Updated on 2023/01/20

写真a

 
OTA Tsutomu
 
Organization
Institute for Planetary Materials Chief super technician
Position
Chief super technician
External link

Degree

  • 博士（理学） ( 新潟大学 )

Research Interests

  • geochemistry

  • Petrology

  • 地球化学

  • 岩石学

Research Areas

  • Natural Science / Solid earth sciences

Education

  • Niigata University   自然科学研究科   環境科学

    - 1997

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    Country： Japan

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  • Niigata University    

    - 1997

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  • Ehime University   理学部   地球科学科

    - 1991

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    Country： Japan

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  • Ehime University    

    - 1991

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Papers

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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   2014.2

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    Language：English   Publisher：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   2014.2

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    Language：English   Publisher：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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  • 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   2012.3

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    Language：English   Publisher：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   2012.3

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    Language：English   Publisher：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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  • 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   2011.11

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    Language：English   Publisher：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.

    DOI： 10.2138/am.2011.3857

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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   2011.11

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    Language：English   Publisher：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.

    DOI： 10.2138/am.2011.3857

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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   2010.7

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    Language：English   Publisher：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   2010.7

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    Language：English   Publisher：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

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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   2008.7

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    Language：English   Publisher：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   2008.7

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    Language：English   Publisher：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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  • 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   2008.1

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    Language：English   Publisher：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   2008.1

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    Language：English   Publisher：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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  • The Taitao ophiolite and related felsic plutonism nearby the Chile ridge subduction zone

    Anma ryo, Komiya Tsuyoshi, Kon Yoshiakai, Shibiya Takazou, Ota Tsutomu, Orihashi Yuji, Armstrong Richard

    Abstracts of Annual Meeting of the Geochemical Society of Japan   55   301 - 301   2008

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    Publisher：GEOCHEMICAL SOCIETY OF JAPAN  

    DOI： 10.14862/geochemproc.55.0.301.0

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  • O-142 Shuffled-cards structure of Kamuikotan high-P/T metamorphic rocks, central Hokkaido, Japan

    Sakakibara Masayuki, Yasumoto Kazumi, Ota Tsutomu, Ikeda Michiharu

    日本地質学会学術大会講演要旨   114   132 - 132   2007.9

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    Language：Japanese   Publisher：The Geological Society of Japan  

    DOI： 10.14863/geosocabst.2007.0.256.0

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  • S-47 Formation and Exhumation process of the Sanbagawa metamorphic belt, central Shikoku, Japan

    Aoki K., Masago H., Terabayashi M., Kaneko Y., Okamoto K., Yamamoto H., Ota T., Maruyama S.

    114   25 - 25   2007.9

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    Language：Japanese   Publisher：The Geological Society of Japan  

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  • Protolith sequence, accretionary process, tectonometamorphism and fluid-rock interaction of Kamuikotan high-P/T metamorphosed accretionary complex, central Hokkaido, Japan

    Sakakibara Masaaki, Yasumoto Kazumi, Ikeda Michiharu, Ota Tsutomu

    Jour. Geol. Soc. Japan, Supplement   113   103 - 118   2007

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    Publisher：The Geological Society of Japan  

    DOI： 10.5575/geosoc.113.S103

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  • Paleo-plateau/-seamount Limestone of the Cambrian Accretionary Complex in the Gorny Altai Mountains, Southern Siberia

    UCHIO Yuko, ISOZAKI Yukio, BUSLOV Mikhail M, OTA Tsutomu, UTSUNOMIYA Atsushi, MARUYAMA Shigenori

    Journal of Geography (Chigaku Zasshi)   112 ( 4 )   563 - 585   2003.8

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    Language：Japanese   Publisher：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.<BR>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.<BR>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.<BR>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 Geology of the Taitao Ophiolite near the Chile Triple Junction

    Anma R., Veloso A., Kaneko Y., Terabayashi M., Ota T., Komiya T., Katayama I., Maruyama S., Herve F.

    Annual Meeting of the Geological Society of Japan   2002   7 - 7   2002

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    Language：Japanese   Publisher：The Geological Society of Japan  

    DOI： 10.14863/geosocabst.2002.0_7_2

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  • P-68 The stratigraphy of Vendiian / Cambrian limestone derived from paleo-seamount in the Gomy Altai mountain, southern Russia

    Uchio Y, Isozaki Y, Kawahata H, Nohda S, Ota T, Buslov M. M, Maruyama S

    Annual Meeting of the Geological Society of Japan   2001 ( 0 )   231 - 231   2001

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    Language：Japanese   Publisher：The Geological Society of Japan  

    DOI： 10.14863/geosocabst.2001.0_231_2

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  • O-126 The Cambrian limestone derived from paleo-seamount in the Gorny Altai mountain, southern Russia : Field occurrence, stratigraphy, radiometric age, microfossil and Carbon isotopic composition

    Uchio Y, Isozaki Y, Kawahata H, Nohda S, Ota T, Buslov M. M, Maruyama S

    Annual Meeting of the Geological Society of Japan   2000 ( 0 )   74 - 74   2000

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    Language：Japanese   Publisher：The Geological Society of Japan  

    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

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  • 390. Temporal development of thermal stucture and its controlling factors in a subduction zone : with an example of Kamuikotan subduction complex

    SAKAKIBARA Masayuki, OTA Tsutomu, NISHIKAWA Kiyoharu

    日本地質学会学術大会講演要旨   101   252 - 252   1994.9

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    Language：Japanese   Publisher：The Geological Society of Japan  

    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

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  • 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

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  • 40Ar-39Ar and K-Ar geochronological studies for Kamuikotan metamorphic rocks

    TAKIGAMI Yutaka, OHTA Tsutomu, SAKAKIBARA Masayuki

    Programme and abstracts the Volcanological Society of Japan   1991 ( 2 )   109 - 109   1991.10

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    Language：Japanese   Publisher：Volcanological Society of Japan  

    DOI： 10.18940/vsj.1991.2.0_109

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  • 304 K-Ar and Ar-Ar Ages of Kamuikotan Metamorphic Rocks, Hokkaido.

    Ohta Tsutomu, Sakakibara Masayuki, Itaya Tetsumaru, Takigami Yutaka

    日本地質学会学術大会講演要旨   98   435 - 435   1991.3

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    Language：Japanese   Publisher：The Geological Society of Japan  

    DOI： 10.14863/geosocabst.1991.0_435

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Research Projects

  • Spatiotemporal scale of isotope disequilibria in the mantle, deduced from lithium isotope compositions of mantle peridotite

    Grant number：17K05706  2017.04 - 2020.03

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)  Grant-in-Aid for Scientific Research (C)

    Ota Tsutomu

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    Grant amount：\4420000 （ Direct expense: \3400000 、 Indirect expense：\1020000 ）

    The present study focused distributions of hydrogen and fluid-mobile elements including lithium isotopes in orogenic peridotites of the Horoman massif, Japan, to estimate spaciotemporal scales of mantle heterogeneity on light elements. The analytical results on the samples collected at various scales from kilometer (an entire massif) through meter (an outcrop) to submillimeter (a mineral) produced the following outcomes.
    The Horoman peridotites were partly affected at 150 Ma by a subduction-zone fluid. However in the core of the massif, they have retained geochemical characteristics derived from sub-seafloor hydrothermal alteration at 1 Ga. The hydrogen abundances are more than 10-times higher than those of a typical residual mantle. The presence of the Horoman massif suggests that ancient oceanic mantle domains formed by sub-seafloor hydrothermal alteration could have survived in the mantle for at least 1 Gy, and have influenced to dynamics and chemical evolution of the mantle.

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  • An integrated study of Paleoproterozoic high-pressure intermediate-type metamorphic belt: Implication for the operation of modern-style subduction processes

    Grant number：15H05212  2015.04 - 2018.03

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)  Grant-in-Aid for Scientific Research (B)

    Tsujimori Tatsuki

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    Grant amount：\15860000 （ Direct expense: \12200000 、 Indirect expense：\3660000 ）

    High-pressure intermediate-type metamorphic belt surrounding the late Archean Tanzania Craton experienced Pacific-type subduction zone metamorphism in Orosirian Period at ca. 2 Ga. Epidote-amphibolite-facies meta-pillow basalts of the belt had a mid-ocean ridge basalt-like affinity. Details of eclogite- and high-pressure granulite-facies metamorphism has also brought new insight into Paleoproterozoic Pacific-type subduction processes.

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  • An integrated study of Paleo- and Neoproterozoic orogenic processes at the Tanzanian craton margin

    Grant number：24403010  2012.04 - 2015.03

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)  Grant-in-Aid for Scientific Research (B)

    TSUJIMORI Tatsuki, OTA Tsutomu, KOBAYASHI Katsura

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    Grant amount：\17160000 （ Direct expense: \13200000 、 Indirect expense：\3960000 ）

    High-pressure metamorphic rocks occurring sporadically around the Archean Tanzanian craton record a crustal evolution related to Paleo- and Neoproterozoic orogeny. Our integrated studies confirmed that the Paleoproterozoic subduction-related units including eclogite-bearing high-pressure intermediate-type metamorphic belt and coeval paired granitic batholiths are overprinted significantly by a Pan-African granulite-facies regional metamorphism and deformation. The Pan-African events intrusions played the most important role in the crustal evolution.

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  • Water content and lithium isotope fractionation in subduction-zone mantle olivine

    Grant number：24540513  2012.04 - 2015.03

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)  Grant-in-Aid for Scientific Research (C)

    OTA Tsutomu, MALFAIT WIM J.

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    Grant amount：\5070000 （ Direct expense: \3900000 、 Indirect expense：\1170000 ）

    In terms of lithium (Li) isotope fractionation between mantle olivine and aqueous fluid, we examined an interaction between mantle and surficial material, which has strongly affected the earth’s chemical evolution.
    Combining an experimental study in a simple system with Li-isotope analysis of natural mantle olivine revealed that the mantle olivine yielded Li isotopic abundances that fractionated by an interaction with aqueous fluid is relatively enriched in hydrogen, compared with the less fractionated ones.
    This result indicates that mantle materials that interacted with surficial materials have maintained their chemical characteristics including Li isotopic abundance, even under high temperature conditions in mantle on a geologic timescale. The mantle materials, interacted with surficial materials, have been transported back to the mantle by lithospheric plate subduction; such cycling has chemically differentiated the mantle and the surface, that is, the earth’s chemical evolution.

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

    Grant number：21244085  2009 - 2012

    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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    Grant amount：\38220000 （ Direct expense: \29400000 、 Indirect expense：\8820000 ）

    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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  • Behavior of lithium isotopes in subduction zone mantle

    Grant number：21540505  2009 - 2011

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)  Grant-in-Aid for Scientific Research (C)

    OTA Tsutomu, MORIGUCHI Takuya, KUNIHIRO Takuya, JAMES G. brophy

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    Grant amount：\4420000 （ Direct expense: \3400000 、 Indirect expense：\1020000 ）

    This study aimed to decipher parameters of lithium partitioning and lithium isotope fractionation between mantle olivine and aqueous fluid, in terms of experimental petrology, in order to understand chemical interaction between surficial and mantle materials in deep subduction zone, which has defined a chemical evolution of the Earth. Lithium isotopic compositions obtained from synthesized olivines suggested that the subduction-zone mantle could have been more significantly fractionated in lithium isotope, rather than expected by previous studies.

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  • Experimental study on boron cycling in the upper mantle

    Grant number：18740346  2006 - 2008

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research Grant-in-Aid for Young Scientists (B)  Grant-in-Aid for Young Scientists (B)

    OOTA Tsutomu

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    Grant amount：\2980000 （ Direct expense: \2800000 、 Indirect expense：\180000 ）

    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

    Cooperative Research 

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    Grant type：Competitive

    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

    共同研究 

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    Grant type：Competitive

    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

    Grant number：97J04187  1998 - 1999

    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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    Grant amount：\2400000 （ Direct expense: \2400000 ）

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  • 広域変成帯の形成・上昇と太平洋型造山運動

    1996 - 2003

    共同研究 

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    Grant type：Competitive

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  • Regional metamorphism and Pacific-type orogeny

    1996 - 2003

    Cooperative Research 

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    Grant type：Competitive

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