研究者詳細 - 芳野　極

Fluorine solubility in bridgmanite: A potential fluorine reservoir in the Earth's mantle 査読

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

Yoshino T, Jaseem V

Earth and Planetary Science Letters 504 106 - 114 2018年12月

Impurity Resistivity of fcc and hcp Fe-Based Alloys: Thermal Stratification at the Top of the Core of Super-Earths 査読

H. Gomi, T. Yoshino

Frontiers in Earth Sciences 6 217 2018年11月

Effects of pressure and water on electrical conductivity of carbonate melt with implications for conductivity anomaly in continental mantle lithosphere 査読

Takashi Yoshino, Benjamin Gruber, Clayton Reinier

Physics of the Earth and Planetary Interiors 281 8 - 16 2018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 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

The effects of ferromagnetism and interstitial hydrogen on the equation of states of hcp and dhcp FeHx 査読

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

Gomi H, Fei Y, Yoshino T

American Mineralogists 103 ( 8 ) 1271 - 1281 2018年8月

Electrical Resistivity of Fe-C Alloy at High Pressure: Effects of Carbon as a Light Element on the Thermal Conductivity of the Earth's Core

Chengwei Zhang, Jung-Fu Lin, Ying Liu, Shaomin Feng, Changqing Jin, Mingqiang Hou, Takashi Yoshino

Journal of Geophysical Research: Solid Earth 123 ( 5 ) 3564 - 3577 2018年5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：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

Supercritical fluid in the mantle transition zone deduced from H–D interdiffusion of wadsleyite 査読

Wei Sun, Takashi Yoshino, Naoya Sakamoto, Hisayoshi Yurimoto

Earth and Planetary Science Letters 484 309 - 317 2018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 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

Negative activation volume of oxygen self-diffusion in forsterite 査読

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

Hongzhan Fei, Michael Wiedenbeck, Naoya Sakamoto, Hisayoshi Yurimoto, Takashi Yoshino, Daisuke Yamazaki, Tomoo Katsura

Physics of the Earth and Planetary Interiors 275 1 - 8 2018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 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

Dehydration of phengite inferred by electrical conductivity measurements: Implication for the high conductivity anomalies relevant to the subduction zones 査読

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

Sibo Chen, Xinzhuan Guo, Takashi Yoshino, Zhenmin Jin, Ping Li

Geology 46 ( 1 ) 11 - 14 2018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：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

Electrical conductivity of the oceanic asthenosphere and its interpretation based on laboratory measurements 査読

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

Tomoo Katsura, Kiyoshi Baba, Takashi Yoshino, Tetsu Kogiso

TECTONOPHYSICS 717 162 - 181 2017年10月

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

Synthesis of boron-doped diamond and its application as a heating material in a multi-anvil high-pressure apparatus 査読

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

Longjian Xie, Akira Yoneda, Takashi Yoshino, Daisuke Yamazaki, Noriyoshi Tsujino, Yuji Higo, Yoshinori Tange, Tetsuo Irifune, Toru Shimei, Eiji Ito

REVIEW OF SCIENTIFIC INSTRUMENTS 88 ( 9 ) 1635 - 1641 2017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 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

Spin transition of ferric iron in the calcium-ferrite type aluminous phase 査読

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

Ye Wu, Fei Qin, Xiang Wu, Haijun Huang, Catherine A. McCammon, Takashi Yoshino, Shuangmeng Zhai, Yuming Xiao, Vitali B. Prakapenka

JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH 122 ( 8 ) 5935 - 5944 2017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

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

Pressure dependence of transverse acoustic phonon energy in ferropericlase across the spin transition 査読

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

Hiroshi Fukui, Alfred Q. R. Baron, Daisuke Ishikawa, Hiroshi Uchiyama, Yasuo Ohishi, Taku Tsuchiya, Hisao Kobayashi, Takuya Matsuzaki, Takashi Yoshino, Tomoo Katsura

JOURNAL OF PHYSICS-CONDENSED MATTER 29 ( 24 ) 2017年6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：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

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

Optical signatures of low spin Fe3+ in NAL at high pressure 査読

Sergey S. Lobanov, Han Hsu, Jung-Fu Lin, Takashi Yoshino, Alexander F. Goncharov

JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH 122 ( 5 ) 3565 - 3573 2017年5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 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>similar to 40GPa.

DOI： 10.1002/2017JB014134

Grain growth of ε-iron: Implications to grain size and its evolution in the Earth's inner core 査読

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

Daisuke Yamazaki, Noriyoshi Tsujino, Akira Yoneda, Eiji Ito, Takashi Yoshino, Yoshinori Tange, Yuji Higo

Earth and Planetary Science Letters 459 238 - 243 2017年2月

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