担当区分：筆頭著者,　責任著者   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.pepi.2023.107123

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担当区分：責任著者   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.2023.118287

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担当区分：筆頭著者,　責任著者   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.2023.118197

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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  

Abstract

Bridgmanite formation and amorphization in shocked meteorites constrain the pressure and temperature conditions during planetary impact. However, the effect of the bridgmanite grain size on its amorphization kinetics is still unclear. Here, the amorphization mechanism and kinetics of fine-grained polycrystalline bridgmanite were studied at high temperatures up to 1080 K. High-temperature time-resolved synchrotron X-ray diffraction measurements showed that significant volume expansion due to temperature-induced amorphization caused static stress, which then hindered amorphization progress. Further, the temperature required for the amorphization of fine-grained bridgmanite (~ 1 μm) was found to be approximately 100 K higher than that required for the amorphization of coarse-grained samples (> 10 μm). We also noted that amorphization preferentially commenced at the twin planes and subgrain boundaries of bridgmanite grains, resulting in lower amorphization temperatures for the coarse-grained samples. The limited number of such specific locations in fine-grained natural bridgmanite suggested that grain boundary amorphization may be the dominant mechanism for bridgmanite amorphization in shocked meteorites. This unique amorphization kinetics would support the preservation of bridgmanite during the post-shock annealing in the shocked meteorite. Although bridgmanite amorphization starts easily at temperatures above ~ 420 K, a small amount of bridgmanite grains can survive at temperatures above 800 K by the effect of amorphization-induced stress.

DOI： 10.1186/s40645-023-00572-0

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その他リンク： https://link.springer.com/article/10.1186/s40645-023-00572-0/fulltext.html

担当区分：筆頭著者,　責任著者   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

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)  

The InSight mission to Mars is currently monitoring the seismic activity of the planet. Interpretation of seismological observations in terms of composition and mineralogy requires the knowledge of density and thermo-elastic properties of constituent materials at pertinent conditions. We thus performed phase equilibria experiments and carried out sound velocity and density measurements on aggregates representative of the Martian mantle over pressures and temperatures directly relevant for Mars’ upper and mid mantle. Our results indicate the stability of magnetite, although in a small amount, in phase assemblages at upper mantle conditions, especially in an oxidized environment. The measured pressure and temperature derivatives of compressional and shear velocities show that the temperature-induced reduction of seismic wave speeds dominates over pressure-induced effects at Mars' shallow mantle conditions for the predicted areotherms and, independently from mineralogy, support the presence of a low-shear-wave-velocity layer between 150 and 350 km depth, in agreement with seismic observations.

DOI： 10.1029/2021gl093977

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

A new experimental setup to continuously and automatically measure ultrasonic elastic wave velocities, X-ray radiography, and X-ray diffraction in large volume press is developed to explore structural change of amorphous materials at in situ high pressure and high temperature conditions. A continuous measurement for Zr50Cu40Al10 metallic glass is carried out during the heating process from 304 to 1102 K under high pressure conditions of 6.8–8.6 GPa. The sample length, elastic wave velocities, and Poisson’s ratio show marked changes at 611, 745, 825, and 874 K, which are interpreted as glass transition temperature (Tg) at 611 K, two polyamorphic structural changes at 745 and 825 K, and crystallization above 874 K, respectively. We find that the 1.2Tg temperature (733 K at ∼8 GPa), where simulations study predicted occurrence of thermal rejuvenation, corresponds to the temperature of the polyamorphic structural change (745 K) in Zr50Cu40Al10 metallic glass.

DOI： 10.1080/08957959.2021.1941000

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掲載種別：研究論文（学術雑誌）  

© 2020 The American Ceramic Society (ACERS) Material properties, such as elasticity data at wide-ranging conditions of pressure and temperature, attract increasing attention for material and earth sciences. In particular, polycrystalline ceramics for next-generation photonic applications are nowadays fabricated by advanced syntheses techniques operating under elevated pressures and temperatures. Herein, the elastic properties of a synthetic transparent and reinforced aluminosilicate nanoceramic composed of triclinic kyanite with minor amounts of trigonal α-alumina crystals are investigated using in situ synchrotron X-ray diffraction and ultrasonic techniques at high-pressure (up to 11 GPa) and high-temperature (300-1500 K) conditions. This not only enables the determination of the equation of state (EoS) parameters by applying the pressure-volume-temperature (P-V-T) data to the high-temperature Birch-Murnaghan EoS but also yields the elastic moduli together with their P and T derivatives from the fit of the compressional and shear wave velocities to a finite strain EoS: KS0,300 = 186(2) GPa, K′S0,300 = 7.2(6), (∂KS0,300/∂T)P = −0.023(2) GPa K−1, G0,300 = 125(1) GPa G′0,300 = 2.3(2), (∂G0,300/∂T)P = −0.017(1) GPa K−1. On the basis of our acquired results, we propose to predict the elastic moduli of aluminosilicate ceramics by a linear function of the ratio of AlO6 octahedra and SiO4 tetrahedra within the constituting phases.

DOI： 10.1111/jace.17464

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Geophysical Union (AGU)  

DOI： 10.1029/2021gl092389

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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)  

Sound velocities of Al-bearing phase D were investigated up to 22 GPa and 1300 K using in situ synchrotron X-ray techniques combined with ultrasonic measurements in a multianvil apparatus. The isothermal bulk modulus of Al-bearing phase D was found to be similar to 16.7% lower than that of Mg-endmember, suggesting a strong effect of Al incorporation on the bulk modulus of phase D. Al-bearing phase D has higherP- (V-P) andS- (V-S) wave velocities compared to other mantle transition zone minerals, up to 4.3% forV(P)and up to 9.6% forV(S)compared with hydrous iron-bearing ringwoodite, which might engender reduction of velocity contrast between anhydrous mantle and hydrous slab components. The accumulation of hydrated slab components carrying Al-phase D in the uppermost lower mantle can explain some local negative shear velocity perturbations (Delta V-S) up to -1.5%, although Delta V-P(-0.5%) is expected to remain below the detection limit of seismological techniques.

DOI： 10.1029/2020gl088877

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その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2020GL088877

担当区分：筆頭著者,　責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Geophysical Union (AGU)  

The partitioning of carbon between the core and mantle during the formation of terrestrial planets may have controlled the distribution of carbon in terrestrial planets. However, the abundance of carbon in the Earth's mantle is higher than a prediction based on previous metal-silicate partitioning experiments of carbon at carbon-saturated conditions by more than an order of magnitude. Here, we report new metal-silicate partitioning experiments of carbon at carbon contents of 0.25–0.5 wt%. We show that the metal-silicate partition coefficient of carbon (Dmet/silC) strongly correlates with nonbridging oxygen per tetrahedral cations (nbo/t) of silicate melts at fO2 conditions where C-H species are stable. Moreover, the results suggest that Dmet/silC at carbon-undersaturated conditions may be lower than that at carbon-saturated condition. Thus, Dmet/silC at low carbon concentrations is essentially important to investigate the distribution of carbon in the Earth during the core formation.

DOI： 10.1029/2019gl084254

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その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2019GL084254

担当区分：筆頭著者,　責任著者   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  

Previous studies have reported that the relative abundances of volatile elements in the silicate Earth are non-chondritic. The abundance and distribution of volatile elements in terrestrial planets would have been predominantly controlled by planetary formation processes, including core-mantle separation, magma ocean crystallization, and volatility-dependent high-temperature fractionation. Thus, the current abundance patterns of volatile elements in the silicate fraction of terrestrial planets are the key to understanding the accretional history of terrestrial volatiles and the chemical differentiation of terrestrial planets. Although the origin of the non-chondritic ratios of volatile elements in terrestrial planets has been previously studied, it is still a matter of debate. In this study, we focused on the super-chondritic F/Cl ratio of the bulk silicate Earth and experimentally investigated the silicate mineral-melt partitioning of fluorine and chlorine at pressures from 18 GPa to 25 GPa. Our experimental results show that fluorine is moderately compatible with mantle minerals, whereas chlorine is highly incompatible. These results support the formation of a solid mantle with high F/Cl ratios, and a residual magma ocean and steam atmosphere with low F/Cl ratios during magma ocean crystallization. Thus, the F/Cl ratio in the residual solid parts of terrestrial planets would have become relatively enriched following escape of volatile elements from the planetary surface into outer space. This model is consistent with the collisional erosion hypothesis of primordial crusts and atmospheres, and current observations on the abundance and distribution of terrestrial fluorine and chlorine. (C) 2019 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2019.05.041

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担当区分：筆頭著者,　責任著者   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.2018.08.012

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Geophysical Union (AGU)  

In the bulk silicate Earth, chlorine is more depleted than other elements with similar volatilities; however, the cause of terrestrial chlorine depletion is not well understood. Two major hypotheses have been proposed to explain this depletion: Incorporation into the Earth's metallic core and escape to space. The former hypothesis can be tested by investigating the partitioning of chlorine between iron-rich metallic liquids and silicate melts. In this study, we investigated the experimental partitioning of chlorine between iron-rich metallic liquids and silicate melts at pressures from 4 to 23 GPa and temperatures from 1,650 to 2,400 degrees C using multi-anvil presses. The results demonstrate that chlorine is moderately to highly lithophile under the experimental conditions. In sulfur-free experiments, chlorine becomes slightly more siderophile as temperature increases and less siderophile as pressure increases. For sulfur-bearing experiments, no significant effects of pressure or temperature were observed. Based on these data and thermodynamic considerations, we obtained empirical laws to estimate chlorine partition coefficients between iron-rich metallic liquids and silicate melts. Under the P-T conditions that would have controlled metal-silicate equilibration during core segregation in the Earth, the calculated metal-silicate partition coefficients for chlorine are much lower than unity. This result suggests that terrestrial chlorine that may have been present in the accreting Earth was not partitioned into its core, supporting that escape to space is the more likely hypothesis. If terrestrial chlorine was lost to space, chlorine depletion may have resulted from the loss of the primordial hydrosphere during the formation of the Earth.

DOI： 10.1002/2017gc007159

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その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/2017GC007159

担当区分：筆頭著者,　責任著者   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.2015.05.007

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担当区分：筆頭著者,　責任著者   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  

It is generally thought that the terrestrial atmosphere at the time of the origin of life was CO2-rich and that organic compounds such as amino acids would not have been efficiently formed abiotically under such conditions. It has been pointed out, however, that the previously reported low yields of amino acids may have been partially due to oxidation by nitrite/nitrate during acid hydrolysis. Specifically, the yield of amino acids was found to have increased significantly (by a factor of several hundred) after acid hydrolysis with ascorbic acid as an oxidation inhibitor. However, it has not been shown that CO2 was the carbon source for the formation of the amino acids detected after acid hydrolysis with ascorbic acid. We therefore reinvestigated the prebiotic synthesis of amino acids in a CO2-rich atmosphere using an isotope labeling experiment. Herein, we report that ascorbic acid does not behave as an appropriate oxidation inhibitor, because it contributes amino acid contaminants as a consequence of its reactions with the nitrogen containing species and formic acid produced during the spark discharge experiment. Thus, amino acids are not efficiently formed from a CO2-rich atmosphere under the conditions studied.

DOI： 10.1007/s11084-012-9296-z

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掲載種別：研究論文（学術雑誌）  

We systematically conducted impact cratering experiments with sedimentary rocks at 0.8-7.1km/s using various projectiles with 1.1-15g/cm 3 in density. The crater diameter, depth, and volume are investigated and compared with the results for igneous rocks. Then, using the non-dimensional parameters, the normalized crater diameter D, the normalized depth d, the normalized volume V, the target strength per specific energy 3, and the target and projectile density ratio 4, the scaling laws, D = (1.43 0.25) 3-0.220.0240.110.07, d = (0.22 0.04) 3-0.250.0240.010.05, and V = (0.11 0.04) 3-0.710.0540.230.17, are obtained. The comparison with the results of igneous rocks suggests that the characteristic properties of sedimentary rocks such as the lower strength and the strong shock wave attenuation rate are actually effective for the cratering of sedimentary rocks. © 2012. American Geophysical Union. All Rights Reserved.

DOI： 10.1029/2012JE004064

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