2024/02/02 更新

写真a

オオタ ツトム
太田 努
OTA Tsutomu
所属
惑星物質研究所 主任スーパーテクニシャン
職名
主任スーパーテクニシャン
外部リンク

学位

  • 博士(理学) ( 新潟大学 )

研究キーワード

  • geochemistry

  • Petrology

  • 地球化学

  • 岩石学

研究分野

  • 自然科学一般 / 固体地球科学

学歴

  • 新潟大学   Graduate School, Division of Science and Technology  

    - 1997年

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  • 新潟大学    

    - 1997年

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    国名: 日本国

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  • 愛媛大学   Faculty of Science   Department of Earth Sciences

    - 1991年

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    国名: 日本国

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  • 愛媛大学   Faculty of Science  

    - 1991年

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論文

  • The Formation of a Rubble Pile Asteroid: Insights from the Asteroid Ryugu 査読

    Tsutomu Ota, Christian Potiszil, Katsura Kobayashi, Ryoji Tanaka, Hiroshi Kitagawa, Tak Kunihiro, Chie Sakaguchi, Masahiro Yamanaka, Eizo Nakamura

    Universe   2023年6月

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    掲載種別:研究論文(学術雑誌)  

    DOI: 10.3390/universe9060293

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  • Organic Matter in the Asteroid Ryugu: What We Know So Far 招待 査読

    Christian Potiszil, Masahiro Yamanaka, Chie Sakaguchi, Tsutomu Ota, Hiroshi Kitagawa, Tak Kunihiro, Ryoji Tanaka, Katsura Kobayashi, Eizo Nakamura

    Life   2023年6月

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    掲載種別:研究論文(学術雑誌)  

    DOI: 10.3390/life13071448

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  • Detection of Meteoritic Amino Acids in Extremely Small Sample Sizes: Implications for Sample Return Missions

    Christian Potiszil, Masahiro Yamanaka, Tsutomu Ota, Ryoji Tanaka, Katsura Kobayashi, Eizo Nakamura

    2023年3月

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    出版者・発行元:MDPI AG  

    Unmetamorphosed carbonaceous chondrites provide important information concerning the formation and evolution of organic matter, such as amino acids. However, terrestrial contamination remains a valid concern when investigating the organic inventory of meteorites that have fallen to Earth. Accordingly, JAXA’s Hayabusa2 and NASA’s OSIRIS-REx have been launched with the task of returning uncontaminated C-type asteroid material to Earth. The successful Hayabusa2 mission has a very limited sample size (5.4 g). Therefore, many conventional compound specific techniques will struggle to detect amino acids above detection limit with available sample amounts (~several mg to 10’s of mg) being much smaller than those typically used. Here a novel method utilizing ultrahigh performance liquid chromatography-Orbitrap-mass spectrometry is validated and applied to very small meteorite samples, thus providing an approach that can overcome the small sample size constraints of sample return missions. The method is highly sensitive, enabling the detection of amino acids in the carbonaceous chondrites Murchison (2.28 mg) and Orgueil (2.30 mg). Furthermore, quantitation was possible for many of the detected amino acids in Murchison and Orgueil. Using the data presented here, both the amino acid reservoirs of Murchison and Orgueil and the potential application of this method to sample return samples are discussed.

    DOI: 10.20944/preprints202302.0374.v2

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  • Insights into the formation and evolution of extraterrestrial amino acids from the asteroid Ryugu

    Christian Potiszil, Tsutomu Ota, Masahiro Yamanaka, Chie Sakaguchi, Katsura Kobayashi, Ryoji Tanaka, Tak Kunihiro, Hiroshi Kitagawa, Masanao Abe, Akiko Miyazaki, Aiko Nakato, Satoru Nakazawa, Masahiro Nishimura, Tatsuaki Okada, Takanao Saiki, Satoshi Tanaka, Fuyuto Terui, Yuichi Tsuda, Tomohiro Usui, Sei-ichiro Watanabe, Toru Yada, Kasumi Yogata, Makoto Yoshikawa, Eizo Nakamura

    Nature Communications   14 ( 1 )   2023年3月

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

    Abstract

    All life on Earth contains amino acids and carbonaceous chondrite meteorites have been suggested as their source at the origin of life on Earth. While many meteoritic amino acids are considered indigenous, deciphering the extent of terrestrial contamination remains an issue. The Ryugu asteroid fragments (JAXA Hayabusa2 mission), represent the most uncontaminated primitive extraterrestrial material available. Here, the concentrations of amino acids from two particles from different touchdown sites (TD1 and TD2) are reported. The concentrations show that N,N-dimethylglycine (DMG) is the most abundant amino acid in the TD1 particle, but below detection limit in the other. The TD1 particle mineral components indicate it experienced more aqueous alteration. Furthermore, the relationships between the amino acids and the geochemistry suggest that DMG formed on the Ryugu progenitor body during aqueous alteration. The findings highlight the importance of aqueous chemistry for defining the ultimate concentrations of amino acids in primitive extraterrestrial samples.

    DOI: 10.1038/s41467-023-37107-6

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    その他リンク: https://www.nature.com/articles/s41467-023-37107-6

  • Nitrogen Incorporation in Potassic and Micro- and Meso-Porous Minerals: Potential Biogeochemical Records and Targets for Mars Sampling

    Matthew P. Nikitczuk, Gray E. Bebout, Charles A. Geiger, Tsutomu Ota, Takuya Kunihiro, John F. Mustard, Sæmundur A. Halldórsson, Eizo Nakamura

    Astrobiology   2022年9月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Mary Ann Liebert Inc  

    DOI: 10.1089/ast.2021.0158

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    その他リンク: https://www.liebertpub.com/doi/pdf/10.1089/ast.2021.0158

  • On the origin and evolution of the asteroid Ryugu: A comprehensive geochemical perspective 査読

    Eizo NAKAMURA, Katsura KOBAYASHI, Ryoji TANAKA, Tak KUNIHIRO, Hiroshi KITAGAWA, Christian POTISZIL, Tsutomu OTA, Chie SAKAGUCHI, Masahiro YAMANAKA, Dilan M. RATNAYAKE, Havishk TRIPATHI, Rahul KUMAR, Maya-Liliana AVRAMESCU, Hidehisa TSUCHIDA, Yusuke YACHI, Hitoshi MIURA, Masanao ABE, Ryota FUKAI, Shizuho FURUYA, Kentaro HATAKEDA, Tasuku HAYASHI, Yuya HITOMI, Kazuya KUMAGAI, Akiko MIYAZAKI, Aiko NAKATO, Masahiro NISHIMURA, Tatsuaki OKADA, Hiromichi SOEJIMA, Seiji SUGITA, Ayako SUZUKI, Tomohiro USUI, Toru YADA, Daiki YAMAMOTO, Kasumi YOGATA, Miwa YOSHITAKE, Masahiko ARAKAWA, Atsushi FUJII, Masahiko HAYAKAWA, Naoyuki HIRATA, Naru HIRATA, Rie HONDA, Chikatoshi HONDA, Satoshi HOSODA, Yu-ichi IIJIMA, Hitoshi IKEDA, Masateru ISHIGURO, Yoshiaki ISHIHARA, Takahiro IWATA, Kosuke KAWAHARA, Shota KIKUCHI, Kohei KITAZATO, Koji MATSUMOTO, Moe MATSUOKA, Tatsuhiro MICHIKAMI, Yuya MIMASU, Akira MIURA, Tomokatsu MOROTA, Satoru NAKAZAWA, Noriyuki NAMIKI, Hirotomo NODA, Rina NOGUCHI, Naoko OGAWA, Kazunori OGAWA, Chisato OKAMOTO, Go ONO, Masanobu OZAKI, Takanao SAIKI, Naoya SAKATANI, Hirotaka SAWADA, Hiroki SENSHU, Yuri SHIMAKI, Kei SHIRAI, Yuto TAKEI, Hiroshi TAKEUCHI, Satoshi TANAKA, Eri TATSUMI, Fuyuto TERUI, Ryudo TSUKIZAKI, Koji WADA, Manabu YAMADA, Tetsuya YAMADA, Yukio YAMAMOTO, Hajime YANO, Yasuhiro YOKOTA, Keisuke YOSHIHARA, Makoto YOSHIKAWA, Kent YOSHIKAWA, Masaki FUJIMOTO, Sei-ichiro WATANABE, Yuichi TSUDA

    Proceedings of the Japan Academy, Series B   98 ( 6 )   227 - 282   2022年6月

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

    DOI: 10.2183/pjab.98.015

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  • Lithium in garnet as a tracer of subduction zone metamorphic reactions: The record in ultrahigh-pressure metapelites at Lago di Cignana, Italy

    Gray E. Bebout, Tsutomu Ota, Takuya Kunihiro, William D. Carlson, Eizo Nakamura

    Geosphere   18 ( 3 )   1020 - 1029   2022年6月

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

    Abstract

    Lithium is of great interest as a tracer of metamorphic reactions and related fluid-mineral interactions because of its potential to isotopically fractionate during inter- and intracrystalline diffusional processes. Study of its transfer through subduction zones, based on study of arc volcanic and metamorphic rocks, can yield insight regarding ocean-to-mantle chemical cycling.

    We investigated major- and trace-element concentrations and δ7Li in garnet in ultrahigh-pressure (UHP) Lago di Cignana metasedimentary rocks, relating these observations to reconstructed prograde devolatilization history. In all garnet crystals we studied, heavy rare earth elements (HREEs), Y, and Li showed strong zoning, with elevated concentrations in cores (15–50 ppm Li) and marked high-concentration anomalies (up to 117 ppm Li, 5500 ppm Y; little or no major-element shift) as growth annuli, in which some crystals showed subtle elevation in δ7Li greater than analytical error of ~3% (2σ). Rutile inclusions appeared abruptly at annuli and outward toward rims, accompanied by inclusions of a highly zoned, Ca- and rare earth element–rich phase and decreased Nb concentrations in garnet. These relationships are interpreted to reflect prograde garnet-forming reaction(s), in part involving titanite breakdown to stabilize rutile, which resulted in delivery of more abundant Y and HREEs at surfaces of growing garnet crystals to produce annuli. Co-enrichments in Li and Y + REEs are attributed to mutual incorporation via charge-coupled substitutions; thus, increased Li uptake was a passive consequence of elevated concentrations of Y + REEs. The small-scale fluctuations in δ7Li (overall range of ~9%) observed in some crystals may correlate with abrupt shifts in major- and trace-element concentrations, suggesting that changes in reactant phases exerted some control on the evolution of δ7Li. For one garnet crystal, late-stage growth following partial resorption produced deviation in major- and trace-element compositions, including Li concentration, accompanied by a 10%–15% negative shift in δ7Li, perhaps reflecting a change in the mechanism of incorporation or source of Li.

    These results highlight the value of measuring the major- and trace-element and isotope compositions of garnets in high-pressure and UHP metamorphic rocks in which matrix mineral assemblages are extensively overprinted by recrystallization during exhumation histories. Lithium concentrations and isotope compositions of the garnets can add valuable information regarding prograde (and retrograde) reaction history, kinetics of porphyroblast growth, intracrystalline diffusion, and fluid-rock interactions. This work, integrated with previous study of devolatilization in the Schistes Lustrés/Cignana metasedimentary suite, indicates retention of a large fraction of the initially subducted sedimentary Li budget to depths approaching those beneath volcanic fronts, despite the redistribution of this Li among mineral phases during complex mineral reaction histories.

    DOI: 10.1130/ges02473.1

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  • Magmatic-hydrothermal processes of the Laojunshan metamorphic massif in Southeastern Asia: Evidence from chemical and B-isotopic variations of deformed tourmalines

    Wei Li, Shuyun Cao, Eizo Nakamura, Tsutomu Ota, Zhong Liu, Yanlong Dong, Tak Kunihiro

    Lithos   412-413   106609 - 106609   2022年3月

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

    DOI: 10.1016/j.lithos.2022.106609

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  • The trace element composition of chondrule constituents: Implications for sample return methodologies and the chondrule silicate reservoir

    Tak Kunihiro, Tsutomu Ota, Masahiro Yamanaka, Christian Potiszil, Eizo Nakamura, Alex, er Krot

    Meteoritics & Planetary Science   57 ( 2 )   429 - 449   2022年2月

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

    Sample return missions represent great opportunities to study terrestrially uncontaminated solar system materials. However, the size of returned samples will be limited, and thus, it is necessary to understand the most appropriate techniques to apply. Accordingly, the sensitivity of laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) and secondary ion mass spectrometry (SIMS) was compared through the analyses of trace elements in reference materials and the Allende CV3 chondrite. While the SIMS method was found to be more sensitive than the laser method toward all elements of interest, the LA-ICPMS appears to be more suitable in terms of precision for certain elements. Using both analytical techniques, we measured chemical composition of an Allende chondrule and its igneous rim. These data were used to understand the nature of the reservoir that interacted with the host chondrule during formation of its igneous rim. We find that the igneous rim is enriched in silica, alkalis, and rare earth elements compared to the host chondrule. We suggest that the igneous rim could be explained by melting of a mixture of the chondrule-like and REE-enriched CAI-like precursors that accreted on the surface of the host chondrule followed by gas-melt interaction with a silica- and alkali-rich gas. Alternatively, these observations could be interpreted as a result of interaction between the chondrule and the melt resulting from partial melting of a pre-existing planetesimal in the early stages of its differentiation.

    DOI: 10.1111/maps.13665

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  • Nitrogenous Altered Volcanic Glasses as Targets for Mars Sample Return: Examples From Antarctica and Iceland

    M. P. Nikitczuk, G. E. Bebout, T. Ota, T. Kunihiro, J. F. Mustard, R. L. Flemming, R. Tanaka, S. A. Halld{\'{o } }rsson, E. Nakamura

    Journal of Geophysical Research: Planets   127 ( 2 )   2022年2月

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

    DOI: 10.1029/2021je007052

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    その他リンク: https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2021JE007052

  • Elements for the Origin of Life on Land: A Deep-Time Perspective from the Pilbara Craton of Western Australia

    Martin J. Van Kranendonk, Raphael Baumgartner, Tara Djokic, Tsutomu Ota, Luke Steller, Ulf Garbe, Eizo Nakamura

    Astrobiology   21 ( 1 )   39 - 59   2021年1月

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

    DOI: 10.1089/ast.2019.2107

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  • Mineralogical alterations in calcite powder flooded with MgCl2 to study Enhanced Oil Recovery (EOR) mechanisms at pore scale

    Mona W. Minde, Merete V. Madl, Udo Zimmermann, Nina Egel, Reidar I. Korsnes, Eizo Nakamura, Katsura Kobayashi, Tsutomu Ota

    Microporous and Mesoporous Materials   304   109402 - 109402   2020年9月

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

    DOI: 10.1016/j.micromeso.2019.03.050

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  • Concentration of meteoritic free organic matter by fluid transport and adsorption

    Tsutomu Ota

    Geochemical Perspectives Letters   13   30 - 35   2020年3月

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    掲載種別:研究論文(学術雑誌)  

    Carbonaceous chondrites contain many abiotic organic compounds, some of which are found in life on Earth. Both the mineral and organic matter phases, of these meteorites, have been affected by aqueous alteration processes. Whilst organic matter is known to be associated with phyllosilicate phases, no such relationship has yet been identified for specific organic compound classes. Furthermore, ongoing sample return missions, Hyabusa 2 and OSIRIS-Rex, are set to return potentially organic rich C-type asteroid samples to the Earth. Consequently, strategies to investigate organic-mineral relationships are required. Here we report spatial data for free/soluble organic matter (FOM/SOM) components (akylimidazole and alkylpyridine homologues) and mineral phases. Low and intermediate molecular weight alkylimidazole homologues are more widely distributed than higher molecular weight members, likely due to their affinity for the aqueous phase. On aqueous alteration of anhydrous mineral phases, transported FOM is adsorbed onto the surface or into the interlayers of the resulting phyllosilicates and thus concentrated and protected from oxidising fluids. Therefore, aiding the delivery of biologically relevant molecules to earth, shortly preceding the origin of life.

    DOI: 10.7185/geochemlet.2010

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  • Boron Isotopes in the Puga Geothermal System, India, and Their Implications for the Habitat of Early Life

    Luke H. Steller, Eizo Nakamura, Tsutomu Ota, Chie Sakaguchi, Mukund Sharma, Martin J. Van Kranendonk

    Astrobiology   19 ( 12 )   1459 - 1473   2019年12月

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

    Boron is associated with several Archean stromatolite deposits, including the tourmaline-rich Barberton stromatolites in South Africa and tourmaline-bearing pyritic laminae associated with stromatolites of the 3.48 Ga Dresser Formation in the Pilbara Craton, Australia. Boron is also a critical element in prebiotic organic chemistry, including in the formation of ribose, a crucial component in RNA. As geological evidence and advances in prebiotic chemistry are now suggesting that hot spring activity may be associated with the origins of life, an understanding of boron and its mobility and isotopic fractionation in geothermal settings may provide important insights into the setting for the origin of life. Here, we report on the boron isotopic compositions and elemental concentrations in a range of fluid, sediment, and mineral samples from the active, boron-rich Puga geothermal system in the Himalayas, India. This includes one of the lowest boron isotope values ever recorded in modern settings: diatom-rich sediments (delta B-11 = -41.0 parts per thousand) in a multiphase fractionation system where evaporation is not the dominant form of isotope fractionation. Instead, the extreme boron isotopic fractionation is ascribed to the incorporation of tetrahedral B-10 borate anions in precipitating amorphous silica. These findings expand the known limits and drivers of boron isotope fractionation, as well as provide insight into the concentration and fractionation of boron in Archean hot spring environments.

    DOI: 10.1089/ast.2018.1966

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  • Tourmaline in a Mesoarchean pelagic hydrothermal system: Implications for the habitat of early life 査読

    Ota, T, Aihara, Y, Kiyokawa, S, Tanaka, R, Nakamura, E

    Precambrian Research   2019年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1016/j.precamres.2019.105475

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  • Lithium- and oxygen-isotope compositions of chondrule constituents in the Allende meteorite

    Eizo Nakamura, Tak Kunihiro, Tsutomu Ota

    Geochimica et Cosmochimica Acta   252   107 - 125   2019年

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

    We report in situ ion-microprobe analyses of Li- and O-isotope compositions for olivine, low-Ca pyroxene, high-Ca pyroxene, and chondrule mesostasis/plagioclase in nine chondrules from the Allende CV3 chondrite. Based on their mineralogy and O-isotope compositions, we infer that the chondrule mesostasis/plagioclase and ferroan olivine rims were extensively modified or formed during metasomatic alteration and metamorphism on the Allende parent asteroid. We excluded these minerals in order to determine the correlations between Li and both O and the chemical compositions of olivines and low-Ca pyroxenes in the chondrules and their igneous rims. Based on the O-isotope composition of the olivines, nine chondrules were divided into three groups. Average Delta O-17 of olivines (Fo(>65)) in group 1 and 2 chondrules are -5.3 +/- 0.4 and -6.2 +/- 0.4 parts per thousand, respectively. Group 3 chondrules are characterized by the presence of O-16-rich relict grains and the Delta O-17 of their olivines range from -23.7 to -6.2 parts per thousand. In group 1 olivines, as Fa content increases, variation of delta Li-7 becomes smaller and delta Li-7 approaches the whole-rock value (2.4 parts per thousand; Seitz et al., 2012), suggesting nearly complete Li-isotope equilibration. In group 2 and 3 olivines, variation of delta Li-7 is limited even with a significant range of Fa content. We conclude that Li-isotope compositions of olivine in group 1 chondrules were modified not by an asteroidal process but by an igneous-rim formation process, thus chondrule olivines retained Li-isotope compositions acquired in the protosolar nebula. In olivines of the group 3 chondrule PO-8, we observed a correlation between O and Li isotopes: In relict O-16-rich olivine grains with Delta O-17 of similar to-25 to -20 parts per thousand, delta Li-7 ranges from -23 to -3 parts per thousand; in olivine grains with Delta O-17 > -20 parts per thousand, delta Li-7 is nearly constant (-8 +/- 4 parts per thousand). Based on the Li-isotope composition of low-Ca pyroxenes, which formed from melt during the crystallization of host chondrules and igneous rims, the existence of a gaseous reservoir with a delta Li-7 similar to -11 parts per thousand is inferred. (C) 2019 Elsevier Ltd. All rights reserved.

    DOI: 10.1016/J.GCA.2019.02.038

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  • Hypervelocity collision and water-rock interaction in space preserved in the Chelyabinsk ordinary chondrite. 査読

    Nakamura E, Kunihiro T, Ota T, Sakaguchi C, Tanaka R, Kitagawa H, Kobayashi K, Yamanaka M, Shimaki Y, Bebout GE, Miura H, Yamamoto T, Malkovets V, Grokhovsky V, Koroleva O, Litasov K

    Proceedings of the Japan Academy. Series B, Physical and biological sciences   95 ( 4 )   165 - 177   2019年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.2183/pjab.95.013

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  • Circa 1 Ga sub-seafloor hydrothermal alteration imprinted on the Horoman peridotite massif 査読

    Ranaweera, L.V, Ota, T, Moriguti, T, Tanaka, R, Nakamaura, E

    Scientific Reports   DOI:10.1038/s41598-018-28219-x ( 1 )   2018年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1038/s41598-018-28219-x

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    その他リンク: http://www.nature.com/articles/s41598-018-28219-x

  • In–situ U–Pb zircon age dating deciphering the formation event of the omphacite growth over relict edenitic pargasite in omphacite–bearing jadeitite of the Itoigawa–Omi area of the Hida–Gaien belt, central Japan

    KUNUGIZA Keitaro, NAKAMURA Eizo, GOTO Atsushi, KOBAYASHI Katsura, OTA Tsutomu, MIYAJIMA Hiroshi, YOKOYAMA Kazumi

    Journal of Mineralogical and Petrological Sciences   112 ( 5 )   256 - 270   2017年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:一般社団法人 日本鉱物科学会  

    <p>Omphacite replacing after relic edenitic pargasite has been found in an omphacite–bearing jadeitite block of the Itoigawa–Omi area in the Hida–Gaien belt. Omphacite occurs sporadically as fine–grained aggregate reaching a few cm in length in a jadeite–albite matrix, and sometimes contains edenitic pargasite as a core. The edenitic pargasite is chemically and optically homogeneous and does not show direct contact with jadeite and albite. An irregular shaped omphacite–diopside mixed area occurs near edenitic pargasite in a coarse omphacite aggregate. The texture suggests that the breakdown of edenitic pargasite was triggered by the addition of a hydrothermal fluid, from which jadeite and albite were precipitated later, passing through diopside and omphacite by the reaction:</p><p>&nbsp;</p><p><img align="middle" src="./Graphics/abst-170402a.jpg"/> </p><p>&nbsp;</p><p>At the periphery of pseudomorphic omphacite, a hydrothermal fluid removed the breakdown components of the reaction other than omphacite.</p><p>&emsp;New in–situ LA–ICP–MS U–Pb dating revealed that zircons in edenitic pargasite yield apparent age up to ~ 590 Ma, with mean ages of 560 ± 16 Ma, interpreted as the minimum age of a precursor rock. A zircon age of 519 ± 21 Ma from jadeitite without omphacite corresponds to a timing of crystallization of omphacite, jadeite, and albite. The studied jadeitite is a typical R–type jadeitite, and the nearly total replacement from a precursor rock to the omphacite–bearing jadeitite has been attributed to hydrothermal activity at Middle Cambrian times.</p>

    DOI: 10.2465/JMPS.170402A

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  • Maruyamaite, K(MgAl<inf>2</inf>)(Al<inf>5</inf>Mg)Si<inf>6</inf>O<inf>18</inf>(BO<inf>3</inf>)<inf>3</inf>(OH)<inf>3</inf>O, a potassium-dominant tourmaline from the ultrahigh-pressure Kokchetav massif, northern Kazakhstan: Description and crystal structure

    Lussier, A., Ball, N.A., Hawthorne, F.C., Henry, D.J., Shimizu, R., Ogasawara, Y., Ota, T.

    American Mineralogist   101 ( 2 )   2016年

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    掲載種別:研究論文(学術雑誌)  

    DOI: 10.2138/am-2016-5359

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  • Ion microprobe U-Th-Pb geochronology and study of micro-inclusions in zircon from the Himalayan high- and ultrahigh-pressure eclogites, Kaghan Valley of Pakistan

    Hafiz Ur Rehman, Katsura Kobayash, Tatsuki Tsujimori, Tsutomu Ota, Hiroshi Yamamoto, Eizo Nakamura, Yoshiyuki Kaneko, Tahseenullah Khan, Masaru Terabayashi, Kenta Yoshida, Takao Hirajima

    Journal of Asian Earth Sciences   63   179 - 196   2013年2月

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    掲載種別:研究論文(学術雑誌)  

    We report ion microprobe U-Th-Pb geochronology of in situ zircon from the Himalayan high- and ultrahigh-pressure eclogites, Kaghan Valley of Pakistan. Combined with the textural features, mineral inclusions, cathodoluminescence image information and the U-Th-Pb isotope geochronology, two types of zircons were recognized in Group I and II eclogites. Zircons in Group I eclogites are of considerably large size (&gt;100. μm up to 500. μm). A few grains are euhederal and prismatic, show oscillatory zoning with distinct core-rim luminescence pattern. Several other grains show irregular morphology, mitamictization, embayment and boundary truncations. They contain micro-inclusions such as muscovite, biotite, quartz and albite. Core or middle portions of zircons from Group I eclogites yielded concordant U-Th-Pb age of 267.6±2.4. Ma (MSWD=8.5), have higher U and Th contents with a Th/U ratio. &gt;1, indicating typical magmatic core domains. Middle and rim or outer portions of these zircons contain inclusions of garnet, omphacite, phengite and these portions show no clear zonation. They yielded discordant values ranging between 210 and 71. Ma, indicating several thermal or Pb-loss events during their growth and recrystalization prior to or during the Himalayan eclogite-facies metamorphism. Zircons in Group II eclogites are smaller in size, prismatic to oval, display patchy or sector zoning and contain abundant inclusions of garnet, omphacite, phengite, quartz, rutile and carbonates. They yielded concordant U-Th-Pb age of 44.9±1.2. Ma (MSWD=4.9). The lower U and Th contents and a lower Th/U ratio (&lt;0.05) in these zircons suggest their formation from the recrystallization of the older zircons during the Himalayan high and ultrahigh-pressure eclogite-facies metamorphism. © 2012 Elsevier Ltd.

    DOI: 10.1016/j.jseaes.2012.04.025

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  • Sm-Nd and Lu-Hf isotope geochemistry of the Himalayan high- and ultrahigh-pressure eclogites, Kaghan valley, Pakistan 招待 査読

    Rehman, H.U., Kobayashi, K., Tsujimori, T., Ota, T., Yamamoto, H., Nakamura, E., Kaneko, Y., Khan, T.

    Geochemistry - Earth's System Processes   105 - 126   2012年

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    記述言語:英語   掲載種別:研究論文(その他学術会議資料等)  

    DOI: 10.5772/32859

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  • Intra-oceanic island arc origin for Iratsu eclogites of the Sanbagawa belt, central Shikoku, southwest Japan

    Utsunomiya, A., Jahn, B.-M., Okamoto, K., Ota, T., Shinjoe, H.

    Chemical Geology   280 ( 1-2 )   2011年

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    掲載種別:研究論文(学術雑誌)  

    DOI: 10.1016/j.chemgeo.2010.11.001

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  • Ophiolites in the non-volcanic Banda outer arc of East Indonesia : Field occurrence and petrological variety of the world's youngest ophiolite

    ISHIKAWA A.

    Journal of Geography (Chigaku Zasshi)   120   2011年

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    掲載種別:研究論文(学術雑誌)  

    DOI: 10.5026/JGEOGRAPHY.120.52

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  • World's youngest blueschist belt from Leti Island in the non-volcanic Banda outer arc of Eastern Indonesia

    Kadarusman, A., Maruyama, S., Kaneko, Y., Ota, T., Ishikawa, A., Sopaheluwakan, J., Omori, S.

    Gondwana Research   18 ( 1 )   2010年

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    掲載種別:研究論文(学術雑誌)  

    DOI: 10.1016/j.gr.2010.02.009

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  • Sr-Nd-Hf-Pb isotopic characteristics of North-Western and Southern Ethiopian lithospheric mantle 査読

    Melesse A, Kunihiro T, Ota T, Tanaka R, Moriguti T, Nakamura E

    Geochimica Et Cosmochimica Acta   74 ( 12 )   A697   2010年

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    掲載種別:研究論文(学術雑誌)  

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  • Are the Taitao granites formed due to subduction of the Chile ridge?

    Anma Ryo, Armstrong Richard, Orihashi Yuji, Ike Shin-ichi, Shin Ki-Cheol, Kon Yoshiaki, Komiya Tsuyoshi, Ota Tsutomu, Kagashima Shin-ichi, Shibuya Takazo, Yamamoto Shinji, Veloso Eugenio E., Fanning Mark, Hervé Francisco

    Lithos   113 ( 1-2 )   246 - 258   2009年

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

    The Taitao granites are distributed around the Late Miocene Taitao ophiolite (5.66 ± 0.33 Ma to 5.19 ± 0.15 Ma) exposed at the western tip of the Taitao peninsula, southern Chile, ~ 50 km southeast from the present day Chile triple junction. In this paper, we report sensitive high mass-resolution ion microprobe (SHRIMP) U–Pb ages for the Taitao granites to elucidate the temporal relationship between the ophiolite and granites, and discuss the origin of the granitic melts. Five intrusive bodies of the Taitao granites have U–Pb ages ranging from 5.70 ± 0.25 Ma (Tres Montes pluton in southeast) to 3.92 ± 0.07 Ma (Cabo Raper pluton in southwest). The Estero Cono, Seno Hoppner and Bahia Barrientos intrusions that fringe eastern margin of the ophiolite have U–Pb ages ranging from 5.17 ± 0.09 Ma to 4.88 ± 0.3 Ma. Recycled zircon cores are common only in the Tres Montes pluton. Our data indicate that the generation of the granitic melts started in the Tres Montes area when a short segment of the Chile ridge system started to subduct ca. 6 Ma ago. This magmatism involved contamination with sediments/basement rocks. A part of the subducting ridge center was emplaced to form the present Taitao ophiolite at ~ 5.6 Ma. Generation of granitic melts continued as the spreading center of the same ridge segment subducted, due perhaps to partial melting of the ophiolite and/or oceanic crust enhanced by heat from upwelling mantle beneath the ridge. Granitic magmas with various compositions developed during subduction of the ridge. Emplacement of the ophiolite and formation of continental crust took place almost simultaneously.

    DOI: 10.1016/j.lithos.2009.05.018

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  • A geochemical and Sr-Nd isotopic study of the Vendian greenstones from Gorny Altai, southern Siberia: Implications for the tectonic setting of the formation of greenstones and the role of oceanic plateaus in accretionary orogen

    Utsunomiya, A., Jahn, B.-m., Ota, T., Safonova, I.Yu.

    Lithos   113 ( 3-4 )   2009年

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    掲載種別:研究論文(学術雑誌)  

    DOI: 10.1016/j.lithos.2009.05.020

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  • Neoproterozoic basalts of the Paleo-Asian Ocean (Kurai accretionary zone, Gorny Altai, Russia): geochemistry, petrogenesis, and geodynamics

    Safonova, I.Yu., Simonov, V.A., Buslov, M.M., Ota, T., Maruyama, Sh.

    Russian Geology and Geophysics   49 ( 4 )   2008年

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    掲載種別:研究論文(学術雑誌)  

    DOI: 10.1016/j.rgg.2007.09.011

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  • Preserved paleo-oceanic plateaus in accretionary complexes : Implications for the contributions of the Pacific Superplume to global environmental change

    UTSUNOMIYA A.

    Gondwana Research   14 ( 1-2 )   115 - 125   2008年

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    掲載種別:研究論文(学術雑誌)  

    DOI: 10.1016/j.gr.2007.11.003

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  • プレート沈み込みによるマントルへのホウ素輸送:含ダイアモンド電気石のホウ素同位体組成とその意義

    太田 努, 小林 桂, 中村 栄三

    日本地球化学会年会要旨集   55   67 - 67   2008年

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    出版者・発行元:日本地球化学会  

    沈み込み帯からマントル深部へ物質が移送される際,その化学組成は,共存する流体との間での元素分配を経て変化するが,その化学進化の過程は必ずしもよくわかっていない.本研究では,沈み込む地殻物質に特徴的であり,かつ流体が関与する過程での移動性が高い元素(ホウ素)に注目し,コクチェタフ超高圧変成岩に産する電気石のホウ素同位体組成を検討した.<BR>コクチェタフ産の電気石には,より低変成度の泥質変成岩に産するNa電気石と,最も変成度が高い含ダイアモンド岩の産地にのみ産するK電気石がある.前者のホウ素同位体組成が10Bに富んでいるのに対して,後者のそれは11Bに富んでいる.地殻物質のみをホウ素の貯蔵庫とする従来のモデルでは,K電気石のホウ素同位体組成を説明できない.そこで,そのホウ素同位体組成が,沈み込んだリソスフェリックマントル中の蛇紋石に由来するという新たなモデルを提案する.

    DOI: 10.14862/geochemproc.55.0.67.0

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  • Multiple generations of forearc mafic-ultramafic rocks in the Timor-Tanimbar ophiolite, eastern Indonesia

    ISHIKAWA A.

    Gondwana Research   11 ( 1-2 )   200 - 217   2007年

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    掲載種別:研究論文(学術雑誌)  

    DOI: 10.1016/j.gr.2006.04.007

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  • History of the Pacific superplume: Implications for Pacific paleogeography since the late proterozoic

    Utsunomiya, A., Ota, T., Windley, B.F., Suzuki, N., Uchio, Y., Munekata, K., Maruyama, S.

    Superplumes: Beyond Plate Tectonics   2007年

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Superplumes: Beyond Plate Tectonics  

    DOI: 10.1007/978-1-4020-5750-2_13

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  • Geology of the Gorny Altai subduction-accretion complex, southern Siberia: Tectonic evolution of an Ediacaran-Cambrian intra-oceanic arc-trench system

    Ota, T., Utsunomiya, A., Uchio, Y., Isozaki, Y., Buslov, M.M., Ishikawa, A., Maruyama, S., Kitajima, K., Kaneko, Y., Yamamoto, H., Katayama, I.

    Journal of Asian Earth Sciences   30 ( 5-6 )   2007年

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    掲載種別:研究論文(学術雑誌)  

    DOI: 10.1016/j.jseaes.2007.03.001

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  • Progressive metamorphism of the Taitao ophiolite; evidence for axial and off-axis hydrothermal alterations

    Shibuya, T., Komiya, T., Anma, R., Ota, T., Omori, S., Kon, Y., Yamamoto, S., Maruyama, S.

    Lithos   98 ( 1-4 )   2007年

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    掲載種別:研究論文(学術雑誌)  

    DOI: 10.1016/j.lithos.2007.04.003

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  • Paleocurrent patterns of the sedimentary sequence of the Taitao ophiolite constrained by anisotropy of magnetic susceptibility and paleomagnetic analyses

    VELOSO E. E.

    Sediment. Geol.   201 ( 3-4 )   446 - 460   2007年

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    掲載種別:研究論文(学術雑誌)  

    DOI: 10.1016/j.sedgeo.2007.07.005

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  • On-going orogeny in the outer-arc of the Timor-Tanimbar region, eastern Indonesia

    Kaneko, Y., Maruyama, S., Kadarusman, A., Ota, T., Ishikawa, M., Tsujimori, T., Ishikawa, A., Okamoto, K.

    Gondwana Research   11 ( 1-2 )   2007年

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    掲載種別:研究論文(学術雑誌)  

    DOI: 10.1016/j.gr.2006.04.013

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  • Accretionary Complex Origin of the Mafic-Ultramafic Bodies of the Sanbagawa Belt, Central Shikoku, Japan

    J. G. Liou, Brian F. Windley, Hiroaki Ozawa, Ryo Anma, Akira Ishikawa, Tsuyoshi Komiya, Ikuo Katayama, Shigenori Maruyama, Tsutomu Ota, Yoshiyuki Kaneko, Hiroshi Yamamoto, Kazuaki Okamoto, Masaru Terabayashi

    International Geology Review   47 ( 10 )   2005年

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    掲載種別:研究論文(学術雑誌)  

    DOI: 10.2747/0020-6814.47.10.1058

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  • Thermobaric structure and metamorphic evolution of the Iratsu eclogite body in the Sanbagawa belt, central Shikoku, Japan

    Ota, T., Terabayashi, M., Katayama, I.

    Lithos   73 ( 1-2 )   2004年

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    掲載種別:研究論文(学術雑誌)  

    DOI: 10.1016/j.lithos.2004.01.001

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  • The oldest mid-oceanic carbonate buildup complex: Setting and lithofacies of the Vendian (Late Neoproterozoic) Baratal limestone in the Gorny Altai Mountains, Siberia

    Uchio Yuko, Isozaki Yukio, Ota Tsutomu, UTSUNOMIYA Atsushi, BUSLOV Mikhail M., MARUYAMA Shigenori

    Proceedings of the Japan Academy. Ser. B: Physical and Biological Sciences   80 ( 9 )   422 - 428   2004年

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

    The Baratal limestone in the Gorny Altai Mountains, southern Siberia, occurs as large allochthonous blocks within a Cambrian accretionary complex that developed around the Siberia craton. Before the final accretion to Siberia in the Cambrian, the terrigenous clastic-free Baratal limestone was deposited directly upon a basaltic basement with a geochemical signature identical to that of modern oceanic plateau. The Baratal limestone with 598&plusmn;25 Ma (Early Vendian) Pb-Pb isochron age consists of three distinct facies; 1) massive lime mudstone with ooids and stromatolites, 2) bedded lime mudstone, and 3) limestone conglomerate/breccia dominated by ooid-bearing lime mudstone clasts. The first represents a shallow marine environment on top of an ancient oceanic plateau, while the latter two represent the deeper slope to bottom-of-slope facies of a plateau. The Vendian Baratal limestone provides the oldest example of a reconstructed shallow marine carbonate buildup complex developed on a plateau/seamount in a mid-ocean.<br> <br> <br> (Communicated by Tatsuro MATSUMOTO, M.J.A.)<br>

    DOI: 10.2183/pjab.80.422

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  • P-T history of garnet-websterites in the Sharyzhalgai complex, southwestern margin of Siberian craton: Evidence for Paleoproterozoic high-pressure metamorphism

    Ota, T., Gladkochub, D.P., Sklyarov, E.V., Mazukabzov, A.M., Watanabe, T.

    Precambrian Research   132 ( 4 )   2004年

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    掲載種別:研究論文(学術雑誌)  

    DOI: 10.1016/j.precamres.2004.03.009

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  • Zircon geochemistry of Mid-Miocene adakites in the southern Patagonian province

    Tsutomu Ota

    Geochimica et Cosmochimica Acta   2003年

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    掲載種別:研究論文(学術雑誌)  

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  • 口絵5 : シベリア南部ゴルニアルタイ山地の古海台 / 海山頂部起源石灰岩の野外の産状と岩相・組織

    内尾 優子, 磯崎 行雄, Mikhail BUSLOV, 太田 努, 宇都宮 敦, 丸山 茂徳

    地学雑誌   112 ( 4 )   Plate9 - Plate10   2003年

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    出版者・発行元:Tokyo Geographical Society  

    DOI: 10.5026/jgeography.112.4_Plate9

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  • P-66 ロシア南部ゴルニアルタイ山地カンブリア紀付加体中の古海山起源石灰岩の層序(10. 地域地質・地域層序,ポスター発表,一般講演)

    内尾 優子, 磯崎 行雄, 太田 努, 宇都宮 敦, Buslov M. M., 丸山 茂徳

    日本地質学会学術大会講演要旨   2002   239 - 239   2002年

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    記述言語:日本語   出版者・発行元:日本地質学会  

    DOI: 10.14863/geosocabst.2002.0_239_2

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  • Contact metamorphism of the Daulet Suite by solid-state emplacement of the Kokchetav UHP-HP metamorphic slab

    Terabayashi, M., Ota, T., Yamamoto, H., Kaneko, Y.

    International Geology Review   44 ( 9 )   2002年

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    掲載種別:研究論文(学術雑誌)  

    DOI: 10.2747/0020-6814.44.9.819

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  • Metamorphic evolution of Late Precambrian eclogites and associated metabasites, Gorny Altai, southern Russia

    Ota, T., Buslov, M.M., Watanabe, T.

    International Geology Review   44 ( 9 )   2002年

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    掲載種別:研究論文(学術雑誌)  

    DOI: 10.2747/0020-6814.44.9.837

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  • Middle paleozoic age of metamorphism in the South Chuya complex in Gorny Altai (results of ar-ar, rb-sr, and u-pb isotope dating)

    Plotnikov, A.V., Titov, A.V., Kruk, N.N., Ota, T., Kabashima, T., Hirata, T.

    Geologiya i Geofizika   42 ( 9 )   2001年

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    掲載種別:研究論文(学術雑誌)  

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  • Archean supracrustal rocks of the Sharyzhalgai Salient and their tectonic implications

    Sklyarov, E.V., Gladkochub, D.P., Watanabe, T., Fanning, M.K., Mazukabzov, A.M., Men'shagin, Yu.V., Ota, T.

    Doklady Earth Sciences   377 A   2001年

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    掲載種別:研究論文(学術雑誌)  

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  • Archean supercrystal rocks of the Sharizhalgay block: Tectonic constrains

    Sklyarov, E.V., Gladkochub, D.P., Watanabe, T., Fanning, M.K., Mazukabzov, A.M., Men'shagin, Yu.V., Ota, T.

    Doklady Akademii Nauk   377 ( 3 )   2001年

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    掲載種別:研究論文(学術雑誌)  

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  • Metamorphic Petrology of Garnet Pyroxenite and Associated Gneiss from the Early Proterozoic Sharyzhalgai Block in the Southwestern Margin of Siberian Craton

    Ota, T., Sklyarov, E.V., Gladkochub, D.P., Watanabe, T.

    Gondwana Research   4 ( 4 )   2001年

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    掲載種別:研究論文(学術雑誌)  

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  • Geology of the Kokchetav UHP-HP metamorphic belt, Northern Kazakhstan

    Kaneko, Y., Maruyama, S., Terabayashi, M., Yamamoto, H., Ishikawa, M., Anma, R., Parkinson, C.D., Ota, T., Nakajima, Y., Katayama, I., Yamamoto, J., Yamauchi, K.

    Island Arc   9 ( 3 )   2000年

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    掲載種別:研究論文(学術雑誌)  

    DOI: 10.1046/j.1440-1738.2000.00278.x

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  • Thermobaric structure of the Kokchetav ultrahigh-pressure-high-pressure Massif deduced from a north-south transect in the Kulet and Saldat-Kol regions, northern Kazakhstan

    OTA T.

    The Island Arc   9 ( 3 )   329 - 358   2000年

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    掲載種別:研究論文(学術雑誌)  

    DOI: 10.1046/j.1440-1738.2000.00282.x

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  • P-257 ロシア南部ゴルニアルタイ山地の原生代/顕生代境界頃の石灰岩 : 岩相の特徴と全岩Pb-Pb同位体年代

    内尾 優子, 磯崎 行雄, 能田 成, 太田 努, 石川 晃, 宇都宮 敦, Buslov M.M., 丸山 茂徳

    日本地質学会学術大会講演要旨   1999   305 - 305   1999年

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    記述言語:日本語   出版者・発行元:日本地質学会  

    DOI: 10.14863/geosocabst.1999.0_305_2

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  • シベリアクラトン南縁部,カンブリア紀付加体に産する緑色岩の岩石学

    宇都宮 敦, 太田 努, 石川 晃, 丸山 茂徳, M. Buslov

    日本地質学会学術大会講演要旨   1998   444 - 444   1998年

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    記述言語:日本語   出版者・発行元:一般社団法人 日本地質学会  

    DOI: 10.14863/geosocabst.1998.0_444

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  • ロシア南部ゴルニアルタイ地域のベンド紀・カンブリア紀石灰岩:野外の産状と岩相

    内尾 優子, 磯崎 行雄, 太田 努, 丸山 茂徳, M.M. Buslov

    日本地質学会学術大会講演要旨   1998   513 - 513   1998年

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    記述言語:日本語   出版者・発行元:一般社団法人 日本地質学会  

    DOI: 10.14863/geosocabst.1998.0_513

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  • カザフ共和国北部・コクチェタフ超高圧変成帯の地質と地質構造(1)

    金子 慶之, 丸山 茂徳, 寺林 優, 山本 啓司, 石川 正弘, 安間 了, C.B Parkinson, 太田 努, 中島 洋一, 片山 郁夫, 山内 一弘, 真砂 秀樹, 小笠原 義秀

    日本地質学会学術大会講演要旨   1998   431 - 431   1998年

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    記述言語:日本語   出版者・発行元:一般社団法人 日本地質学会  

    DOI: 10.14863/geosocabst.1998.0_431

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  • カザフ共和国コクチェタフ超高圧変成帯Barchikol地域のエクロジャイトの岩石学

    真砂 秀樹, 太田 努, クリス パーキンソン, 寺林 優, 中島 洋一, 丸山 茂徳

    日本地質学会学術大会講演要旨   1998   432 - 432   1998年

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    記述言語:日本語   出版者・発行元:一般社団法人 日本地質学会  

    DOI: 10.14863/geosocabst.1998.0_432

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  • Modes of occurrence of sodic amphibole from the Kamuikotan metabasites, west of Asahikawa, central Hokkaido and the metamorphic history.

    Ota, Tsutomu

    JOURNAL OF MINERALOGY, PETROLOGY AND ECONOMIC GEOLOGY   92 ( 3 )   103 - 123   1997年

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    掲載種別:研究論文(学術雑誌)  

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  • 181 原生代大陸衝突型造山帯西オーストラリアカプリコーン造山帯の変成分帯

    真砂 英樹, 金子 慶之, 太田 努, 丸山 茂徳, 磯崎 行雄

    日本地質学会学術大会講演要旨   1997   193 - 193   1997年

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    記述言語:日本語   出版者・発行元:日本地質学会  

    DOI: 10.14863/geosocabst.1997.0_193_1

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  • Metamorphic evolution of the Kamuikotan high-pressure and low- temperature metamorphic rocks in central Hokkaido, Japan

    Sakakibara, M., Ota, T.

    Journal of Geophysical Research   99 ( B11 )   1994年

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    掲載種別:研究論文(学術雑誌)  

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  • K-Ar ages of the Kamuikotan metamorphic rocks in Hokkaido, Japan

    Ota, T., Sakakibara, M., Itaya, T.

    Journal - Geological Society of Japan   99 ( 5 )   1993年

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    掲載種別:研究論文(学術雑誌)  

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▼全件表示

MISC

  • Supervolcano eruptions driven by melt buoyancy in large silicic magma chambers

    Wim J. Malfait, Rita Seifert, Sylvain Petitgirard, Jean-Philippe Perrillat, Mohamed Mezouar, Tsutomu Ota, Eizo Nakamura, Philippe Lerch, Carmen Sanchez-Valle

    NATURE GEOSCIENCE   7 ( 2 )   122 - 125   2014年2月

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    記述言語:英語   出版者・発行元:NATURE PUBLISHING GROUP  

    Super-eruptions that dwarf all historical volcanic episodes in erupted volume(1) and environmental impact(2) are abundant in the geological record. Such eruptions of silica-rich magmas form large calderas. The mechanisms that trigger these super-eruptions are elusive because the processes occurring in conventional volcanic systems cannot simply be scaled up to the much larger magma chambers beneath supervolcanoes. Over-pressurization of the magma reservoir, caused by magma recharge, is a common trigger for smaller eruptions(3), but is insufficient to generate eruptions from large supervolcano magma chambers(4). Magma buoyancy can potentially create sufficient overpressure(4), but the efficiency of this trigger mechanism has not been tested. Here we use synchrotron measurements of X-ray absorption(5) to determine the density of silica-rich magmas at pressures and temperatures of up to 3.6 GPa and 1,950 K, respectively. We combine our results with existing measurements of silica-rich magma density at ambient pressures(6,7) to show that magma buoyancy can generate an overpressure on the roof of a large supervolcano magma chamber that exceeds the critical overpressure of 10-40 MPa required to induce dyke propagation(4), even when the magma is undersaturated in volatiles. We conclude that magma buoyancy alone is a viable mechanism to trigger a super-eruption, although magma recharge and mush rejuvenation(8), volatile saturation(9) or tectonic stress(10) may have been important during specific eruptions.

    DOI: 10.1038/NGEO2042

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  • Supervolcano eruptions driven by melt buoyancy in large silicic magma chambers

    Wim J. Malfait, Rita Seifert, Sylvain Petitgirard, Jean-Philippe Perrillat, Mohamed Mezouar, Tsutomu Ota, Eizo Nakamura, Philippe Lerch, Carmen Sanchez-Valle

    NATURE GEOSCIENCE   7 ( 2 )   122 - 125   2014年2月

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    記述言語:英語   出版者・発行元:NATURE PUBLISHING GROUP  

    Super-eruptions that dwarf all historical volcanic episodes in erupted volume(1) and environmental impact(2) are abundant in the geological record. Such eruptions of silica-rich magmas form large calderas. The mechanisms that trigger these super-eruptions are elusive because the processes occurring in conventional volcanic systems cannot simply be scaled up to the much larger magma chambers beneath supervolcanoes. Over-pressurization of the magma reservoir, caused by magma recharge, is a common trigger for smaller eruptions(3), but is insufficient to generate eruptions from large supervolcano magma chambers(4). Magma buoyancy can potentially create sufficient overpressure(4), but the efficiency of this trigger mechanism has not been tested. Here we use synchrotron measurements of X-ray absorption(5) to determine the density of silica-rich magmas at pressures and temperatures of up to 3.6 GPa and 1,950 K, respectively. We combine our results with existing measurements of silica-rich magma density at ambient pressures(6,7) to show that magma buoyancy can generate an overpressure on the roof of a large supervolcano magma chamber that exceeds the critical overpressure of 10-40 MPa required to induce dyke propagation(4), even when the magma is undersaturated in volatiles. We conclude that magma buoyancy alone is a viable mechanism to trigger a super-eruption, although magma recharge and mush rejuvenation(8), volatile saturation(9) or tectonic stress(10) may have been important during specific eruptions.

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  • Space environment of an asteroid preserved on micrograins returned by the Hayabusa spacecraft

    Eizo Nakamura, Akio Makishima, Takuya Moriguti, Katsura Kobayashi, Ryoji Tanaka, Tak Kunihiro, Tatsuki Tsujimori, Chie Sakaguchi, Hiroshi Kitagawa, Tsutomu Ota, Yusuke Yachi, Toru Yada, Masanao Abe, Akio Fujimura, Munetaka Ueno, Toshifumi Mukai, Makoto Yoshikawa, Jun'ichiro Kawaguchi

    PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA   109 ( 11 )   E624 - E629   2012年3月

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    記述言語:英語   出版者・発行元:NATL ACAD SCIENCES  

    Records of micrometeorite collisions at down to submicron scales were discovered on dust grains recovered from near-Earth asteroid 25143 (Itokawa). Because the grains were sampled from very near the surface of the asteroid, by the Hayabusa spacecraft, their surfaces reflect the low-gravity space environment influencing the physical nature of the asteroid exterior. The space environment was examined by description of grain surfaces and asteroidal scenes were reconstructed. Chemical and O isotope compositions of five lithic grains, with diameters near 50 mu m, indicate that the uppermost layer of the rubble-pile-textured Itokawa is largely composed of equilibrated LL-ordinary-chondrite-like material with superimposed effects of collisions. The surfaces of the grains are dominated by fractures, and the fracture planes contain not only sub-mu m-sized craters but also a large number of sub-mu m-to several-mu m-sized adhered particles, some of the latter composed of glass. The size distribution and chemical compositions of the adhered particles, together with the occurrences of the sub-mu m-sized craters, suggest formation by hypervelocity collisions of micrometeorites at down to nm scales, a process expected in the physically hostile environment at an asteroid's surface. We describe impact-related phenomena, ranging in scale from 10(-9) to 10(4) meters, demonstrating the central role played by impact processes in the long-term evolution of planetary bodies. Impact appears to be an important process shaping the exteriors of not only large planetary bodies, such as the moon, but also low-gravity bodies such as asteroids.

    DOI: 10.1073/pnas.1116236109

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  • Space environment of an asteroid preserved on micrograins returned by the Hayabusa spacecraft

    Eizo Nakamura, Akio Makishima, Takuya Moriguti, Katsura Kobayashi, Ryoji Tanaka, Tak Kunihiro, Tatsuki Tsujimori, Chie Sakaguchi, Hiroshi Kitagawa, Tsutomu Ota, Yusuke Yachi, Toru Yada, Masanao Abe, Akio Fujimura, Munetaka Ueno, Toshifumi Mukai, Makoto Yoshikawa, Jun'ichiro Kawaguchi

    PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA   109 ( 11 )   E624 - E629   2012年3月

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    記述言語:英語   出版者・発行元:NATL ACAD SCIENCES  

    Records of micrometeorite collisions at down to submicron scales were discovered on dust grains recovered from near-Earth asteroid 25143 (Itokawa). Because the grains were sampled from very near the surface of the asteroid, by the Hayabusa spacecraft, their surfaces reflect the low-gravity space environment influencing the physical nature of the asteroid exterior. The space environment was examined by description of grain surfaces and asteroidal scenes were reconstructed. Chemical and O isotope compositions of five lithic grains, with diameters near 50 mu m, indicate that the uppermost layer of the rubble-pile-textured Itokawa is largely composed of equilibrated LL-ordinary-chondrite-like material with superimposed effects of collisions. The surfaces of the grains are dominated by fractures, and the fracture planes contain not only sub-mu m-sized craters but also a large number of sub-mu m-to several-mu m-sized adhered particles, some of the latter composed of glass. The size distribution and chemical compositions of the adhered particles, together with the occurrences of the sub-mu m-sized craters, suggest formation by hypervelocity collisions of micrometeorites at down to nm scales, a process expected in the physically hostile environment at an asteroid's surface. We describe impact-related phenomena, ranging in scale from 10(-9) to 10(4) meters, demonstrating the central role played by impact processes in the long-term evolution of planetary bodies. Impact appears to be an important process shaping the exteriors of not only large planetary bodies, such as the moon, but also low-gravity bodies such as asteroids.

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  • In situ ion-microprobe determination of trace element partition coefficients for hornblende, plagioclase, orthopyroxene, and apatite in equilibrium with natural rhyolitic glass, Little Glass Mountain Rhyofite, California

    James G. Brophy, Tsutomu Ota, Tak Kunihro, Tatsuki Tsujimori, Eizo Nakamura

    AMERICAN MINERALOGIST   96 ( 11-12 )   1838 - 1850   2011年11月

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    記述言語:英語   出版者・発行元:MINERALOGICAL SOC AMER  

    Partially crystalline hornblende gabbro inclusions from the Little Glass Mountain Rhyolite contain euhedral plagioclase, orthopyroxene, hornblende, and apatite crystals in contact with interstitial rhyolitic (71-76% SiO(2)) glass. Textural and mineral compositional data indicate that the gabbros crystallized sufficiently slowly that surface equilibrium was closely approached at the interface between crystals and the liquid. This rare occurrence represents a natural dynamic crystallization experiment with a "run time" that is not realistically achievable in the laboratory. SIMS analysis of mineral rim-glass pairs have permitted the determination of high-quality, equilibrium trace-element partition coefficients for all four minerals. These data augment the limited partition coefficient database for minerals in high-SiO(2) rhyolitic systems. For all minerals, the D values are consistent with those anticipated from crystal-chemical considerations. These data further support a liquid SiO(2) control on the REEs (and presumably other elements) partitioning wherein D values systematically increase with increasing liquid SiO(2) content.

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  • In situ ion-microprobe determination of trace element partition coefficients for hornblende, plagioclase, orthopyroxene, and apatite in equilibrium with natural rhyolitic glass, Little Glass Mountain Rhyofite, California

    James G. Brophy, Tsutomu Ota, Tak Kunihro, Tatsuki Tsujimori, Eizo Nakamura

    AMERICAN MINERALOGIST   96 ( 11-12 )   1838 - 1850   2011年11月

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    記述言語:英語   出版者・発行元:MINERALOGICAL SOC AMER  

    Partially crystalline hornblende gabbro inclusions from the Little Glass Mountain Rhyolite contain euhedral plagioclase, orthopyroxene, hornblende, and apatite crystals in contact with interstitial rhyolitic (71-76% SiO(2)) glass. Textural and mineral compositional data indicate that the gabbros crystallized sufficiently slowly that surface equilibrium was closely approached at the interface between crystals and the liquid. This rare occurrence represents a natural dynamic crystallization experiment with a "run time" that is not realistically achievable in the laboratory. SIMS analysis of mineral rim-glass pairs have permitted the determination of high-quality, equilibrium trace-element partition coefficients for all four minerals. These data augment the limited partition coefficient database for minerals in high-SiO(2) rhyolitic systems. For all minerals, the D values are consistent with those anticipated from crystal-chemical considerations. These data further support a liquid SiO(2) control on the REEs (and presumably other elements) partitioning wherein D values systematically increase with increasing liquid SiO(2) content.

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  • Blueschists, eclogites, and subduction zone tectonics: Insights from a review of Late Miocene blueschists and eclogites, and related young high-pressure metamorphic rocks

    Tsutomu Ota, Yoshiyuki Kaneko

    GONDWANA RESEARCH   18 ( 1 )   167 - 188   2010年7月

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

    In this paper, Late Miocene blueschist and eclogite belts, including the world's youngest blueschist belt in Timor-Tanimbar Island chain, eastern Indonesia, and the world's youngest coesite-bearing eclogite, Papua New Guinea, together with selected Cenozoic high-pressure and ultrahigh-pressure metamorphic rocks are reviewed. From a synthesis of the geology, metamorphism and chronology of these rocks, the formation and exhumation process are evaluated and the significance on tectonics at convergent plate boundaries is discussed. (c) 2010 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.gr.2010.02.013

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  • Blueschists, eclogites, and subduction zone tectonics: Insights from a review of Late Miocene blueschists and eclogites, and related young high-pressure metamorphic rocks

    Tsutomu Ota, Yoshiyuki Kaneko

    GONDWANA RESEARCH   18 ( 1 )   167 - 188   2010年7月

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

    In this paper, Late Miocene blueschist and eclogite belts, including the world's youngest blueschist belt in Timor-Tanimbar Island chain, eastern Indonesia, and the world's youngest coesite-bearing eclogite, Papua New Guinea, together with selected Cenozoic high-pressure and ultrahigh-pressure metamorphic rocks are reviewed. From a synthesis of the geology, metamorphism and chronology of these rocks, the formation and exhumation process are evaluated and the significance on tectonics at convergent plate boundaries is discussed. (c) 2010 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.gr.2010.02.013

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  • Transitional time of oceanic to continental subduction in the Dabie orogen: Constraints from U-Pb, Lu-Hf, Sm-Nd and Ar-Ar multichronometric dating

    Cheng, H, King, R. L, Nakamura, E, Vervoort, J. D, Zheng, Y.-F, Ota, T, Wu, Y.-B, Kobayashi, K, Zhou, Z.-Y

    Lithos   110 ( 1-4 )   327 - 342   2009年

  • Boron cycling by subducted lithosphere; insights from diamondiferous tourmaline from the Kokchetav ultrahigh-pressure metamorphic belt

    Tsutomu Ota, Katsura Kobayashi, Takuya Kunihiro, Eizo Nakamura

    GEOCHIMICA ET COSMOCHIMICA ACTA   72 ( 14 )   3531 - 3541   2008年7月

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    記述言語:英語   出版者・発行元:PERGAMON-ELSEVIER SCIENCE LTD  

    Subduction of lithosphere, involving surficial materials, into the deep mantle is fundamental to the chemical evolution of the Earth. However, the chemical evolution of the lithosphere during subduction to depth remains equivocal. In order to identify materials subjected to geological processes near the surface and at depths in subduction zones, we examined B and Li isotopes behavior in a unique diamondiferous, K-rich tourmaline (K-tourmaline) from the Kokchetav ultrahigh-pressure metamorphic belt. The K-tourmaline, which includes microdiamonds in its core, is enriched in B-11 relative to B-10 (delta B-11 = -1.2 to +7.7) and Li-7 relative to Li-6 (delta Li-7 = -1.1 to +3.1). It is suggested that the K-tourmaline crystallized at high-pressure in the diamond stability field from a silicate melt generated at high-pressure and temperature conditions of the Kokchetav peak metamorphism. The heavy isotope signature of this K-tourmaline differs from that of ordinary Na-tourmalines in crustal rocks, enriched in the light B isotope (delta B-11 = -16.6 to -2.3), which experienced isotope fractionation through metamorphic dehydration reactions. A possible source of the heavy B-isotope signature is serpentine in the subducted lithospheric mantle. Serpentinization of the lithospheric mantle, with enrichment of heavy B-isotope, can be produced by normal faulting at trench-outer rise or trench slope regions, followed by penetration of seawater into the lithospheric mantle. Serpentine breakdown in the lithospheric mantle subducted in subarc regions likely provided fluids with the heavy B-isotope signature, which was acquired during the serpentinization prior to subduction. The fluids could ascend and cause partial melting of the overlying crustal layer, and the resultant silicate melt could inherit the heavy B-isotope signature. The subducting lithospheric mantle is a key repository for modeling the flux of fluids and associated elements acquired at a near the surface into the deep mantle. (c) 2008 Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.gca.2008.05.002

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  • Boron cycling by subducted lithosphere; insights from diamondiferous tourmaline from the Kokchetav ultrahigh-pressure metamorphic belt

    Tsutomu Ota, Katsura Kobayashi, Takuya Kunihiro, Eizo Nakamura

    GEOCHIMICA ET COSMOCHIMICA ACTA   72 ( 14 )   3531 - 3541   2008年7月

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    記述言語:英語   出版者・発行元:PERGAMON-ELSEVIER SCIENCE LTD  

    Subduction of lithosphere, involving surficial materials, into the deep mantle is fundamental to the chemical evolution of the Earth. However, the chemical evolution of the lithosphere during subduction to depth remains equivocal. In order to identify materials subjected to geological processes near the surface and at depths in subduction zones, we examined B and Li isotopes behavior in a unique diamondiferous, K-rich tourmaline (K-tourmaline) from the Kokchetav ultrahigh-pressure metamorphic belt. The K-tourmaline, which includes microdiamonds in its core, is enriched in B-11 relative to B-10 (delta B-11 = -1.2 to +7.7) and Li-7 relative to Li-6 (delta Li-7 = -1.1 to +3.1). It is suggested that the K-tourmaline crystallized at high-pressure in the diamond stability field from a silicate melt generated at high-pressure and temperature conditions of the Kokchetav peak metamorphism. The heavy isotope signature of this K-tourmaline differs from that of ordinary Na-tourmalines in crustal rocks, enriched in the light B isotope (delta B-11 = -16.6 to -2.3), which experienced isotope fractionation through metamorphic dehydration reactions. A possible source of the heavy B-isotope signature is serpentine in the subducted lithospheric mantle. Serpentinization of the lithospheric mantle, with enrichment of heavy B-isotope, can be produced by normal faulting at trench-outer rise or trench slope regions, followed by penetration of seawater into the lithospheric mantle. Serpentine breakdown in the lithospheric mantle subducted in subarc regions likely provided fluids with the heavy B-isotope signature, which was acquired during the serpentinization prior to subduction. The fluids could ascend and cause partial melting of the overlying crustal layer, and the resultant silicate melt could inherit the heavy B-isotope signature. The subducting lithospheric mantle is a key repository for modeling the flux of fluids and associated elements acquired at a near the surface into the deep mantle. (c) 2008 Elsevier Ltd. All rights reserved.

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  • Tourmaline breakdown in a pelitic system: implications for boron cycling through subduction zones

    Tsutomu Ota, Katsura Kobayashi, Tomoo Katsura, Eizo Nakamura

    CONTRIBUTIONS TO MINERALOGY AND PETROLOGY   155 ( 1 )   19 - 32   2008年1月

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    記述言語:英語   出版者・発行元:SPRINGER  

    Pressure-temperature conditions of tourmaline breakdown in a metapelite were determined by high-pressure experiments at 700-900 degrees C and 4-6 GPa. These experiments produced an eclogite-facies assemblage of garnet, clinopyroxene, phengite, coesite, kyanite and rare rutile. The modal proportions of tourmaline clearly decreased between 4.5 and 5 GPa at 700 degrees C, between 4 and 4.5 GPa at 800 degrees C, and between 800 and 850 degrees C at 4 GPa, with tourmaline that survived the higher temperature conditions appearing corroded and thus metastable. Decreases in the modal abundance of tourmaline are accompanied by decreasing modal abundance of coesite, and increasing that of clinopyroxene, garnet and kyanite; the boron content of phengite increases significantly. These changes suggest that, with increasing pressure and temperature, tourmaline reacts with coesite to produce clinopyroxene, garnet, kyanite, and boron-bearing phengite and fluid. Our results suggest that: (1) tourmaline breakdown occurs at lower pressures and temperatures in SiO(2)-saturated systems than in SiO(2)-undersaturated systems. (2) In even cold subduction zones, subducting sediments should release boron-rich fluids by tourmaline breakdown before reaching depths of 150 km, and (3) even after tourmaline breakdown, a significant amount of boron partitioned into phengite could be stored in deeply subducted sediments.

    DOI: 10.1007/s00410-007-0228-2

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  • Tourmaline breakdown in a pelitic system: implications for boron cycling through subduction zones

    Tsutomu Ota, Katsura Kobayashi, Tomoo Katsura, Eizo Nakamura

    CONTRIBUTIONS TO MINERALOGY AND PETROLOGY   155 ( 1 )   19 - 32   2008年1月

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    記述言語:英語   出版者・発行元:SPRINGER  

    Pressure-temperature conditions of tourmaline breakdown in a metapelite were determined by high-pressure experiments at 700-900 degrees C and 4-6 GPa. These experiments produced an eclogite-facies assemblage of garnet, clinopyroxene, phengite, coesite, kyanite and rare rutile. The modal proportions of tourmaline clearly decreased between 4.5 and 5 GPa at 700 degrees C, between 4 and 4.5 GPa at 800 degrees C, and between 800 and 850 degrees C at 4 GPa, with tourmaline that survived the higher temperature conditions appearing corroded and thus metastable. Decreases in the modal abundance of tourmaline are accompanied by decreasing modal abundance of coesite, and increasing that of clinopyroxene, garnet and kyanite; the boron content of phengite increases significantly. These changes suggest that, with increasing pressure and temperature, tourmaline reacts with coesite to produce clinopyroxene, garnet, kyanite, and boron-bearing phengite and fluid. Our results suggest that: (1) tourmaline breakdown occurs at lower pressures and temperatures in SiO(2)-saturated systems than in SiO(2)-undersaturated systems. (2) In even cold subduction zones, subducting sediments should release boron-rich fluids by tourmaline breakdown before reaching depths of 150 km, and (3) even after tourmaline breakdown, a significant amount of boron partitioned into phengite could be stored in deeply subducted sediments.

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  • チリ海嶺沈み込み帯にみられるオフィオライトと珪長質深成岩類

    安間 了, 小宮 剛, 昆 慶明, 渋谷 岳造, 太田 努, 折橋 裕二, Armstrong Richard

    日本地球化学会年会要旨集   55   301 - 301   2008年

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    出版者・発行元:日本地球化学会  

    チリ海嶺が沈み込みつつあるタイタオ半島の西端部には、5.7 Maのオフィオライトとそれを取り囲むように5つの角閃石-黒雲母花崗岩体が分布する。これらの珪長質深成岩体のU-Pb年代測定と全岩化学分析をおこなった。リサイクル・ジルコンはほとんど見られず、若くて熱い海洋地殻の部分溶融や結晶分化作用によって、花崗岩マグマが生成し得たことを示した。海嶺の衝突・沈み込みという一連のテクトニックな過程の結果、さまざまな組成を持つ花崗岩が生成しうるということを議論したい。

    DOI: 10.14862/geochemproc.55.0.301.0

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  • O-142 北海道中央部の神居古潭変成岩類におけるシャッフルカード構造(14.付加体,口頭発表,一般講演)

    榊原 正幸, 安元 和己, 太田 努, 池田 倫治

    日本地質学会学術大会講演要旨   114   132 - 132   2007年9月

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    記述言語:日本語   出版者・発行元:日本地質学会  

    DOI: 10.14863/geosocabst.2007.0.256.0

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  • S-47 四国中央部三波川変成帯の形成と上昇機構((5)プレート収束境界における岩石の沈み込み・上昇テクトニクス : 造山帯(変成帯)形成過程研究の新展開,口頭発表,シンポジウム)

    青木 一勝, 眞砂 英樹, 寺林 優, 金子 慶之, 岡本 和明, 山本 啓司, 太田 努, 丸山 茂徳

    日本地質学会学術大会講演要旨   114   25 - 25   2007年9月

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    記述言語:日本語   出版者・発行元:日本地質学会  

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  • 深部付加体としての神居古潭変成岩類の原岩層序・付加プロセス・変形変成作用および流体-岩石相互作用

    榊原 正幸, 安元 和己, 池田 倫治, 太田 努

    地質学雑誌   113   103 - 118   2007年

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    出版者・発行元:The Geological Society of Japan  

    北海道の中軸部を占める神居古潭変成帯は,従来から多くの研究者によって地質学的,構造地質学的,変成岩岩石学的および年代学的に研究されてきた.本巡検では,これまでの研究成果を総括し,神居古潭変成岩の原岩層序およびその形成プロセス,沈み込み帯深部における海山・海洋島などの海洋性地殻や遠洋性堆積物の底付けプロセスおよびその際の変形・変成作用を観察する.また,同変成岩から発見された沈み込み帯変成作用後に流入した流体による交代作用についても観察する.

    DOI: 10.5575/geosoc.113.S103

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  • シベリア南部ゴルニアルタイ山地のカンブリア紀付加体に産する古海台/海山頂部起源石灰岩

    内尾 優子, 磯崎 行雄, Buslov Mikhail M, 太田 努, 宇都宮 敦, 丸山 茂徳

    地學雜誌   112 ( 4 )   563 - 585   2003年8月

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    記述言語:日本語   出版者・発行元:公益社団法人 東京地学協会  

    Vendian-Cambrian Baratal limestone occurs as large allochthonous blocks in the Cambrian accretionary complex of the Gorny Altai Mountains, southern Russia. We analyzed the primary stratigraphy and depositional environments of Baratal limestone in the Kurai and Akkaya areas in the eastern part of the Gorny Altai Mountains.&lt;BR&gt;In the Kurai and the Akkaya areas, Baratal limestone conformably overlies basaltic greenstone. Geochemistry of this greenstone is similar to that found in modern oceanic plateau basalt or oceanic island basalt. The limestone lacks terrigeneous elastic influx. These suggest that the Baratal limestone was originally deposited on and around a plateau or seamount far from the continents in a mid-oceanic environment.&lt;BR&gt;Baratal limestone in the study area is lithologically divided into four types; 1) massive lime mudstone, 2) massive limestone conglomerate 3) bedded lime mudstone with slump structures, and 4) laminated lime mudstone. Massive lime mudstone contains stromatolites and ooids. This evidence suggests that the massive lime mudstone was formed in a shallowmarine environment. The massive limestone conglomerate contains angular clasts of lime mudstone, greenstone and chert. Its poorly graded and poorly sorted characteristics suggest that the limestone conglomerate was formed as debris flow deposits. Some parts of bedded lime mudstone have slump structures, and are interpreted as sliding deposits. In addition, laminated lime mudstone that shares an affinity with limestone turbidite, is associated with the massive limestone conglomerate.&lt;BR&gt;Sedimentary environments of these four types of limestone are inferred, respectively as follows ; massive lime mudstone may have been diposited on the top of a paleo-plateau/ -seamount, while massive limestone conglomerate, bedded lime mudstone with slump structures, and laminated lime mudstone on the slope of a paleo-plateau/-seamount.

    DOI: 10.5026/jgeography.112.4_563

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  • O-12 チリ海嶺沈み込み帯東部のタイタオ半島に露出する鮮新世オフィオライトの地質-予報-(2. オフィオライト・マントル岩体・付加体緑色岩・海洋底岩石,口頭発表,一般講演)

    安間 了, Veloso A., 金子 慶之, 寺林 優, 太田 努, 小宮 剛, 片山 郁夫, 丸山 茂徳, Herve F.

    日本地質学会学術大会講演要旨   2002   7 - 7   2002年

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    記述言語:日本語   出版者・発行元:日本地質学会  

    DOI: 10.14863/geosocabst.2002.0_7_2

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  • P-68 ロシア南部ゴルニアルタイ山地中の原生代/顕生代境界頃の古海山頂部起源石灰岩の層序(11. 年代層序スケール,ポスターセッション,一般発表)

    内尾 優子, 磯崎 行雄, 川幡 穂高, 能田 成, 太田 努, Buslov M. M, 丸山 茂徳

    日本地質学会学術大会講演要旨   2001 ( 0 )   231 - 231   2001年

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    記述言語:日本語   出版者・発行元:一般社団法人 日本地質学会  

    DOI: 10.14863/geosocabst.2001.0_231_2

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  • O-126 ロシア南部ゴルニアルタイ山地のカンブリア紀古海山頂部石灰岩 : その産状・層序・放射性年代・微化石および炭素同位体比(12. 年代層序スケール,口頭発表,一般発表)

    内尾 優子, 磯崎 行雄, 川幡 穂高, 能田 成, 太田 努, Buslov M. M, 丸山 茂徳

    日本地質学会学術大会講演要旨   2000 ( 0 )   74 - 74   2000年

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    記述言語:日本語   出版者・発行元:一般社団法人 日本地質学会  

    DOI: 10.14863/geosocabst.2000.0_74_1

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  • 神居古潭変成帯の発達史-変形変成史に基づく白雲母K-Ar年代の再検討を踏まえて. 総合研究(A) : 日本列島のジュラ紀-古第三紀付加体形成における緑色岩の意義

    太田努

    研究報告   ( 1 )   51 - 68   1996年

  • 390. 沈み込み帯における熱構造の時間的変化とその要因 : 神威古潭変成帯を例として

    榊原 正幸, 太田 努, 西川 清治

    日本地質学会学術大会講演要旨   101   252 - 252   1994年9月

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    記述言語:日本語   出版者・発行元:日本地質学会  

    DOI: 10.14863/geosocabst.1994.0_252_1

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  • 低温高圧型変成岩の白雲母K-Ar年代の不一致-白雲母組成からのアプローチ-

    太田努

    日本地質学会第101年学術大会講演要旨   252   1994年

  • 北海道, 旭川西方の神居古潭変成岩類の地質と変成作用

    太田努

    日本地質学会第99年学術大会演旨   477   1992年

  • B39 神居古潭変成岩類の ^<40>Ar-^<39>Ar、 K-Ar 年代

    瀧上 豊, 太田 努, 榊原 正幸

    日本火山学会講演予稿集   1991 ( 2 )   109 - 109   1991年10月

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    記述言語:日本語   出版者・発行元:特定非営利活動法人日本火山学会  

    DOI: 10.18940/vsj.1991.2.0_109

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  • 304 北海道,神居古潭変成岩類のK-Ar及びAr-Ar年代

    大田 努, 榊原 正幸, 板谷 徹丸, 瀧上 豊

    日本地質学会学術大会講演要旨   98   435 - 435   1991年3月

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    記述言語:日本語   出版者・発行元:日本地質学会  

    DOI: 10.14863/geosocabst.1991.0_435

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共同研究・競争的資金等の研究

  • カンラン岩のリチウム同位体組成にみるマントル内同位体非平衡の時空間スケール

    研究課題/領域番号:17K05706  2017年04月 - 2020年03月

    日本学術振興会  科学研究費助成事業 基盤研究(C)  基盤研究(C)

    太田 努

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    配分額:4420000円 ( 直接経費:3400000円 、 間接経費:1020000円 )

    典型的なマントルカンラン岩を産する幌満岩体について,水流体と共に挙動する元素の分布を,水素のそれと合わせて調べた結果,同岩体には約十億年前の海洋底熱水変質と約一億五千万年前の沈み込み帯流体との反応が記録されていることがわかった.
    岩体縁部は後のイベントによる再平衡に達しているが,岩体中央の幅約1キロメートルの領域では,約十億年前の熱水変質によるリチウム同位体比や微量元素濃度が保持されており,その水素濃度は典型的なマントルの十倍以上に相当する.幌満岩体の存在は,少なくとも十億年前以降のマントルにおいて,キロメートル規模の含水物質の不均質分布が,そのダイナミクスや化学進化に寄与していたことを示す.

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  • 現行型沈み込み帯出現の地質学的証拠:古原生代、高圧中間群変成帯の総合研究

    研究課題/領域番号:15H05212  2015年04月 - 2018年03月

    日本学術振興会  科学研究費助成事業 基盤研究(B)  基盤研究(B)

    辻森 樹, 平野 直人, 太田 努

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    配分額:15860000円 ( 直接経費:12200000円 、 間接経費:3660000円 )

    本研究は東アフリカ、タンザニア地塊外縁造山帯(太古代タンザニア地塊を取り囲む原生代造山帯)に産する約20億年前の高圧中間群変成帯とそれに対をなす古原生代のバソリス帯において野外地質調査を行い、採取した岩石試料を解析した。低変成度の結晶片岩地域の変成枕状玄武岩の地球化学的特徴や高変成度岩の変成作用の特徴、さらにバソリス帯の活動時期を総合的に検討した結果、海洋プレート沈み込みに伴う約20億年前の太平洋型造山帯の実体が明らかとなった。

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  • 大陸地殻の改変と構造侵食の実像:タンザニア地塊外縁造山帯約15億年間の変遷解読

    研究課題/領域番号:24403010  2012年04月 - 2015年03月

    日本学術振興会  科学研究費助成事業 基盤研究(B)  基盤研究(B)

    辻森 樹, 太田 努, 小林 桂

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    配分額:17160000円 ( 直接経費:13200000円 、 間接経費:3960000円 )

    「太古代安定地塊がどうのように縮小するのか?安定地塊を核とした原生代造山帯はどのように発達し、それらが他の固体地球プロセスにどのように影響しているのか?」本研究は、太古代タンザニア地塊を核に成長した原生代の地塊外縁造山帯を野外地質調査し、地塊外縁造山帯の約15億年間の地史の情報抽出において鍵となる岩石試料に先端的な総合分析を応用した。タンザニア地塊を取り囲む地塊外縁造山帯は汎アフリカ造山時期の地殻改変と短縮が顕著であるが、古原生、いわゆるエブルニア造山時期の情報は、高圧中間群変成帯とそれに関連した花こう岩バソリスが記録しており、顕生代以降の太平洋型造山帯に近似可能であることがわかった。

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  • 沈み込み帯マントルカンラン石の微量元素組成とリチウム同位体分別

    研究課題/領域番号:24540513  2012年04月 - 2015年03月

    日本学術振興会  科学研究費助成事業 基盤研究(C)  基盤研究(C)

    太田 努, マルファット ウィム・J

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    配分額:5070000円 ( 直接経費:3900000円 、 間接経費:1170000円 )

    地球の化学進化を理解するため、代表的マントル鉱物であるカンラン石中のリチウムに注目し、深部マントルとプレート運動によって運びこまれた表層物質との間の相互作用の解明を目指した。
    単純系での同位体分別係数を実験的に決定し、天然のマントルカンラン岩を分析した結果、水流体との間で同位体分別したカンラン石は、含水量が高いことがわかった。このことは、水流体との反応でカンラン石に固定されたリチウムの同位体組成は、地質学的時間規模でマントルの高温条件に置かれても保持されており、そうした同位体分別とプレート運動による物質循環が繰り返されることによって、表層とマントルの間での化学分化が進んできたことを示唆する。

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  • 希ガス同位体を用いた「Old Rock Geochemistry」の展開

    研究課題/領域番号:21244085  2009年 - 2012年

    日本学術振興会  科学研究費助成事業 基盤研究(A)  基盤研究(A)

    松本 拓也, 松田 准一, 辻森 樹, 太田 努, 山下 勝行, 宮川 千絵

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    配分額:38220000円 ( 直接経費:29400000円 、 間接経費:8820000円 )

    本年度は、中国東南部各地から採取したマントル捕獲岩の希ガス同位体分析を完了した。この地域の大陸下lithosphereは比較的最近に大規模な剥奪過程を経験したことが先行研究などにより提唱されており、希ガス同位体がどのような特徴を示すかで、大陸中央部のlithospbereの進化過程に制約条件を与えうると期待できる。分析した試料の特徴としては一様に希ガス含有量がオーストラリアで産出する同様の岩石と比べて少なく、結果として同位体分析もかなり困難であった。ヘリウムの同位体が典型的な上部マントルの億よりも10-20%低い億を示すものもあったため、比較的最近のガスの寄与というよりは、ある程度の期間マントル内で放射集変起源成分の蓄積された領域が存在し、その領域に起因する流体が付加されたものであると推定できる。また、インド洋意の玄武岩試料の分析も完了し中央インド洋海嶺のセグメント毎に明確なヘリウム同位体比の特徴の違いを発見した。一部のセグメントで明確にレユニオンマントルブルームに起因する成分の寄与を発見するとともに.あるセグメントでは上部マントルの値よりも低い3He/4Heが発見され、その様な値は脱ガスを経験した上部マントルがその後少なくとも1000万年以上の期間放射起線のヘリウムを蓄積し、その領域からのガスが特定のセグメントにヘリウムを供給する必要がある。上記2つの研究は対象は異なっているが、いずれも上部マントル内でのローカルな同位体進化を反映した同位体不均一の存在を示唆しており、地球内部の同位体進化を探る上で今後考慮すべき事柄である。また、一部のダイアモンドで見られるネオン同位体の特徴を解釈するために、ネオンの同位体進化曲線をモデル計算し論文として発表した。昨年度来から継続したオーストラリア東部の研究については論文を発表するとともに国際学会にて発表を行った。

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  • 沈み込み帯マントルにおけるリチウム同位体の挙動

    研究課題/領域番号:21540505  2009年 - 2011年

    日本学術振興会  科学研究費助成事業 基盤研究(C)  基盤研究(C)

    太田 努, 森口 拓弥, 国広 卓也, ジェイムズ G・ブロフィー

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    配分額:4420000円 ( 直接経費:3400000円 、 間接経費:1020000円 )

    本研究では,地球の進化を方向付けた,沈み込み帯における表層由来物質とマントル物質との化学的相互作用を理解するために,代表的マントル鉱物のカンラン石と水流体の間でのリチウム分配・同位体分別のパラメータを実験的に明らかにすることを目指した.合成実験によって得られたカンラン石の分析から,今までの研究から予想されていたよりも有意に大きなリチウム同位体分別が,沈み込み帯マントルで起こりうることが示された.

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  • 上部マントルにおけるホウ素循環経路の解明:実験岩石学的アプローチ

    研究課題/領域番号:18740346  2006年 - 2008年

    日本学術振興会  科学研究費助成事業 若手研究(B)  若手研究(B)

    太田 努

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    配分額:2980000円 ( 直接経費:2800000円 、 間接経費:180000円 )

    地球という惑星の大部分はマントルで占められている.このマントルの活動によって形成された表層の物質は,プレート運動によって沈み込み帯からマントルへと戻っていく.その際,ある特定の化学成分は表層物質に濃集し,沈み込む際には表層物質から取り去られてマントルには戻ってこない.このような物質循環によって地球は進化してきた.本研究では,表層物質の沈み込み過程を高温高圧実験によって再現したり,マントル深部へ沈み込んだ岩石の化学組成を分析しりして,表層物質がマントル深部へ沈み込んでいく際に,ホウ素(およびリチウム)という元素がどのような挙動をするのかを明らかにし,地球マントルの化学進化の理解に貢献した.

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  • Chemical evolution of Earth through material differentiation at subduction zone

    2004年

    Cooperative Research 

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    資金種別:競争的資金

    With approaches from experimental petrology and petrography on natural samples, we attempt to quantify a series of parameters on chemical interactions between fluid and crustal and mantle materials at depths of subduction zone, and to decode chemical evolution of Earth

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  • 沈み込み帯における物質分化と地球の化学進化

    2004年

    共同研究 

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    資金種別:競争的資金

    実験岩石学的手法,および天然試料の記載岩石学を通じて,プレート沈み込み帯深部で進行する流体ー岩石間の化学的相互作用を定量化し,地球の大部分を占めるマントルの化学進化過程を明らかにする.

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  • 中生代の南太平洋スーパープルームの活動と環太平洋型高圧変成帯の上昇

    研究課題/領域番号:97J04187  1998年 - 1999年

    日本学術振興会  科学研究費助成事業 特別研究員奨励費  特別研究員奨励費

    太田 努

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    配分額:2400000円 ( 直接経費:2400000円 )

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  • 広域変成帯の形成・上昇と太平洋型造山運動

    1996年 - 2003年

    共同研究 

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    資金種別:競争的資金

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  • Regional metamorphism and Pacific-type orogeny

    1996年 - 2003年

    Cooperative Research 

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    資金種別:競争的資金

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