)/T-2(K)} + 0.99.
Our results are consistent with the carbon isotope distribution between graphite and cohenite (Fe3C) observed in iron meteorites. We propose that temperature-dependent fractionation of carbon isotopes between iron carbide melt and graphite/diamond might have created a "C-12-enriched core" with a significant difference in the distribution of carbon isotopes between the carbon in the metallic core and bulk silicate Earth during the accretion and differentiation of early Earth. Recent findings of low delta C-13 carbonados and diamonds of deep mantle origin supports the presence of a C-12 enriched source. The possible presence of a reservoir of C-12-enriched carbon in the Earth&apos;s core implies that it can generate large perturbations in the surface and shallow carbon-isotope system by the flux of lighter carbon from the core-mantle boundary. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2011.08.008

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

The electrical conductivity anisotropy of deformed natural talc rocks and serpentinites was investigated using a Kawai-type multi-anvil press in the temperature range of 500-1000 K at 3 GPa. The electrical conductivities of the samples were measured by an impedance analyzer with a frequency range of 10(-3)-10(6) Hz along three sample directions: the direction parallel to the lineation of oriented minerals (x direction), the direction perpendicular to the lineation on the foliation plane (y direction), and the direction perpendicular to the foliation (z direction). For both rock types, electrical conductivities parallel to the x and the z directions were the highest and the lowest, respectively. Electrical conductivities of talc rocks and serpentinites were at least two orders of magnitude lower than previous reports. Electrical conductivities of the serpentinites were higher than those of the talc rocks. Electrical conductivity anisotropy for the talc rocks was stronger than that for the serpentinites at the same oxygen buffer condition. Electrical conductivity and its anisotropy of the serpentinites become higher with higher oxygen fugacity. The activation enthalpy of talc rocks was the lowest (0.59 eV) in the x direction and highest (0.68 eV) in the z direction. The activation enthalpies of the serpentinites in different directions show similar values: about 0.74 eV and 0.68 eV for the experiments using Mo and Ni electrodes, respectively. Impedance spectra for both rock types show the presence of two conduction paths: grain interior and grain boundary conductions. The total electrical conductivities were reduced by grain boundary conduction. Electrical conductivities of hydrous minerals show strong dependence on hydrogen concentration and hydrogen mobility. The conduction mechanism probably was proton migration through extrinsic vacancies derived from a presence of ferric iron perpendicular to the c axis of the crystals and through interstitial mechanisms parallel to the c axis. In both warm and cold subduction zones, high electrical conductors (similar to 10(-15) S/m) cannot be explained by the presence of talc or serpentinites. The electrical conductivity anisotropy in a subduction zone would be inconspicuously small (within one order) unless we consider other well aligned high conductive phases. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2011.06.012

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

The origin of high electrical conductive anomalies in the lower crust is a long-standing and controversial problem. Although it has been proposed that saturated saline water or partial melt increases electrical conductivity, graphite film has also been recognized as a potential cause of high conductivity since the discovery of fine graphite films on the grain boundaries of high-grade metamorphic rocks. To investigate the stability of graphite film on grain boundary of silicate minerals under lower crustal conditions, electrical conductivity of graphite film on synthetic grain boundaries of quartz bicrystals was measured by means of impedance spectroscopy at 1 GPa and up to 1200 K in a multianvil apparatus. At first heating, the electrical conductivity of the thin graphite film with thickness less than 100 nm was initially very high but decreased with time during annealing. Under high temperature conditions (&gt;1000 K), the conductivity of a thin carbon film rapidly decreases and approaches the quartz conductivity. This indicates that graphite film on a grain boundary between two quartz crystals is not stable at high temperatures. Optical microscopic observation of the run products suggested a disconnected feature of graphite on a quartz grain boundary. Disconnection of graphite film can be caused by higher interfacial energy between graphite and silicate minerals than that of the grain boundary energy. Therefore, a thin graphite film is not a likely candidate to account for high conductivity anomalies in the middle and lower continental crust (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2011.04.003

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER GEOPHYSICAL UNION  

AC measurements of the electrical conductivity of synthetic quartz along various orientations were made between 0.1 and 1 MHz, at similar to 855 similar to 1601 K and at 1.0 GPa. In addition, the electrical conductivity of quartz along the c axis has been studied at 1.0-3.0 GPa. The impedance arcs representing bulk conductivity occur in the frequency range of 10(3)-10(6) Hz, and the electrical responses of the interface between the sample and the electrode occur in the 0.1 similar to 10(3) Hz range. The pressure has a weak effect on the electrical conductivity. The electrical conductivity experiences no abrupt change near the alpha - beta phase transition point. The electrical conductivity of quartz is highly anisotropic; the electrical conductivity along the c axis is strongest and several orders of magnitude larger than in other directions. The activation enthalpies along various orientations are determined to be 0.6 and 1.2 eV orders of magnitude, respectively. The interpretation of the former is based on the contribution of alkali ions, while the latter effect is attributed to additional unassociated aluminum ions. Comparison of determined anisotropic conductivity of quartz determined with those from field geophysical models shows that the quartz may potentially provide explanations for the behavior of electrical conductivity of anisotropy in the crust that are inferred from the transverse magnetic mode.

DOI： 10.1029/2009JB006695

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

Electrical impedance measurements were performed on two types of partial molten samples with basaltic and carbonatitic melts in a Kawai-type multi-anvil apparatus in order to investigate melt fraction-conductivity relationships and melt distribution of the partial molten mantle peridotite under high pressure. The silicate samples were composed of San Carlos olivine with various amounts of mid-ocean ridge basalt (MORB), and the carbonate samples were a mixture of San Carlos olivine with various amounts of carbonatite. High-pressure experiments on the silicate and carbonate systems were performed up to 1600 K at 1.5 GPa and up to at least 1650 K at 3 GPa, respectively. The sample conductivity increased with increasing melt fraction. Carbonatite-bearing samples show approximately one order of magnitude higher conductivity than basalt-bearing ones at the similar melt fraction. A linear relationship between log conductivity (sigma(bulk)) and log melt fraction (phi) can be expressed well by the Archie's law (Archie, 1942) (sigma(bulk)/sigma(melt)=C phi(n)) with parameters C = 0.68 and 0.97, n = 0.87 and 1.13 for silicate and carbonate systems, respectively. Comparison of the electrical conductivity data with theoretical predictions for melt distribution indicates that the model assuming that the grain boundary is completely wetted by melt is the most preferable melt geometry. The gradual change of conductivity with melt fraction suggests no permeability jump due to melt percolation at a certain melt fraction. The melt fraction of the partial molten region in the upper mantle can be estimated to be 1-3% and similar to 0.3% for basaltic melt and carbonatite melt, respectively. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2010.04.050

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：SCIENCE CHINA PRESS  

The electrical conductivity of (Mg(0.9)Fe(0.1)) SiO(3) enstatite has been measured at pressures of 10 similar to 20 GPa and temperatures of 750 similar to 1600 K using a Kawai-type multianvil high-pressure apparatus. The experimental results demonstrate that there are two conduction mechanisms, small polaron is the dominant mechanism in the high temperature regions, while proton is in charge of the low temperature regions as water is determined in the recovered sample in this study. On the other hand, we observe a pressure induced phase transition from enstatite to ringwoodite under pressure of 20 GPa by X-ray diffraction. The conductivity of ringwoodite with water at 20 GPa is in good agreement with the available measurements of hydrous ringwoodite.

DOI： 10.3969/j.issn.0001-5733.2010.03.032

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記述言語：英語   出版者・発行元：SPRINGER  

Electrical conductivity structures of the Earth's mantle estimated from the magnetotelluric and geomagnetic deep sounding methods generally show increase of conductivity from 10(-4)-10(-2) to 10(0) S/m with increasing depth to the top of the lower mantle. Although conductivity does not vary significantly in the lower mantle, the possible existence of a highly conductive layer has been proposed at the base of the lower mantle from geophysical modeling. The electrical properties of mantle rocks are controlled by thermodynamic parameters such as pressure, temperature and chemistry of the main constituent minerals. Laboratory electrical conductivity measurements of mantle minerals have been conducted under high pressure and high temperature conditions using solid medium high-pressure apparatus. To distinguish several charge transport mechanisms in mantle minerals, it is necessary to measure the electrical conductivity in a wider temperature range. Although the correspondence of data has not been yet established between each laboratory, an outline tendency of electrical conductivity of the mantle minerals is almost the same. Most of mineral phases forming the Earth's mantle exhibit semiconductive behavior. Dominant conduction mechanism is small polaron conduction (electron hole hopping between ferrous and ferric iron), if these minerals contain iron. The phase transition olivine to high-pressure phases enhances the conductivity due to structural changes. As a result, electrical conductivity increases in order of olivine, wadsleyite and ringwoodite along the adiabat geotherm. The phase transition to post-spinel at the 660 km discontinuity further can enhance the conductivity. In the lower mantle, the conductivity once might decrease in the middle of the lower mantle due to the iron spin transition and then abruptly increase at the condition of the DaEuro(3) layer. The impurities in the mantle minerals strongly control the formation, number and mobility of charge carriers. Hydrogen in nominally anhydrous minerals such as olivine and high-pressure polymorphs can enhance the conductivity by the proton conduction. However, proton conduction has lower activation enthalpy compared with small polaron conduction, a contribution of proton conduction becomes smaller at high temperatures, corresponding to the mantle condition. Rather high iron content in mantle minerals largely enhances the conductivity of the mantle. This review focuses on a compilation of fairly new advances in experimental laboratory work together with their explanation.

DOI： 10.1007/s10712-009-9084-0

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

The electrical conductivity of sintered polycrystalline periclase has been measured at 20GPa and temperatures up to 1700 K with a KAWAI-type multi-anvil apparatus. Arrhenius plot of the electrical conductivity shows two linear regions, implying a change of charge transport mechanism with temperature in this experiment. At temperatures below 700K small polaron conduction dominates, with an activation energy of 0.2 eV. At higher temperatures, the activation energy is determined to be 1.18 eV, which is much higher than 0.2 eV at low temperature. Our observations suggest the high-temperature conduction is attributed to a large polaron process with magnesium vacancy trapping hole on oxygen. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2009.08.036

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IOP PUBLISHING LTD  

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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IOP PUBLISHING LTD  

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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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IOP PUBLISHING LTD  

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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

The electrical conductivity of the major upper mantle minerals, namely, olivine, wadsleyite and ringwoodite, is reviewed in this paper. There are mainly three electrical conduction mechanisms for three upper mantle minerals: hopping, ionic and proton conductions. The charge carriers for these conduction mechanisms are an electron hole in Fe ion, a vacancy in Mg site, and a proton, respectively. Hopping conduction is the most essential conduction mechanism for the major upper mantle minerals. Because ionic conduction has high activation energy, it becomes a dominant conduction mechanism only at high temperatures. Proton conduction contributes at relatively low temperatures. If the mantle minerals contain large amount of water (more than 0.1 wt.%), proton conduction can be a dominant conduction mechanism, even at high temperatures. (C) 2009, IGM, Siberian Branch of the RAS. Published by Elsevier B. V. All rights reserved.

DOI： 10.1016/j.rgg.2009.11.012

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

The electrical conductivity of San Carlos olivine aggregate of various water content was measured at a pressure of 10 GPa in a Kawai-type multi-anvil apparatus. Conductivity measurements were performed on two sets of samples to determine the effect on conductivity of water in olivine: 1) a hydrogen-doped sample and 2) a hydrogen-undoped sample. To minimize water escape from the hydrogen-doped samples, the conductivity measurement was carried out below 1000 K. Three conduction mechanisms were identified from the Arrhenian behavior of the undoped samples, which include a small amount of water. A change in the activation enthalpy indicated that the dominant conduction mechanism changed from proton conduction to small polaron conduction with increasing temperature. At temperatures above 1700 K. the activation enthalpy exceeds 2 eV suggesting that the dominant mechanism of charge transport would be ionic conduction. The conductivity increased with increasing water content. The activation enthalpy for proton conduction tends to decrease slightly with increasing water content. The activation enthalpy determined for each run had similar values (similar to 0.9 eV). Taking the water concentration dependence of activation enthalpy into account for proton conduction, all data were fitted to the electrical conductivity formula (sigma=sigma(01)exp[-E-1/kT]+sigma(OH)exp[-E-H/kT]+sigma(OP)C(W)exp[-(E-0-alpha C-W(1/3))/kT], where sigma(0) represents a pre-exponential term, C-W is the water content in weight percent, E is the activation enthalpy, E-0 is the activation enthalpy for proton conduction at very low water concentration, alpha is the geometrical factor, k is the Boltzmann constant, T is absolute temperature and subscripts 1, H and P denote ionic, hopping (small polaron) and proton conductions, respectively. The conductivity jump at the 410 km discontinuity (olivine-wadsleyite transition) is much smaller than that previously predicted. Since the contribution of proton conduction to the bulk electrical conductivity decreases with increasing temperature the high conductivity anomaly at the top of the asthenosphere cannot be explained by olivine hydration. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2009.09.032

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記述言語：英語   出版者・発行元：AMER GEOPHYSICAL UNION  

DOI： 10.1029/2009GL039318

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

Electrical conductivity of ringwoodite with various iron contents [Fe/Fe + Mg) = 0.09, 0.2 and 0.3] was measured at pressure (20 GPa) and temperature (up to 1900 K) conditions of the lower part of the mantle transition zone in a Kawai-type multi-anvil apparatus. The conductivity increased with increasing total iron content. All electrical conductivity data were fitted to the formula of electrical conductivity sigma = sigma(0) X-Fe exp(-H/kT), where sigma(0) is the pre-exponential term, X-Fe is the mole fraction of iron content in the Mg site, H is the activation enthalpy, k is the Boltzmann constant and T is absolute temperature. The activation enthalpy becomes higher at a certain temperature. At high temperatures, the activation enthalpy decreased from 1.44 to 0.92 eV with increasing total Fe content. At low temperatures less than 1000 K, the activation enthalpy also decreases from 1.15 to 0.74 eV with total Fe content. Dependence of the activation enthalpy on Fe content suggests that the dominant mechanism of charge transport is Fe2+-Fe3+ hopping (small polaron). Recent electrical conductivity-depth profiles of the transition zone beneath the Pacific Ocean obtained from the electromagnetic induction Study shows that the conductivity values between 520 and 660 km depths may be explained by ringwoodite with Fe/Fe + Mg) = 0.10. On the other hand, assuming a normal geotherm, conductivity values beneath the continent or stable craton are considerably lower than those of ringwoodite with Fe/(Fe + Mg) = 0.10. Taking into consideration results from the global seismic tomographic studies, relatively low conductivity in these regions can be explained by the existence of a cooler region compared with the surrounding mantle, rather than the presence of iron-poor ringwoodite, or a combination of both. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2008.09.015

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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DOI： 10.1016/j.pepi.2009.01.012

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

Electrical conductivity of wadsleyite was measured at 16 GPa using a KAWAI-type multi-anvil press under controlled oxygen fugacity. Water-doped and -undoped samples were used to examine the effect of water on conductivity. Two water-doped wadsleyite samples used for the conductivity measurements contained 0.3 +/- 0.01 and 1.2 +/- 0.02 wt.% water. The temperature ranges for the conductivity measurements were 500-2000 K for water-undoped samples and 500-1000 K for water-doped samples. Above 1500 K, the electrical conductivity values are essentially the same among different runs with an average activation enthalpy of 1.5 eV, suggesting that small polaron conduction should dominate. Below 1000 K, the conductivity systematically increases with increasing water content, suggesting proton conduction as a dominant conduction mechanism. Electrical conductivity of anhydrous wadsleyite in the mantle transition zone should be about 3 x 10(-2) S/m in the normal geotherm. Hydration enhances the conductivity of wadsleyite; by containing 0.1 wt.% water, the conductivity of wadsleyite increases by 0.3 log units. The conductivity jump associated with the dry olivine-wadsleyite transition is only 0.7 log units. A dry olivine-wadsleyite conductivity model well agrees with the current semi-global conductivity-depth profiles, thus the concept of a globally hydrated mantle transition zone is not necessary in view of electrical conductivity. The high conductivity observed in the wedge mantle cannot be explained by hydrous wadsleyite. Alternatively, the presence of either phase E or supercritical fluids in the wedge mantle is proposed. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2008.06.001

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

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記述言語：日本語  

The electrical conductivity of the major upper mantle minerals, namely, olivine, wadsleyite and ringwoodite is reviewed in this paper. There are mainly three electrical conduction mechanisms for the major upper mantle minerals, namely, ionic, hopping and proton conductions. The charge carriers for these mechanisms are electron hole in Fe ion, vacancy in the Mg site and proton, respectively. An electron hole in an Fe ion forms a small polaron, which causes a higher activation energy (1.4-1.6 eV) than mere transfer of electron holes (0.1 eV). Hopping conduction is the most essential conduction mechanisms for the major upper mantle minerals. Ionic conduction is a dominant conduction mechanism only at high temperatures, because ionic conduction has high activation energy (4.3 eV for olivine). Proton conduction could play an important role because the major upper mantle minerals can contain certain amount of water. Proton conduction contributes more at lower temperatures because of its low activation energies (0.5-1.0 eV). If the mantle minerals contain large amount of water (&gt
0.1 wt%), proton conduction can be a dominant conduction mechanism of the mantle minerals even at high temperatures.

DOI： 10.2465/gkk.38.33

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER GEOPHYSICAL UNION  

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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：NATURE PUBLISHING GROUP  

The Earth's mantle transition zone could potentially store a large amount of water, as the minerals wadsleyite and ringwoodite incorporate a significant amount of water in their crystal structure(1,2). The water content in the transition zone can be estimated from the electrical conductivities of hydrous wadsleyite and ringwoodite, although such estimates depend on accurate knowledge of the two conduction mechanisms in these minerals ( small polaron and proton conductions), which early studies have failed to distinguish between(3,4). Here we report the electrical conductivity of these two minerals obtained by high- pressure multi- anvil experiments. We found that the small polaron conductions of these minerals are substantially lower than previously estimated. The contributions of proton conduction are small at temperatures corresponding to the mantle transition zone and the conductivity of wadsleyite is considerably lower than that of ringwoodite for both mechanisms. The dry model mantle shows considerable conductivity jumps associated with the olivine- wadsleyite, wadsleyite- ringwoodite and post- spinel transitions. Such a dry model explains well the currently available conductivity- depth profiles(5) obtained from geoelectromagnetic studies. We therefore conclude that there is no need to introduce a significant amount of water in the mantle transition to satisfy electrical conductivity constraints.

DOI： 10.1038/nature06427

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：SPRINGER  

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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

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

DOI： 10.1016/j.epsl.2007.02.002

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Grain growth kinetics of CaIrO3perovskite 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: Gn-G0n= k · t (k = k0exp(- 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&quot; discontinuity would lead to maintenance of small grain size in the D&quot; layer. If diffusion creep is the dominant deformation mechanism of post-perovskite, the phase transformation would induce the significant softening of the D&quot; layer due to slow growth rate of post-perovskite compared with a situation without the phase transition. © 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2007.01.010

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：NATURE PUBLISHING GROUP  

The oceanic asthenosphere is observed to have high electrical conductivity, which is highly anisotropic in some locations(1,2). In the directions parallel and normal to the plate motion, the conductivity is of the order of 10(-1) and 10(-2) Sm(-1), respectively, which cannot be explained by the conductivity of anhydrous olivine(2). But because hydrogen can be incorporated in olivine at mantle pressures(3-5), this observation has been attributed to olivine hydration, which might cause anisotropically high conductivity by proton migration(1,2,6,7). To examine this hypothesis, here we report the effect of water on electrical conductivity and its anisotropy for hydrogen-doped and undoped olivine at 500 - 1,500 K and 3 GPa. The hydrous olivine has much higher conductivity and lower activation energy than anhydrous olivine in the investigated temperature range. Nevertheless, extrapolation of the experimental results suggests that conductivity of hydrous olivine at the top of the asthenosphere should be nearly isotropic and only of the order of 10(-2) Sm(-1). Our data indicate that the hydration of olivine cannot account for the geophysical observations(2), which instead may be explained by the presence of partial melt elongated in the direction of plate motion.

DOI： 10.1038/nature05223

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：SPRINGER  

The pore geometry of texturally equilibrated rocks is controlled by the interfacial energy ratio between grain boundaries and solid-liquid boundaries. Faceting at pore walls, which is a common feature of pore networks in rocks, strongly affects the liquid distribution. We investigated the effects of faceting on the equilibrium pore geometries based on image analysis of several systems with various degrees of faceting and dihedral angles. The degree of faceting was assessed by the F value, which is the ratio of the flat interface length at the pore wall to the length of total interfacial boundary between solid and liquid. The F values tend to increase with increasing liquid volume fraction. Little-faceted systems show relatively homogeneous liquid distribution. Moderately-faceted systems with a higher dihedral angle (similar to 55 degrees) are characterized by development of large pores surrounded by faceted walls and complementary shrinkage of triple junction tubes, whereas strongly faceted systems with a low dihedral angle show no evidence of shrinking triple junction tubes, although most pores are surrounded by faceted pore walls. The faceted systems tend to produce more facet boundaries at the pore walls due to the difference of interfacial energies between the flat and curved surfaces. In the systems with the same degree of faceting, heterogeneity of liquid distribution tends to decrease with dihedral angle. For faceting systems, the permeability of texturally equilibrated rocks with low liquid fraction would be significantly decreased by the relative reduction of triple junction volumes or by closure of channels along grain edge due to the truncation of facet walls.

DOI： 10.1007/s00410-006-0099-y

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER GEOPHYSICAL UNION  

Melt- or fluid- filled pore geometry in texturally equilibrated aggregates characterized by various dihedral angles and degrees of faceting was investigated quantitatively by measuring the grain boundary wetness, which is defined as the ratio of solid- liquid boundary area over the total area of interphase boundaries. The wetness ( psi) increases monotonically with increasing liquid volume fraction ( phi). For systems showing no faceting and low dihedral angle, the relation between phi and psi agrees well with the theoretical prediction for an ideal isotropic model assuming tetrakaidecahedral packing. This is true for the olivine- basalt system, whereas partially molten lherzolite shows systematically lower wetness. For systems showing strong faceting, the wetness is systematically lower than the theoretical prediction. For all systems, the obtained psi-phi relationship can be fitted well to the formulae psi = A phi(1/ 2) with fitting parameter A, indicating that the three- dimensional pore shape is a tubular one. Seismic wave velocities are calculated for the model systems in terms of the equivalent aspect ratio ( EAR) of the oblate spheroid model based on the above psi-phi relation. Calculated EARs can be used to predict f in texturally equilibrated rocks using V-P or V-S data and also to interpret the seismologically observed variation of dlnV(S)/ dlnV(P) in terms of the variation of pore geometry. Our results show that seismic wave velocities of partially molten peridotites are not significantly affected by faceting and that values of dlnV(S)/ dlnV(P) larger than 1.5 cannot be explained by texturally equilibrated partially molten rocks.

DOI： 10.1029/2004JB003544

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

The growth kinetics of molten FeS pools in partially molten peridotite were investigated by time-series experiments in a piston-cylinder apparatus. The starting materials were mixed powders of peridotite +FeS, with FeS=6%, 12% and 18% by volume in order to characterize the effect of volume fraction on the growth laws of Fes. The initial particle size of Fes was about 3.5 mu m. The samples were annealed at temperatures between 1573 and 1723 K at 1.5 GPa for durations ranging from a few seconds to 100 h. The size of Fes pools was determined by analysis of backscattered electron images. The increase of pool size (G) of FeS with time (t) follows a growth law: G(n) - G(0) = k (.) t (k=k(0) exp(- Q/RT)). Samples with higher Fes volume fraction have larger pool size at the same conditions. The growth exponent (n) at 1573 K strongly depends on initial volume fraction of Fes and varies between similar to 2.6 and similar to 6.4, whereas those at 1723 K are almost constant (similar to 2.3) irrespective of the initial volume fraction. The growth exponent (n) tends to decrease with increasing temperature and volume fraction of silicate melt for each run series of different initial volume fraction of Fes. Low volume fractions of Fes and silicate melt leads to sluggish growth of the pools due to pinning of the silicate mineral phases. The activation enthalpy for pool growth is 331 +/- 40 kJ/mol based on the results from samples with 18 vol.% FeS, which show the smallest variation of growth exponent over a range of temperature. These Fes coarsening experiments may serve as tentative analogs for the behavior of a liquid metal phase in hot proto-planetary objects. Assuming exponential heating of such bodies in the early solar system-and allowing for a significant Zener pinning effect of Fe pools-the time spent above the silicate solidus may be insufficient to grow the pools beyond the size where diffusive equilibration with the silicate surroundings can be maintained: in other words, diffusive equilibration may assured because of slow coarsening kinetics. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2005.04.021

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

Magmatic accretion is potentially an important mechanism in the growth of the continental crust and the formation of granulites. In this study, the thermal evolution of a magmatic arc in response to magmatic accretion is modeled using numerical solutions of the one-dimensional heat conduction equation. The initial and boundary conditions used in the model are constrained by geological observations made in the Kohistan area, NW Himalayas. Taking consideration of the preferred intrusion locations for basaltic magmas, we consider two plausible modes of magmatic accretion: the first involves the repeated intrusion of basalt at mid-crustal depths ('intraplate model'), and the second evaluates the simultaneous intrusion of basalt and picrite at mid-crustal depths and the base of the crust respectively ('double-plate model'). The results of the double-plate model account for both the inferred metamorphic P-T paths of the Kohistan mafic granulites and the continental geotherm determined from peak P-T conditions observed for granulite terranes. The double-plate model may be applicable as a key growth process for the production of thick mafic lower crust in magmatic arcs.

DOI： 10.1093/petrology/egh056

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have investigated the effect of Al3+ on the room-temperature compressibility of perovskite for stoichiometric compositions along the MgSiO3-AlO1.5 join with up to 25 mol% AlO1.5. Aluminous Mg-perovskite was synthesized from glass starting materials, and was observed to remain a stable phase in the range of ∼30-100 GPa at temperatures of ∼2000 to 2600 K. Lattice parameters for orthorhombic ( Pbnm ) perovskite were determined using in situ X-ray diffraction at SPring8, Japan. Addition of Al3+ into the perovskite structure increases orthorhombic distortion and unit cell volume at ambient conditions ( V0). Compression causes anisotropic decreases in axial length, with the a axis more compressive than the b and c axes by about 25% and 3%, respectively. The magnitude of orthorhombic distortion increases with pressure, but aluminous perovskite remains stable to pressures of at least 100 GPa. Our results show that substitution of Al3+ causes a mild increase in compressibility, with the bulk modulus ( K0) decreasing at a rate of -67±35 GPa/XAl. This decrease in K0 is consistent with recent theoretical calculations if essentially all Al3+ substitutes equally into the six- and eight-fold sites by charge-coupled substitution with Mg2+ and Si4+. In contrast, the large increase in compressibility reported in some studies with addition of even minor amounts of Al is consistent with substitution of Al3+ into six-fold sites via an oxygen-vacancy forming substitution reaction. Schematic phase relations within the ternary MgSiO3-AlO1.5-SiO2 indicate that a stability field of ternary defect Mg-perovskite should be stable at uppermost lower mantle conditions. Extension of phase relations into the quaternary MgSiO3-AlO1.5-FeO1.5-SiO2 based on recent experimental results indicates the existence of a complex polyhedral volume of Mg-perovskite solid solutions comprised of a mixture of charge-coupled and oxygen-vacancy Al3+ and Fe3+ substitutions. Primitive mantle with about 5 mol% AlO1.5 and an Fe3+/(Fe3++Fe2+) ratio of ∼0.5 is expected to be comprised of ferropericlase coexisiting with Mg-perovskite that has a considerable component of Al3+ and Fe3+ defect substitutions at conditions of the uppermost lower mantle. Increased pressure may favor charge-coupled substitution reactions over vacancy forming reactions, such that a region could exist in the lower mantle with a gradient in substitution mechanisms. In this case, we expect the physical and transport properties of Mg-perovskite to change with depth, with a softer, probably more hydrated, defect dominated Mg-perovskite at the top of the lower mantle, grading into a stiffer, dehydrated, charge-coupled substitution dominated Mg-perovskite at greater depth. © 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2004.03.014

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

The connectivity of molten Fe-S in peridotite has been experimentally investigated by means of in situ electrical conductivity measurements at high temperatures and 1 GPa. Starting materials were powdered mixtures of peridotite KLB-1 with various amounts (0, 3, 6, 13, 19, 24 vol.%) of the 1 GPa eutectic composition in the Fe-FeS binary system. At temperatures above the eutectic point in the Fe-FeS system ( similar to 980 degreesC) and below the solidus of KLB1 ( similar to 1200 degreesC), molten Fe-S in a solid silicate matrix interconnects when the volume fraction is over similar to 5%. Conductivity-temperature paths indicate that in the presence of partial silicate melting the connectivity of molten Fe-S in a peridotite matrix is inhibited. Based on observations of retrieved samples, the percolation threshold of Fe-S melts in the presence of low to moderate degrees of silicate melt is estimated at 13 +/- 2 vol.%. These results indicate that if the volume fraction of Fe-alloy in a planetesimal was initially greater than 5%, and if early heating by decay of radionuclides raised the temperature of the interior above the Fe-alloy melting point, initial metal segregation was controlled by permeable flow of molten iron alloy in a solid silicate matrix. These conditions were likely met by many terrestrial objects in the early solar nebula. Efficient removal of residual Fe-alloy (5 vol.%) from silicate requires high-degree melting of silicate so that metal can segregate as droplets. Giant impacts during the final stage of accretion of large planetary objects could supply the energy required for high-degrees of melting. Alternatively, if initial metal segregation were delayed until a planetary object grew to large size ( similar to 1000 km in diameter), release of gravitational potential energy due to metal segregation could contribute enough heat to form a magma ocean. (C) 2004 Elsevier B.V All rights reserved.

DOI： 10.1016/j.epsl.2004.03.010

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その他リンク： http://orcid.org/0000-0002-5422-7396

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER GEOPHYSICAL UNION  

[1] Phase relations of the olivine-wadsleyite transition in the system (Mg, Fe)(2)SiO4 have been determined at 1600 and 1900 K using the quench method in a Kawai-type high-pressure apparatus. Pressure was determined at a precision better than 0.2 GPa using in situ X-ray diffraction with MgO as a pressure standard. The transition pressures of the end-member Mg2SiO4 are estimated to be 14.2 and 15.4 GPa at 1600 and 1900 K, respectively. Partition coefficients for Fe and Mg between olivine and wadsleyite are 0.51 at 1600 K and 0.61 at 1900 K. By comparing the depth of the discontinuity with the transition pressure, the temperature at 410 km depth is estimated to be 1760 +/- 45 K for a pyrolitic upper mantle. The mantle potential temperature is estimated to be in the range 1550-1650 K. The temperature at the bottom of the upper mantle is estimated to be 1880 +/- 50 K. The thickness of the olivine-wadsleyite transition in a pyrolitic mantle is determined to be between 7 and 13 km for a pyrolitic mantle, depending on the efficiency of vertical heat transfer. Regions of rapid vertical flow ( e. g., convection limbs), in which thermal diffusion is negligible, should have a larger transition interval than stagnant regions, where thermal diffusion is effective. This is in apparent contradiction to short-period seismic wave observations that indicate a maximum thickness of &lt;5 km. An upper mantle in the region of the 410 km discontinuity with about 40% olivine and an Mg# of at least 89 can possibly explain both the transition thickness and velocity perturbation at the 410 km discontinuity.

DOI： 10.1029/2003JB002438

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その他リンク： http://orcid.org/0000-0002-5422-7396

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER GEOPHYSICAL UNION  

[1] The geometrical distribution of the aqueous fluid in textural equilibrium with eclogite was investigated by measurements of the dihedral angles at aqueous fluid-clinopyroxene-clinopyroxene (thetacc), at aqueous fluid-garnet-garnet (thetagg) and at aqueous fluid- clinopyroxene-garnet (thetacg) triple junctions at 3-5 GPa and 700-800degreesC with a Kawai-type multianvil high-pressure apparatus. The dihedral angles, qcc, qgg, and qcg range from 62degrees to 68degrees and appear constant within the experimental uncertainties at the pressures and temperatures investigated. The constant dihedral angle values could be explained by the counterbalance of the effects of pressure, temperature, and the difference in Mg/(Mg + Fe) in the minerals and the aqueous fluid. The present results lead to the suggestion that the aqueous fluid in eclogite at pressures from 3 to 5 GPa (corresponding to depths of similar to90-150 km) exists as isolated pores, provided circumstances of chemical and textural equilibrium prevail. It is suggested that up to about 1-2 vol% aqueous fluid could be trapped as an interstitial fluid in eclogite and be transported to the Earth's interior at depths of at least 150 km by the subduction of the oceanic crust and by the delamination of the crustal roots.

DOI： 10.1029/2002JB001960

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：NATURE PUBLISHING GROUP  

The tungsten isotope composition of meteorites indicates that core formation in planetesimals occurred within a few million years of Solar System formation(1,2). But core formation requires a mechanism for segregating metal, and the 'wetting' properties of molten iron alloy in an olivine-rich matrix is thought to preclude segregation by permeable flow unless the silicate itself is partially molten(3-5). Excess liquid metal over a percolation threshold, however, can potentially create permeability in a solid matrix, thereby permitting segregation. Here we report the percolation threshold for molten iron-sulphur compounds of approximately 5 vol.% in solid olivine, based on electrical conductivity measurements made in situ at high pressure and temperature. We conclude that heating within planetesimals by decay of short-lived radionuclides can increase temperature sufficiently above the iron-sulphur melting point (similar to1,000degreesC) to trigger segregation of iron alloy by permeable flow within the short time-frame indicated by tungsten isotopes. We infer that planetesimals with radii greater than about 30 km and larger planetary embryos are expected to have formed cores very early, and these objects would have contained much of the mass in the terrestrial region of the protoplanetary nebula. The Earth and other terrestrial planets are likely therefore to have formed by accretion of previously differentiated planetesimals, and Earth's core may accordingly be viewed as a blended composite of preformed cores.

DOI： 10.1038/nature01459

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その他リンク： http://orcid.org/0000-0002-5422-7396

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

The effect of pressure and temperature on the dihedral angles of aqueous fluid in a pyrope matrix was investigated. Experiments were performed on an H2O-pyrope system in a multianvil apparatus over the pressure and temperature ranges of 4-13 GPa and 900-1200degreesC, respectively. The dihedral angle of the fluid in contact with the pyrope exhibited a significant change at pressures around 8-9 GPa. The dihedral angles increased with increasing pressure up to 9 GPa. At pressures above 9 GPa, the dihedral angles were greater than 60degrees at temperatures below 1000degreesC. Therefore, the efficient percolation of aqueous fluid in a pyrope matrix is not feasible in the upper mantle and the transition zone. The fluid released from the breakdown reactions of the hydrous minerals lawsonite and phengite exists in the oceanic crust, which mainly consists of garnet in the upper mantle and transition zone. We conclude that a part of the aqueous fluid released from the hydrous minerals may be retained in the subducted oceanic crust, and transferred into the deep mantle by the subduction process. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0012-821X(02)00920-2

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その他リンク： http://orcid.org/0000-0002-5422-7396

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER GEOPHYSICAL UNION  

[1] The connectivity of C-H-O fluids in anorthite aggregate was assessed by measurements of the dihedral angle, theta, at conditions of 800-1000 degreesC and 0.8-1.2 GPa for duration of 1-21 days. The longer-duration experiments show reduction of the effect of crystal anisotropy on pore geometry. Especially, fluid-filled small pores (&lt; 5 mu m) in anorthite aggregate quickly approach to textural equilibrium controlled by minimization of surface energies in &lt;3 days. Anorthite aggregates with CO2 fluid show large dihedral angle over 120degrees. In the anorthite aggregates with aqueous fluid the dihedral angles are over 60degrees at pressure of 1.0 GPa and decrease across critical angle of 60degrees with increasing pressure. Over the range of experimental conditions, isopleths of dihedral angle show nearly zero to negative dP/dT slope with increasing temperature. The observed reduction in dihedral angle with increasing pressure and temperature may be attributed to increase in plagioclase solubility in aqueous fluid. Natural anorthite (with small amounts of albite component) shows smaller dihedral angle than pure anorthite. At higher temperature conditions the anorthite content of the run products deviates progressively from that of starting material. This suggests that preferential solubility of albite component relative to anorthite affects the equilibrium fluid distributions of plagioclase by aqueous fluid. Experimental results point to the likelihood that plagioclase-rich lower continental crust will not allow intergranular fluid flow of C-H-O fluids even in the presence of high geothermal gradient.

DOI： 10.1029/2001JB000440

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Scapolites developed variably in the deep-seated metagabbros of the Kohistan Arc, north Pakistan, were investigated to evaluate the distribution and migration of C-O-H-S fluid and origin of carbon in the lower crust. Scapolites can be classified, based on their distinct difference in occurrence and chemical composition, into carbonate type and sulfate-rich type. Carbonate-type scapolites occur around carbonate pods in the layered gabbros at the mid-crustal levels and were formed by an increase in the CaO activity in the country rocks and simultaneous decarbonation of calcite. Predicted equilibrium CO2 mole fraction in fluid (Xco2) is sufficiently low to be consistent with removal of CO2. Sulfate-rich scapolites occur in the garnet-bearing granulites at the lower crustal level and were formed by breakdown reactions of garnet and plagioclase under relatively higher CO2 activity (aco2) and oxygen fugacity. The carbon isotopic composition (δ13C) in carbonate scapolite is equivalent to the juvenile mantle (-5 to -6‰), whereas sulfate-rich scapolite has heavy carbon stable isotope values close to 0‰. These results reveal that carbonate scapolite was formed by decarbonation and metasomatism of igneous carbonate pods with the host metagabbros under granulite facies conditions, and sulfate-rich scapolites were formed by infiltration of CO2-rich fluid derived from decarbonation of carbonate-bearing sediments in the subducting slab.

DOI： 10.1007/s004100000207

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その他リンク： http://orcid.org/0000-0002-5422-7396

記述言語：英語   出版者・発行元：東京大学  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

A deep-level crustal section of the Cretaceous Kohistan are is exposed in the northern part of the Jijal complex. The occurrence of mafic to ultramafic granulite-facies rocks exhibits the nature and metamorphic evolution of the lower crust. Mafic granulites are divided into two rock types: two-pyroxene granulite (orthopyroxene + clinopyroxene + plagioclase +/- quartz [1]): and garnet-clinopyroxene granulite (garnet + clinopyroxene + plagioclase + quartz [2]). Two-pyroxene granulite occurs in the northeastern part of the Jijal complex as a relict host rock of garnet-clinopyroxene granulite, where the orthopyroxene-rich host is transected by elongated patches and bands of garnet-clinopyroxene granulite. Garnet-clinopyroxene granulite, together with two-pyroxene granulite, has been partly replaced by amphibolite (hornblende +/- garnet + plagioclase + quartz [3]). The garnet-bearing assemblage [2] is expressed by a compression-dehydration reaction: hornblende + orthopyroxene + plagioclase = garnet + clinopyroxene + quartz + H2O up arrow. Subsequent amphibolitization to form the assemblage [3] is expressed by two hydration reactions: garnet + clinopyroxene + plagioclase + H2O = hornblende + quartz and plagioclase + hornblende + H2O = zoisite + chlorite + quartz. The mafic granulites include pod- and lens-shaped bodies of ultramafic granulites which consist of garnet hornblendite (garnet + hornblende + clinopyroxene [4]) associated with garnet clinopyroxenite, garnetite, and hornblendite. Field relation and comparisons in modal-chemical compositions between the mafic and ultramafic granulites indicate that the ultramafic granulites were originally intrusive rocks which dissected the protoliths of the mafic granulites and then have been metamorphosed simultaneously with the formation of garnet-clinopyroxene granulite, The results combined with isotopic ages reported elsewhere give the following tectonic constraints: (1) crustal thickening, through the development of the Kohistan are and the subsequent KKohistan-Asia collision caused the high-pressure granulite-facies metamorphism in the Jijal complex; (2) local amphibolitization of the mafic granulites occurred after the collision. (C) 1998 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0024-4937(98)00014-0

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その他リンク： http://orcid.org/0000-0002-5422-7396

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Blackwell Publishing Inc.  

The lower-crustal rocks of the Kohistan complex (northern Pakistan) are mostly composed of metabasic rocks such as pyroxene granulites, garnet granulites and amphibolites. We have investigated P-T trajectories of the relic two-pyroxene granulites, which are the protolith of the amphibolites within the Kamila amphibolite belt. Aluminous pyroxene retains igneous textures such as exsolution lamellae developed in the core. The significant amount of Al in clinopyroxene is buffered by breakdown reactions of plagioclase accompanied by film-like quartz as a product at grain boundaries between plagioclase and clinopyroxene. Distinct Al zoning profiles are preserved in pyroxene with exsolution lamellae in the core and in plagioclase adjacent to clinopyroxene in pyroxene granulites. In the northern part of the Kamila amphibolite belt, Al in clinopyroxene increases towards the rim and abruptly decreases at the outer rim, and anorthite in plagioclase decreases towards the rim and abruptly increases near the grain boundary between plagioclase and clinopyroxene. In the southern part of the Kamila amphibolite belt, Al in clinopyroxene and anorthite in plagioclase simply increase towards the margins of the grains. The anorthite zoning in plagioclase is in agreement with the zoning profiles of Ca-Tschermaks and jadeite components inferred from variations of Al, Na, Ti and Fe3+ in clinopyroxene. Assuming that the growth surface between them was in equilibrium, geothermobarometry based on Al zoning in clinopyroxene coexisting with plagioclase indicates that metamorphic pressures significantly increased with increasing temperature under granulite facies metamorphism. The peak of granulite facies metamorphism occurred at conditions of about 800°C and 800-1100 MPa. These prograde P-T paths represent a crustal thickening process of the Kohistan arc during the Early to Middle Cretaceous. The crustal thickening of the Kohistan arc was caused by accretion of basaltic magma at mid-crustal depths.

DOI： 10.1111/j.1525-1314.1998.00168.x

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その他リンク： http://orcid.org/0000-0002-5422-7396

総ページ数：xv, 497 p.   記述言語：英語

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総ページ数：xv, 530 p.   記述言語：英語

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総ページ数：xvi, 479p, 図版 [8] p   記述言語：日本語

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総ページ数：2 v.   記述言語：英語

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© Springer International Publishing Switzerland 2015. We discuss conductivity heterogeneities of the oceanic upper mantle using available experimental data. The activation energy of the polaron conduction in olivine, wadsleyite, and ringwoodite is similar, at 1.4-1.6 eV. The ionic conduction is significant in olivine, but not in wadsleyite and ringwoodite. Its activation energy is much larger than that of the small polaron conduction (7-12 eV). The proton conductions have a smaller activation energy than the small polaron conduction (less than 1 eV) and are negligible at high temperatures in the depleted MORB mantle. The effects of the secondary minerals are negligible. No significant conductivity jump is associated with the olivine-wadsleyite transition. Volatile components greatly increase conductivity of basaltic melt. The anisotropy in both intrinsic and proton conditions in olivine is small. Sheared, partially molten peridotite can show conductivity anisotropy. The high conductivity below mid-oceanic ridges could be caused by partial melting. Conductivity at several locations suggests a melt fraction of the order of 0.1 vol.%, whereas that under the East Pacific Rise at 9°N suggests one of 15 vol.%. Lithosphere has low conductivity, which should be primarily due to its low temperature. However, the conductivity is too high, judging from the temperature structure and intrinsic conduction of olivine. The circulation of water does not provide enough explanation. The high-conductivity layer at the top of the asthenosphere is not a ubiquitous feature of the mantle- it is relatively limited to regions under young plates. The associated conductivity anisotropy suggests its partial melting origin. The conductivity in the mantle transition zone can be explained by the intrinsic conduction of wadsleyite and ringwoodite. Estimations of water content in the transition zone are largely affected by the uncertainty of geophysical modeling. The MT studies do not detect mantle plumes, although the seismic studies show the presence of low-velocity zones. The conductivity anomalies, whose origins are not understood, are observed under the southern Philippine Sea and the broad region north of Hawaii.

DOI： 10.1007/978-3-319-15627-9_6

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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&lt;sup&gt;-5&lt;/sup&gt;. Several test experiments exhibited resolvable Q&lt;sup&gt;-1&lt;/sup&gt; (10&lt;sup&gt;-2&lt;/sup&gt;) above 1273 K. The results are generally consistent with previously reported data.

DOI： 10.4131/jshpreview.24.126

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