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Atsushi Okamoto

Section

Graduate School of Environmental Studies

Job title

Professor

Degree

博士（理学）（東京大学）
修士（理学）（東京大学）

researchmap

https://researchmap.jp/winchite

J-GLOBAL ID

201801005284009363

Research History 5

2020/04 - Present

Tohoku University　Graduate School of Environmental Studies
2011/10 - 2020/03

Tohoku University　Graduate School of Environmental Studies
2007/04 - 2011/09

Tohoku University　Graduate School of Environmental Studies
2005/10 - 2007/04

Tohoku University　Graduate School of Environmental Studies
2003/04 - 2005/09

Shizuoka University

Education 3

The University of Tokyo

2000/04 - 2003/03
The University of Tokyo

1998/04 - 2000/03
The University of Tokyo

1994/04 - 1998/03

Committee Memberships 5

日本地球惑星科学連合　広報普及委員会

2024/05 - Present
日本鉱物科学会　応用鉱物科学賞選考委員会

2024/04 - Present
Japan Geoscience Union　Delegate of JpGU

2022/04 - Present
日本鉱物科学会行事委員

2019 - 2022/09
日本地質学会　日本地質学雑誌編集委員

2017 - 2022/09

Professional Memberships 7

American Geophysical Union

2020/07 - Present
Geochemical Society
European Geoscience Union
日本地球惑星科学連合
日本地熱学会
日本鉱物科学会
日本地質学会

︎Show all ︎Show first 5

Research Interests 12

海底硫化物チムニーの電気特性
Carbonation
silica
Oman Ophiolite
Sanbagawa metamorphic belt
serpentinization
パターン形成
水熱実験
岩石組織
地熱システム
変成作用
岩石ー水相互作用

Research Areas 2

Energy / Earth resource engineering, energy science /
Natural sciences / Solid earth science /

Awards 5

小藤文次郎賞

2024/09　日本地質学会　Rupture of wet mantle wedge by self-promoting carbonation
H.E. ナウマン賞

2024/09　日本地質学会　岩石組織に基づく地殻・マントルにおける岩石－水相互作用のダイナミクスの解読
Nishida Prize

2021/04　Japan Geoscience Union　Research on the water-rock interaction within the Earth’s interior and the development of rock texture
日本地質学会柵山雅則賞

2013/09　日本地質学会　沈み込み帯における流体移動と水—岩石相互作用に関する岩石学的実験的研究
日本鉱物科学会研究奨励賞

2013/09　日本鉱物科学会　天然試料解析，および水熱実験による岩石-水相互作用に関する研究

Papers 189

Biobased biodegradable chelating agents enhance coupled ex situ and in situ carbon dioxide mineralization via peridotite dissolution and wormholing

Luis Salalá, Noriaki Watanabe, Jiajie Wang, Atsushi Okamoto

Communications Earth & Environment　2025/08/21

DOI： 10.1038/s43247-025-02687-2 　
Extreme maldistribution of high field strength elements along subduction zones revealed by baddeleyite aggregates in serpentinite

Hikaru Sawada, Ryosuke Oyanagi, Sota Niki, Takafumi Hirata, Kazuki Yoshida, Mitsuhiro Nagata, Atsushi Okamoto

Scientific Reports　2025/07/04

DOI： 10.1038/s41598-025-07698-9 　
Oscillations in fluid pressure caused by silica precipitation in a fracture

Atsushi Okamoto, Edward Vinis

Nature Communications　2025/02/20

DOI： 10.1038/s41467-025-57199-6 　
Data-driven depth direction super-resolution framework for X-ray CT images of rock samples by deep learning

Ryogo Kagawa, Atsushi Okamoto, Toshiaki Omori

Nonlinear Theory and Its Applications, IEICE　2025

DOI： 10.1587/nolta.16.390 　
Visualization of four-dimensional X-ray absorption fine structure data using a virtual reality system

Haruo Igarashi, Daiki Kido, Yutaka Ishii, Yasuhiro Niwa, Atsushi Okamoto, Masao Kimura

Journal of Synchrotron Radiation　32　(1)　162-170　2025/01/01
Publisher: International Union of Crystallography (IUCr)
DOI： 10.1107/s1600577524011226 　

eISSN： 1600-5775

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X-ray spectromicroscopy is extensively utilized for nondestructive mapping of chemical states in materials. However, understanding and analyzing the geometric and topological aspects of such data pose challenges due to their representation in 4D space, encompassing (x, y, z) coordinates along with the energy (E) axis and often extending to 5D space with the inclusion of time (t) or reaction degree. In this study, we addressed this challenge by developing a new approach and introducing a device named `4D-XASView', specifically designed for visualizing X-ray absorption fine structures (XAFS) data in 4D (comprising 3D space and energy), through a multi-projection system, within the virtual reality (VR) environment. As a test case for the new system, X-ray spectromicroscopy measurements were conducted on a specimen prepared from serpentinized harzburgite sourced from the upper mantle section of the Oman ophiolite. Our 4D-XASView facilitates the visualization and analysis of the geometric and topological aspects of the data using VR goggles, enabling detailed exploration of microstructures via rotation and zooming functionalities. This capability allows us to extract XAFS spectral data by selecting specific positions and regions, thereby aiding in the identification of `trigger sites' (magnetite in serpentine), which are characteristic locations within materials that substantially influence the macroscopic propagation of reactions. Our methodology establishes a new platform for analyzing 4D or 5D XAFS data that has applicability potential in various other multidimensional datasets, including microstructures coupled with spectroscopy and diffraction data.
Estimating the iron oxidation state of serpentinite using X-ray absorption fine structure spectroscopy

Kazuki Yoshida, Atsushi Okamoto, Ryosuke Oyanagi, Yasuhiro Niwa, Masao Kimura

American Mineralogist　2025/01/01
Publisher: Mineralogical Society of America
DOI： 10.2138/am-2024-9571 　

ISSN： 0003-004X

eISSN： 1945-3027

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Abstract Iron can exist in serpentinite in various oxidation states. Changes in the oxidation state of Fe play a crucial role in geological processes, including supporting diverse biological systems on the ocean floor and the redox states of aqueous fluids released in subduction zones. Synchrotron X-ray absorption near-edge structure (XANES) spectroscopy has been used to measure the oxidation state of Fe in serpentine minerals; however, a general scheme for estimating the oxidation state of Fe in serpentinite composed of several Fe-bearing minerals has not been established. We have evaluated the accuracy of using XANES spectra to estimate the Fe3+/ΣFe ratio (molar ratio of Fe3+ to total Fe) of physical olivine–magnetite mixtures and serpentinites. Two approaches were tested: (1) linear combination fitting (LCF) and (2) pre-edge peak analysis of XANES spectra. Estimating Fe3+/ΣFe using analysis of the pre-edge peaks was not always suitable when magnetite was included. Using LCF, XANES spectra are well fitted by the optimal combination of Fe-bearing minerals, even for mixtures of magnetite and Fe-bearing silicate minerals (i.e., serpentine and olivine). The Fe3+/ΣFe ratios of the serpentinites were estimated with a root mean squared error (RMSE) of 0.14 with LCF. These results demonstrate that LCF of XANES spectra is useful for estimating the oxidation state of Fe in serpentinites.
Tracking HFSE associated with high salinity fluid during HP metamorphism in the Zavkhan Terrane, Western Mongolia

Manzshir Bayarbold, Atsushi Okamoto, Masaoki Uno, Otgonbayar Dandar, Mayuko Fukuyama, Geri Agroli, Noriyoshi Tsuchiya

Lithos　490-491　2024/12/15

DOI： 10.1016/j.lithos.2024.107853 　

ISSN： 0024-4937

eISSN： 1872-6143
Relationship between characteristic ore textures and geologic situation of the Kuroko deposits Peer-reviewed

Ryoichi Yamada, Jumpei Sugioka, Atsushi Okamoto

74　(2)　79-94　2024/12
Multiscale off-fault brecciation records coseismic energy budget of principal fault zone

Geri Agroli, Atsushi Okamoto, Masaoki Uno, Noriyoshi Tsuchiya

Scientific Reports　14　(1)　2024/12

DOI： 10.1038/s41598-024-62838-x 　

eISSN： 2045-2322
Experimental constraints on serpentinite carbonation in the presence of a H<inf>2</inf>O–CO<inf>2</inf>–NaCl fluid

Yongsheng Huang, Satoshi Okumura, Kazuhisa Matsumoto, Naoko Takahashi, Hong Tang, Guoji Wu, Tatsuki Tsujimori, Michihiko Nakamura, Atsushi Okamoto, Yuan Li

Contributions to Mineralogy and Petrology　179　(11)　2024/11

DOI： 10.1007/s00410-024-02175-4 　

ISSN： 0010-7999

eISSN： 1432-0967
Subducted carbon weakens the forearc mantle wedge in a warm subduction zone International-journal Peer-reviewed

Ryosuke Oyanagi, Atsushi Okamoto

Nature Communications　15　(7159)　2024/08/26
Publisher: Springer Nature
DOI： 10.1038/s41467-024-51476-6 　

eISSN： 2041-1723
Ultramafic Rocks from the Sanbagawa Belt: Records of Mantle Wedge Processes

Atsushi Okamoto, Takayoshi Nagaya, Shunsuke Endo, Tomoyuki Mizukami

Elements　20　(2)　83-88　2024/04

DOI： 10.2138/gselements.20.2.83 　

ISSN： 1811-5209

eISSN： 1811-5217
Reaction-induced fracturing during serpentinite carbonation promoted by selective dissolution of brucite International-journal Peer-reviewed

Masaoki Uno, Taiki Igarashi, Atsushi Okamoto

EGU General Assembly 2024　2024/03/08

DOI： 10.5194/egusphere-egu24-4303 　
Characterization of serpentinization in olivine‐orthopyroxene‐H2O system revealed by thermogravimetric and multivariate statistical analyses

Atsushi Okamoto, Shuhei Tanaka, Masaoki Uno, Otgonbayar Dandar, Kazuki Yoshida

Island Arc　33　(1)　2024/01

DOI： 10.1111/iar.12519 　

ISSN： 1038-4871

eISSN： 1440-1738
Porosity generation via spatially uncoupled dissolution precipitation during plagioclase replacement in quartz undersaturated fluids

Astin Nurdiana, Atsushi Okamoto, Masaoki Uno, Noriyoshi Tsuchiya

Contributions to Mineralogy and Petrology　179　(1)　2024/01

DOI： 10.1007/s00410-023-02088-8 　

ISSN： 0010-7999

eISSN： 1432-0967
Seafloor Alteration Governed by Oceanic Crustal Age and Redox Conditions: Insights from Machine Learning-based Elemental Transfer Analyses

Satoshi Matsuno, Masaoki Uno, Atsushi Okamoto

2023/12/27

DOI： 10.22541/essoar.170365347.78533593/v1 　
Effects of hydrothermal alteration on shear localization and weakening in the mantle lithosphere

Maki Semba, Ken ichi Hirauchi, Tomohiro Ohuchi, Atsushi Okamoto, Yui Kouketsu

Tectonophysics　868　2023/12/05

DOI： 10.1016/j.tecto.2023.230081 　

ISSN： 0040-1951
Super-resolution of X-ray CT images of rock samples by sparse representation: applications to the complex texture of serpentinite

Toshiaki Omori, Shoi Suzuki, Katsuyoshi Michibayashi, Atsushi Okamoto

Scientific Reports　13　(1)　2023/12

DOI： 10.1038/s41598-023-33503-6 　

eISSN： 2045-2322
Continuous thermal structures of the present-day and contact-metamorphic geothermal systems revealed by drill cuttings in the Kakkonda geothermal field, Japan

Masaoki Uno, Atsushi Okamoto, Takashi Akatsuka, Noriyoshi Tsuchiya

Geothermics　115　102806-102806　2023/12
Publisher: Elsevier BV
DOI： 10.1016/j.geothermics.2023.102806 　

ISSN： 0375-6505
Multiphase-solid fluid inclusions in HP-LT eclogite facies rock (Zavkhan Terrane, Western Mongolia): evidence for the evolution from saline to hypersaline fluids during metamorphism in subduction zone

Manzshir Bayarbold, Atsushi Okamoto, Masaoki Uno, Kenta Yoshida, Alexey Kotov, Geri Agroli, Otgonbayar Dandar, Yasuhiro Niwa, Masao Kimura, Noriyoshi Tsuchiya

Contributions to Mineralogy and Petrology　178　(11)　2023/11/04
Publisher: Springer Science and Business Media LLC
DOI： 10.1007/s00410-023-02055-3 　

ISSN： 0010-7999

eISSN： 1432-0967

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Abstract Fluid inclusions in high- and ultrahigh-pressure metamorphic rocks provide direct information on the composition of the fluids that evolved during metamorphism and fluid-rock interactions in deep subduction zones. We investigate the fluid inclusions in the Khungui eclogite of the Zavkhan Terrane, Central Asian Orogenic Belt. Fluid inclusions are observed in garnet and quartz in the eclogite samples that underwent metamorphism during subduction. The primary fluid inclusions in quartz are composed of liquid and vapor with high salinities (15.7–16.4 wt.% NaCl eq.), whereas the secondary fluid inclusions in quartz are classified as: relatively high salinity (Type I:12.5–16.3 wt.% NaCl eq.) and low salinity (Type II:6.7–10.6 wt.% NaCl eq.). The garnet shows compositional zoning from Ca-poor cores to Ca-rich rims, and the rims that grew during the eclogite-stage metamorphism (2.1–2.2 GPa at 580–610 °C) preferentially contain numerous primary fluid inclusions. The primary fluid inclusions in garnet are commonly bi-phases (liquid and vapor); however, some are multiphase-solid fluid inclusions composed of fluids (liquid and vapor) and combinations of several minerals (halite, quartz, apatite, calcite, biotite, chlorite, and actinolite). Bi-phase fluid inclusions preferentially occur in the inner parts of the Ca-rich garnet rim, whereas multiphase-solid fluid inclusions occur along the margins of the Ca-rich rim. We hypothesize that the multiphase-solid fluid inclusions are formed via interactions between trapped fluids, trapped minerals, and the host garnet during exhumation. By combination of FIB–SEM and synchrotron X-ray CT analyses, the detailed occurrences, volumes, and compositions of the solid phases in the fluid inclusion was analyzed. We then conduct mass balance analysis to reconstruct accurate fluid compositions using data from the FIB–SEM and synchrotron X-ray CT images of the multiphase-solid fluid inclusion. The results of these analyses reveal that (1) fluid changed from an H₂O-dominated saline fluid (13–16 wt. % NaCl eq.) at the prograde to the earlier eclogite stage to H₂O–CO₂-dominated hypersaline fluid at later eclogite stage (~ 32 wt. % NaCl eq., 7.3 wt. % CO₂ and ~ 19 molal dissolved cations); (2) a variety of mineral assemblages in multiphase-solid fluid inclusions are produced by post-entrapment reactions between the trapped hypersaline fluid, trapped minerals and the fluid host mineral. The evolution of fluids from saline to hypersaline during the eclogite facies stage is probably caused by the formation of hydrous minerals (i.e., barroisite) under a near-closed system.
Mantle hydration initiated by Ca metasomatism in a subduction zone: An example from the Chandman meta-peridotite, western Mongolia

Otgonbayar Dandar, Atsushi Okamoto, Masaoki Uno, Noriyoshi Tsuchiya

Lithos　452-453　107212-107212　2023/09
Publisher: Elsevier BV
DOI： 10.1016/j.lithos.2023.107212 　

ISSN： 0024-4937

eISSN： 1872-6143
Si- versus Mg-metasomatism at the crust–mantle interface: insights from experiments, natural observations and geochemical modeling

Atsushi Okamoto, Ryosuke Oyanagi

Progress in Earth and Planetary Science　10　(1)　2023/07/18
Publisher: Springer Science and Business Media LLC
DOI： 10.1186/s40645-023-00568-w 　

eISSN： 2197-4284
Progressive carbonation and Ca-metasomatism of serpentinized ultramafic rocks: insights from natural occurrences and hydrothermal experiments International-journal Peer-reviewed

Nomuulin Amarbayar, Otgonbayar Dandar, Jiajie Wang, Atsushi Okamoto, Masaoki Uno, Undarmaa Batsaikhan, Hideko Takayanagi, Yasufumi Iryu, Noriyoshi Tsuchiya

Contributions to Mineralogy and Petrology　178　2023/07
Publisher: SpringerNature
DOI： 10.1007/s00410-023-02013-z 　

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Hydration, carbonation, and related metasomatism of mantle peridotite play a significant role in the global geochemical cycle. In this study, we combined an analysis of carbonated serpentinite with hydrothermal experiments on carbonation and Ca-metasomatism for samples from the Manlay ophiolite, southern Mongolia to investigate that carbonation mechanism of the serpentinite body after serpentinization. Samples show that the serpentinite was either transected by calcite and dolomite veins or was completely replaced by carbonates (calcite with minor dolomite) and quartz, in which the original mesh texture of serpentinite was preserved. Carbonation occurred after low-temperature serpentinization (lizardite/chrysotile), suggesting that carbonation occurred at temperatures lower than 300 ˚C. Calcite in the serpentinite showed δ13 CVPDB values ranging from -8.83 to -5.11 ‰ and δ18 OVSMOW from + 20.1 to + 24.4 ‰, suggesting that CO2 in the fluids could be derived from the degradation of organic material or methanotrophic processes rather than the origin of seafloor limestone. Three batch-type experiments, i.e., single step experiments (1) Olivine + NaHCO3,aq + CaCl2,aq and (2) Chrysotile + NaHCO3,aq + wollastonite (Ca source), and two steps experiment (3) Olivine carbonation and Ca-metasomatism, were conducted at 275 °C and 5.7 MPa to constrain the mechanism of calcite replacement of serpentinite. We found that calcite precipitated from the solution directly in the first two experiments, but replacement of serpentinite by calcite was not observed. In contrast, the third experiment caused the initial carbonation to form magnesite and then changed to calcite by later alteration. The natural occurrences and experiments revealed the possibility that the carbonation of olivine followed by Ca-rich fluid infiltration produced calcite in the carbonated serpentinite. Such Ca-metasomatism of Mg carbonates could easily occur in the ultramafic bodies and significantly affect the global carbon cycle.
Oxidation-induced nanolite crystallization triggered the 2021 eruption of Fukutoku-Oka-no-Ba, Japan

Kenta Yoshida, Akira Miyake, Shota H. Okumura, Hidemi Ishibashi, Satoshi Okumura, Atsushi Okamoto, Yasuhiro Niwa, Masao Kimura, Tomoki Sato, Yoshihiko Tamura, Shigeaki Ono

Scientific Reports　13　(1)　2023/05/09
Publisher: Springer Science and Business Media LLC
DOI： 10.1038/s41598-023-34301-w 　

eISSN： 2045-2322

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Abstract Nanometer-sized crystals (nanolites) play an important role in controlling eruptions by affecting the viscosity of magmas and inducing bubble nucleation. We present detailed microscopic and nanoscopic petrographic analyses of nanolite-bearing and nanolite-free pumice from the 2021 eruption of Fukutoku-Oka-no-Ba, Japan. The nanolite mineral assemblage includes biotite, which is absent from the phenocryst mineral assemblage, and magnetite and clinopyroxene, which are observed as phenocrysts. The boundary between the nanolite-bearing brown glass and nanolite-free colorless glass is either sharp or gradational, and the sharp boundaries also appear sharp under the transmitted electron microscope. X-ray absorption fine structure (XAFS) analysis of the volcanic glass revealed that the nanolite-free colorless glass records an oxygen fugacity of QFM + 0.98 (log units), whereas the nanolite-bearing brown glass records a higher apparent oxygen fugacity (~ QFM + 2). Thermodynamic modelling using MELTS indicates that higher oxygen fugacities increase the liquidus temperature and thus induced the crystallization of magnetite nanolites. The hydrous nanolite mineral assemblage and glass oxygen fugacity estimates suggest that an oxidizing fluid supplied by a hot mafic magma induced nanolite crystallization in the magma reservoir, before the magma fragmentation. The oxidation-induced nanolite crystallization then enhanced heterogeneous bubble nucleation, resulting in convection in the magma reservoir and triggering the eruption.
Metasomatism at a metapelite–ultramafic rock contact at the subduction interface: Insights into mass transfer and fluid flow at the mantle wedge corner

Ryosuke Oyanagi, Masaoki Uno, Atsushi Okamoto

Contributions to Mineralogy and Petrology　178　(5)　2023/04/14
Publisher: Springer Science and Business Media LLC
DOI： 10.1007/s00410-023-02011-1 　

ISSN： 0010-7999

eISSN： 1432-0967
Geological records of transient fluid drainage into the shallow mantle wedge

Kazuki Yoshida, Ryosuke Oyanagi, Masao Kimura, Oliver Plümper, Mayuko Fukuyama, Atsushi Okamoto

Science Advances　9　(14)　2023/04/05
Publisher: American Association for the Advancement of Science (AAAS)
DOI： 10.1126/sciadv.ade6674 　

eISSN： 2375-2548
Role of mantle carbonation in trench outer‐rise region in the global carbon cycle

Ikuo Katayama, Keishi Okazaki, Atsushi Okamoto

Island Arc　2023/01

DOI： 10.1111/iar.12499 　
Development of Open Transport of Aqueous Fluid from Pegmatite Revealed by Trace Elements in Garnet

Astin Nurdiana, Atsushi Okamoto, Masaoki Uno, Noriyoshi Tsuchiya

GEOFLUIDS　2022　2022/10

DOI： 10.1155/2022/8786250 　

ISSN： 1468-8115

eISSN： 1468-8123
Dehydration of brucite + antigorite under mantle wedge conditions: insights from the direct comparison of microstructures before and after experiments

Takayoshi Nagaya, Atsushi Okamoto, Masanori Kido, Jun Muto, Simon R. Wallis

Contributions to Mineralogy and Petrology　2022/09

DOI： 10.1007/s00410-022-01956-z 　
Continental arc-derived eclogite in the Zavkhan Terrane, western Mongolia: Implications for the suture zone in the northern part of the Central Asian Orogenic Belt

Bayarbold, M., Okamoto, A., Dandar, O., Uno, M., Tsuchiya, N.

Journal of Asian Earth Sciences　229　105150-105150　2022/05
Publisher: Elsevier BV
DOI： 10.1016/j.jseaes.2022.105150 　

ISSN： 1367-9120
Rupture of serpentinized mantle wedge by self-promoting carbonation: insights from Sanbagawa metamorphic belt

Atsushi Okamoto, Ryosuke Oyanagi, Kazuki Yoshida, Masaoki Uno, Hiroyuki Shimizu, Madhusoodhan Satish-Kumar

2022/03/28
Publisher: Copernicus {GmbH}
DOI： 10.5194/egusphere-egu22-13148 　
Chemistry breaks rocks and self-accelerate fluid flow in the lithosphere: Experimental insights from MgO–H2O system

Masaoki Uno, Atsushi Okamoto, Noriyoshi Tsuchiya

2022/03/28
Publisher: Copernicus {GmbH}
DOI： 10.5194/egusphere-egu22-13126 　
Formation of the garnet aggregate of the Khungui eclogite in the Zavkhan Terrane, Western Mongolia

Manzshir Bayarbold, Atsushi Okamoto, Otgonbayar Dandar, Masaoki Uno, Noriyoshi Tsuchiya

2022/03/28
Publisher: Copernicus {GmbH}
DOI： 10.5194/egusphere-egu22-6935 　
Pulverized rock and episodic hydrothermal brecciation along the Median Tectonic Line, Japan

Geri Agroli, Masaoki Uno, Atsushi Okamoto, Noriyoshi Tsuchiya

2022/03/28
Publisher: Copernicus {GmbH}
DOI： 10.5194/egusphere-egu22-6926 　
Transient fluid migration recorded in antigorite veins formed by subduction-related fluids

Yoshida Kazuki, Oyanagi Ryosuke, Kimura Masao, Plümper Oliver, Fukuyama Mayuko, Okamoto Atsushi

Annual Meeting of the Geological Society of Japan　2022　30　2022
Publisher: The Geological Society of Japan
DOI： 10.14863/geosocabst.2022.0_30 　

ISSN： 1348-3935

eISSN： 2187-6665
Machine-learning techniques for quantifying the protolith composition and mass transfer history of metabasalt

Matsuno, S., Uno, M., Okamoto, A., Tsuchiya, N.

Scientific Reports　12　(1)　2022

DOI： 10.1038/s41598-022-05109-x 　

ISSN： 2045-2322
Volatile-consuming reactions fracture rocks and self-accelerate fluid flow in the lithosphere

Uno, M., Koyanagawa, K., Kasahara, H., Okamoto, A., Tsuchiya, N.

Proceedings of the National Academy of Sciences of the United States of America　119　(3)　2022

DOI： 10.1073/pnas.2110776118 　

ISSN： 1091-6490 0027-8424
Multi-stage serpentinization of ultramafic rocks in the Manlay Ophiolite, southern Mongolia

Amarbayar Nomuulin, Noriyoshi Tsuchiya, Otgonbayar Dandar, Atsushi Okamoto, Masaoki Uno, Undarmaa Batsaikhan, Jiajie Wang

Mongolian Geoscientist　26　(53)　1-17　2021/12/30
Publisher: Mongolian Journals Online
DOI： 10.5564/mgs.v26i53.1787 　

ISSN： 2220-0622

eISSN： 2663-5151

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Serpentinization of ultramafic rocks in ophiolites is key to understanding the global cycle of elements and changes in the physical properties of lithospheric mantle. Mongolia, a central part of the Central Asian Orogenic Belt (CAOB), contains numerous ophiolite complexes, but the metamorphism of ultramafic rocks in these ophiolites has been little studied. Here we present the results of our study of the serpentinization of an ultramafic body in the Manlay Ophiolite, southern Mongolia. The ultramafic rocks were completely serpentinized, and no relics of olivine or orthopyroxene were found. The composition of Cr-spinels [Mg# = Mg/(Mg + Fe2+) = 0.54 and Cr# = Cr/(Cr + Al) = 0.56] and the bulk rock chemistry (Mg/Si = 1.21–1.24 and Al/Si < 0.018) of the serpentinites indicate their origin from a fore-arc setting. Lizardite occurs in the cores and rims of mesh texture (Mg# = 0.97) and chrysotile is found in various occurrences, including in bastite (Mg# = 0.95), mesh cores (Mg# = 0.92), mesh rims (Mg# = 0.96), and later-stage large veins (Mg# = 0.94). The presence of lizardite and chrysotile and the absence of antigorite suggests low-temperature serpentinization (<300 °C). The lack of brucite in the serpentinites implies infiltration of the ultramafic rocks of the Manlay Ophiolite by Si-rich fluids. Based on microtextures and mineral chemistry, the serpentinization of the ultramafic rocks in the Manlay Ophiolite took place in three stages: (1) replacement of olivine by lizardite, (2) chrysotile formation (bastite) after orthopyroxene and as a replacement of relics of olivine, and (3) the development of veins of chrysotile that cut across all previous textures. The complex texture of the serpentinites in the Manlay Ophiolite indicates multiple stages of fluid infiltration into the ultramafic parts of these ophiolites in southern Mongolia and the CAOB.
Cataclastic and crystal-plastic deformation in shallow mantle-wedge serpentinite controlled by cyclic changes in pore fluid pressures

Ken ichi Hirauchi, Yurina Nagata, Kengo Kataoka, Ryosuke Oyanagi, Atsushi Okamoto, Katsuyoshi Michibayashi

Earth and Planetary Science Letters　576　2021/12/15

DOI： 10.1016/j.epsl.2021.117232 　

ISSN： 0012-821X
Hadal aragonite records venting of stagnant paleoseawater in the hydrated forearc mantle

Ryosuke Oyanagi, Atsushi Okamoto, Madhusoodhan Satish-Kumar, Masayo Minami, Yumiko Harigane, Katsuyoshi Michibayashi

Communications Earth & Environment　2　(1)　2021/12
Publisher: Springer Science and Business Media LLC
DOI： 10.1038/s43247-021-00317-1 　

eISSN： 2662-4435

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<title>Abstract</title>The hadal zone at trenches is a unique region where forearc mantle rocks are directly exposed at the ocean floor owing to tectonic erosion. Circulation of seawater in the mantle rock induces carbonate precipitation within the deep-sea forearc mantle, but the timescale and rates of the circulation are unclear. Here we investigated a peculiar occurrence of calcium carbonate (aragonite) in forearc mantle rocks recovered from ~6400 m water depth in the Izu–Ogasawara Trench. On the basis of microtextures, strontium–carbon–oxygen isotope geochemistry, and radiocarbon analysis, we found that the aragonite is sourced from seawater that accumulated for more than 42,000 years. Aragonite precipitation is triggered by episodic rupture events that expel the accumulated fluids at 10⁻²–10⁻¹ m s⁻¹ and which continue for a few decades at most. We suggest that the recycling of subducted seawater from the shallowest forearc mantle influences carbon transport from the surface to Earth’s interior.
Experimental fracture sealing in reservoir sandstones and its relation to rock texture

Busch, B., Okamoto, A., Garbev, K., Hilgers, C.

Journal of Structural Geology　153　2021/12

DOI： 10.1016/j.jsg.2021.104447 　

ISSN： 0191-8141
1-D inversion analysis of a shallow landslide triggered by the 2018 Eastern Iburi earthquake in Hokkaido, Japan

Kameda, J., Okamoto, A.

Earth, Planets and Space　73　(1)　2021/12

DOI： 10.1186/s40623-021-01443-y 　

ISSN： 1880-5981 1343-8832

eISSN： 1880-5981
Rupture of wet mantle wedge by self-promoting carbonation Peer-reviewed

Atsushi Okamoto, Ryosuke Oyanagi, Kazuki Yoshida, Masaoki Uno, Hiroyuki Shimizu, Madhusoodhan Satish-Kumar

Communications Earth & Environment　2　(1)　2021/12
Publisher: Springer Science and Business Media {LLC}
DOI： 10.1038/s43247-021-00224-5 　

eISSN： 2662-4435
Formation of amorphous silica nanoparticles and its impact on permeability of fractured granite in superhot geothermal environments Peer-reviewed

Watanabe, N., Abe, H., Okamoto, A., Nakamura, K., Komai, T.

Scientific Reports　11　(1)　2021/12

DOI： 10.1038/s41598-021-84744-2 　

ISSN： 2045-2322

eISSN： 2045-2322
Generation of oxidising fluids by comminution of fault rocks

J. Kameda, A. Okamoto

Geochemical Perspectives Letters　32-35　2021/10
Publisher: European Association of Geochemistry
DOI： 10.7185/geochemlet.2131 　

ISSN： 2410-339X

eISSN： 2410-3403
Crucial Scientific Issues in Earth Science Revealed Only by Mantle Drilling: Understanding the Current State of the Oceanic Plates of a Life-bearing Planet

Morishita, T., Fujie, G., Hirauchi, K.-I., Katayama, I., Kouketsu, Y., Kuroda, J.-I., Okamoto, A., Ono, S., Michibayashi, K., Morono, Y., Yamamoto, S.

Journal of Geography (Chigaku Zasshi)　130　(4)　483-506　2021/08/25

DOI： 10.5026/JGEOGRAPHY.130.483 　

ISSN： 1884-0884 0022-135X

eISSN： 1884-0884
Albite–K-feldspar–quartz equilibria in hydrothermal fluids at 400, 420°C and 20–35 MPa: Experimental measurements and thermodynamic calculations Peer-reviewed

Okamoto, A., Ishii, H., Oyanagi, R., Tsuchiya, N.

Geothermics　94　2021/07

DOI： 10.1016/j.geothermics.2021.102109 　

ISSN： 0375-6505
Multi-stage infiltration of Na- and K-rich fluids from pegmatites at mid-crustal depths as revealed by feldspar replacement textures Peer-reviewed

Nurdiana, A., Okamoto, A., Yoshida, K., Uno, M., Nagaya, T., Tsuchiya, N.

Lithos　388-389　2021/05

DOI： 10.1016/j.lithos.2021.106096 　

ISSN： 1872-6143 0024-4937

eISSN： 1872-6143
Fe(III)-distribution at serpentinized crust-mantle boundary within the Oman ophiolite

Okamoto Atsushi, Yoshida Kazuki, Oyanagi Ryosuke, Fujii Masakazu, Niwa Yasuhiro, Takeichi Yasuo, Kimura Masao

Annual Meeting of the Geological Society of Japan　2021　072　2021
Publisher: The Geological Society of Japan
DOI： 10.14863/geosocabst.2021.0_072 　

ISSN： 1348-3935

eISSN： 2187-6665
Redistribution of magnetite during multi-stage serpentinization: Evidence from the Taishir Massif, Khantaishir ophiolite, western Mongolia

Dandar, O., Okamoto, A., Uno, M., Tsuchiya, N.

Journal of Mineralogical and Petrological Sciences　116　(3)　176-181　2021

DOI： 10.2465/jmps.201130a 　

ISSN： 1349-3825 1345-6296

eISSN： 1349-3825
Fluid Infiltration Through Oceanic Lower Crust in Response to Reaction-Induced Fracturing: Insights From Serpentinized Troctolite and Numerical Models Peer-reviewed

Yoshida, K., Okamoto, A., Shimizu, H., Oyanagi, R., Tsuchiya, N.

Journal of Geophysical Research: Solid Earth　125　(11)　2020/11/30
Publisher: American Geophysical Union ({AGU})
DOI： 10.1029/2020JB020268 　

ISSN： 2169-9356 2169-9313

eISSN： 2169-9356
Rapid fluid infiltration and permeability enhancement during middle–lower crustal fracturing: Evidence from amphibolite–granulite-facies fluid–rock reaction zones, Sør Rondane Mountains, East Antarctica Peer-reviewed

Diana Mindaleva, Masaoki Uno, Fumiko Higashino, Takayoshi Nagaya, Atsushi Okamoto, Noriyoshi Tsuchiya

Lithos　372-373　2020/11/01

DOI： 10.1016/j.lithos.2020.105521 　

ISSN： 0024-4937

eISSN： 1872-6143
Inferring fracture forming processes by characterizing fracture network patterns with persistent homology Peer-reviewed

A. Suzuki, M. Miyazawa, A. Okamoto, H. Shimizu, I. Obayashi, Y. Hiraoka, T. Tsuji, P. K. Kang, T. Ito

Computers and Geosciences　143　104550-104550　2020/10

DOI： 10.1016/j.cageo.2020.104550 　

ISSN： 0098-3004
Crystallographic preferred orientation of talc determined by an improved EBSD procedure for sheet silicates: Implications for anisotropy at the slab-mantle interface due to Si-metasomatism Peer-reviewed

Takayoshi Nagaya, Atsushi Okamoto, Ryosuke Oyanagi, Yusuke Seto, Akira Miyake, Masaoki Uno, Jun Muto, Simon R. Wallis

American Mineralogist　105　(6)　873-893　2020/06/25

DOI： 10.2138/am-2020-7006 　

ISSN： 0003-004X

eISSN： 1945-3027
Characteristics of hydrogen production with carbon storage by CO<inf>2</inf>-rich hydrothermal alteration of olivine in the presence of Mg–Al spinel Peer-reviewed

Jiajie Wang, Noriaki Watanabe, Atsushi Okamoto, Kengo Nakamura, Takeshi Komai

International Journal of Hydrogen Energy　45　(24)　13163-13175　2020/05/05

DOI： 10.1016/j.ijhydene.2020.03.032 　

ISSN： 0360-3199

eISSN： 1879-3487
Transport and evolution of supercritical fluids during the formation of the erdenet CU–MO deposit, Mongolia Peer-reviewed

Geri Agroli, Atsushi Okamoto, Masaoki Uno, Noriyoshi Tsuchiya

Geosciences (Switzerland)　10　(5)　201-221　2020/05

DOI： 10.3390/geosciences10050201 　

eISSN： 2076-3263
Thermodynamic modeling of hydrous-melt–olivine equilibrium using exhaustive variable selection Peer-reviewed

Ueki, K., Kuwatani, T., Okamoto, A., Akaho, S., Iwamori, H.

Physics of the Earth and Planetary Interiors　300　106430-106430　2020/03
Publisher: Elsevier {BV}
DOI： 10.1016/j.pepi.2020.106430 　

ISSN： 0031-9201
Stabilizing and enhancing permeability for sustainable and profitable energy extraction from superhot geothermal environments Peer-reviewed

Noriaki Watanabe, Kohei Saito, Atsushi Okamoto, Kengo Nakamura, Takuya Ishibashi, Hanae Saishu, Takeshi Komai, Noriyoshi Tsuchiya

Applied Energy　260　114306　2020/02/15

DOI： 10.1016/j.apenergy.2019.114306 　

ISSN： 0306-2619

eISSN： 1872-9118
Silica controls on hydration kinetics during serpentinization of olivine: Insights from hydrothermal experiments and a reactive transport model Peer-reviewed

Ryosuke Oyanagi, Atsushi Okamoto, Noriyoshi Tsuchiya

Geochimica et Cosmochimica Acta　270　21-42　2020/02

DOI： 10.1016/j.gca.2019.11.017 　

ISSN： 0016-7037

eISSN： 1872-9533
Impact of fluid pressure on failure mode in shear zones: Numerical simulation of en-echelon tensile fracturing and transition to shear Peer-reviewed

Atsushi Okamoto, Kazumasa Fuse, Hiroyuki Shimizu, Takatoshi Ito

Tectonophysics　774　228277-228277　2020/01
Publisher: Elsevier {BV}
DOI： 10.1016/j.tecto.2019.228277 　

ISSN： 0040-1951
Super-resolution of X-ray CT images of rock core samples by sparse representation: methodology and applications to serpetinized peridotite from CM1A Peer-reviewed

Atsushi Okamoto, Toshiaki Omari, Masao Kimura, Katsuyoshi Michibayashi

the International Conference on Ophiolites and the Oceanic Lithosphere　2020
Silica Nanoparticles Produced by Flash Vaporization from Supercritical Fluids Peer-reviewed

Atsushi OKAMOTO, Takamasa NIIBE, Takashi AMAGAI, Nobuo HIRANO, Noriyoshi TSUCHIYA

World Geothermal Congress　2020
Fracture and permeability of granite in superhot geothermal environments Invited Peer-reviewed

N. Watanabe, K. Sakaguchi, H. Saishu, R. Goto, T. Ishibashi, A. Okamoto, Y. Chen, S.E. Ingebritsen, T. Komai, N. Tsuchiya

Proceedings of the YSRM2019 & REIF2019　Paper number KL4　2019/12
Silica nanoparticles produced by explosive flash vaporization during earthquakes Peer-reviewed

Takashi Amagai, Atsushi Okamoto, Takamasa Niibe, Nobuo Hirano, Kenichi Motomiya, Noriyoshi Tsuchiya

Scientific Reports　9　(1)　9738　2019/12

DOI： 10.1038/s41598-019-46320-7 　

ISSN： 2045-2322

eISSN： 2045-2322
Melt–fluid infiltration along detachment shear zones in oceanic core complexes: Insights from amphiboles in gabbro mylonites from the Godzilla Megamullion, Parece Vela Basin, the Philippine Sea Peer-reviewed

Yumiko Harigane, Atsushi Okamoto, Tomoaki Morishita, Jonathan E. Snow, Akihiro Tamura, Hiroyuki Yamashita, Katsuyoshi Michibayashi, Yasuhiko Ohara, S. Arai

Lithos　344-345　217-231　2019/11/01

DOI： 10.1016/j.lithos.2019.06.019 　

ISSN： 0024-4937

eISSN： 1872-6143
Formation of secondary olivine after orthopyroxene during hydration of mantle wedge: evidence from the Khantaishir Ophiolite, western Mongolia Peer-reviewed

Otgonbayar Dandar, Atsushi Okamoto, Masaoki Uno, Ryosuke Oyanagi, Takayoshi Nagaya, Ulziiburen Burenjargal, Tsuyoshi Miyamoto, Noriyoshi Tsuchiya

Contributions to Mineralogy and Petrology　174　(11)　86　2019/11
Publisher: Springer Science and Business Media {LLC}
DOI： 10.1007/s00410-019-1623-1 　

ISSN： 0010-7999

eISSN： 1432-0967
Geological and engineering features of developing ultra-high-temperature geothermal systems in the world Peer-reviewed

Kyosuke Okamoto, Hiroshi Asanuma, Takuya Ishibashi, Yusuke Yamaya, H. Saishu, N. Yanagisawa, Toru Mogi, Noriyoshi Tsuchiya, Atsushi Okamoto, Shigemi Naganawa, Y. Ogawa, Kazuya Ishitsuka, Yasuhiro Fujimitsu, K. Kitamura, Tatsuya Kajiwara, S. Horimoto, Kuniaki Shimada

Geothermics　82　267-281　2019/11

DOI： 10.1016/j.geothermics.2019.07.002 　

ISSN： 0375-6505

eISSN： 1879-3576
Pyroxene control of H<inf>2</inf> production and carbon storage during water-peridotite-CO<inf>2</inf> hydrothermal reactions Peer-reviewed

Jiajie Wang, Noriaki Watanabe, Atsushi Okamoto, Kengo Nakamura, Takeshi Komai

International Journal of Hydrogen Energy　44　(49)　26835-26847　2019/10/11

DOI： 10.1016/j.ijhydene.2019.08.161 　

ISSN： 0360-3199

eISSN： 1879-3487
NaHCO<inf>3</inf>-promoted olivine weathering with H<inf>2</inf> generation and CO<inf>2</inf> sequestration in alkaline hydrothermal system Peer-reviewed

J. Wang, K. Nakamura, N. Watanabe, A. Okamoto, T. Komai

IOP Conference Series: Earth and Environmental Science　257　(1)　1-7　2019/05/10

DOI： 10.1088/1755-1315/257/1/012017 　

ISSN： 1755-1307

eISSN： 1755-1315
Acceleration of hydrogen production during water-olivine-CO<inf>2</inf> reactions via high-temperature-facilitated Fe(II) release Peer-reviewed

Jiajie Wang, Noriaki Watanabe, Atsushi Okamoto, Kengo Nakamura, Takeshi Komai

International Journal of Hydrogen Energy　44　(23)　11514-11524　2019/05/03

DOI： 10.1016/j.ijhydene.2019.03.119 　

ISSN： 0360-3199

eISSN： 1879-3487
Enhanced hydrogen production with carbon storage by olivine alteration in CO <inf>2</inf> -rich hydrothermal environments Peer-reviewed

Jiajie Wang, Noriaki Watanabe, Atsushi Okamoto, Kengo Nakamura, Takeshi Komai

Journal of CO2 Utilization　30　205-213　2019/03

DOI： 10.1016/j.jcou.2019.02.008 　

ISSN： 2212-9820

eISSN： 2212-9839
Trace element compositions of amphiboles in gabbro mylonites from the Godzilla Megamullion, Parece Vela Basin, Philippine Sea Peer-reviewed

Harigane Y, Okamoto A, Morishita T, Snow JE, Tamura A, Yamashita H, Michibayashi K, Ohara Y, Arai S

Lithos　344　217-231　2019
Multiple kinetic parameterization in a reactive transport model using the exchange Monte Carlo method Peer-reviewed

Ryosuke Oyanagi, Atsushi Okamoto, Noriyoshi Tsuchiya

Minerals　8　(12)　579　2018/12

DOI： 10.3390/min8120579 　

eISSN： 2075-163X
Loop energy: A useful indicator of the hardness of minerals from depth-sensing indentation tests Peer-reviewed

Toshiaki Masuda, Yasutomo Omori, Ryoko Sakurai, Tomoya Miyake, Mirai Yamanouchi, Yumiko Harigane, Atsushi Okamoto, Katsuyoshi Michibayashi

Journal of Structural Geology　117　96-104　2018/12

DOI： 10.1016/j.jsg.2018.09.004 　

ISSN： 0191-8141
Recovering the past history of natural recording media by Bayesian inversion Peer-reviewed

Tatsu Kuwatani, Hiromichi Nagao, Shin Ichi Ito, Atsushi Okamoto, Kenta Yoshida, Takamoto Okudaira

Physical Review E　98　(4)　043311　2018/10/31

DOI： 10.1103/PhysRevE.98.043311 　

ISSN： 2470-0045

eISSN： 2470-0053
Al-zoning of serpentine aggregates in mesh texture induced by metasomatic replacement reactions Peer-reviewed

Ryosuke Oyanagi, Atsushi Okamoto, Yumiko Harigane, Noriyoshi Tsuchiya

Journal of Petrology　59　(4)　613-634　2018/04

DOI： 10.1093/petrology/egy039 　

ISSN： 0022-3530

eISSN： 1460-2415
Kinetic study of phase transition of amorphous silica under sub- and supercritical conditons.

Niibe Takamasa, Okamoto Atsushi, Takashi Amagai, Noriyoshi Tsuchiya

Abstracts for Annual Meeting of Japan Association of Mineralogical Sciences　2018　22　2018
Publisher: Japan Association of Mineralogical Sciences
DOI： 10.14824/jakoka.2018.0_22 　

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Solubility of quartz changes greatly depending on temperature and pressure. Hydrothermal experiments for understanding silica precipitation and dissolution including phase transition were carried out under sub- and supercritical conditions. In the result, amorphous silica changed to cristobalite within 5 days on 350℃ and 400℃, and the Si concentration roughly agreed with the solubility of amorphous silica at the day 11 and 15 in the experiment at 400°C.
DRONE BRINGS NEW ADVANCE OF GEOLOGICAL MAPPING IN MONGOLIA: OPPORTUNITIES AND CHALLENGES Peer-reviewed

Otgonbayar Dandar, Atsushi Okamoto, Masaoki Uno, Undarmaa Batsaikhan, Burenjargal Ulziiburen, Noriyoshi Tsuchiya

Mongolian Geoscientist　47　53-57　2018

DOI： 10.5564/mgs.v0i47.1063 　
Experimental investigation on changes in mechanical properties of volcanic sandstones under CO<inf>2</inf> geological storage conditions Peer-reviewed

Koki Hattori, Noriaki Watanabe, Atsushi Okamoto, Kengo Nakamura, Takeshi Komai, Tetsuya Tamagawa

ISRM International Symposium - 10th Asian Rock Mechanics Symposium, ARMS 2018　2018
Silica precipitation potentially controls earthquake recurrence in seismogenic zones Peer-reviewed

Hanae Saishu, Atsushi Okamoto, Makoto Otsubo

Scientific Reports　7　(1)　13337　2017/12

DOI： 10.1038/s41598-017-13597-5 　

ISSN： 2045-2322

eISSN： 2045-2322
Fluid Pocket Generation in Response to Heterogeneous Reactivity of a Rock Fracture Under Hydrothermal Conditions Peer-reviewed

A. Okamoto, H. Tanaka, N. Watanabe, H. Saishu, N. Tsuchiya

Geophysical Research Letters　44　(20)　10,306-10,315　2017/10/28

DOI： 10.1002/2017GL075476 　

ISSN： 0094-8276

eISSN： 1944-8007
Reaction-induced grain boundary cracking and anisotropic fluid flow during prograde devolatilization reactions within subduction zones Peer-reviewed

Atsushi Okamoto, Hiroyuki Shimizu, Jun ichi Fukuda, Jun Muto, Takamoto Okudaira

Contributions to Mineralogy and Petrology　172　(9)　75　2017/09/01

DOI： 10.1007/s00410-017-1393-6 　

ISSN： 0010-7999

eISSN： 1432-0967
Excess water generation during reaction-inducing intrusion of granitic melts into ultramafic rocks at crustal P–T conditions in the Sør Rondane Mountains of East Antarctica Peer-reviewed

Masaoki Uno, Atsushi Okamoto, Noriyoshi Tsuchiya

Lithos　284-285　625-641　2017/07

DOI： 10.1016/j.lithos.2017.04.016 　

ISSN： 0024-4937

eISSN： 1872-6143
Potentially exploitable supercritical geothermal resources in the ductile crust Peer-reviewed

Noriaki Watanabe, Tatsuya Numakura, Kiyotoshi Sakaguchi, Hanae Saishu, Atsushi Okamoto, Steven E. Ingebritsen, Noriyoshi Tsuchiya

Nature Geoscience　10　(2)　140-144　2017/02/01

DOI： 10.1038/ngeo2879 　

ISSN： 1752-0894

eISSN： 1752-0908
Opal-CT in chert beneath the toe of the Tohoku margin and its influence on the seismic aseismic transition in subduction zones Peer-reviewed

Jun Kameda, Atsushi Okamoto, Kiminori Sato, Koichiro Fujimoto, Asuka Yamaguchi, Gaku Kimura

Geophysical Research Letters　44　(2)　687-693　2017/01/28

DOI： 10.1002/2016GL071784 　

ISSN： 0094-8276

eISSN： 1944-8007
Antigorite CPO formation mechanism in the shallow wedge mantle: Case studies from the Besshi and Shiraga bodies of the Sanbagawa metamorphic belt in central Shikoku, Japan

Nagaya Takayoshi, Wallis Simon R, Okamoto Atsushi, Uehara Seiichiro, Michibayashi Katsuyoshi, Nishii Aya

Annual Meeting of the Geological Society of Japan　2017　(0)　2017

DOI： 10.14863/geosocabst.2017.0_336 　

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[Program canceled for typhoon] Program canceled for typhoon. However, This abstract is quotable and viewable on PDF.
Porosity and permeability evolution induced by precipitation of silica under hydrothermal conditions Peer-reviewed

Atsushi Okamoto, Ryo Yamada, Hanae Saishu, Noriyoshi Tsuchiya

15TH WATER-ROCK INTERACTION INTERNATIONAL SYMPOSIUM, WRI-15　17　249-252　2017

DOI： 10.1016/j.proeps.2016.12.046 　

ISSN： 1878-5220
Mechanisms of serpentinization utilizing olivine-plagioclase-H2O system under hydrothermal conditions Peer-reviewed

Ryosuke Oyanagi, Atsushi Okamoto, Noriyoshi Tsuchiya

15TH WATER-ROCK INTERACTION INTERNATIONAL SYMPOSIUM, WRI-15　17　686-689　2017

DOI： 10.1016/j.proeps.2016.12.153 　

ISSN： 1878-5220
In situ observation of critical phenomena of multicomponent geofluids and seawater by using visible-type autoclave Peer-reviewed

Tsuchiya, Noriyoshi, Sekiguchi, Chizu, Ishikawa, Satoru, Okamoto, Atsushi, Hirano, Nobuo

15TH WATER-ROCK INTERACTION INTERNATIONAL SYMPOSIUM, WRI-15　17　296-299　2017

DOI： 10.1016/j.proeps.2016.12.062 　

ISSN： 1878-5220
Pressure solution and permeability evolution in fractured granite at elastic and plastic deformation regimes Peer-reviewed

Kohei Saito, Noriaki Watanabe, Atsushi Okamoto, Noriyoshi Tsuchiya, Takuya Ishibashi, Hanae Saishu

Transactions - Geothermal Resources Council　41　945-955　2017

ISSN： 0193-5933
Information extraction from metamorphic rock textures and compositional zoning of minerals : Forward models and inversion analyses Peer-reviewed

123　(9)　733-745　2017
Publisher:
DOI： 10.5575/geosoc.2017.0034 　

ISSN： 0016-7630
Bayesian inversion analysis of nonlinear dynamics in surface heterogeneous reactions Peer-reviewed

Toshiaki Omori, Tatsu Kuwatani, Atsushi Okamoto, Koji Hukushima

Physical Review E　94　(3)　033305　2016/09/28

DOI： 10.1103/PhysRevE.94.033305 　

ISSN： 2470-0045

eISSN： 2470-0053
The roles of fluid transport and surface reaction in reaction-induced fracturing, with implications for the development of mesh textures in serpentinites Peer-reviewed

Hiroyuki Shimizu, Atsushi Okamoto

Contributions to Mineralogy and Petrology　171　(8-9)　73　2016/09/01

DOI： 10.1007/s00410-016-1288-y 　

ISSN： 0010-7999

eISSN： 1432-0967
Reaction-induced rheological weakening enables oceanic plate subduction Peer-reviewed

Ken Ichi Hirauchi, Kumi Fukushima, Masanori Kido, Jun Muto, Atsushi Okamoto

Nature Communications　7　12550　2016/08/26

DOI： 10.1038/ncomms12550 　

ISSN： 2041-1723

eISSN： 2041-1723
Contrast in stress-strain history during exhumation between high- and ultrahigh-pressure metamorphic units in the Western Alps: Microboudinage analysis of piemontite in metacherts Peer-reviewed

Yasutomo Omori, Antonello Barresi, Nozomi Kimura, Atsushi Okamoto, Toshiaki Masuda

Journal of Structural Geology　89　168-180　2016/08/01

DOI： 10.1016/j.jsg.2016.06.004 　

ISSN： 0191-8141
Phase-field modeling of epitaxial growth of polycrystalline quartz veins in hydrothermal experiments Peer-reviewed

F. Wendler, A. Okamoto, P. Blum

Geofluids　16　(2)　211-230　2016/05/01

DOI： 10.1111/gfl.12144 　

ISSN： 1468-8115

eISSN： 1468-8123
20pPSA-24 Approximate Bayesian Computation of surface-area model selection in water-rock interactions

Hukushima K., Okamoto A., Kuwatani T., Omori T.

Meeting Abstracts of the Physical Society of Japan　71　2923-2923　2016
Publisher: The Physical Society of Japan (JPS)
DOI： 10.11316/jpsgaiyo.71.1.0_2923 　

ISSN： 2189-079X
22pBT-5 Statistical Estimation of Heterogeneous Reactions for Rock-Water Interaction

Omori Toshiaki, Kuwatani Tatsu, Okamoto Atsushi, Hukushima Koji

Meeting Abstracts of the Physical Society of Japan　71　3130-3130　2016
Publisher: The Physical Society of Japan (JPS)
DOI： 10.11316/jpsgaiyo.71.1.0_3130 　

ISSN： 2189-079X
Developing the thermodynamic model of hydrous melt-olivine equilibrium using machine-learning technique

Ueki Kenta, Kuwatani Tatsu, Okamoto Atsushi, Iwamori Hikaru

Abstracts for Annual Meeting of Japan Association of Mineralogical Sciences　2016　(0)　7-7　2016
Publisher: Japan Association of Mineralogical Sciences
DOI： 10.14824/jakoka.2016.0_7 　

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We develop a thermodynamic model to calculate phase equilibrium between the hydrous melt and olivine using machine-learning. Cross-validation, a method to evaluate the model predictability, is used to obtain the optimal set of equation and parameters. <br>
Contrasting geochemical signatures of devonian and permian granitoids from the tseel terrane, sw mongolia Peer-reviewed

Ulziiburen Burenjargal, Atsushi Okamoto, Noriyoshi Tsuchiya, Masaoki Uno, Kenji Horie, Tomokazu Hokada

Journal of Geosciences (Czech Republic)　61　(1)　51-66　2016

DOI： 10.3190/jgeosci.210 　

ISSN： 1802-6222

eISSN： 1803-1943
The relationship between the permeable-impermeable boundary of the Earth's crust and the precipitation of mineral due to the change in a state of water at the geothermal fields Peer-reviewed

Hanae Saishu, Atsushi Okamoto, Noriyoshi Tsuchiya

Journal of the Geothermal Research Society of Japan　38　(1)　17-25　2016

DOI： 10.11367/grsj.38.17 　

ISSN： 0388-6735

eISSN： 1883-5775
Free-energy landscape and nucleation pathway of polymorphic minerals from solution in a Potts lattice-gas model Peer-reviewed

Atsushi Okamoto, Tatsu Kuwatani, Toshiaki Omori, Koji Hukushima

Physical Review E - Statistical, Nonlinear, and Soft Matter Physics　92　(4)　042130　2015/10/12

DOI： 10.1103/PhysRevE.92.042130 　

ISSN： 1539-3755

eISSN： 1550-2376
Competitive hydration and dehydration at olivine-quartz boundary revealed by hydrothermal experiments: Implications for silica metasomatism at the crust-mantle boundary Peer-reviewed

Ryosuke Oyanagi, Atsushi Okamoto, Nobuo Hirano, Noriyoshi Tsuchiya

Earth and Planetary Science Letters　425　44-54　2015/09/01

DOI： 10.1016/j.epsl.2015.05.046 　

ISSN： 0012-821X

eISSN： 1385-013X
Contrasting fracture patterns induced by volume-increasing and -decreasing reactions: Implications for the progress of metamorphic reactions Peer-reviewed

Atsushi Okamoto, Hiroyuki Shimizu

Earth and Planetary Science Letters　417　9-18　2015/05/01

DOI： 10.1016/j.epsl.2015.02.015 　

ISSN： 0012-821X

eISSN： 1385-013X
Fundamental Study for Beyond Brittle Geothermal Reservoirs Peer-reviewed

N. Tsuchiya, H. Asanuma, A. Okamoto, K. Sakaguchi, N. Hirano, A. Kizaki, N. Watanabe

Proceedings World Geothermal Congress 2015　paper number 12019　2015/04
Permeability and porosity structure change by dissolution of granite fracture under high temperature and confining pressure

Tanaka Hiroto, Okamoto Atsushi, Watanabe Noriaki, Tsuchiya Noriyoshi

Annual Meeting of the Geological Society of Japan　2015　204-204　2015
Publisher: The Geological Society of Japan
DOI： 10.14863/geosocabst.2015.0_204 　
Multi-stage alteration processes of ultramafic rocks from the Hantaishir ophiolite, western Mongolia

DANDAR Otgonbayar, UNO Masaoki, OKAMOTO Atsushi, TSUCHIYA Noriyoshi

Annual Meeting of the Geological Society of Japan　2015　408-408　2015
Publisher: The Geological Society of Japan
DOI： 10.14863/geosocabst.2015.0_408 　
A case study of multiple deformations without involving folding: microstructures and lattice preferred orientation of quartz in a pebble of metachert collected from the Sambagawa metamorphic belt in eastern Shikoku, Japan

Masuda Toshiaki, Nishiawaki shinn, Omori Yashutomo, Matsumura Taroujirou, Michibayashi Katsuyoshi, Satsukawa Takako, Okamoto Atsushi

Annual Meeting of the Geological Society of Japan　2015　216-216　2015
Publisher: The Geological Society of Japan
DOI： 10.14863/geosocabst.2015.0_216 　
Vein texture: A window for fluid dynamics in the crust Peer-reviewed

Atsushi Okamoto

Japanese Magazine of Mineralogical and Petrological Sciences　43　(1)　25-29　2015

DOI： 10.2465/gkk.131129 　

ISSN： 1345-630X

eISSN： 1349-7979
Beyond-laboratory-scale prediction for channeling flows through subsurface rock fractures with heterogeneous aperture distributions revealed by laboratory evaluation Peer-reviewed

Takuya Ishibashi, Noriaki Watanabe, Nobuo Hirano, Atsushi Okamoto, Noriyoshi Tsuchiya

Journal of Geophysical Research: Solid Earth　120　(1)　106-124　2015/01

DOI： 10.1002/2014JB011555 　

ISSN： 2169-9313

eISSN： 2169-9356
Rheological properties of the detachment shear zone of an oceanic core complex inferred by plagioclase flow law: Godzilla Megamullion, Parece Vela back-arc basin, Philippine Sea Peer-reviewed

Katsuyoshi Michibayashi, Yumiko Harigane, Yasuhiko Ohara, Jun Muto, Atsushi Okamoto

Earth and Planetary Science Letters　408　16-23　2014/12/05

DOI： 10.1016/j.epsl.2014.10.005 　

ISSN： 0012-821X

eISSN： 1385-013X
Thermal evolution of the Tseel terrane, SW Mongolia and its relation to granitoid intrusions in the Central Asian Orogenic Belt Peer-reviewed

U. Burenjargal, A. Okamoto, T. Kuwatani, S. Sakata, T. Hirata, N. Tsuchiya

Journal of Metamorphic Geology　32　(7)　765-790　2014/09/01

DOI： 10.1111/jmg.12090 　

ISSN： 0263-4929

eISSN： 1525-1314
The significance of silica precipitation on the formation of the permeable-impermeable boundary within Earth's crust Peer-reviewed

Hanae Saishu, Atsushi Okamoto, Noriyoshi Tsuchiya

TERRA NOVA　26　(4)　253-259　2014/08

DOI： 10.1111/ter.12093 　

ISSN： 0954-4879

eISSN： 1365-3121
Distribution of CO2 fluids in the Shimanto belt on Muroto Peninsula, SW Japan: possible injection of magmatic CO2 into the accretionary prism Peer-reviewed

Atsushi Okamoto, Michimasa Musya, Yoshitaka Hashimoto, Noriyoshi Tsuchiya

EARTH PLANETS AND SPACE　66　33　2014/05

DOI： 10.1186/1880-5981-66-33 　

ISSN： 1880-5981
Predicting channeling flows through subsurface rock fractures beyond laboratory scale

T. Ishibashi, N. Watanabe, N. Hirano, A. Okamoto, N. Tsuchiya

Proceedings of the Grand Renewable Energy 2014 Internationl Conference　O-Ge-9-4　2014
Beyond-laboratory-scale prediction for channeling flows through subsurface rock fractures Peer-reviewed

N. Watanabe, T. Ishibashi, N. Hirano, A. Okamoto, N. Tsuchiya

ISRM International Symposium - 8th Asian Rock Mechanics Symposium, ARMS 2014　1662-1671　2014
Possibility to remedy CO2 leakage from geological reservoir using CO2 reactive grout Peer-reviewed

Takatoshi Ito, Tianfu Xu, Hidenori Tanaka, Yuhki Taniuchi, Atsushi Okamoto

INTERNATIONAL JOURNAL OF GREENHOUSE GAS CONTROL　20　310-323　2014/01

DOI： 10.1016/j.ijggc.2013.11.014 　

ISSN： 1750-5836

eISSN： 1878-0148
Millimeter- to decimeter-scale compositional mapping using a scanning X-ray analytical microscope and its application to a reaction zone in high-grade metamorphic rock Peer-reviewed

Masaoki Uno, Atsushi Okamoto, Noriyoshi Tsuchiya

Journal of Mineralogical and Petrological Sciences　109　(6)　271-278　2014

DOI： 10.2465/jmps.140613b 　

ISSN： 1345-6296

eISSN： 1349-3825
Radiocarbon Dating Historical Tsunami Deposits from the Sendai Plain, Northeastern Japan: Preliminary Age Model of HS Continuous Soil Sediment Series Peer-reviewed

WATANABE Takahiro, HOSODA Norihiro, TSUCHIYA Noriyoshi, NAKAMURA Toshio, HIRANO Nobuo, OKAMOTO Atsushi, NARA Fumiko W., Tohoku University Tsunami Sediment Research Group

J. Geogr.　123　(6)　904-922　2014
Publisher: Tokyo Geographical Society
DOI： 10.5026/jgeography.123.904 　

ISSN： 0022-135X

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Ancient tsunami deposits are distributed in paddy fields throughout the Sendai plain, on the Pacific coast of the Tohoku area in northeastern Japan. These deposits contain gravel, mud, shells, and microfossils originating from the seafloor, sandy beaches, and coastal soils. Paleotsunami deposits offer valuable clues for identifying past tsunami inundation areas, but previous studies had difficulty dating tsunami deposits for correlation with historic disaster events. This study collects age data from continuous soil profiles that include tsunami deposits. Nine continuous soil sediment samples are collected using a Handy Geoslicer (Fukken Co. Ltd.) near the coast of Sendai Bay in northeastern Japan. The soil slices (HS1–9) are 84–183 cm long and consist of cultivated surface soils, peaty clay, silt, and fine to medium sands. Slices HS2–7 are subsampled at 1-cm intervals and water contents of 689 discrete samples are measured. Plant residues are extracted from the samples for radiocarbon (¹⁴C) dating with a Tandetron accelerator mass spectrometry system (Model 4130 AMS, HVEE) at the Center for Chronological Research, Nagoya University. Water contents range from 6.2 to 83.0 wt.%, and the lowest values are observed in layers of well-rounded medium sand. Variations in water content agree well with changes in sedimentary facies. Total organic carbon contents of plant residues range from 45.9 to 54.5 wt.% (50.4 wt.% on average) and their stable carbon isotope ratios range from -25.1 to -30.1 permil (vs. PDB), which are consistent with the ratios of modern terrestrial C3 plants. The calibrated ages of plant residues from these tsunami deposits are about 1000–1300 cal BP, which agree well with the date of the Jogan Earthquake and tsunami on the Sendai plain (869 AD).
Seawater-leaching Testing for Arsenic and Heavy Metals in Tsunami Deposits Produced by the 2011 off the Pacific Coast of Tohoku Earthquake, Northeastern Japan Peer-reviewed

WATANABE Takahiro, TSUCHIYA Noriyoshi, YAMASAKI Shin-ichi, YAMADA Ryoichi, HIRANO Nobuo, OKAMOTO Atsushi, NARA Fumiko W., Tohoku Tsunami Sediment Research Group

J. Geogr.　123　(6)　835-853　2014
Publisher: Tokyo Geographical Society
DOI： 10.5026/jgeography.123.835 　

ISSN： 0022-135X

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Tsunami deposits in Northeastern Japan produced by the 2011 off the Pacific coast of Tohoku Earthquake and tsunami contain relatively high concentrations of arsenic and heavy metals. Because the impacts of tsunamis on the distribution and behavior of arsenic and heavy metals should be considered carefully in surface soils and the underground environment after a major disaster, standards are needed for seawater leaching tests to identify arsenic and heavy metals in tsunami deposits. For that purpose, tsunami deposits from the 2011 off the Pacific coast of Tohoku Earthquake were sampled at Kesen-numa city, Minamisanriku town, Ishinomaki city, and Shiogama city in Miyagi Prefecture, Northeastern Japan. Seventeen inorganic elements including As and heavy metals (Li, Sc, V, Cr, Co, Ni, Cu, Zn, As, Rb, Sr, Mo, Cd, Cs, Ba, Pb, U) were measured in a solution leached from tsunami deposits with pure water, artificial seawater, and natural seawater using inductively coupled plasma-mass spectrometry (ICP-MS) and hydride generation-atomic absorption spectrometry (HG-AAS). In the leachate obtained using pure water, concentrations of As and heavy metals were quantified successfully with the ICP-MS method. Concentrations of V, Cr, Co, Ni, Cu, and Zn did not differ from background levels in artificial seawater and natural seawater. When measuring As in seawater leaching tests, HG-AAS is a useful method for performing high-sensitivity analyses. In particular, HG-AAS is superior to ICP-MS for detecting low As concentrations (less than 30 μg/l) in a seawater leaching test.
Spectroscopic determination of the critical temperatures and pressures of H2O, CO2, and C2H5OH Peer-reviewed

Chizu Sekiguchi, Nobuo Hirano, Atsushi Okamoto, Noriyoshi Tsuchiya

JOURNAL OF MINERALOGICAL AND PETROLOGICAL SCIENCES　108　(6)　356-361　2013/12

DOI： 10.2465/jmps.130620b 　

ISSN： 1345-6296

eISSN： 1349-3825
Decompression with heating associated with granitoid intrusion deduced from spatial variation in garnet zonings in the Tseel Terrane, SW Mongolia Peer-reviewed

Ulziiburen Burenjargal, Atsushi Okamoto, Tatsu Kuwatani, Noriyohi Tsuchiya

Mongolian Geoscientist　39　12-27　2013/10
Coupled reactions and silica diffusion during serpentinization Peer-reviewed

Ogasawara, Yuichi, Okamoto, Atsushi, Hirano, Nobuo, Tsuchiya, Noriyoshi

GEOCHIMICA ET COSMOCHIMICA ACTA　119　212-230　2013/10

DOI： 10.1016/j.gca.2013.06.001 　

ISSN： 0016-7037

eISSN： 1872-9533
The effect of Al and Na on the precipitation rate of silica minerals: hydrothermal flow-through experiments at 430 degrees C and 31 MPa Peer-reviewed

Hanae Saishu, Atsushi Okamoto, Noriyoshi Tsuchiya

PROCEEDINGS OF THE FOURTEENTH INTERNATIONAL SYMPOSIUM ON WATER-ROCK INTERACTION, WRI 14　7　762-765　2013

DOI： 10.1016/j.proeps.2013.03.042 　

ISSN： 1878-5220
Effect of silica transport on serpentinization in the Ol-Opx-H2O system Peer-reviewed

Atsushi Okamoto, Yuichi Ogasawara, Nobuo Hirano, Noriyoshi Tsushiya

PROCEEDINGS OF THE FOURTEENTH INTERNATIONAL SYMPOSIUM ON WATER-ROCK INTERACTION, WRI 14　7　628-631　2013

DOI： 10.1016/j.proeps.2013.03.015 　

ISSN： 1878-5220
Mineralogical variation of silica induced by Al and Na in hydrothermal solutions Peer-reviewed

Hanae Saishu, Atsushi Okamoto, Noriyoshi Tsuchiya

AMERICAN MINERALOGIST　97　(11-12)　2060-2063　2012/11

DOI： 10.2138/am.2012.4258 　

ISSN： 0003-004X
Upgrading of Aperture Model Based on Surface Geometry of Natural Fracture for Evaluating Channeling Flow Peer-reviewed

Takuya Ishibashi, Noriaki Watanabe, Nobuo Hirano, Atsushi Okamoto, Noriyoshi Tsuchiya

Geotehrmal Rwsources Council Transactions　36　481-486　2012/09/30
Leaching behaviors of the rocks in the Shimanto belt and their roles on calcite precipitation in hydrothermal conditions

MUSHA Michimasa, TSUCHIYA Noriyoshi, OKAMOTO Atsushi

Abstracts for Annual Meeting of Japan Association of Mineralogical Sciences　2012　12-12　2012/09/15
Publisher: Japan Association of Mineralogical Sciences
DOI： 10.14824/jakoka.2012.0_12 　

ISSN： 1348-6543

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It is considered to be difficult to precipitate calcite in reasonable timescale for carbon storage. In contrast, calcite veins are common in natural geological settings. The purpose of this study is to understand the mechanism of calcite precipitation in hydrothermal environments. The leaching experiments revealed that several cations were leached from the rocks, resulting in alkaline fluids supersaturated with calcite. The flow-through experiments revealed that the acidic solution made by CO₂ bubbling was undersaturated with calcite. Alkaline fluids with NaHCO₃ reacted with pelitic rocks to produce calcite crystals with size of 0.01 mm precipitated on the calcite substrates.
An exhumation pressure-temperature path and fluid activities during metamorphism in the Tseel terrane, SW Mongolia: Constraints from aluminosilicate-bearing quartz veins and garnet zonings in metapelites Peer-reviewed

Ulziiburen Burenjargal, Atsushi Okamoto, Yuichi Meguro, Noriyoshi Tsuchiya

JOURNAL OF ASIAN EARTH SCIENCES　54-55　214-229　2012/08

DOI： 10.1016/j.jseaes.2012.04.017 　

ISSN： 1367-9120

eISSN： 1878-5786
GeoFlow: A novel model simulator for prediction of the 3-D channeling flow in a rock fracture network Peer-reviewed

Ishibashi, Takuya, Watanabe, Noriaki, Hirano, Nobuo, Okamoto, Atsushi, Tsuchiya, Noriyoshi

WATER RESOURCES RESEARCH　48　2012/07

DOI： 10.1029/2011WR011226 　

ISSN： 0043-1397
Variation of garnet zoning pattern in the pelitic gneisses and it's implications to thermal history of Tseel terrane, SW Mongolia

Ulziiburen Burenjargal, Atsushi Okamoto, Noriyoshi Tsuchiya

Annual Meeting of the Geological Society of Japan　2012　167-167　2012
Publisher: The Geological Society of Japan
DOI： 10.14863/geosocabst.2012.0_167 　
Mechanism of the formation of mineral inclusions: an example from quartz inclusions in garnet porphyroblasts

Okamoto Atsushi, Fukuda Jun-ichi, Muto Jun

Annual Meeting of the Geological Society of Japan　2012　172-172　2012
Publisher: The Geological Society of Japan
DOI： 10.14863/geosocabst.2012.0_172 　
Impact of 3D channeling flow on well productivity in the yufutsu oil/gas field Peer-reviewed

Takuya Ishibashi, Noriaki Watanabe, Tetsuya Tamagawa, Nobuo Hirano, Atsushi Okamoto, Noriyoshi Tsuchiya

18th Formation Evaluation Symposium of Japan 2012　2012
Experimental and numerical evaluation of channeling flow in fractured type of geothermal reservoir Peer-reviewed

T. Ishibashi, N. Watanabe, N. Hirano, A. Okamoto, N. Tsuchiya

Proceedings of 37th Workshop on Geothermal Reservoir Engineering　759-766　2012/01
Risk assessments of Arsenic in tsunami sediments from Iwate, Miyagi and Fukushima Prefectures, Northeast Japan, by the 2011 off the Pacific coast of Tohoku Earthquake Peer-reviewed

Tsuchiya Noriyoshi, Inoue Chihiro, Yamada Ryoichi, Yamasaki Shin-ichi, Hirano Nobuo, Okamoto Atsushi, Ogawa Yasumasa, Watanabe Takahiro, Watanabe Nara Fumiko, Watanabe Noriaki

Jour. Geol. Soc. Japan　118　(7)　419-430　2012
Publisher: The Geological Society of Japan
DOI： 10.5575/geosoc.2012.0043 　

ISSN： 0016-7630

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The Pacific coast of Tohoku District in Northeast Japan (Iwate, Miyagi, and Fukushima Prefectures) was seriously damaged by a violent tsunami resulting from the 2011 off the Pacific coast of Tohoku Earthquake on March 11 2011. The disaster area was covered by tsunami sediments, which are mainly marine sediments. We collected 137 tsunami sediments from Kuji City, Iwate Prefecture through to Minamisoma City, Fukushima Prefecture (40°11′N, 141°58′E to 37°43′N, 140°51′E). Analysis of bulk sediment chemistry and leaching test by pure water and seawater were carried out to access arsenic contamination. In addition, chemical forms of arsenic in different size fractions (<3 kDa, 3 kDa to 0.2 μm, 0.2 μm to 0.45 μm, and ≥0.45 μm) from the leachates were investigated by filtering techniques.<br>Arsenic concentrations in the pure water leachates of 45 samples had higher arsenic levels than the Japanese Environmental Quality Standards for Soil Pollution (10 μg/l). In particular, tsunami sediments from the Ohya area in Kesen-numa City, Miyagi Prefecture, had arsenic levels 39 times greater than this threshold, reflecting the influence of gold mines in this region. The fraction of arsenic species < 3 kDa in size in leachates of the high arsenic samples was ca. 70%, indicating that most of the arsenic in the leachates is present as fine colloidal particles and/or dissolved species.
Distribution of artificial radionuclides (Ag-110m, Te-129m, Cs-134, Cs-137) in surface soils from Miyagi Prefecture, northeast Japan, following the 2011 Fukushima Dai-ichi nuclear power plant accident Peer-reviewed

Watanabe, Takahiro, Tsuchiya, Noriyoshi, Oura, Yasuji, Ebihara, Mitsuru, Inoue, Chihiro, Hirano, Nobuo, Yamada, Ryoichi, Yamasaki, Shin-ichi, Okamoto, Atsushi, Nara, Fumiko Watanabe, Nunohara, Keishi

GEOCHEMICAL JOURNAL　46　(4)　279-285　2012

DOI： 10.2343/geochemj.2.0205 　

ISSN： 0016-7002

eISSN： 1880-5973
Rate of serpentinization at oceanic lithosphere : Insights from hydrothermal experiments Peer-reviewed

OKAMOTO Atsushi

Japanese Magazine of Mineralogical and Petrological Sciences　41　(5)　185-192　2012
Publisher: Japan Association of Mineralogical Sciences
DOI： 10.2465/gkk.120604 　

ISSN： 1345-630X

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Serpentinization is a hydration process that causes significant changes in physical and chemical properties of the oceanic lithosphere. Based on hydrothermal experiments, the reaction rates of serpentinization have been empirically obtained for typical reaction (i.e., Olivine+H₂O → Serpentine+Brucite) as a function of temperature and initial grain size of the reactant mineral. However, the rate equations used for these analyses take quite empirical forms, in which the solution chemistry (saturation state) is not taken into consideration; therefore, it is difficult to extrapolate the results to different conditions and to predict evolution of the fluid chemistry in the hydrothermal systems. Serpentinization reactions are characterized by coupled dissolution of primary minerals (Olivine, Pyroxenes) and formation of secondary minerals (Serpentine, Brucite, Talc, Magnetite); therefore, the rates of elementary reactions between individual minerals and solution will be required for estimating the rate of overall hydration reaction. I also discuss the effects of competitive processes among grain surface reactions, element diffusion, water supply and structural development during serpentinization.<br>
Textures of syntaxial quartz veins synthesized by hydrothermal experiments Peer-reviewed

Atsushi Okamoto, Kotaro Sekine

JOURNAL OF STRUCTURAL GEOLOGY　33　(12)　1764-1775　2011/12

DOI： 10.1016/j.jsg.2011.10.004 　

ISSN： 0191-8141
Progress of hydration reactions in olivine-H2O and orthopyroxenite-H2O systems at 250 degrees C and vapor-saturated pressure Peer-reviewed

Atsushi Okamoto, Yuichi Ogasawara, Yasumasa Ogawa, Noriyoshi Tsuchiya

CHEMICAL GEOLOGY　289　(3-4)　245-255　2011/10

DOI： 10.1016/j.chemgeo.2011.08.007 　

ISSN： 0009-2541

eISSN： 1878-5999
Experimental study on calcite precipitation in hydrothermal environments

MUSHA Michimasa, TSUCHIYA Noriyoshi, OKAMOTO Atsushi

Abstracts for Annual Meeting of Japan Association of Mineralogical Sciences　2011　3-3　2011/09/05
Publisher: Japan Association of Mineralogical Sciences
DOI： 10.14824/jakoka.2011.0.3.0 　

ISSN： 1348-6543

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To reduce greenhouse gas, the carbon storage underground has been tried; however, it is considered to be difficult to precipitate calcite in reasonable timescale. In contrast, calcite veins are very common in the oceanic crusts, metamorphic rocks, and accretionary prisms.The purpose of this study is to understand the controlling factors on calcite precipitation. As a first step, we conducted hydrothermal flow-through experiments to precipitate calcite at 300 ˚C and 30 MPa by using the temperature dependency of solubility. After the run of 240 h (10 days), the total increase of weight of calcite substrates was 0.051 g. Observation of the surface reveal that euhedral calcite crystals with size of 0.02-0.03 mm grew from the calcite in the substrates. Our results suggest that calcite veins could be formed around 300 ˚C, if fluids saturated with calcite at lower temperature would be brought accompanying with subduction of slabs.
Progress of hydration in olivine-H2O and orthopyroxene-H2O systems at Psat

OGASAWARA Y., OKAMOTO A., TSUCHIYA N.

Abstracts for Annual Meeting of Japan Association of Mineralogical Sciences　2011　15-15　2011/09/05
Publisher: Japan Association of Mineralogical Sciences
DOI： 10.14824/jakoka.2011.0.15.0 　

ISSN： 1348-6543

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Hydration of ultramafic rocks (sperpentinization) commonly occurs in mid-ocean ridges, and the extent and distribution of hydrated mantle plays an important role on the global circulation of H2O fluids. In this study, we conducted hydrothermal experiments on serpentinization to clarify the relationship between the temporal evolution of solution chemistry, progress of hydration reaction and textural developments. The starting materials were powders of olivine or orthopyroxene. The powders and the distilled water were set in the batch type vessel. The temperatures were 250 degreeC at the liquid-vapor saturation curve. The duration was up to 1008 hours. We will show these experimental results and olivine-orthopyroxene-water system experimental result in poster.
Kinetics of precipitation of silica minerals depending on the Al concentration in fluids and the discussion of vein formation

SAISHU Hanae, OKAMOTO Atsushi, TSUCHIYA Noriyoshi

Abstracts for Annual Meeting of Japan Association of Mineralogical Sciences　2011　7-7　2011/09/05
Publisher: Japan Association of Mineralogical Sciences
DOI： 10.14824/jakoka.2011.0.7.0 　

ISSN： 1348-6543

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The hydrothermal flow-through experiments of precipitation of silica minerals were conducted at 430°C and 31MPa. With increasing of the Al concentration in the input solution (0–6.7 ppm), the change of dominant precipitation of silica mineral was revealed such as amorphous silica → cristobalite → quartz, and the logarithmic precipitation rate increased linearly. The precipitation via nucleation is determined the third–order reaction. The rate equations of surface reaction and nucleation suggest that, for example, the dominant reaction is nucleation in the fracture of 0.1 mm width whereas it is surface reaction in the fracture of 0.01 mm width when the precipitation occurs from the solution of Ω = 2 at 200°C. This trend coincides with that the formation of blocky veins occurred in wider fractures comparatively in nature.
In situ observation of the crystallization pressure induced by Halite crystal growth in a microfuidic channel Peer-reviewed

Kotaro Sekine, Atsushi Okamoto, Kazuo Hayashi

American Mineralogist　96　(7)　1012-1019　2011/07

DOI： 10.2138/am.2011.3765 　

ISSN： 0003-004X 1945-3027
Thermodynamic forward modeling of progressive dehydration reactions during subduction of oceanic crust under greenschist facies conditions Peer-reviewed

Tatsu Kuwatani, Atsushi Okamoto, Mitsuhiro Toriumi

EARTH AND PLANETARY SCIENCE LETTERS　307　(1-2)　9-18　2011/07

DOI： 10.1016/j.epsl.2011.01.027 　

ISSN： 0012-821X

eISSN： 1385-013X
Application of the microboudin method to palaeodifferential stress analysis of deformed impure marbles from Syros, Greece: Implications for grain-size and calcite-twin palaeopiezometers Peer-reviewed

Toshiaki Masuda, Tomoya Miyake, Nozomi Kimura, Atsushi Okamoto

JOURNAL OF STRUCTURAL GEOLOGY　33　(1)　20-31　2011/01

DOI： 10.1016/j.jsg.2010.11.002 　

ISSN： 0191-8141
Evaluation and Prediction of fluid flow through fracture under confining pressure in various scales Peer-reviewed

T. Ishibashi, N. Watanabe, N. Hirano, A. Okamoto, N. Tsuchiya

Proceedings of 17th Formation Evaluation Symposium of Japan　2011
Mineralogical and textural variation of silica minerals in hydrothermal flow-through experiments: Implications for quartz vein formation Peer-reviewed

Atsushi Okamoto, Hanae Saishu, Nobuo Hirano, Noriyoshi Tsuchiya

GEOCHIMICA ET COSMOCHIMICA ACTA　74　(13)　3692-3706　2010/07

DOI： 10.1016/j.gca.2010.03.031 　

ISSN： 0016-7037
New Concept Discrete Fracture Network Model Simulator, GeoFlow, and Three Dimensional Channeling Flow in Fracture Network Peer-reviewed

Nobuo Hirano, Takuya Ishibashi, Noriaki Watanabe, Atsushi Okamoto, Noriyoshi Tsuchiya

Proceedings of World Geothermal Congress 2010　2010/04/25
Determination of amphibole fracture strength for quantitative palaeostress analysis using microboudinage structures Peer-reviewed

Nozomi Kimura, Shotaro Nakayama, Katsuhiro Tsukimura, Shinko Miwa, Atsushi Okamoto, Toshiaki Masuda

JOURNAL OF STRUCTURAL GEOLOGY　32　(2)　136-150　2010/02

DOI： 10.1016/j.jsg.2009.10.008 　

ISSN： 0191-8141
Visualization of three dimensional channeling flow in fracture system by new concept model simulator, GeoFlow.

T. Ishibashi, N. Watanabe, N. Hirano, A. Okamoto, N. Tsuchiya

Proceedings of G-COE Symposium 2010 Dynamic Earth and Heterogeneous Structure　2010
Observation of quartz fracturing under the hydrothermal condition using visible type autoclave Peer-reviewed

N. Hirano, K. Yamamoto, A. Okamoto, N. Tsuchiya

WATER-ROCK INTERACTION (WRI-13)　13　653-656　2010
Precipitation of silica minerals in hydrothermal flow-through experiments Peer-reviewed

H. Saishu, A. Okamoto, N. Tsuchiya

WATER-ROCK INTERACTION (WRI-13)　13　669-672　2010
Experimental Study to Detect Organic Matter and Microbes in Fluid Isolated in a Rock without Contamination Peer-reviewed

Yasutaka Nakajima, Nobuo Hirano, Koichi Suto, Atsushi Okamoto, Chihiro Inoue, Noriyoshi Tsuchiya

J. Geochem Res. Soc. Japan　32　(1)　41-48　2010/01
Publisher:
DOI： 10.11367/grsj.32.41 　

ISSN： 0388-6735
Three dimensional analysis of channeling flow by new discrete fracture network model simulator, GeoFlow

T. Ishibashi, N. Watanabe, N. Hirano, A. Okamoto, N. Tsuchiya

Proceedings of the 15th Formation Evaluation Symposium of Japan　N1-N6　2009/10
Velocity of vertical fluid ascent within vein-forming fractures Peer-reviewed

Atsushi Okamoto, Noriyoshi Tsuchiya

GEOLOGY　37　(6)　563-566　2009/06

DOI： 10.1130/G25680A.1 　

ISSN： 0091-7613

eISSN： 1943-2682
A propose for a parallelogram rule for indentation deformation in minerals

Masuda Toshiaki, Sakurai Ryouko, Miyake Tomoya, Ymanouchi Mirai, Omori Yasutomo, Harigane Yumiko, Okamoto Atsushi

Annual Meeting of the Geological Society of Japan　2009　208-208　2009
Publisher: The Geological Society of Japan
DOI： 10.14863/geosocabst.2009.0.208.0 　

ISSN： 1348-3935

eISSN： 2187-6665
Development of discrete fracture network model simulator, GeoFlow, for evaluation of three dimensional channeling flow Peer-reviewed

T. Ishibashi, N. Watanabe, N. Hirano, A. Okamoto, N. Tsuchiya

Society of Petroleum Engineers - International Petroleum Technology Conference 2009, IPTC 2009　1　352-357　2009
Magnitude of sigma(1), sigma(2), and sigma(3) at mid-crustal levels in an orogenic belt: Microboudin method applied to an impure metachert from Turkey Peer-reviewed

Toshiaki Masuda, Shotaro Nakayama, Nozomi Kimura, Atsushi Okamoto

TECTONOPHYSICS　460　(1-4)　230-236　2008/11

DOI： 10.1016/j.tecto.2008.08.025 　

ISSN： 0040-1951

eISSN： 1879-3266
Precipitation of Silica Minerals by Hydrothermal Flow-Through Experiments at 200-430 °C and 30 MPa Peer-reviewed

Atsushi Okamoto, Hanae Saishu, Nobuo Hirano, Atsushi Okamoto, Hanae Saishu, Nobuo Hirano

Transactions of Geothermal Resources Counsil　32　389-392　2008/10
Variations in stable isotope compositions (delta C-13, delta O-18) of calcite within exhumation-related veins from the Sanbagawa metamorphic belt Peer-reviewed

Keisuke Morohashi, Atsushi Okamoto, M. Satish-Kumar, Noriyoshi Tsuchiya

JOURNAL OF MINERALOGICAL AND PETROLOGICAL SCIENCES　103　(5)　361-364　2008/10

DOI： 10.2465/jmps.080620b 　

ISSN： 1345-6296

eISSN： 1349-3825
Mineral distribution within polymineralic veins in the Sanbagawa belt, Japan: implications for mass transfer during vein formation Peer-reviewed

Atsushi Okamoto, Taketo Kikuchi, Noriyoshi Tsuchiya

CONTRIBUTIONS TO MINERALOGY AND PETROLOGY　156　(3)　323-336　2008/09

DOI： 10.1007/s00410-008-0288-y 　

ISSN： 0010-7999
Kinetics and textural development of quartz veins Peer-reviewed

Atsushi Okamoto, Noriyoshi Tsuchiya

GEOCHIMICA ET COSMOCHIMICA ACTA　72　(12)　A703-A703　2008/07

ISSN： 0016-7037

eISSN： 1872-9533
Precipitation of silica by hydrothermal flow-through experiments

Okamoto Atsushi, Hirano Nobuo, Tsuchiya Noriyoshi

Abstracts for Annual Meeting of Japan Association of Mineralogical Sciences　2008　13-13　2008
Publisher: Japan Association of Mineralogical Sciences
DOI： 10.14824/jakoka.2008.0.13.0 　

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We conducted hydrothermal flow-through experiments to observe silica precipitation on granite substrates so as to understand the controls and mechanism of textural development of quartz veins. The precipitation conditions were 400-430 degreeC and 31 MPa, at which quartz solubility, CSi, ,qtz,eq is 80-100 ppm. The various Si-saturated solutions were initially created by dissolution of sands of quartz, amorphous silica and granite at 350-370 degreeC. It is revealed that the precipitated silica species (quartz, cristobalite and amorphous silica) and their textures generally vary depending on Si concentration in the solution and precipitation sites, indicating that the texture of natural quartz veins is suggestive of chemical compositions of the solutions during vein formation.
Effect of lithology on calcite-vein formation in the Sanbagawa metamorphic rocks Peer-reviewed

K. Morohashi, A. Okamoto, N. Tsuchiya

WATER DYNAMICS　987　119-122　2008

DOI： 10.1063/1.2896955 　

ISSN： 0094-243X
Variable microstructure of peridotite samples from the southern Mariana Trench: Evidence of a complex tectonic evolution Peer-reviewed

Katsuyoshi Michibayashi, Miki Tasaka, Yasuhiko Ohara, Teruaki Ishii, Atsushi Okamoto, Patricia Fryer

TECTONOPHYSICS　444　(1-4)　111-118　2007/11

DOI： 10.1016/j.tecto.2007.08.010 　

ISSN： 0040-1951
Vermicular chlorite

KAMEDA J., OKAMOTO A., JIGE M

Abstracts for Annual Meeting of Japan Association of Mineralogical Sciences　2007　224-224　2007/09/22
Publisher: Japan Association of Mineralogical Sciences
DOI： 10.14824/jakoka.2007.0.216.0 　

ISSN： 1348-6543
Cessation of plastic deformation during exhumation of metamorphic tectonites revealed by microboudinage structures Peer-reviewed

Toshiaki Masuda, Nozomi Kimura, Atsushi Okamoto, Tomoya Miyake, Yasutomo Omori

JOURNAL OF STRUCTURAL GEOLOGY　29　(1)　159-165　2007

DOI： 10.1016/j.jsg.2006.06.019 　

ISSN： 0191-8141
Mineral growth within fluid-filled cracks: Example of polymineralic Veins from the Sanbagawa metamorphic belt, Japan Peer-reviewed

A. Okamoto, T. Kikuchi, N. Tsuchiya

AIP Conference Proceedings　898　(898)　8-11　2007

DOI： 10.1063/1.2721240 　

ISSN： 0094-243X 1551-7616
Reaction progress related to indentation structures at glaucophane/ glaucophane contacts in an impure marble from Syros, Greece Peer-reviewed

A. Okamoto, T. Miyake, T. Masuda

Journal of Metamorphic Geology　24　(8)　703-713　2006/10

DOI： 10.1111/j.1525-1314.2006.00663.x 　

ISSN： 0263-4929 1525-1314
Seismic anisotropy in the uppermost mantle, back-arc region of the northeast Japan arc: Petrophysical analyses of Ichinomegata peridotite xenoliths Peer-reviewed

Katsuyoshi Michibayashi, Natsue Abe, Atsushi Okamoto, Takako Satsukawa, Kenta Michikura

GEOPHYSICAL RESEARCH LETTERS　33　(10)　2006/05

DOI： 10.1029/2006GL025812 　

ISSN： 0094-8276
O-178 Structual analyses of Imono peridotite body in the Sanbagawa belt, central Shikoku

Tasaka Miki, Michibayashi Katsuyoshi, Okamoto Atsushi

Annual Meeting of the Geological Society of Japan　2006　132-132　2006
Publisher: The Geological Society of Japan
DOI： 10.14863/geosocabst.2006.0_132_1 　
O-197 Dynamics of the southernmost Mariana mantle wedge : Insights from peridotites dredged from Challenger Deep

Michibayashi K., Ohara Y., Tasaka M., Kuroda T., Okamoto A., Ishii T.

Annual Meeting of the Geological Society of Japan　2006　141-141　2006
Publisher: The Geological Society of Japan
DOI： 10.14863/geosocabst.2006.0_141_2 　
O-115 Microstructure of mineral veins in Creaceous Shimanto complexes observed by SEM-CL

Kikuchi Taketo, Okamoto Atsushi, Tsuchiya Noriyoshi

Annual Meeting of the Geological Society of Japan　2006　100-100　2006
Publisher: The Geological Society of Japan
DOI： 10.14863/geosocabst.2006.0_100_2 　
O-180 Fluid migration recorded in microstructures of sealed cracks from the Sanbagawa metamorphic belt

Annual Meeting of the Geological Society of Japan　2006　133-133　2006
Publisher: The Geological Society of Japan
DOI： 10.14863/geosocabst.2006.0_133_1 　
O-199 Application of Differential Thermodynamic Forward Modeling for Retrograde Hydration Reactions

Kuwatani Tatsu, Toriumi Mitsuhiro, Okamoto Atsushi, Katayama Ikuo

Annual Meeting of the Geological Society of Japan　2006　142-142　2006
Publisher: The Geological Society of Japan
DOI： 10.14863/geosocabst.2006.0_142_2 　
P-81 Microboudin method for palaeostress analysis of tourmaline-bearing pelitic rock from the Ryoke metamorphic belt in the Yanai district : comparison to the absolute magnitude of palaeodifferential stress of the Sambagawa metamorphic belt

Kimura Nozomi, Okudaira Takamoto, Okamoto Atsushi, Masuda Toshiaki

Annual Meeting of the Geological Society of Japan　2006　208-208　2006
Publisher: The Geological Society of Japan
DOI： 10.14863/geosocabst.2006.0_208_2 　
Rapid growth of garnet within a metamorphic vein inferred from misorientation angle porphyroblasts Peer-reviewed

Atsushi Okamoto, Katsuyoshi Michibayashi

WATER DYNAMICS　833　167-+　2006

ISSN： 0094-243X
Progressive shape evolution of a mineral inclusion under differential stress at high temperature : Example of garnet inclusions within a granulite-facies quartzite from the Lützow-Holm Complex, East Antarctica

Okamoto Atsushi, Michibayashi Katsuyoshi

Journal of Geophysical Research　110　B11203　2005/11/04
Publisher: American Geophysical Union
DOI： 10.1029/2004JB003526 　

ISSN： 0148-0227
Progress of actinolite-forming reactions in mafic schists during retrograde metamorphism: An example from the Sanbagawa metamorphic belt in central Shikoku, Japan Peer-reviewed

A. Okamoto, M. Toriumi

Journal of Metamorphic Geology　23　(5)　335-356　2005/06

DOI： 10.1111/j.1525-1314.2005.00580.x 　

ISSN： 0263-4929
Volume holographic recording with spatial spread-spectrum multiplexing technique

T. Ito, A. Okamoto

Optics InfoBase Conference Papers　2005
Publisher: Optical Society of America (OSA)
DOI： 10.1364/isom_ods.2005.mp20 　

ISSN： 2162-2701
Triaxial stress state deep in orogenic belts: An example from Turkey Peer-reviewed

T. Masuda, S. Nakayama, N. Kimura, K. Onodera, A. Okamoto

Journal of Structural Geology　26　(12)　2203-2209　2004/12

DOI： 10.1016/j.jsg.2004.06.005 　

ISSN： 0191-8141
Application of Gibbs Method to Amphibole

OKAMOTO Atsushi

J. Geogr.　113　(5)　587-599　2004/10/25
Publisher: Tokyo Geographical Society
DOI： 10.5026/jgeography.113.5_587 　

ISSN： 0022-135X

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The differential thermodynamic method (Gibbs method) is applied to amphibole zonings in a metabasaltic system. A common mineral assemblage in metabasites (amphibole+epidote+ plagioclase+chlorite+quartz water) is analyzed in the system of SiO₂-Al₂O₃-Fe₂O₃-FeO-MgO-CaO-Na₂O-H₂O. Because the number of end-members of amphibole is larger than the degree of thermodynamic freedom, we can estimate pressure-temperature conditions solely from amphibole chemistries. Analyses for numerous amphiboles from Sanbagawa schists show stable P-T fields of calcic and subcalcic amphiboles, and reveal that typical zoning of the albitebiotite zone (barroisite-hornblende-actinolite) yields the decompression P-T path.<BR>The gibbs method analysis minimizes systematic uncertainty when choosing the equilibrium set of mineral compositions, because the compositionset of coexisting minerals are not needed for the analysis. On the other hand, the propagated random uncertainty for calculated dT and dP becomes larger, as the change of monitor parameter becomes larger. To obtain accurate P-T paths, an appropriate way of minimizing total uncertainty is requied.
Orientation contrast images of garnet in granulite-facies quartzite, Lutzow-Holm Complex, East Antarctica Peer-reviewed

Michibayashi, K, Okamoto, A, Masuzawa, T, Kawakami, T, Ikeda, T, Yasuda, H

The Journal of the Geological Society of Japan　110　(3)　V-VI　2004/03
Publisher: The Geological Society of Japan
DOI： 10.5575/geosoc.110.3.V_VI 　

ISSN： 0016-7630
O-223 The degree of hydration in mafic schists during retrograde metamorphism

Okamoto Atsushi

Annual Meeting of the Geological Society of Japan　2004　137-137　2004
Publisher: The Geological Society of Japan
DOI： 10.14863/geosocabst.2004.abst.0_137_1 　
P-215 Water production rates during subduction of oceanic crust estimated by forward model

Kuwatani Tatsu, Okamoto Atsushi, Toriumi Mitsuhiro

Annual Meeting of the Geological Society of Japan　2004　267-267　2004
Publisher: The Geological Society of Japan
DOI： 10.14863/geosocabst.2004.abst.0_267_1 　
O-139 Estimate of the stress exponent for the power-law rheology of quartz from stress-strain analysis of naturally deformed metachert

Masuda T, Nakayama S, Kimura N, Kugimiya Y, Okamoto A

Annual Meeting of the Geological Society of Japan　2004　95-95　2004
Publisher: The Geological Society of Japan
DOI： 10.14863/geosocabst.2004.abst.0_95_1 　
Optimal mixing properties of calcic and subcalcic amphiboles: Application of Gibbs' method to the Sanbagawa schists, SW Japan Peer-reviewed

A. Okamoto, M. Toriumi

Contributions to Mineralogy and Petrology　146　(5)　529-545　2004/01

DOI： 10.1007/s00410-003-0526-2 　

ISSN： 0010-7999
Uncertainties in P-T paths estimated by Gibbs' method

Okamoto Atsushi

Annual Meeting of the Geological Society of Japan　2003　289-289　2003
Publisher: The Geological Society of Japan
DOI： 10.14863/geosocabst.2003.0_289_1 　
Application of differential thermodynamics (Gibbs' method) to amphibole zonings in the metabasic system Peer-reviewed

Atsushi Okamoto, Mitsuhiro Toriumi

Contributions to Mineralogy and Petrology　141　(3)　268-286　2001
Publisher: Springer Verlag
DOI： 10.1007/s004100100242 　

ISSN： 0010-7999

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Misc. 77

Transient fluid flow recorded in the Crust-Mantle transition zone of the Oman Ophiolite

Kazuki Yoshida, Ryosuke Oyanagi, Masao Kimura, Oliver Plümper, Mayuko Fukuyama, Atsushi Okamoto

2023/05/15

DOI： 10.5194/egusphere-egu23-8443 　
Machine-learning application to igneous and metamorphic rock compositions: Quantitative estimation of compositional changes recorded in subduction-related metamorphic rocks

松野哲士, 宇野正起, 岡本敦

日本地球化学会年会要旨集(Web)　70th　2023
Mineralogical and textural diversity induced by water-rock interaction within a hydrated ductile shear zone occurred in the vicinity of the Moho in oceanic plate

夏目樹, 纐纈佑衣, 道林克禎, 岡本敦

日本地質学会学術大会(Web)　130th　2023

ISSN： 2187-6665
Rapid fluid infiltration recorded in the brucite-rich reaction zone along the antigorite veins from the Oman ophiolite

Kazuki Yoshida, Atsushi Okamoto, Ryosuke Oyanagi, Masao Kimura

2022/03/27
Publisher: Copernicus {GmbH}
DOI： 10.5194/egusphere-egu22-3483 　
Intensity evaluation of of element transfer and its controlling parameters: Differences between Northwest and South Pacific oceanic plates.

松野哲士, 宇野正起, 岡本敦

日本地質学会学術大会(Web)　129th　2022

ISSN： 2187-6665
Fluid and carbon cycling in the shallow forearc mantle revealed by serpentinized peridotite from hadal seafloor

大柳良介, 大柳良介, 岡本敦, SATISH-KUMAR Madhusoodhan, 南雅代, 針金由美子, 道林克禎, 道林克禎

日本地球惑星科学連合大会予稿集(Web)　2022　2022
LILE mobility at each metamorphic stage recorded in the Sanbagawa metamorphic belt: Application of Protolith Reconstruction Model

松野哲士, 宇野正起, 岡本敦, 土屋載芳

日本鉱物科学会年会講演要旨(Web)　2021　2021
Fracturing in paleo-mantle wedge serpentinite at high pore fluid pressures and implications for cycles of deep slow earthquakes

平内健一, 永田有里奈, 大柳良介, 岡本敦, 道林克禎

日本地質学会学術大会(Web)　128th　2021

ISSN： 2187-6665
Multiphase “former supercritical” fluid inclusion originated from the high-temperature pre-Sanbagawa metamorphism

Yoshida Kenta, Okamoto Atsushi, Niwa Yasuhiro, Kimura Masao, Oyanagi Ryosuke, Sawada Hikaru, Niki Sota, Yoshida Kazuki

Annual Meeting of the Geological Society of Japan　2021　211　2021
Publisher: The Geological Society of Japan
DOI： 10.14863/geosocabst.2021.0_211 　

ISSN： 1348-3935

eISSN： 2187-6665
Estimation of mass transfer and protolith composition for mafic metamorphic rocks using machine learning

松野哲士, 宇野正起, 岡本敦, 土屋範芳

日本地球惑星科学連合大会予稿集(Web)　2020　2020
Dehydration, volume change and element transport during carbonation of mantle wedge

岡本敦, 大柳良介, 吉田一貴, 宇野正起, SATISH-KUMAR M.

日本鉱物科学会年会講演要旨(Web)　2020　2020
Formation of amorphous silica particles and its influences on permeability of granite fractures in supercritical geothermal environments

阿部光, 渡邉則昭, 中村謙吾, 岡本敦, 駒井武

日本地熱学会学術講演会講演要旨集　2020　2020
Technology for evaluating supercritical geothermal resources and drilling bit life using artificial intelligence-Resource evaluation using artificial intelligence

石塚師也, 山谷祐介, 渡邉教弘, 岡本京祐, 村田泰章, 浅沼宏, 鈴木浩一, 小林洋介, 岡本敦, 鈴木杏奈, 茂木透, 北村圭吾, 梶原竜哉, 杉本健, 齋藤遼一

日本地熱学会学術講演会講演要旨集　2020　2020
AIによる超臨界地熱資源評価技術

渡邉教弘, 山谷祐介, 岡本京祐, 村田泰章, 浅沼宏, 鈴木浩一, 小林洋介, 岡本敦, 鈴木杏奈, 茂木透, 石塚師也, 北村圭吾, 梶原竜哉, 杉本健, 斎藤遼一

日本地熱学会学術講演会講演要旨集　2019　2019
多成分溶液の光散乱現象を用いた臨界点決定方法の実験的研究

平野伸夫, 大島悠太, 岡本敦, 土屋範芳

日本地球惑星科学連合大会予稿集(Web)　2019　ROMBUNNO.SCG58‐P04 (WEB ONLY)　2019
機械学習を用いた地熱地域の温度構造推定手法の開発

石塚師也, 小林洋介, 宇郷翼, 鈴木浩一, 茂木透, 渡邉教弘, 山谷祐介, 岡本京祐, 村田泰章, 浅沼宏, 鈴木杏奈, 岡本敦, 土屋範芳, 北村圭吾, 梶原竜哉, 杉本健, 斎藤遼一

資源・素材(Web)　2019　ROMBUNNO.3K0701‐08‐05 (WEB ONLY)　2019
数値シミュレーションと組み合わせた構造解析による蛇紋岩の形成メカニズム推定

宮澤美幸, 鈴木杏奈, 岡本敦, 清水浩之, 大林一平, 平岡裕章, 平岡裕章, 伊藤高敏

日本地質学会学術大会講演要旨　125th　116　2018/09

ISSN： 1348-3935
海洋底蛇紋岩作用におけるSi交代作用の律速過程

大柳良介, 岡本敦, 土屋範芳

日本地質学会学術大会講演要旨　125th　51　2018/09/01

ISSN： 1348-3935
超臨界条件の岩石‐水相互作用と斜長石の溶解・析出

岡本敦, 天谷宇志, 大柳良介, NURDIANA Astin, 土屋範芳

日本地質学会学術大会講演要旨　125th　114　2018/09/01

ISSN： 1348-3935
CO₂地中貯留条件下における火山性砂岩の力学特性変化

服部晃己, 渡邉則昭, 岡本敦, 中村謙吾, 駒井武, 玉川哲也

石油技術協会誌　83　(4)　286　2018/07

ISSN： 0370-9868
世界の超高温地熱システムの特徴

岡本京祐, 石橋琢也, 最首花恵, 山谷祐介, 柳澤教雄, 渡邉教弘, 浅沼宏, 茂木透, 石塚師也, 土屋範芳, 岡本敦, 長縄成実, 小川康雄, 藤光康宏, 北村圭吾, 梶原竜哉, 堀本誠記, 島田邦明

日本地熱学会学術講演会講演要旨集　2018　2018
事例調査に基づく各国超臨界地熱システムのモデル化と比較

岡本京祐, 浅沼宏, 柳澤教雄, 山谷祐介, 渡邉教弘, 石橋琢也, 最首花恵, 茂木透, 石塚師也, 土屋範芳, 岡本敦, 長縄成実, 小川康雄, 藤光康宏, 北村圭吾, 梶原竜哉, 堀本誠記, 島田邦明

日本地球惑星科学連合大会予稿集(Web)　2018　2018
高温延性花崗岩き裂における圧力溶解・自由表面溶解による透水性変化

斎藤耕平, 渡邉則昭, 岡本敦, 土屋範芳, 駒井武, 石橋琢也, 最首花恵, 渡邉教弘

日本地熱学会学術講演会講演要旨集　2018　2018
CO₂地中貯留条件下における火山性砂岩の力学特性変化

服部晃己, 渡邉則昭, 岡本敦, 中村謙吾, 駒井武, 玉川哲也

石油技術協会特別講演会・春季講演会(シンポジウム・個人講演)要旨集　2018　2018
Estimation of Nonlinear Dynamics in Heterogeneous Reactions Using Sequential Monte Carlo Method

61　5p　2017/05/23
Publisher: システム制御情報学会
Silica precipitation induced by flash vaporization from sub- to supercritical conditions

天谷宇志, 岡本敦, 平野伸夫, 最首花恵, 土屋範芳

日本鉱物科学会年会講演要旨(Web)　2017　ROMBUNNO.S2‐07 (WEB ONLY)　2017
減圧沸騰による岩石の破壊現象と弾性波速度変化

平野伸夫, 青島聡, 岡本敦, 土屋範芳

日本鉱物科学会年会講演要旨集　2016　29　2016/09/16

ISSN： 1348-6543
Fluid volumes and rates for the formation of mineral veins around the seismogenic megasplay fault Nobeoka Thrust, southwestern Japan

Otsubo Makoto, Saishu Hanae, Okamoto Atsushi, Miyakawa Ayumu

Annual Meeting of the Geological Society of Japan　2016　(0)　2016
Publisher: The Geological Society of Japan
ISSN： 1348-3935
蔵王火山で過去100年間に見られた活発化と現在の状況

後藤章夫, 土屋範芳, 平野伸夫, 渡邊隆広, 松中哲也, 久利美和, 宇野正起, 岡本敦, 中村謙吾, 町澄秋

日本地球惑星科学連合大会予稿集(Web)　2016　ROMBUNNO.SVC47‐P04 (WEB ONLY)　2016
吸水反応における多結晶体の力学的応答―CaSO₄‐H₂O系における反応誘起応力・歪の実験的研究―

宇野正起, 増田俊太郎, 平野伸夫, 岡本敦, 土屋範芳

日本地球惑星科学連合大会予稿集(Web)　2016　ROMBUNNO.SCG63‐05 (WEB ONLY)　2016
減圧沸騰環境下における岩石の破壊現象

平野伸夫, 青島聡, 岡本敦, 土屋範芳

日本鉱物科学会年会講演要旨集　2015　12　2015/09/18

ISSN： 1348-6543
超臨界水熱環境下での減圧沸騰に伴う岩石破壊に関する実験的研究

青島聡, 平野伸夫, 岡本敦, 土屋範芳

日本地熱学会学術講演会講演要旨集　2015　A16　2015
東北地方太平洋沖地震による津波堆積物の微量元素含量

山崎慎一, 渡邊隆広, 岡本敦, 平野伸夫, 山田亮一, 布原啓史, 土屋範芳

日本土壌肥料学会講演要旨集　60　(60)　252-252　2014/09/09
Publisher: 一般社団法人日本土壌肥料学会
ISSN： 0288-5840
加速器質量分析法によるSND7ジオスライサー試料から採取した植物残渣の¹⁴C年代測定―仙台平野・津波堆積物の年代測定―

渡邊隆広, 細田憲弘, 土屋範芳, 中村俊夫, 澤井祐紀, 駒井武, 岡本敦, 平野伸夫, 奈良郁子

名古屋大学加速器質量分析計業績報告書　25　97-102　2014/03
Publisher: 名古屋大学年代測定資料研究センター
Water-rock interaction around brittle-ductile transition within geothermal areas

36　(2)　63-67　2014/02
Publisher: 海洋出版
ISSN： 0387-3498
高温高圧熱水環境下での減圧沸騰による岩石破壊現象の実験的検討

平野伸夫, 青島聡, 笠原尚也, 岡本敦, 土屋範芳

日本地熱学会学術講演会講演要旨集　2014　A04　2014
仙台平野・静岡平野における津波堆積物の汚染評価と化学判別

渡邊隆広, 土屋範芳, 井上千弘, 北村晃寿, 駒井武, 山崎慎一, 山田亮一, 平野伸夫, 岡本敦, 細田憲弘, 奈良郁子

日本鉱物科学会年会講演要旨集　2013　20-20　2013/09/05

ISSN： 1348-6543
分光計測を用いた(H₂O‐(CO₂)‐NaCl)系の臨界現象の観察と臨界点の決定

関口知寿, 平野伸夫, 岡本敦, 土屋範芳

日本鉱物科学会年会講演要旨集　2013　42-42　2013/09/05

ISSN： 1348-6543
流体相変化による析出シリカ鉱物の産状とき裂間隙構造の発達プロセス

山田稜, 岡本敦, 最首花恵, 中村美千彦, 奥村聡, 佐々木理, 土屋範芳

日本鉱物科学会年会講演要旨集　2013　2013

ISSN： 1348-6543
流体相変化に伴うシリカの沈殿挙動と鉱物脈形成

山田稜, 岡本敦, 最首花恵, 中村美千彦, 奥村聡, 佐々木理, 土屋範芳

日本地質学会学術大会講演要旨　120th　2013

ISSN： 1348-3935
高温高圧熱水状態からの減圧沸騰による岩石鉱物き裂の発生

平野伸夫, 青島聡, 笠原尚也, 渡邉則明, 岡本敦, 土屋範芳

日本地熱学会学術講演会講演要旨集　2013　103　2013
東北地方太平洋沖地震による津波堆積物の多量元素含量

山崎慎一, 渡邊隆広, 木村和彦, 岡本敦, 平野伸夫, 山田亮一, 布原啓史, 土屋範芳

日本土壌肥料学会講演要旨集　59　(0)　254-254　2013
Publisher: 一般社団法人日本土壌肥料学会
DOI： 10.20710/dohikouen.59.0_254_1 　

ISSN： 0288-5840
分光計測による地殻流体の臨界現象と臨界点の観察に関する実験的研究

関口知寿, 平野伸夫, 岡本敦, 土屋範芳

日本鉱物科学会年会講演要旨集　2012　13-13　2012/09/15
Publisher: Japan Association of Mineralogical Sciences
DOI： 10.14824/jakoka.2012.0_13 　

ISSN： 1348-6543

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Spectroscopic measurements in the range from 350 nm to 1050 nm for pure H₂O, CO₂ and C₂H₅OH fluids under high temperatures and pressures were carried out to observe critical phenomena by using visible-type autoclave. Intensity of transmitted light though the fluid became low drastically around the critical point in both cases of H₂O and C₂H₅OH. Intensity of transmitted light through CO₂ was very low under subcritical condition and was high in supercritical region. Differences between experimentally determined critical temperature and reference data in literature of pure fluids were within ca. 1.6°C, and pressure differences were less than 0.3 MPa.
流体の減圧沸騰による岩石の破壊現象

土屋範芳, 山本啓司, 平野伸夫, 岡本敦

日本鉱物科学会年会講演要旨集　2012　10-10　2012/09/15
Publisher: Japan Association of Mineralogical Sciences
DOI： 10.14824/jakoka.2012.0_10 　

ISSN： 1348-6543

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Veins are defined as mineral aggregates that precipitated from a geofluid. Veins, including igneous dikes, have two meanings for  understanding the Earth processes. One is mineral aggregate and mineral assemblages which could indicate multi-component equilibrium and kinetics of geofluids, and another one is failure of the Earth’s crust.Fluids has great role to create fracture networks as an explosive failure. Recent progress in field observational, experimental and theoretical research concerning "Hydrothermal Brecciation" and "Hydrothermally Derived Fracturing" will be presented.
東日本大震災の津波堆積物を用いた津波堆積物の地球化学的判別方法の開発

土屋範芳, 山崎慎一, 山田亮一, 平野伸夫, 岡本敦, 小川康正, 渡邊隆広

日本地質学会学術大会講演要旨　119th　155-298　2012/09/10
Publisher: The Geological Society of Japan
DOI： 10.14863/geosocabst.2012.0_298 　

ISSN： 1348-3935
東北地方太平洋沖地震による津波堆積物のヒ素とイオウの含量および過酸化水素処理によるpHの変化

山崎慎一, 渡邊隆広, 岡本敦, 平野伸夫, 山田亮一, 小川泰正, 布原啓史, 土屋範芳

日本土壌肥料学会講演要旨集　58　(58)　25-25　2012/09/04
Publisher: 一般社団法人日本土壌肥料学会
ISSN： 0288-5840
東日本大震災被災地域の土壌の諸特性第1報津波堆積物の理化学性

山崎慎一, 小川泰正, 岡本敦, 平野伸夫, 山田亮一, 土屋範芳

日本土壌肥料学会講演要旨集　58　(58)　258-258　2012/09/04
Publisher: 一般社団法人日本土壌肥料学会
ISSN： 0288-5840
GeoFlowによるマルチスケールフラクチャーネットワークの流体流動特性の評価と予測

石橋琢也, 渡邉則昭, 平野伸夫, 岡本敦, 土屋範芳

石油技術協会誌　77　(4)　292　2012/07

ISSN： 0370-9868
Verification of principal stress axis using the microboudin analysis Peer-reviewed

Nishiwaki Shin, Omori Yasutomo, Kimura Nozomi, Okamoto Atsushi, Satsukawa Takako, Michibayashi Katsuyoshi, Masuda Toshiaki

Annual Meeting of the Geological Society of Japan　2012　(0)　425-425　2012
Publisher: The Geological Society of Japan
DOI： 10.14863/geosocabst.2012.0_425 　
熱水環境下における流体の接触または相変化に伴う鉱物の破壊に関する実験的検討

平野伸夫, 山本啓司, 岡本敦, 渡邉則昭, 土屋範芳

日本地熱学会学術講演会講演要旨集　2012　94　2012
3Dチャネリングフローのモデリング手法とフィールドスケールへの拡張

石橋琢也, 渡邉則昭, 平野伸夫, 岡本敦, 土屋範芳, 玉川哲也

日本地熱学会学術講演会講演要旨集　2012　106　2012
分光計測を用いた地熱流体の臨界点計測に関する基礎的研究

関口知寿, 平野伸夫, 岡本敦, 土屋範芳

日本地熱学会学術講演会講演要旨集　2012　30　2012
In situ observation of crystallization pressure induced by halite crystal growth in a microfluidic channel

OKAMOTO Atsushi, SEKINE Kotaro

2011　51-51　2011/09/05

ISSN： 1348-6543
Hydration by intrusion of pegmatitic vein : An example in Sor Rodane Mountains, East Antarctica

TSUCHIYA N, ISHIKAWA M, KIMAR Satish, KAWAKAMI T, GRANTHAM Geoff, MEGURO Y, OKAMOTO A

Abstracts for Annual Meeting of Japan Association of Mineralogical Sciences　2011　9-9　2011/09/05
Publisher: Japan Association of Mineralogical Sciences
DOI： 10.14824/jakoka.2011.0.9.0 　

ISSN： 1348-6543

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We observed magma-driven hydraulic fracturing and fluid infiltration in the Sor Rondane Mountains, East Antarctica. We studied homogeneous temperature and salinity of fluid inclusions, hydration reaction process of metamorphic minerals, and mineral assemblages of host and vein rocks. According those observation and measurements formation of microcrack around magmatic vein had dominant role to input geofluids into the host rocks from pegmatitic vein rather than homogeneous diffusion in matrix.
東日本大震災の津波堆積物の性質とリスク評価(第一報)

土屋範芳, 山崎慎一, 山田亮一, 平野伸夫, 岡本敦, 小川康正, 渡邊隆広

日本地質学会学術大会講演要旨　118th　144　2011/09/05

DOI： 10.14863/geosocabst.2011.0.311.0 　

ISSN： 1348-3935
封圧下におけるフラクチャー内流体流動のマルチスケールモデリング

石橋琢也, 渡邉則昭, 平野伸夫, 岡本敦, 土屋範芳

石油技術協会誌　76　(4)　358　2011/07

ISSN： 0370-9868
高温岩石への高温流体接触によるブレッチャ形成の可能性とその応用

平野伸夫, 山本啓司, 岡本敦, 土屋範芳

日本地熱学会学術講演会講演要旨集　2011　86　2011
二次元フラクタル則による岩石き裂内流体流動モデルのスケールアップ

石橋琢也, 渡邉則昭, 平野伸夫, 岡本敦, 土屋範芳

日本地熱学会学術講演会講演要旨集　2011　54　2011
花崗岩フラクチャーの間隙構造における寸法依存性の評価

石橋琢也, 渡邉則昭, 平野伸夫, 岡本敦, 土屋範芳

石油技術協会誌　75　(4)　314-315　2010/07

ISSN： 0370-9868
シリカ鉱物析出反応速度とき裂の閉塞プロセス

最首花恵, 岡本敦, 平野伸夫, 土屋範芳

日本地熱学会学術講演会講演要旨集　2010　43　2010
奥奥八九朗温泉における炭酸塩堆積物形成の実験的検討

平野伸夫, 竹之下愛, 山田亮一, 岡本敦, 土屋範芳

日本鉱物科学会年会講演要旨集　2010　55-55　2010

DOI： 10.14824/jakoka.2010.0.55.0 　

ISSN： 1348-6543
温泉水からの炭酸塩シンター形成の実験的検討―秋田県奥奥八九朗温泉を例として―

平野伸夫, 竹之下愛, 岡本敦, 土屋範芳, 山田亮一

日本地熱学会学術講演会講演要旨集　2010　71　2010
地熱を利用した硫化鉱物脱硫の水熱反応システム

雪下隼, 土屋範芳, 平野伸夫, 岡本敦

日本地熱学会学術講演会講演要旨集　2010　46　2010
熱水条件下での石英フラクチャリングに関する実験的検討

山本啓司, 平野伸夫, 岡本敦, 土屋範芳

日本地熱学会学術講演会講演要旨集　2010　37　2010
鉱物‐流体界面における二酸化炭素の分子挙動

土屋範芳, 古川俊輔, 平野伸夫, 岡本敦

日本鉱物科学会年会講演要旨集　2010　54　2010

DOI： 10.14824/jakoka.2010.0.54.0 　

ISSN： 1348-6543
三次元チャネリングフロー解析のためのDFNモデルシミュレータ“GeoFlow”の開発

石橋琢也, 渡邉則昭, 平野伸夫, 岡本敦, 土屋範芳

石油技術協会誌　74　(5)　507-508　2009/09

ISSN： 0370-9868
水熱反応によるシリカ鉱物析出様式と組織発達

岡本敦, 最首花恵, 平野伸夫, 土屋範芳

日本地質学会学術大会講演要旨　116th　139　2009/09/01

ISSN： 1348-3935
地殻流体からのシリカ鉱物析出速度

最首花恵, 岡本敦, 平野伸夫, 土屋範芳

日本地質学会学術大会講演要旨　116th　263　2009/09/01

DOI： 10.14863/geosocabst.2009.0.512.0 　

ISSN： 1348-3935
三次元チャネリングフロー解析のためのDFNモデルシミュレータ“GeoFlow”の開発

石橋琢也, 渡邉則昭, 平野伸夫, 岡本敦, 土屋範芳

石油技術協会誌　74　(4)　370　2009/07

ISSN： 0370-9868
O-215 Fluid migration inferred from isotope compositions of calcite-bearing veins in Sanbagawa metamorphic belt

Morohashi Keisuke, Okamoto Atsushi, Mudhusoodhan Satish-Kumar, Tsuchiya Noriyoshi

115　138-138　2008/09/15
Publisher: The Geological Society of Japan
O-139 Successful application of the microboudin method for palaeo : stress analysis to deformed impure marbles from Syros, Greece

Masuda T., Miyake T., Okamoto A.

115　101-101　2008/09/15
Publisher: The Geological Society of Japan
S-59 Brittle failure mineral-filling vein in the Hidaka high grade metamorphic rocks

Tsuchiya Noriyoshi, Tanabe Hiroshi, Okamoto Atsushi

114　31-31　2007/09/01
Publisher: The Geological Society of Japan
P-94 Stacking structures of chlorite in a serpentinite-hosted chlorite schist

Kameda J., Okamoto A., Kawabata K.

114　262-262　2007/09/01
Publisher: The Geological Society of Japan
流通式反応器を用いた石英の溶解・析出実験

岡本敦, 平野伸夫, 渡辺則昭, 土屋範芳

日本地質学会学術大会講演要旨　114th　298-298　2007/09/01
Publisher: The Geological Society of Japan
DOI： 10.14863/geosocabst.2007.0.584.0 　

ISSN： 1348-3935
Misorientations of garnet aggregate within a vein: An example from Sanbagawa metamorphic belt, Japan Peer-reviewed

Okamoto, A., Michibayashi, K.

Journal of Metamorphic Geology　24　(5)　353-366　2006/06

DOI： 10.1111/j.1525-1314.2006.00642.x 　

ISSN： 0263-4929 1525-1314
一の目潟カンラン岩ゼノリスの微細構造と地震波特性

佐津川貴子, 道林克禎, 阿部なつ江, 岡本敦

日本地質学会学術大会講演要旨　113th　2006

ISSN： 1348-3935
Progressive shape evolution of a mineral inclusion under differential stress at high temperature: Example of garnet inclusions within a granulite-facies quartzite from the Lutzow-Holm Complex, East Antarctica Peer-reviewed

Okamoto A, Michibayashi K

JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH　110　(B11)　1-16　2005/11/04

DOI： 10.1029/2004JB003526 　

ISSN： 2169-9313

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Books and Other Publications 1

沈み込み帯の含水マントルの炭酸塩化作用ー自己促進的な反応ー破壊カップリング現象ー

岡本敦

月刊地球「スロー地震に関する地質学的・実験的・地震学的研究の連携と進展」　2022

Presentations 46

機械学習を用いた地熱地域の温度構造推定手法の開発

石塚師也, 小林洋介, 宇郷翼, 鈴木浩一, 茂木透, 渡邉教弘, 山谷祐介, 岡本京祐, 村田泰章, 浅沼宏, 鈴木杏奈, 岡本敦, 土屋範芳, 北村圭吾, 梶原竜哉, 杉本健, 斎藤遼一

資源・素材(Web)　2019
多成分溶液の光散乱現象を用いた臨界点決定方法の実験的研究

平野伸夫, 大島悠太, 岡本敦, 土屋範芳

日本地球惑星科学連合大会予稿集(Web)　2019
超臨界条件の水—岩石相互作用の理解のための熱力学データ構築の試み

岡本敦, 大柳良介, 天谷宇志, 土屋範芳

日本地熱学会　2018/11/16
超臨界条件の岩石—水相互作用と斜長石の溶解・析出

岡本敦, 天谷宇志, 大柳良介, Astin Nurdiana, 土屋範芳

日本地球惑星科学連合大会　2018/09/07
超臨界条件の岩石‐水相互作用と斜長石の溶解・析出

岡本敦, 天谷宇志, 大柳良介, NURDIANA Astin, 土屋範芳

日本地質学会学術大会講演要旨　2018/09/01
海洋底蛇紋岩作用におけるSi交代作用の律速過程

大柳良介, 岡本敦, 土屋範芳

日本地質学会学術大会講演要旨　2018/09/01
数値シミュレーションと組み合わせた構造解析による蛇紋岩の形成メカニズム推定

宮澤美幸, 鈴木杏奈, 岡本敦, 清水浩之, 大林一平, 平岡裕章, 平岡裕章, 伊藤高敏

日本地質学会学術大会講演要旨　2018/09
CO₂地中貯留条件下における火山性砂岩の力学特性変化

服部晃己, 渡邉則昭, 岡本敦, 中村謙吾, 駒井武, 玉川哲也

石油技術協会誌　2018/07
岩石―水反応の理解に向けた水熱実験とデータ駆動型アプローチ

岡本敦, 桑谷立, 土屋範芳

日本地球惑星科学連合大会　2018/05/22
地熱地帯の超臨界条件下の岩石ー水相互作用と熱水変成作用の理解に向けて

岡本敦, 根津悠介, 天谷宇志, 土屋範芳

日本地質学会　2018/05/21
Silica nanoparticles produced by flash vaporization and their rapid diagenesis in hydrothermal fluids International-presentation

Atsushi Okamoto

2018/04/10
Some unsolved problems on supercritical water – rock interaction International-presentation

Atsushi Okamoto

International Symposium on Water Dynamics　2018/03/16
Silica precipitation induced by flash vaporization from sub- to supercritical conditions

天谷宇志, 岡本敦, 平野伸夫, 最首花恵, 土屋範芳

日本鉱物科学会年会講演要旨(Web)　2017
減圧沸騰による岩石の破壊現象と弾性波速度変化

平野伸夫, 青島聡, 岡本敦, 土屋範芳

日本鉱物科学会年会講演要旨集　2016/09/16
吸水反応における多結晶体の力学的応答―CaSO₄‐H₂O系における反応誘起応力・歪の実験的研究―

宇野正起, 増田俊太郎, 平野伸夫, 岡本敦, 土屋範芳

日本地球惑星科学連合大会予稿集(Web)　2016
蔵王火山で過去100年間に見られた活発化と現在の状況

後藤章夫, 土屋範芳, 平野伸夫, 渡邊隆広, 松中哲也, 久利美和, 宇野正起, 岡本敦, 中村謙吾, 町澄秋

日本地球惑星科学連合大会予稿集(Web)　2016
Fluid volumes and rates for the formation of mineral veins around the seismogenic megasplay fault Nobeoka Thrust, southwestern Japan

Otsubo Makoto, Saishu Hanae, Okamoto Atsushi, Miyakawa Ayumu

Annual Meeting of the Geological Society of Japan　2016
減圧沸騰環境下における岩石の破壊現象

平野伸夫, 青島聡, 岡本敦, 土屋範芳

日本鉱物科学会年会講演要旨集　2015/09/18
超臨界水熱環境下での減圧沸騰に伴う岩石破壊に関する実験的研究

青島聡, 平野伸夫, 岡本敦, 土屋範芳

日本地熱学会学術講演会講演要旨集　2015
東北地方太平洋沖地震による津波堆積物の微量元素含量

山崎慎一, 渡邊隆広, 岡本敦, 平野伸夫, 山田亮一, 布原啓史, 土屋範芳

日本土壌肥料学会講演要旨集　2014/09/09
加速器質量分析法によるSND7ジオスライサー試料から採取した植物残渣の¹⁴C年代測定―仙台平野・津波堆積物の年代測定―

渡邊隆広, 細田憲弘, 土屋範芳, 中村俊夫, 澤井祐紀, 駒井武, 岡本敦, 平野伸夫, 奈良郁子

名古屋大学加速器質量分析計業績報告書　2014/03
高温高圧熱水環境下での減圧沸騰による岩石破壊現象の実験的検討

平野伸夫, 青島聡, 笠原尚也, 岡本敦, 土屋範芳

日本地熱学会学術講演会講演要旨集　2014
分光計測を用いた(H₂O‐(CO₂)‐NaCl)系の臨界現象の観察と臨界点の決定

関口知寿, 平野伸夫, 岡本敦, 土屋範芳

日本鉱物科学会年会講演要旨集　2013/09/05
仙台平野・静岡平野における津波堆積物の汚染評価と化学判別

渡邊隆広, 土屋範芳, 井上千弘, 北村晃寿, 駒井武, 山崎慎一, 山田亮一, 平野伸夫, 岡本敦, 細田憲弘, 奈良郁子

日本鉱物科学会年会講演要旨集　2013/09/05
東北地方太平洋沖地震による津波堆積物の多量元素含量

山崎慎一, 渡邊隆広, 木村和彦, 岡本敦, 平野伸夫, 山田亮一, 布原啓史, 土屋範芳

日本土壌肥料学会講演要旨集　2013
高温高圧熱水状態からの減圧沸騰による岩石鉱物き裂の発生

平野伸夫, 青島聡, 笠原尚也, 渡邉則明, 岡本敦, 土屋範芳

日本地熱学会学術講演会講演要旨集　2013
流体の減圧沸騰による岩石の破壊現象

土屋範芳, 山本啓司, 平野伸夫, 岡本敦

日本鉱物科学会年会講演要旨集　2012/09/15
分光計測による地殻流体の臨界現象と臨界点の観察に関する実験的研究

関口知寿, 平野伸夫, 岡本敦, 土屋範芳

日本鉱物科学会年会講演要旨集　2012/09/15
東日本大震災の津波堆積物を用いた津波堆積物の地球化学的判別方法の開発

土屋範芳, 山崎慎一, 山田亮一, 平野伸夫, 岡本敦, 小川康正, 渡邊隆広

日本地質学会学術大会講演要旨　2012/09/10
東日本大震災被災地域の土壌の諸特性第1報津波堆積物の理化学性

山崎慎一, 小川泰正, 岡本敦, 平野伸夫, 山田亮一, 土屋範芳

日本土壌肥料学会講演要旨集　2012/09/04
東北地方太平洋沖地震による津波堆積物のヒ素とイオウの含量および過酸化水素処理によるpHの変化

山崎慎一, 渡邊隆広, 岡本敦, 平野伸夫, 山田亮一, 小川泰正, 布原啓史, 土屋範芳

日本土壌肥料学会講演要旨集　2012/09/04
GeoFlowによるマルチスケールフラクチャーネットワークの流体流動特性の評価と予測

石橋琢也, 渡邉則昭, 平野伸夫, 岡本敦, 土屋範芳

石油技術協会誌　2012/07
分光計測を用いた地熱流体の臨界点計測に関する基礎的研究

関口知寿, 平野伸夫, 岡本敦, 土屋範芳

日本地熱学会学術講演会講演要旨集　2012
3Dチャネリングフローのモデリング手法とフィールドスケールへの拡張

石橋琢也, 渡邉則昭, 平野伸夫, 岡本敦, 土屋範芳, 玉川哲也

日本地熱学会学術講演会講演要旨集　2012
熱水環境下における流体の接触または相変化に伴う鉱物の破壊に関する実験的検討

平野伸夫, 山本啓司, 岡本敦, 渡邉則昭, 土屋範芳

日本地熱学会学術講演会講演要旨集　2012
東日本大震災の津波堆積物の性質とリスク評価(第一報)

土屋範芳, 山崎慎一, 山田亮一, 平野伸夫, 岡本敦, 小川康正, 渡邊隆広

日本地質学会学術大会講演要旨　2011/09/05
Hydration by intrusion of pegmatitic vein : An example in Sor Rodane Mountains, East Antarctica

TSUCHIYA N, ISHIKAWA M, KIMAR Satish, KAWAKAMI T, GRANTHAM Geoff, MEGURO Y, OKAMOTO A

Abstracts for Annual Meeting of Japan Association of Mineralogical Sciences　2011/09/05

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We observed magma-driven hydraulic fracturing and fluid infiltration in the Sor Rondane Mountains, East Antarctica. We studied homogeneous temperature and salinity of fluid inclusions, hydration reaction process of metamorphic minerals, and mineral assemblages of host and vein rocks. According those observation and measurements formation of microcrack around magmatic vein had dominant role to input geofluids into the host rocks from pegmatitic vein rather than homogeneous diffusion in matrix.
封圧下におけるフラクチャー内流体流動のマルチスケールモデリング

石橋琢也, 渡邉則昭, 平野伸夫, 岡本敦, 土屋範芳

石油技術協会誌　2011/07
二次元フラクタル則による岩石き裂内流体流動モデルのスケールアップ

石橋琢也, 渡邉則昭, 平野伸夫, 岡本敦, 土屋範芳

日本地熱学会学術講演会講演要旨集　2011
高温岩石への高温流体接触によるブレッチャ形成の可能性とその応用

平野伸夫, 山本啓司, 岡本敦, 土屋範芳

日本地熱学会学術講演会講演要旨集　2011
花崗岩フラクチャーの間隙構造における寸法依存性の評価

石橋琢也, 渡邉則昭, 平野伸夫, 岡本敦, 土屋範芳

石油技術協会誌　2010/07
熱水条件下での石英フラクチャリングに関する実験的検討

山本啓司, 平野伸夫, 岡本敦, 土屋範芳

日本地熱学会学術講演会講演要旨集　2010
地熱を利用した硫化鉱物脱硫の水熱反応システム

雪下隼, 土屋範芳, 平野伸夫, 岡本敦

日本地熱学会学術講演会講演要旨集　2010
温泉水からの炭酸塩シンター形成の実験的検討―秋田県奥奥八九朗温泉を例として―

平野伸夫, 竹之下愛, 岡本敦, 土屋範芳, 山田亮一

日本地熱学会学術講演会講演要旨集　2010
奥奥八九朗温泉における炭酸塩堆積物形成の実験的検討

平野伸夫, 竹之下愛, 山田亮一, 岡本敦, 土屋範芳

日本鉱物科学会年会講演要旨集　2010
シリカ鉱物析出反応速度とき裂の閉塞プロセス

最首花恵, 岡本敦, 平野伸夫, 土屋範芳

日本地熱学会学術講演会講演要旨集　2010

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Research Projects 31

データ記述科学を用いた材料解析とそのイノベーション展開

木村正雄, 武市泰男, 稲田康宏, 赤木和人, 岡本敦

Offer Organization: 日本学術振興会

System: 科学研究費助成事業

Category: 学術変革領域研究(A)

Institution: 大学共同利用機関法人高エネルギー加速器研究機構

2022/06/16 - 2027/03/31

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本課題では、(1)材料中の組織や化学状態のX線分光顕微鏡による解明、 (2)得られた多次元データの高次元可視化、 (3)様々な物性値の‘かたち’やその‘うごき’の観点から、材料の機能発現や機能劣化の起点（＝“trigger sites”）を特定する数理的アプローチの開発、を進める。今年度は、社会インフラ構造材料の劣化・破壊、およびエネルギー関連材料(電池)の機能発現に加えて、新たな展開領域として地球科学分野の反応解析、を追加した。それぞれの分野での進捗は下記の通り。・航空機用の構造材料である炭素繊維強化プラスチック（CFRP）について、2022年度に確立した放射光X線顕微鏡による観察を進め、亀裂の発生・進展挙動の最大の支配因子である炭素繊維の配列について、パーシステントホモロジーを用いた位相的データ解析による定量化が可能であることを見いだした。さらに亀裂の‘かたち’とその‘うごき’そのものの数理的記述法についても検討をすすめた。・化学状態をマッピングするための硬X線分光顕微鏡の空間分解能を1/10に高度化することに成功し、鉄鉱石（Fe-Ca-Oの複合酸化物）の還元に伴う変化を観察するのに必要な高空間分解能化を実現した。・X線分光顕微鏡を用いて充放電サイクル中のリチウムイオン電池の活物質内の充電相、放電相の‘かたち’の変化をパーシステントホモロジーを用いた位相的データ解析により定量化が可能であることを見いだし、化学種（リチウム）と電子の移動による電気化学反応メカニズムについて検討を進めた。・海洋底岩石圏の鉱物の生成反応について、様々なX線顕微鏡を用いて化学反応に伴う特徴的な鉱物組織の変化の可視化に成功し、それが過去に起こった反応のメカニズム推定に有力な新情報を提供可能であることを確認した。
Generation of CO2 fluid and mantle carbonation in subduction zones

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (S)

Category: Grant-in-Aid for Scientific Research (S)

Institution: Tohoku University

2022/04/27 - 2027/03/31
Spatio-temporal dynamism of fluid pressure and permeability in arc crust

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Scientific Research (B)

Institution: Tohoku University

2022/04/01 - 2027/03/31
Spatio-temporal dynamisms of fluid-pressure and permeability in arc crusts

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)

Category: Grant-in-Aid for Scientific Research (B)

Institution: Tohoku University

2022/04/01 - 2027/03/31
Development of thermoelectric conversion function associated with the development of zonal structure in submarine hydrothermal vents.

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Challenging Research (Exploratory)

Institution: Tohoku University

2024/06/28 - 2026/03/31
Do quartz veins record fluid pressure fluctuations in seismogenic zones? -Verification from synthetic quartz veins

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Transformative Research Areas (A)

Institution: Tohoku University

2024/04/01 - 2026/03/31
Mechanisms of accelerated mineral carbonation through self-promoting reactions

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Research (Exploratory)

Category: Grant-in-Aid for Challenging Research (Exploratory)

Institution: Tohoku University

2022/06/30 - 2025/03/31
Unified understanding of fault friction in subduction zones considering material diversity and diagenesis

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Scientific Research (B)

Institution: The University of Tokyo

2021/04/01 - 2025/03/31
A unified understanding of fault friction in subduction zone considering material diversity and diagenesis

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)

Category: Grant-in-Aid for Scientific Research (B)

Institution: The University of Tokyo

2021/04/01 - 2025/03/31
Exploration of p-type semiconductor chimneys at seafloor based on microstructural analysis and thermoelectric characterization

Okamoto Atsushi

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Research (Exploratory)

Category: Grant-in-Aid for Challenging Research (Exploratory)

Institution: Tohoku University

2022/06/30 - 2024/03/31

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Submarine hydrothermal vents mix hot, reducing hydrothermal fluids with cold, oxidizing seawater to form chimneys composed of sulfates and sulfides. Sulfides are semiconductors and have thermoelectric conversion performance, converting heat to electricity, but no studies have investigated submarine sulfide chimneys. In this study, electrical conductivity and thermal electromotive force were measured for chimneys collected from the Izu-Ogasawara region. As a result, the initial stage of chimney formation is composed of sulfate and ZnS, which has low electrical conductivity, and thermoelectric conversion does not function. As the chimney grows and matures, PbS, CuFeS2, FeS2, etc., which exhibit high electrical conductivity and thermal electromotive force, form around the distribution holes and release electrical energy to the deep-sea floor environment.
Solution chemistry dependency on fluid-rock reactions within subduction zones and its hydrological responses

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research Grant-in-Aid for Transformative Research Areas (A)

Category: Grant-in-Aid for Transformative Research Areas (A)

Institution: Tohoku University

2022/06/16 - 2024/03/31
Permeability behavior in high-temperature ductile crust and prediction of spatiotemporal evolution in supercritical geothermal resource

Watanabe Noriaki

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)

Category: Grant-in-Aid for Scientific Research (B)

Institution: Tohoku University

2017/04/01 - 2022/03/31

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The scale and characteristics of new geothermal resources, "supercritical geothermal resources", which consist of fractured rocks containing supercritical water, are highly dependent on the permeability of the intrusive rocks and its host rocks. On the other hand, it has been suggested that the permeability may change drastically due to changes in mechanical properties or rocks such as the brittle-ductile transition, and fast, nucleation-type precipitation associated with fluid phase changes, but the details are unknown. In this study, we derived model equations of permeability behaviors involving changes in the mechanical properties of rocks and phase changes of fluids through laboratory experiments, and clarified the possibility of a prediction method of spatio-temporal evolution of supercritical geothermal resources by conducting spatio-temporal evolution simulations.
Development of rock texture and fluid generation processes within convergent plate boundary

Atsushi Okamoto

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)

Category: Grant-in-Aid for Scientific Research (B)

Institution: Tohoku University

2017/04/01 - 2021/03/31

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Fluid generation and reaction processes in subduction zones are left as mirostructures of minerals in metamorphic rocks and serpentinites. In this study, we examined the crystal size distribution and compositional zoning of garnet in eclogite of high-pressure metamorphic belt and found that crystal growth is size-dependent and that the distribution, or fluid generation rate, varies from layer to layer in the same rock. We also found that carbonation of mantle wedge-derived serpentinites is caused by the inflow of CO2 fluids originating from carboniferous materials, and that it proceeded in self-promoting ways induced by the decrease in solid volume, high pore pressure, and magnesium mobility. Furthermore, through hydrothermal experiments and geochemical modeling, it was shown that solution pH varies along the subduction zone and has a significant effect on the reaction and volume change.
Physical properties of uppermost mantle structure and the Mohorovicic seismic discontinuity

Michibayashi Katsuyoshi

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (S)

Category: Grant-in-Aid for Scientific Research (S)

2016/05/31 - 2021/03/31

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In order to clarify the structure of the uppermost mantle and the formation process of the Mohorovicic discontinuity (Moho), which is the crust-mantle boundary, this study was carried out using a multifaceted approach, including microstructural analysis, measurements of physical properties, and rock-water reaction experiments, mainly on marine and terrestrial peridotites. We confirmed that the microstructure of peridotite at depths of 6,000 m or more in the Ogasawara Trench has been affected by water, and elucidated the new dynamics of deep fluids involved in rock-water reactions. We drilled the Oman ophiolite body in the Arabian Peninsula and successfully recovered continuous samples of crustal to mantle materials, and their analyses provided numerous insights for quantitative understanding of rock-fluid reaction processes in oceanic plates. Based on these results, we have developed a new model for the formation of the Moho surface and a model for the uppermost mantle structure.
Multi-scale modeling of water-fluid reactions based on observations on nano strtuctures

Okamoto Atsushi

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research Fund for the Promotion of Joint International Research (Fostering Joint International Research (A))

Category: Fund for the Promotion of Joint International Research (Fostering Joint International Research (A))

Institution: Tohoku University

2019 - 2021

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Reactions involving mass transfer in rock-fluid systems produce characteristic structures ranging from the nanoscale to the macroscopic scale. In this project, in collaboration with Utrecht University and Karlsruhe Institute of Technology, the products of hydrothermal reactions in natural and laboratory experiments were analyzed in detail. Unusual spherical pyrite particles were found in black ore deposits, and crystal orientation analysis revealed that they grew dynamically while floating in submarine hydrothermal vents. The importance of micropores formation associated with hydrothermal alteration such as serpentinization and chloritization on the seafloor and in subduction zones was clarified. The growth mechanism of quartz particles via metastable phases in fluid flow along fractures and the influence of the basement were also clarified. Through this project, an international network has been expanded by co-organizing a research meeting at Utrecht University.
Super-resolution imaging for understanding hierarchical structures produced by water-rock reactions and mass transfer

Okamoto Atsushi

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research Challenging Research (Exploratory)

Category: Challenging Research (Exploratory)

Institution: Tohoku University

2018/06/29 - 2020/03/31

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bbbX-ray tomography (CT) is a non-destructive method for investigating three-dimensional structures. In recent years, this method has been widely applied to rock drill core samples. However, when imaging a wide area, there is a problem that the resolution is not enough for analyzing microstructure of rocks. In this research, I challenged to develop a new method of decoding rock textures that connects micro and macro, based on "sparse super-resolution technology". The analyzed sample was a serpentinized peridotite taken from the Oman Drilling Project, and the same part of the rock core was imaged at different resolutions. By sparse super-resolution, a small number of characteristic (sparse) basis images were extracted, and high-performance super-resolution was successful compared to conventional interpolation methods. Furthermore, it was found that stepwise super-resolution is effective when there is a large difference in resolution.
Earth Process Model Development by Data Driven Analysis based on Sparse Modeling

Komai Takeshi, TSUCHIYA Noriyoshi, NAKAMURA Kengo, YOSHIDA Kenta

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)

Category: Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)

Institution: Tohoku University

2013/06/28 - 2018/03/31

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The development of comprehensive framework to extract intrinsic physico-chemical processes hidden in multi-dimensional huge data has been conducted, by introducing the original sparse modeling techniques in the field of earth science. The research areas are the discrimination of tsunami deposits faced on the disaster prevention and the application to basic understanding in solid-earth science and geology, in order to bring fusional approach in the field of big data analysis in earth sciences. For the specific research targets, we have conducted the following three topics for the implementation of data driven analysis. 1) The application to tsunami deposits discrimination method by geochemical data analysis, 2) The risk assessment and behaviors of toxic metals in tsunami deposits, and 3) The introduction of developed sparse modeling to the soli-earth scientific problems.
Energetic ion induced excitation dynamics of hydrogen molecule in divertor plasma

Okamoto Atsushi, TAKAHASHI HIROYUKI

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Scientific Research (C)

2014/04/01 - 2017/03/31

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Plasma, the ionized state of gas, suffers from recombination, reverse process of ionization, in the divertor region of magnetically confined fusion devices. Effect of energetic ion flowing into the divertor region on the recombination processes is investigated. Combining a plasma experimental device and a ion beam injector, we have developed a divertor plasma simulating environment, which enables us to control experimental condition more precisely and more easily than actual fusion devices. We have found population density of excited states, which is an indicator of the recombining processes, decreases when the energetic ion density increases experimentally for the first time. A model we have developed by including the effect of energetic ion on production-annihilation processes of excited state qualitatively agree with the experiment.
Fundamental study on mineral vein formation by sealing experiment of rock fracture

Atsushi Okamoto, Muto Jun, Yamada Ryo, Saishu Hanae, Tanaka Hiroto, Wendler Frank

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)

Category: Grant-in-Aid for Scientific Research (B)

Institution: Tohoku University

2014/04/01 - 2017/03/31

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A new hydrothermal flow-through apparatus was developed, which enables us to investigate the dissolution and precipitation processes of fractured rocks at sub to supercritical conditions under confining pressure, and the evolution of aperture structures by X-ray CT. In the dissolution experiments of fractured granite, large pores and preferential flow paths were created by rapid dissolution of quartz and gauge parts, suggesting that formation of large fluid pockets induced by water-rock interaction within the crusts. In silica precipitation experiment at supercritical condition, amorphous silica precipitated at the inlet, which caused fracture sealing effectively, compared to quartz overgrowth from the fracture walls. The fracture sealing by silica precipitation produced a characteristic fluid pressure oscillation, which may indicate an importance analogue of the cycle of silica precipitation - fluid pressure rise (earthquake).
Science and Technology of Geothermal Energy Frontier

TSUCHIYA Noriyoshi, ASANUMA Hiroshi, OKMOTO Atsushi, SAKAGUCHI Kiyotoshi, WATANABE Noriaki, HIRANO Nobuo, KIZAKI Akihisa, MORIYA Hirokazu

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research Grant-in-Aid for Specially Promoted Research

Category: Grant-in-Aid for Specially Promoted Research

Institution: Tohoku University

2013 - 2017

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Geological models and the properties of supercritical geothermal reservoirs are described with respect to supercritical geofluids, mechanical behaviors of reservoir rocks, crustal permeability and tectonic settings. Mechanical conditions at the elastic-plastic boundaries of granitic rocks indicate potentially exploitable supercritical geothermal resources. Tensile fracturing is possible even in ductile rocks, and some permeability-depth relations proposed for the continental crust show no drastic permeability reduction at the BDT (Brittle-Ductile Transition). The reservoir permeability (>10^[-16] m^2) could be maintained even under supercritical conditions. The permeable-impermeable boundary of the crust and geothermal reservoirs were affected by water-rock interaction such as dissolution and precipitation of silica minerals. NE Japan is representative of an Island-Arc setting in a subduction system, and it is highly possible that exploitable supercritical geothermal resources may be located on and around the present volcanic front.
Modeling of fracturing induced by hydration and hydration reactions

Atsushi Okamoto, SHIMIZU Hiroyuki

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Exploratory Research

Category: Grant-in-Aid for Challenging Exploratory Research

Institution: Tohoku University

2014/04/01 - 2016/03/31

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Hydration and dehydration of rocks play crucial roles on global circulation of H2O in the Earth’s interior. It is known that these reactions commonly proceed with fracturing, but the detailed mechanism is still poorly understood. In this study, based on a distinct element method, we succeeded in making a novel model for the coupled processes of surface reaction-fluid flow-fracturing. We revealed that typical prograde metamorphism (volume-decreasing dehydration) and retrograde metamorphism (volume-increasing hydration) produce contrasting fracture patterns mainly induced by stress fields due to the solid volume change. Such a feedback also controls the effective reaction rate of serpentinization within the oceanic lithosphere.
蛇紋岩化作用に伴う反応－物質移動のフィードバック

岡本敦

Offer Organization: 日本学術振興会

System: 科学研究費助成事業新学術領域研究(研究領域提案型)

Category: 新学術領域研究(研究領域提案型)

Institution: 東北大学

2012/04/01 - 2014/03/31

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地殻物質とマントル物質の境界を模擬して，かんらん石－石英－水系において反応帯の形成実験を行った．実験条件は，２５０℃，飽和蒸気圧であり，また、反応を促進させるために， pH13.5のNaOH水溶液を用いた．反応物の空間分布を明らかにするために，メインのオートクレーブ内に片側だけが空いた反応チューブを設置し，石英とかんらん石の粉末を設置した．実験時間は最大46日であり，実験後は，X線回折，熱重量測定を行うとともに，走査型電子顕微鏡による薄片の画像解析から各鉱物量と空隙の測定を行った．かんらん石/石英の境界から，系統的な反応物の変化が観察された．境界に近い部分では，スメクタイト＋蛇紋石が生成し，境界よりも1cm程度離れた部分では蛇紋石＋ブルース石＋マグネタイトが形成した．シリカ活量が高い部分では滑石の形成が予想されたが，今回は滑石組成に少しNaが加わったスメクタイトが形成した．反応チューブ外側の溶液のシリカ活量は蛇紋石＋ブルーサイトの平衡とほぼ一致しており，わずか1 cm程度で３桁ほどのシリカ活量の勾配が出来ていたことを示唆する．かんらん石の加水反応は時間とともに進行し，もっとも進行していた部分ではおよそ80%のかんらん石が反応している．また、反応管内の含水量は石英との境界において低いことが明らかとされた．より詳細な反応メカニズムを明らかにするために，それぞれの鉱物の生成反応の反応進行度を求めた．その結果，かんらん石の加水反応と，シリカ交代作用による２つの脱水反応が競合して起こっていることが明らかになった．シリカ交代作用は水を吐き出すとともに固体体積が増加する反応であるために，反応帯が進行するに従って，局所的な間隙水圧の上昇がおこる．このようなプロセスは沈み込み帯におけるマントルウェッジとスラブとの境界面においても、ダイナミックな物性変化を起こしえることが予想される．
Mechanism of serpentinization and fluid transport in oceanic lithosphere

ATSUSHI Okamoto

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research Grant-in-Aid for Young Scientists (A)

Category: Grant-in-Aid for Young Scientists (A)

Institution: Tohoku University

2011/11/18 - 2014/03/31

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Serpentinization is an important process for global water circulation; however, the mechanism of serpentinization is still poorly understood. In this study, we carried out the hydrothermal experiments on serpentinization in the olivne-H2O system, by using both olivine powder and olivine sintered aggregate. We found that serpentinization proceeds effectively with fracturing of olivine grains, and reaction progress of sintered olivine aggregate changes depending on initial porosity. Similarity in the reaction texture between natural and synthetic serpentinites indicates that volume expansion, fracturing and effective mass transport becomes important during the hydration of oceanic lithosphere.
Fractionation during formation of mineral/fluid inclusions: A new approach for understanding of rock-forming processes

OKAMOTO Atsushi

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Exploratory Research

Category: Grant-in-Aid for Challenging Exploratory Research

Institution: Tohoku University

2011 - 2012

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I have revealed what controls the formation of fluid/mineral inclusions in porphyroblasts, based on hydrothermal experiments on quartz crystal growth and the analyses of garnets in the metamorphic rocks.
Upgrading of Geosphere Environmental Informatics for diversity of soil environmental standard

TSUCHIYA Noriyoshi, OKAMOTO Atsushi, OGAWA Yasumasa, HIRANO Nobuo

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)

Category: Grant-in-Aid for Scientific Research (A)

Institution: Tohoku University

2010 - 2012

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Osaka area (Akita Prefecture) was selected as a model field for this study, where is representative mining are in Japan. Watershed of the Kosaka river was subdivided into polygons for the upstream to downstream, and we have six monitoring points along the Kosaka main stream for sampling and measuring of river water flow. By using GIS (Geomorphological Information System), we analyze land utility of the area, heavy metal concentration in river water and their relationship between old mines and PRTR factory. We could find undiscovered heavy metal sources by those analytical method, which is closely related untreated of mine drainage of uncertain old mines.
沈み込み帯浅部における流体移動と水―岩石相互作用に関する実験的研究

岡本敦

Offer Organization: 日本学術振興会

System: 科学研究費助成事業新学術領域研究(研究領域提案型)

Category: 新学術領域研究(研究領域提案型)

Institution: 東北大学

2010 - 2011

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本年度は、前年度に行った流通式水熱反応装置により作成したシリカ鉱物析出物の詳細な分析を行った。析出するシリカ鉱物は、溶液に含まれるAl濃度が0ppmから7ppmに増加するにつれて、アモルファスシリカ、クリストバライト、石英とより準安定な相へと変化する。電子プローブ顕微鏡でシリカ析出物中のAlとNa濃度を測定したところ、溶液中の濃度が増加すると増加する傾向にあり、特に石英の中では、NaとAlがほぼ等量含まれることが明らかになった。このことは、石英の結晶格子のSiを電荷を合わせるようにAl+Naで置き換えていることが示唆される。また、Alを含まない高Si溶液からはアモルファスシリカが核形成し、クリストバライト、石英へと変化するのに対して、Alが増加すると直接石英が析出するという現象に対して、核形成に関するモンテカルロシミュレーションを行い、定性的には水-シリカ、シリカ-シリカ間の界面エネルギーと溶解度(バルクの自由エネルギー)の相対的な大きさがこのようなバリエーションを生み出すことを明らかにした。本実験条件である高温(430℃)、高過飽和度(アモルファスシリカの溶解度より高Si濃度)は、地殻の内部において静岩圧から静水圧に変化したときに起こりえる。そのような際に、周囲の長石から溶け出す微量なAlの有無によって、シリカ析出量が全く異なる(Alを含む場合は含まない場合の5倍以上)ということを本研究結果は示唆している。地殻の水理学的・力学的性質は亀裂内のシリカ析出速度に大きく影響されるため、微量なALの与える影響は非常に大きいことが明らかにされた。また、葛根田地熱発電所のボーリングコアサンプルの中に存在する鉱物脈とシリカスケールのサンプルを入手し、化学組成と成長組織の解析を行い、水熱実験によるシリカ析出物との類似性を見いだした。
Fluid flow and mineral precipitation within fractures under crustalenvironments

OKAMOTO Atsushi

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research Grant-in-Aid for Young Scientists (B)

Category: Grant-in-Aid for Young Scientists (B)

Institution: Tohoku University

2008 - 2009

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Fractures play as dominant fluid pathways in the Earth's crust. Mineral veins, that are fractures sealed by minerals (i.e. quartz and calcite) show a variety of microtextures. In this study, we conducted hydrothermal experiments to precipitation of silica minerals under crustal conditions. We clarified that mechanisms and textural developments in precipitation of silica minerals systematically vary depending on Si concentration, minor elements in solutions and rock substrates.
Mechanisms of extraction of heavy metals from marine sediments development of sealing technology

TSUCHIYA Noriyoshi, HIRANO Nobuo, OKAMOTO Atsushi, OGAWA Yasumasa

Offer Organization: Japan Society for the Promotion of Science

System: Grants-in-Aid for Scientific Research

Category: Grant-in-Aid for Scientific Research (A)

Institution: Tohoku University

2007 - 2009

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Pliocene marine sediments were widely distributed in Tohoku District. Those sediments contain much amount of heavy metals such as As, Cd and Pb, and some of them were higher than limit of environmental regulation. Extraction properties of As and other heavy metals were affected by form of them, which was corresponded to sedimentary environment.
固体圧変形実験による反応進行下における玄武岩の変形メカニズムの解明

岡本敦

Offer Organization: 日本学術振興会

System: 科学研究費助成事業若手研究(B)

Category: 若手研究(B)

Institution: 東北大学

2006 - 2007

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本年度は、沈み込み帯深部において脱水反応によって生成された流体が、周囲の岩石とどのような相互作用をするかと周囲の岩石の脆性破壊の結果である亀裂中の流体移動について野外調査と流通式反応実験により明らかにした。【関東山地・長瀞地域の三波川帯鉱物脈の解析】脱水反応による流体は沈み込み帯の地殻深度では岩石中に亀裂を発生させ、鉱物脈として記録される。沈み込み帯の情報を記録する三波川帯に発達する鉱物脈の解析を行い、(1)形成条件が200-400度、1-4kbarであること、(2)形状、内部組織、鉱物種から3タイプが存在することを明らかにした。TypeIとTypeIIは石英+曹長石+緑泥石+カリ長石からなり、母岩の鉱物から成長する。TypeIIは石英+曹長石+方解石からなり、微結晶により充填され、その空間分布は母岩の鉱物分布とは無関係である。これらの系統的な関係により、TypeIとIIIは、物質移動はそれぞれ母岩からの元素拡散と流体の移流によって支配されていることが明らかになった。【流通式反応実験による石英脈合成]高温高圧環境下(200-430度、30MPa)においてSiに過飽和な溶液を流すことにより、岩石基盤上に石英を析出させることに成功し、その反応速度解析を行った。また、その析出様式は、同じ温度条件下(430度)における析出でも、平衡に近い溶液からは基盤岩石中の石英の上にのみ成長するのに対して、過飽和度が高い条件(C/C_<eq>>3)では流体中で核形成が起こり成長するということを明らかにした。このことは、三波川帯のTypeIIIの鉱物脈がよりSi濃度の高い流体が深部から運ばれてきたこと、すなわち、地殻深度における主要な流体移動の流路であったことを示唆する。
角閃石を用いた高圧変成岩の温度・圧力・歪み速度履歴の定量的解析

岡本敦

Offer Organization: 日本学術振興会

System: 科学研究費助成事業特別研究員奨励費

Category: 特別研究員奨励費

2003 - 2005

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本年は特別研究員としての最終年度としてこれまでの研究成果をまとめて発表するとともに(1,2)、高圧変成岩中の組織から結晶成長速度、変形-反応との関連性について新たな知見(3,4)を得た。 1.三波川変成帯の角閃石の成長時の組成変化(組成累帯構造)を定量的に評価して、その吸水反応の進行度を定量的に評価した。その結果、岩体上昇期の後退変成反応の進行度は角閃石の脆性破壊と強い相関を持つこと、またザクロ石帯の高温部が非常に強く変形と反応が進行したことが明らかになった。この成果はJournal of metamorphic Geologyに掲載された。 2.高温の変成岩中に包有物として存在するザクロ石の形態(縦横比)-粒子サイズの分布パターンを理解するために、3つの機構(1)転位クリープ、(2)拡散クリープ、(3)粒界拡散による球状化をモデル化した。その結果、変形機構、変形時間、差応力についての新たな知見を得た。この成果はJournal of Geophysical Researchに掲載された。 3.三波川変成帯の鉱物脈中のザクロ石の集合体の結晶間の角度差(ミスオリエンテーション)を解析した。その結果、このザクロ石斑状変晶は多数の粒子が成長時に衝突合体し、核形成時のランダムな結晶方位がそのまま保持されたものであることを明らかにした。また、これまで報告された同様の組織との対応により、ミスオリエンテーション分布パターンの発達は結晶成長の速度に依存して変化することを明らかにした。この成果はJournal of Metamorphic Geologyに受理された。 4.ギリシャ・シロス島に産する高圧変成岩中の角閃石の粒子境界での圧入組織を解析し、差応力が反応の進行に大きな影響を与えると言うことを明らかにした。この成果はJournal of Metamorphic Geologyに投稿中である。
岩石学・構造地質学的手法による三波川変成帯発達過程の解明

岡本敦

Offer Organization: 日本学術振興会

System: 科学研究費助成事業特別研究員奨励費

Category: 特別研究員奨励費

Institution: 東京大学

2000 - 2002

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西南日本に露出する三波川変成帯の塩基性片岩の温度圧力経路と歪みの増分を定量化し対応させた。塩基性片岩中に一般的に存在する角閃石という鉱物の組成変化を電子プローブ顕微鏡を用いて詳細に分析し、熱力学的な解析によって温度圧力経路を推定した。その結果、1.変成帯の上昇期の経路を記録していること、2.変成度が高くなるにつれて最高温度圧力は徐々に高くなること、3.曹長石黒雲母帯では高温部(500度以上)では温度圧力経路のdP/dTが大きいのに対して、のちの低温部ではdP/dTが小さいということが明らかとなった。角閃石は塩基性片岩の中で剛体として振る舞い、結晶の長軸方向に垂直に脆性破壊し、引き伸ばされる。このマイクロブーディン組織を用いて歪み解析を行った。割れた隙間を埋めている角閃石の組成から、変形は400-500度,0.3-0.6GPaという変成帯の上昇における後期に対応していることが分かる。その歪みの増分は自然対数歪みで最大1.0である。マイクロブーディン組織は岩石全体の歪みを必ずしも反映しているとは限らない。本研究では新たに独立な指標として後退変成反応の進行度を測定して、変形との関係を調べた。塩基性片岩の反応進行度はマスバランスの関係から、Xact(角閃石の中でアクチノ閃石の占める割合)によって代表させることが出来る。このXactを組成マップを用いて画像解析をすることによって定量化した。歪み解析との対応から、アクチノ閃石を生成する後退変成反応が進むにつれて塩基性片岩の変形が進行することが明らかとなった。また、四国別子地域におけるXactの空間分布より、ザクロ石帯とザクロ石帯-曹長石黒雲母帯の境界部が上昇の後期において非常に変形が集中していたことが示された。

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Teaching Experience 4

環境地球科学
Thermodynamics I　Tohoku University
Crustal Processes　Tohoku University
Thermodynamics II　Tohoku University