研究者詳細 - 芳野　極

論文 - 芳野　極

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Effect of graphite on the electrical conductivity of the lithospheric mantle 査読

Baohua Zhang, Takashi Yoshino

GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS 18 ( 1 ) 23 - 40 2017年1月

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

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

Pressure dependence of electrical conductivity in forsterite 査読

Takashi Yoshino, Baohua Zhang, Brandon Rhymer, Chengcheng Zhao, Hongzhan Fei

JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH 122 ( 1 ) 158 - 171 2017年1月

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

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

Pressure generation to 65GPa in a Kawai-type multi-anvil apparatus with tungsten carbide anvils 査読

Takayuki Ishii, Daisuke Yamazaki, Noriyoshi Tsujino, Fang Xu, Zhaodong Liu, Takaaki Kawazoe, Takafumi Yamamoto, Dmitry Druzhbin, Lin Wang, Yuji Higo, Yoshinori Tange, Takashi Yoshino, Tomoo Katsura

HIGH PRESSURE RESEARCH 37 ( 4 ) 507 - 515 2017年

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

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

An experimental kinetic study on the structural evolution of natural carbonaceous material to graphite 査読

Nakamura, Yosihihro, Yoshin, Takashi, Satish-Kumar, Madhusoodhan

American Mineralogist 102 ( 1-2 ) 135 - 148 2017年

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' 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's crust.

DOI： 10.2138/am-2017-5733

Phase relations of Fe3C and Fe7C3 up to 185 GPa and 5200 K: Implication for the stability of iron carbide in the Earth's core 査読

Jin Liu, Jung-Fu Lin, Vitali B. Prakapenka, Clemens Prescher, Takashi Yoshino

GEOPHYSICAL RESEARCH LETTERS 43 ( 24 ) 12415 - 12422 2016年12月

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

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

Effect of temperature, pressure and iron content on the electrical conductivity of orthopyroxene 査読

Baohua Zhang, Takashi Yoshino

CONTRIBUTIONS TO MINERALOGY AND PETROLOGY 171 ( 12 ) 2016年12月

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 > 0.2), orthopyroxene has little influence on the electrical structure of the upper mantle.

DOI： 10.1007/s00410-016-1315-z

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

Short-period cyclic loading system for in situ X-ray observation of anelastic properties at high pressure 査読

Takashi Yoshino, Daisuke Yamazaki, Yoshinori Tange, Yuji Higo

REVIEW OF SCIENTIFIC INSTRUMENTS 87 ( 10 ) 2016年10月

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 (< 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

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

The CaCO<inf>3</inf>–Fe interaction: Kinetic approach for carbonate subduction to the deep Earth's mantle 査読

N. S. Martirosyan, N. S. Martirosyan, T. Yoshino, A. Shatskiy, A. Shatskiy, A. D. Chanyshev, A. D. Chanyshev, K. D. Litasov, K. D. Litasov

Physics of the Earth and Planetary Interiors 259 1 - 9 2016年10月

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

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

Two-stage spin transition of iron in FeAl-bearing phase D at lower mantle 査読

Xiang Wu, Ye Wu, Jung-Fu Lin, Jin Liu, Zhu Mao, Xinzhuan Guo, Takashi Yoshino, Catherine McCammon, Vitali B. Prakapenka, Yuming Xiao

JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH 121 ( 9 ) 6411 - 6420 2016年9月

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

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

Electrical conductivity of mantle clinopyroxene as a function of water content and its implication on electrical structure of uppermost mantle 査読

Chengcheng Zhao, Takashi Yoshino

EARTH AND PLANETARY SCIENCE LETTERS 447 1 - 9 2016年8月

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

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

Major element composition of an Early Enriched Reservoir: constraints from Nd-142/Nd-144 isotope systematics in the early Earth and high-pressure melting experiments of a primitive peridotite 査読

Nozomi Kondo, Takashi Yoshino, Kyoko N. Matsukage, Tetsu Kogiso

PROGRESS IN EARTH AND PLANETARY SCIENCE 3 ( 1 ) 2016年8月

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

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

Elasticity of single-crystal NAL phase at high pressure: A potential source of the seismic anisotropy in the lower mantle 査読

Ye Wu, Jing Yang, Xiang Wu, Maoshuang Song, Takashi Yoshino, Shuangmeng Zhai, Shan Qin, Haijun Huang, Jung-Fu Lin

JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH 121 ( 8 ) 5696 - 5707 2016年8月

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 <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

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

Electrical conductivity model of Al-bearing bridgmanite with implications for the electrical structure of the Earth's lower mantle 査読

Takashi Yoshino, Seiji Kamada, Chengcheng Zhao, Eiji Ohtani, Naohisa Hirao

EARTH AND PLANETARY SCIENCE LETTERS 434 208 - 219 2016年1月

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 (<1400 K) and ionic conduction at higher temperatures (>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

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

Spin transition of ferric iron in the NAL phase: Implications for the seismic heterogeneities of subducted slabs in the lower mantle 査読

Ye Wu, Xiang Wu, Jung-Fu Lin, Catherine A. McCammon, Yuming Xiao, Paul Chow, Vitali B. Prakapenka, Takashi Yoshino, Shuangmeng Zhai, Shan Qin

EARTH AND PLANETARY SCIENCE LETTERS 434 91 - 100 2016年1月

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

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

Graphite-boron composite heater in a Kawai-type apparatus: the inhibitory effect of boron oxide and countermeasures 査読

Longjian Xie, Akira Yoneda, Takashi Yoshino, Hongzhan Fei, Eiji Ito

HIGH PRESSURE RESEARCH 36 ( 2 ) 105 - 120 2016年

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

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

Hydrogen self-diffusivity in single crystal ringwoodite: Implications for water content and distribution in the mantle transition zone 査読

Wei Sun, Takashi Yoshino, Naoya Sakamoto, Hisayoshi Yurimoto

GEOPHYSICAL RESEARCH LETTERS 42 ( 16 ) 6582 - 6589 2015年8月

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 (<1000 ppm by weight (ppmw)) but lower at higher water content range (>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

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

Oligomerization and carbonization of polycyclic aromatic hydrocarbons at high pressure and temperature 査読

Artem D. Chanyshev, Konstantin D. Litasov, Anton F. Shatskiy, Yoshihiro Furukawa, Takashi Yoshino, Eiji Ohtani

CARBON 84 ( 1 ) 225 - 235 2015年4月

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

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

Electrical conductivity of albite-(quartz)-water and albite-water-NaCl systems and its implication to the high conductivity anomalies in the continental crust 査読

Xinzhuan Guo, Takashi Yoshino, Akira Shimojuku

EARTH AND PLANETARY SCIENCE LETTERS 412 1 - 9 2015年2月

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

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

Electrical conductivity anisotropy in partially molten peridotite under shear deformation 査読

Baohua Zhang, Takashi Yoshino, Daisuke Yamazaki, Geeth Manthilake, Tomoo Katsura

EARTH AND PLANETARY SCIENCE LETTERS 405 98 - 109 2014年11月

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

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

Interconnection of ferro-periclase controls subducted slab morphology at the top of the lower mantle 査読

Daisuke Yamazaki, Takashi Yoshino, Tomoeki Nakakuki

EARTH AND PLANETARY SCIENCE LETTERS 403 352 - 357 2014年10月

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

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

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