2021/05/13 更新

写真a

タカザワ エイイチ
高澤 栄一
TAKAZAWA Eiichi
所属
教育研究院 自然科学系 地球・生物科学系列 教授
理学部 教授
自然科学研究科 環境科学専攻 教授
職名
教授
外部リンク

学位

  • 博士(Ph.D.) ( 1996年9月   マサチューセッツ工科大学 )

研究キーワード

  • マントル岩石学

研究分野

  • 自然科学一般 / 宇宙惑星科学

  • 自然科学一般 / 固体地球科学

  • 自然科学一般 / 固体地球科学

経歴

  • 新潟大学   教授

    2013年5月 - 現在

  • 新潟大学   自然科学研究科 環境科学専攻   教授

    2013年5月 - 現在

  • 新潟大学   自然科学研究科 環境科学専攻   教授

    2013年5月 - 現在

  • 新潟大学   地質科学科   教授

    2013年5月 - 2017年3月

  • 新潟大学   地質科学科   准教授

    2004年4月 - 2013年4月

  • 新潟大学   理学部   講師

    1997年1月 - 1999年9月

▶ 全件表示

 

論文

  • High resolution X–ray computed tomography and scanning electron microscopy studies of multiphase solid inclusions in Oman podiform chromitite: implications for post–entrapment modification 査読

    Yuan YAO, Eiichi TAKAZAWA, Sayantani CHATTERJEE, Antonin RICHARD, Christophe MORLOT, Laura CRÉON, Salim AL–BUSAIDI, Katsuyoshi MICHIBAYASHI

    Journal of Mineralogical and Petrological Sciences115 ( 3 ) 247 - 260   2020年4月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Japan Association of Mineralogical Sciences  

    DOI: 10.2465/jmps.191008

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  • The non-chondritic Ni isotope composition of Earth’s mantle 査読

    Klaver Martijn, Ionov Dmitri A, Takazawa Eiichi, Elliott Tim

    Geochimica Cosmochimica et Acta268   405 - 421   2020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)  

    DOI: 10.1016/j.gca.2019.10.017

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  • Scientific Drilling Across the Shoreline 査読

    Sean P.S. Gulick, Kenneth Miller, Peter Kelemen, Joanna Morgan, Jean-Noel Proust, Eiichi Takazawa

    Oceanography32   157 - 159   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: 10.5670/oceanog.2019.139

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  • Tectonic affinities of the accreted basalts in southern Taiwan 査読

    Hsin-Yu Chen, Huai-Jen Yang, Yung-Hsin Liu, Kuo-Fang Huang, Eiichi Takazawa

    JOURNAL OF ASIAN EARTH SCIENCES158   253 - 265   2018年6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:PERGAMON-ELSEVIER SCIENCE LTD  

    Tectonic affinities of accreted basalts provide constraints on mass transport in convergent boundaries, improving our understandings on the evolution of regional geology. In this study, nineteen accreted basalts from the southernmost tip of Taiwan Island, which is on the convergent boundary between the Eurasian and Philippine Sea Plates, were analyzed for element concentrations as well as Sr, Nd, Hf, and Pb isotope ratios to investigate their tectonic affinities. All the samples contain > 3% LOI, reflecting post-magmatic alteration. LOI and Nb variation diagrams together with comparisons to oceanic basalt compositions indicated that the concentrations of most major elements and Rb, Sr, and Ba were modified by post-magmatic processes to varying extents, while P2O5, REE and HFSE remained immobile. Although some samples show Pb loss, most samples have Pb concentrations not affected by post-magmatic processes. Isotope ratios of Pb, Nd and Hf, generally reflect the mantle source characteristics. The epsilon(Nd)-epsilon(Hf) relationship and trace element abundance ratios indicated that the LREE-depleted samples were mostly scraped off the subducting South China Sea floor, reflecting the volumetric dominance of N-MORB on ocean floors. The overriding Philippine Sea Plate contributed both N-MORB and E-MORB to the accretionary prism. The tectonic affinities of the LREE-enriched samples, however, could not be unambiguously determined for the large geochemical variability of OIB from both subducting and overlying slabs. Based on our results, it is proposed that the tectonic affinity of the basalts in an accretionary prism can indicate the subduction polarity of the associated convergent boundary, providing a constraint for regional geology evolution.

    DOI: 10.1016/j.jseaes.2018.02.015

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  • Evaluation of time-resolved mean-of-ratios reduction for laser ablation zircon U-Pb dating using quadrupole ICPMS 査読

    Hayato Ueda, Eiichi Takazawa, Rinpei Kato, Yoshiko Adachi

    GEOCHEMICAL JOURNAL52 ( 3 ) 241 - 254   2018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:GEOCHEMICAL SOC JAPAN  

    We examined quality of zircon U-Pb dating results by mean-of-ratios (MOR) reduction of time-resolved analysis acquired with quadrupole inductively coupled plasma mass spectrometer (ICPMS) and 213 nm YAG laser ablation system. Time-resolved MOR reduction has an advantage to enable statistic evaluation of stability of isotopic ratios and detect accidents in each measurement. We practically applied internal mean square weighted deviation (iMSWD) and correlation coefficient of linear regression to dating of five reference zircons. The MOR reduction provided reasonably accurate U-Pb ages with 2-3% errors of precision. However, their iMSWD suggested dispersion of isotopic ratios in excess of counting errors. The dispersion is inferably attributed to non-simultaneous measurements by quadrupole ICPMS, in addition to potential heterogeneity of samples. We also tested quality of age results from manually trimmed time profiles. The test suggested that ages from clipped profiles as short as 5 sec. are still useful if reduction of precision is acceptable. The method enables to extract meaningful ages from measurements containing accidents, when statistically stable parts out of accidents are properly clipped from the time profiles.

    DOI: 10.2343/geochemj.2.0509

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  • In situ carbon mineralization in ultramafic rocks: Natural processes and possible engineered methods 査読

    Kelemen P.B, Aines R, Bennett E, Benson S.M, Carter E, Coggon J.A, Obeso J.C, Evans O, Gadikota G, Dipple G.M, Godard M, Harris M, Higgins J.A, Johnson K.T.M, Kourim F, Michibayashi K, Morishita T, Takazawa E. ほ

    Energy Procedia146   92 - 102   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: 10.1016/j.egypro.2018.07.013

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  • Reductive Heating Experiments on BOF-Slag: Simultaneous Phosphorus Re-Distribution and Volume Stabilization for Recycling 査読

    Tung-Hsin Su, Huai-Jen Yang, Yu-Chen Lee, Yen-Hong Shau, Eiichi Takazawa, Ming-Fong Lin, Jin-Luh Mou, Wei-Teh Jiang

    STEEL RESEARCH INTERNATIONAL87 ( 11 ) 1511 - 1526   2016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)   出版者・発行元:WILEY-V C H VERLAG GMBH  

    Basic-oxygen furnace (BOF) slag is the second abundant by-product from the steel-making process. It is not readily recycled for high phosphorus content and volume instability. To eliminate its phosphorus-hosting dicalcium silicate (C2S) and volumetrically unstable free-lime, reductive heating experiments on BOF-slag are carried out at 1300-1600 degrees C using quartz-sand or serpentine as a basicity modifier. In the products, C2S and free-lime are consumed through reacting with CaO and MgO, which are produced by Ca-ferrite and Mg-wustite reduction, respectively, to formmerwinite and akermanite. The products are also characterized by silicatemetal segregation and the extent of that increases with increasing temperature and decreasing particle size of starting mixtures. Thermodynamic calculations show that phosphorus in C2S is mostly converted to Fe2P in the metal domain. Compared to the slag-serpentine experiments, the slag-quartz experiments resulted in higher extents of silicate-metal segregation with lower phosphorus contents of approximate to 0.1% in the silicate domain, which therefore is recyclable. To optimize silicate-metal segregation for recycling BOF-slag, it is suggested (i) bringing the BOF-slag composition within the low-temperature side of the C2S-merwinite-akermanite Alkemade triangle by adding quartz-sand; (ii) reductively heating to 1500-1600 degrees C; and (iii) cooling slowly then quenching to suppress C2S crystallization from melts.

    DOI: 10.1002/srin.201500441

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  • Distribution and hosts of arsenic in a sediment core from the Chianan Plain in SW Taiwan: Implications on arsenic primary source and release mechanisms 査読

    Huai-Jen Yang, Chi-Yu Lee, Yu-Ju Chiang, Jiin-Shuh Jean, Yen-Hong Shau, Eiichi Takazawa, Wei-Teh Jiang

    SCIENCE OF THE TOTAL ENVIRONMENT569   212 - 222   2016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)   出版者・発行元:ELSEVIER  

    High arsenic abundance of 50-700 mu g/L in the groundwater from the Chianan Plain in southwestern Taiwan is a well-known environmental hazard. The groundwater-associated sediments, however, have not been geochemically characterized, thus hindering a comprehensive understanding of arsenic cycling in this region. In this study, samples collected from a 250 m sediment core at the centre of the Chianan Plain were analyzed for arsenic and TOC concentrations (N = 158), constituent minerals (N = 25), major element abundances (N = 105), and sequential arsenic extraction (N = 23). The arsenic data show a prevalence of >10 mg/kg with higher concentrations of 20-50 mg/kg concentrated at 60-80 and 195-210 m. Arsenic was extracted mainly as an adsorbate on clay minerals, as a co-precipitate in amorphous iron oxyhydroxide, and as a structural component in clay minerals. Since the sediments consist mainly of quartz, chlorite, and illite, the correlations between arsenic concentration and abundances of K2O and MgO pinpoint illite and chlorite as the major arsenic hosts. The arsenic-total iron correlation reflects the role of chlorite along with the contribution from amorphous iron oxyhydroxide as indicated by arsenic extraction data. Organic matter is not the dominant arsenic host for low TOC content, low arsenic abundance extracted from it, and a relatively low R-2 of the arsenic-TOC correlation. The major constituent minerals in the sediments are the same as those of the upriver metapelites, establishing a sink-source relationship. Composition data from two deep groundwater samples near the sediment core show Eh values and As(V)/As(III) ratios of reducing environments and high arsenic, K, Mg, and Fe contents necessary for deriving arsenic from sediments by desorption from clay and dissolution of iron oxyhydroxide. Therefore, groundwater arsenic was mainly derived from groundwater-associated sediments with limited contributions from other sources, such as mud volcanoes. (C) 2016 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.scitotenv.2016.06.122

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  • Sr and Nd Isotopic evidence in metacarbonate rocks for an extinct Island arc-ocean system in East Antarctica 査読

    Naho Otsuji, M. Satish-Kumar, Atsushi Kamei, Eiichi Takazawa, Noriyoshi Tsuchiya, G. H. Grantham, Tetsuo Kawakami, Masahiro Ishikawa, Yasuhito Osanai

    JOURNAL OF MINERALOGICAL AND PETROLOGICAL SCIENCES111 ( 3 ) 170 - 180   2016年6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:JAPAN ASSOC MINERALOGICAL SCIENCES  

    Chemically precipitated carbonate sediments directly record seawater composition that helps to decode the Earth's paleo-environment, the existence of paleo-oceans, and provide valuable clues on the paleo-tectonic position of continents through Earth's history. In addition, the geochemical and isotopic composition of carbonate rocks have a strong dependence on the depositional tectonic setting and surrounding source rock composition. This was particularly important in the Precambrian, during which biological activity was less prominent and vegetation was virtually absent. Here we present evidence for the existence of an extinct East Antarctic Ocean and its peripheral oceanic island arc system that preceded the formation of the East Antarctic continent in the Neoproterozoic before the final assembly of Gondwana. Applying a multi-element isotope geochemical approach on chemostratigraphically well-constrained metacarbonate rocks collected from the remote Sor Rondane Mountains in East Antarctica, we present a model on carbonate deposition surrounding an island arc system, mid-ocean volcanic islands and a shallow marine continental shelf of a yet unidentified interior Antarctic continent, all of which accreted in the late Neoproterozoic to early Paleozoic to form the present day East Antarctic continent prior to the final amalgamation of Gondwana supercontinent. Our results support the presence of an oceanic island arc system that might have separated the Mozambique ocean and East Antarctic ocean.

    DOI: 10.2465/jmps.151029a

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  • CO2 sequestration utilizing basic-oxygen furnace slag: Controlling factors, reaction mechanisms and V-Cr concerns 査読

    Tung-Hsin Su, Huai-Jen Yang, Yen-Hong Shau, Eiichi Takazawa, Yu-Chen Lee

    JOURNAL OF ENVIRONMENTAL SCIENCES41   99 - 111   2016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:SCIENCE PRESS  

    Basic-oxygen furnace slag (BOF-slag) contains >35% CaO, a potential component for CO2 sequestration. In this study, slag-water-CO2 reaction experiments were conducted with the longest reaction duration extending to 96 hr under high CO2 pressures of 100-300 kg/cm(2) to optimize BOF-slag carbonation conditions, to address carbonation mechanisms, and to evaluate the extents of V and Cr release from slag carbonation. The slag carbonation degree generally reached the maximum values after 24 hr slag-water-CO2 reaction and was controlled by slag particle size and reaction temperature. The maximum carbonation degree of 71% was produced from the experiment using fine slag of <= 0.5 mm under 100 degrees C and a CO2 pressure of 250 kg/cm(2) with a water/slag ratio of 5. Vanadium release from the slag to water was significantly enhanced (generally >2 orders) by slag carbonation. In contrast, slag carbonation did not promote chromium release until the reaction duration exceeded 24 hr. However, the water chromium content was generally at least an order lower than the vanadium concentration, which decreased when the reaction duration exceeded 24 hr. Therefore, long reaction durations of 48-96 hr are proposed to reduce environmental impacts while keeping high carbonation degrees. Mineral textures and water compositions indicated that Mg-wustite, in addition to CaO-containing minerals, can also be carbonated. Consequently, the conventional expression that only considered carbonation of the CaO-containing minerals undervalued the CO2 sequestration capability of the BOF-slag by similar to 20%. Therefore, the BOF-slag is a better CO2 storage medium than that previously recognized. (C) 2015 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.

    DOI: 10.1016/j.jes.2015.06.012

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  • Across-arc variations in geochemistry of Oligocene to Quaternary basalts from the NE Japan arc: Constraints on source composition, mantle melting and slab input composition. 査読

    Shuto, K, Nohara-Imanaka, R, Sato, M, Takahashi, T, Takazawa, E, Kawabata, H, Takanashi, K, Ban, M, Watanabe, N, Fujibayashi, N

    Journal of Petrology56   2257 - 2294   2015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)  

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  • Decoupling of the Lu-Hf, Sm-Nd, and Rb-Sr isotope systems in eclogites and a garnetite from the Sulu ultra-high pressure metamorphic terrane: Causes and implications 査読

    Yung-Hsin Liu, Huai-Jen Yang, Eiichi Takazawa, Madhusoodhan Satish-Kumar, Chen-Feng You

    LITHOS234   1 - 14   2015年10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 SCIENCE BV  

    The whole-rock Hf, Sr and Nd isotope data of five high-Fe-Ti eclogites, nine high-Al edogites, and a garnetite from the Sulu ultrahigh pressure (UHF) metamorphic terrane at eastern China were analyzed to resolve the causes for the decoupling of the Lu-Hf, Sm-Nd, and Rb-Sr isotope systems in these UHP rocks and to infer their protolith characteristics. Seven of the nine high-Al eclogites define an Rb-87/Sr-86-Sr-87/Sr-86 errorchron age of 192 +/- 43 Ma (MSWD = 2.8), which is within the time span of retrograde metamorphism despite the large uncertainty. The high-Fe-Ti eclogites and garnetite, however, have low Rb-87/Sr-86 ratios of <0.031 with scattered Sr-87/Sr-86 ratios of 0.7042-0.7058. Accordingly, it is inferred that the Rb-Sr isotope system in the samples reflects the effects of processes postdating the UHP metamorphism. Despite having different constituent mineral assemblages and whole rock geochemistry, the samples, however, define a Sm-147/Nd-144-Nd-143/Nd-144 errorchron age of 232 +/- 36 Ma (MSWD = 4.6). Although the uncertainty of +/-36 Ma implies incomplete Nd isotope equilibrium among the samples, the large overlap between this errorchron age span and the mineral isochron ages of 245-210 Ma for the UHP metamorphism indicates the control of peak metamorphism on the Sm-Nd isotope system. The incomplete Nd isotope re-equilibration was accompanied by metamorphic modification on the Sm/Nd ratios as indicated by the U-shaped LREE patterns. The initial epsilon(Nd)(780) values of the protolith rocks calculated from the Sm/Nd ratios of the samples deviate from the igneous initial epsilon(Nd)(t)-epsilon(Hf)(t) trend to significantly lower values, consistent with the metamorphic increase in the Sm/Nd ratios. In contrast, the Lu/Hf ratios are generally within the range for basalts and do not vary systematically with the Hf-176/Hf-177 ratios. The protolith epsilon(Hf)(780) values calculated from the Lu/Hf ratios of the samples are nearly identical to the initial epsilon(Hf)(t) values of the -780 Ma magmatic zircon cores from the Yangtze craton, suggesting the dominance of protolith characteristics on the Lu-Hf isotope system, Being controlled by different processes, the Rb-Sr, Sm-Nd, and Lu-Hf isotope systems of the investigated samples are therefore decoupled. The epsilon(Nd)(220)-epsilon(Hf)(220) compositions of the samples deviate from the epsilon(Nd)(t)-epsilon(Hf)(t) trend of intraplate lavas to high epsilon(Hf)(220) at a given epsilon(Nd)(220) and are within the arc lava field. The protolith epsilon(Nd)(780)-epsilon(Hf)(780) compositions calculated from metamorphic initials using igneous Sm/Nd and Lu/Hf ratios show a similar distribution pattern, strengthening the arc affinity of the eclogites. These arc signatures together with the felsic-mafic bimodal geochemical features of the UHF rocks from the Sulu terrane are explained as the characteristics of protoliths generated by backarc rifting. (C) 2015 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.lithos.2015.07.013

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  • The influence of melt infiltration on the Li and Mg isotopic composition of the Horoman Peridotite Massif 査読

    Yi-Jen Lai, Philip A. E. Pogge von Strandmann, Ralf Dohmen, Eiichi Takazawa, Tim Elliott

    GEOCHIMICA ET COSMOCHIMICA ACTA164   318 - 332   2015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:PERGAMON-ELSEVIER SCIENCE LTD  

    We have analysed the Li and Mg isotope ratios of a suite of samples from the Horoman Peridotite Massif. Our results show that most Li and all Mg isotopic compositions of the Horoman peridotites are constant over 100 metres of continuous outcrop, yielding values for pristine mantle of delta Li-7 = 3.8 +/- 1.4 parts per thousand (2SD, n = 9), delta Mg-25 = -0.12 +/- 0.02 parts per thousand and delta Mg-26 = -0.23 +/- 0.04 parts per thousand (2SD, n = 17), in keeping with values for undisturbed mantle xenoliths. However, there are also some anomalously low delta Li-7 values (-0.2 parts per thousand to 1.6 parts per thousand), which coincide with locations that show enrichment of incompatible elements, indicative of the prior passage of small degree melts. We suggest Li diffused from infiltrating melts with high [Li] into the low [Li] minerals and kinetically fractionated Li-7/Li-6 as a result. Continued diffusion after the melt flow had ceased would have resulted in the disappearance of this isotopically light signature in less than 15 Ma. In order to preserve this feature, the melt infiltration must have been a late stage event and the massif must have subsequently cooled over a maximum of similar to 0.3 Ma from peak temperature (950 degrees C, assuming the melts were hydrous) to Li closure temperature (700 degrees C), likely during emplacement. The constant delta Mg-26 values of Horoman peridotites suggest that chemical potential gradients caused by melt infiltration were insufficient to drive associated delta Mg-26 fractionation greater than our external precision of 0.03 parts per thousand. (C) 2015 Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.gca.2015.05.006

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  • Compositional and Sr-Nd-Hf isotopic variations of Baijingsi eclogites from the North Qilian orogen, China: Causes, protolith origins, and tectonic implications 査読

    Choon-Muar Ker, Huai-Jen Yang, Jianxin Zhang, Yen-Hong Shau, Chia-Ju Chieh, Fancong Meng, Eiichi Takazawa, Chen-Feng You

    GONDWANA RESEARCH28 ( 2 ) 721 - 734   2015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  

    Eclogites from the Baijingsi area in the North Qilian orogen at NW China were analyzed for major and trace element abundances as well as Sr, Nd, and Hf isotope ratios to evaluate the impacts from subduction processes on these compositional parameters and to reveal the complexity in protolith characteristics. The major element compositions of the Baijingsi eclogites are within the ranges for basalts. However, the absence of systematic variations among major oxides indicates varying extents of metamorphic modifications. Seven samples are characterized by profound Nb and Ta depletions. Six of them form coherent trends in the La versus Th, HFSE, and LREE plots. They are classified as the Group 1 samples. Other eight samples, referred to as the Group 2 samples, define distinct La-Zr and La-Sm trends and have flat variation patterns with slight Th-Nb-Ta-LREE depletions in the primitive mantle-normalized multiple-element diagram. Group 1 dominates the Sr-87/Sr-86-Rb-87/Sr-86, Nd-143/Nd-144-Sm-147/Nd-144 and Hf-176/Hf-177-Lu-176/Hf-177 trends for relatively larger variations in the isotope and abundance ratios. Based on the errorchron ages from the samples, closure temperatures of the isotope systems, and isotope ratio versus 1/X plots (e.g., Sr-87/Sr-86-1/Sr), it is inferred that the Rb-Sr isotope system was subjected to metamorphic modification, whereas the Sm-Nd and Lu-Hf isotope systems mainly reflect protolith characteristics. In addition to the Nb and Ta depletions, the Group 1 samples generally have epsilon(Hf)(510) values (protolith initial at 510 Ma) higher than those of MORB at a given epsilon(Nd)(510), reflecting derivation from relatively high Lu/Hf ratio sources. They also plot within the fields for arc lavas in the Ta/Yb-Th/Yb and Th-Ta-Hf/3 diagrams. All these features are consistent with derivation from protoliths of an arc origin. In contrast, the Group 2 samples have eNd(510) values slightly higher than those of the Group 1 samples at a given epsilon(Hf)(510), plotting on the low epsilon(Nd)(510) margin of the MORB field. They also deviate from the Ta/Yb-Th/Yb trend defined by MORE and OIB toward higher Th/Yb values within the fields of back-arc basin basalts. Therefore, it is inferred that the protoliths of the Group 2 samples were generated as back-arc basin basalts possibly associated with the protoliths of the Group 1 samples in a common supra-subduction zone. The epsilon(Nd)(510)-epsilon(Hf)(510) relationship of the Baijingsi eclogites shows an affinity to the Indian ocean type mantle, implying protolith generation at the southern hemisphere on the margin or a fragment of the Gondwana continent, most likely in the Qilian Block. Based on the current tectonic configuration, a southward subduction is required for protolith generation and might eclogitize the arc protoliths by subduction erosion. Alternatively, the northward subduction in a bidirectional subduction system might become dominant during the amalgamation of the Qilian Block and the North China Craton to eclogitize the arc protoliths in the Qilian Block. Resolving these two possibilities requires more petrological, geochemical, and structural evidence from the North Qilian orogen. (C) 2014 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.gr.2014.06.006

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  • Melt extraction and metasomatism recorded in basal peridotites above the metamorphic sole of the northern Fizh massif, Oman ophiolite 査読

    Masako Yoshikawa, Marie Python, Akihiro Tamura, Shoji Arai, Eiichi Takazawa, Tomoyuki Shibata, Akira Ueda, Tsutomu Sato

    TECTONOPHYSICS650   53 - 64   2015年5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  

    The Oman ophiolite is one of the best preserved sections of oceanic crust and upper mantle worldwide, and consists of multiple massifs that lie along more than 400 km of the Arabian coast. In the northernmost massifs, the oceanic crust preserves a record of polygenetic magmatism from mid-ocean ridge to subduction-related stages. The lherzolites and clinopyroxene (Cpx)-rich harzburgites of the Fizh block are located a few tens to a hundred meters above the metamorphic sole of the ophiolite and the geochemistry of these Cpx-rich peridotites provides evidence of a genetic link between oceanic crust and mantle. These Cpx-rich peridotites contain olivine with a restricted range of forsterite contents (90-91), but variable Cr-spinel Cr# (Cr/(Cr + Al) atomic ratio) values (0.12-0.33), suggesting that these Cpx-rich peridotites have undergone variable degrees of melt extraction. Cpxs within the Cpx-rich peridotites have chondrite-normalised trace element variation patterns that slope either gently or steeply between the heavy rare earth elements (REEs) and the middle REEs ((Sm/Yb)(N) = 0.08-0.55, where N chondrite-normalised) and are enriched in highly incompatible elements such as Rb, Ba and Nb. This Cpx chemistry can be explained by a polygenetic evolution whereby an initial 4-12% of melt was extracted from the depleted mantle source before this mantle was metasomatised by interaction with fluids derived from dehydration of the metamorphic sole during subduction initiation and obduction. A comparison between Nd-143/Nd-144 versus Sm-147/Nd-144 for Cpx in the Fizh basal Cpx-rich peridotites and a mineral-whole rock Sm-Nd isochron for a gabbro from the same massif suggests a genetic link between crustal and mantle rocks in this area. In addition, Cpxs within the basal Cpx-rich peridotites have highly variable Sr isotopic compositions that are indicative of a significant contribution of seawater from the metamorphic sole, originally derived from subducted oceanic crustal material. (C) 2014 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.tecto.2014.12.004

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  • Repeated magmatism at 34 Ma and 23-20 Ma producing high magnesian adakitic andesites and transitional basalts on southern Okushiri Island, NE Japan arc 査読

    Makoto Sato, Kenji Shuto, Rikako Nohara-Imanaka, Eiichi Takazawa, Yasuhito Osanai, Nobuhiko Nakano

    LITHOS205   60 - 83   2014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 SCIENCE BV  

    The southern part of Okushiri Island in the present-day back-arc margin of the NE Japan arc is one of the rare convergent plate boundaries where similar magma types (high-magnesian adakitic andesite (HMAA) and high-TiO2 basalt (HTB)) have been erupted concurrently at more than one time. Oligocene HMAA can be divided into two types: HMAA-I is characterized by high Sr/Y and low Y, and HMAA-II by relatively low Sr/Y and high Y. HMAA-I is primitive in terms of MgO (8.5 wt.%), Mg# (67), Ni (232 ppm) and Cr (613 ppm) contents, and the most Mg-rich olivine phenocrysts plot within the mantle olivine array in terms of Fo and NiO. The similar Cr versus Ni relations of types I and II HMAA indicate some interaction of slab-derived adaldtic melts with mantle peridotite, whereas Ni contents are higher than those of most boninites derived by partial melting of mantle peridotite at a given Cr content Types I and II HMAA have more enriched Stand Nd isotopic compositions than N-MORB. The petrography and geochemistry of these rocks, combined with published results on the genesis of high-magnesian andesite (HMA) indicate that types I and II HMAA could be produced by interaction of slab (N-MORB and sediment)derived adakitic melts with mantle peridotite. The comagmatism of HMAA and HTB is ascribed to the following model. A cool, less hydrous, adakite magma (spherical diapir) would rise from the subducting slab (Pacific Plate) and become more hydrous as a result of its interaction with overlying hydrous peridotite. This hydrated adakitic diapir further ascends and is heated on entering the overlying mantle wedge. Subsequently, the temperature and H2O gradients in the ascending adakitic diapir and surrounding mantle peridotite would have been established. The HTB magma segregated from the surrounding mantle peridotite region (high temperature and low H2O content) at a depth of 60 km or more, whereas the adakitic diapir (low temperature and high H2O content) continued to rise, with its chemical composition modified due to interaction with the surrounding mantle peridotite. Type I HMAA then segregated at about 50 km.The most attractive tectono-magmatic model to account for production of adakitic magma at two different periods in the same cool subduction zone region involves upwelling of depleted hot asthenosphere into the subcontinental lithosphere beneath the back-arc margin of the NE Japan arc, coincident with back-arc rifting which took place at the initiation of the Japan Sea opening. The unusually high temperature conditions established in the mantle wedge due to upwelling of depleted hot asthenosphere caused partial melting of a limited part of the cool oceanic crust subducting beneath the NE Japan arc, resulting in the generation of adakitic magma. (C) 2014 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.lithos.2014.06.008

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  • A kilometre-scale highly refractory harzburgite zone in the mantle section of the northern oman ophiolite (fizh block): Implications for flux melting of oceanic lithospheric mantle 査読

    Nami Kanke, Eiichi Takazawa

    Geological Society Special Publication392 ( 1 ) 229 - 246   2014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:Geological Society of London  

    We report the major element compositions of constituent minerals in 278 harzburgites and of 101 whole rocks from the northern Fizh mantle section in the northern Oman Ophiolite to investigate the formation and evolution of oceanic lithospheric mantle. Olivine Fo varies from 90 to 92 whereas spinel Cr# (=Cr/(Cr + Al) atomic ratio) varies from 0.15 to 0.78. The Cr# of spinels in a large number of harzburgites exceeds 0.6, which is the upper bound for abyssal peridotites. In the northern Fizh mantle section, highly refractory harzburgites with spinel Cr# greater than 0.7 are distributed in a 3-km-wide band along a NW-SE-striking shear zone. We infer a two-stage depletion process in the northern Fizh mantle section. In the first stage, asthenospheric mantle was partially melted beneath a mid-ocean ridge, producing a harzburgitic residual column. In the second stage during detachment of oceanic lithosphere an H2O-rich fluid, released from the metamorphic sole due to thermal metamorphism of altered oceanic crust, extensively infiltrated the northern Fizh mantle section where the ridge segment boundary region was previously located. The residual harzburgites were subjected to flux melting, resulting in a highly refractory harzburgite zone with spinel Cr# greater than 0.7. © The Geological Society of London 2014.

    DOI: 10.1144/SP392.12

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  • オマーンオフィオライト・サラヒ岩体南西部に分布する超苦鉄質複合岩体の成因 査読

    野本有希, 高澤栄一

    岩石鉱物科学42 ( 3 ) 123-135 (J-STAGE)   2013年

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    記述言語:日本語  

    DOI: 10.2465/gkk.120624

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  • Scientific drilling and related research in the samail ophiolite, sultanate of Oman 査読

    Peter Kelemen, Ali Al Rajhi, Marguerite Godard, Benoit Ildefonse, Jürgen Köpke, Chris MacLeod, Craig Manning, Katsu Michibayashi, Sobhi Nasir, Everett Shock, Eiichi Takazawa, Damon Teagle

    Scientific Drilling ( 15 ) 64 - 71   2013年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.2204/iodp.sd.15.10.2013

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  • スコットランド南東部シッカー岬とハットンの不整合 査読

    道林克禎, 森下知晃, 村山雅史, 西弘嗣, 尾鼻浩一郎, 鈴木庸平, 高澤栄一, 山田泰広, 横山祐典

    地質学雑誌118 ( 11 ) IX-X   2012年11月

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  • 緒言 査読

    森下 知晃, 阿部 なつ江, 水上 知行, 小澤 一仁, 高澤 栄一

    岩石鉱物科学41 ( 5 ) 171 - 173   2012年9月

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    記述言語:日本語   出版者・発行元:一般社団法人 日本鉱物科学会  

    &amp;nbsp;&amp;nbsp;How much do we know the Earth&#039;s mantle? We would like to make clear what we want to know, what we can know and what we will be able to know the Earth&#039;s mantle. This special issue focuses on recent scientific advances in serpentinization, pressure-temperature paths including thermal history of the earth, tectono-magmatic processes, geochemical recycling, rheology and chemical compositions of the Earth&#039;s mantle based on analyses of mantle-derived materials including volcanic rocks. These topics provide useful information for a wide range of earth scientific communities.&lt;br&gt;

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  • オマーンオフィオライト・マントルセクションの組成マッピングからみた初期島弧におけるマントル溶融と反応過程 査読

    高澤栄一

    岩石鉱物科学41 ( 6 ) 257 - 266   2012年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.2465/gkk.120704

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  • The mohole: A crustal journey and mantle quest, workshop in Kanazawa, Japan, 3-5 June 2010 査読

    Benoît Ildefonse, Natsue Abe, Donna K. Blackman, J. Pablo Canales, Yoshio Isozaki, Shuichi Kodaira, Greg Myers, Kentaro Nakamura, Mladen Nedimovic, Alexander C. Skinner, Nobukazu Seama, Eiichi Takazawa, Damon A.H. Teagle, Masako Tominaga, Susumu Umino, Douglas S. Wilson, Masaoki Yamao

    Scientific Drilling10, 56-63 ( 10 ) 56 - 63   2010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)  

    DOI: 10.2204/iodp.sd.10.07.2010

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  • Shallow Mantle Composition and Dynamics: Fifth International Orogenic Lherzolite Conference 査読

    Martin Menzies, Peter Kelemen, Henry Dick, Jean-Louis Bodinier, Francoise Boudier, Greg Hirth, Tim Grove, Andrea Tommasi, Eiichi Takazawa

    JOURNAL OF PETROLOGY51 ( 1-2 ) 3 - 7   2010年1月

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    記述言語:英語   出版者・発行元:OXFORD UNIV PRESS  

    DOI: 10.1093/petrology/egp098

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  • Primary melting sequence of a deep (&gt; 250 km) lithospheric mantle as recorded in the geochemistry of kimberlite-carbonatite assemblages, Snap Lake dyke system, Canada 査読

    A. M. Agashev, N. P. Pokhilenko, E. Takazawa, J. A. McDonald, M. A. Vavilov, T. Watanabe, N. V. Sobolev

    Chemical Geology255 ( 3-4 ) 317 - 328   2008年10月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    Geochemistry of kimberlites and associated carbonatites from the Snap Lake dyke system, Slave craton, Canada, shows that kimberlites are similar, but not identical to Group I kimberlites from South Africa and Siberia. Snap Lake kimberlites are enriched in most incompatible elements such as U, Th, Nb and LREE (up to 1400 times chondritic abundances), and are weakly differentiated relative to primitive mantle in their Sr and Nd isotope compositions. The Snap Lake carbonatites and kimberlites are enriched or depleted in certain trace elements relative to each other. Carbonatites are depleted in Cs, Rb, K, Ta and Ti but enriched in U, Sr, P, Zr, Hf, middle and heavy REEs relative to kimberlites. The observed element distributions are not consistent with experimental data on distribution of trace elements between immiscible carbonate and silicate liquids. However, the chemistry of these rocks shows a continuous systematic change from carbonatites to kimberlites, suggesting their genetic relationship. The range of major element concentrations from low SiO2 (3 wt.%) magmas to typical kimberlites are in excellent agreement with experimental data for melting of carbonated lherzolite at high pressure. Carbonatites have significantly superchondritic Nb/Ta (22-81) and Zr/Hf (57-128) ratios, which systematically decrease with increase of SiO2. Modeling of partial melting requires that the source for Snap Lake dyke rocks was enriched in incompatible elements but depleted in HREE relative to the primitive mantle. The most appropriate source rocks are metasomatically enriched peridotites of the deep lithospheric mantle roots. In the melting sequence of this source, the incipient magma was carbonatitic in composition but subsequently became kimberlitic as the degree of partial melting increased to 1%. Rocks of the Snap Lake dyke represent a natural example of primary melting process within a deep (&gt
    250 km) lithospheric mantle. © 2008 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.chemgeo.2008.07.003

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  • Corundum-bearing mafic granulites in the Horoman (Japan) and Ronda (Spain) peridotite massifs: Possible remnants of recycled crustal materials in the mantle 査読

    Tomoaki Morishita, Eiichi Takazawa, Shoji Arai, Masaaki Obata, Tadahiro Kodera, Tadahiro Kodera, Fernando Gervilla

    Island Arc15   2 - 3   2006年3月

  • Geochemical secular variation of magma source during Early to Middle Miocene time in the Niigata area, NE Japan: Asthenospheric mantle upwelling during back-arc basin opening 査読

    K Shuto, H Ishimoto, Y Hirahara, M Sato, K Matsui, N Fujibayashi, E Takazawa, K Yabuki, M Sekine, M Kato, AI Rezanov

    LITHOS86 ( 1-2 ) 1 - 33   2006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:ELSEVIER SCIENCE BV  

    In the Niigata region of the NE Japan arc, basaltic and intermediate to felsic volcanic rocks (silicic andesite, dacite and rhyolite) have been produced during the Early Miocene, Middle Miocene and Pliocene ages, spanning the pre-Japan Sea opening to post-opening stages. Early Miocene basaltic rocks are characterized by enriched Sr and Nd isotopic signatures (initial Sr-87/Sr-86 (SrI) = 0.70557 to 0.70592 and initial Nd-143/Nd-144 (NdI)=0.51255 to 0.51262), whereas Middle Miocene and Pliocene basaltic rocks are slightly enriched than MORB in terms of SrI (0.70314-0.70416) and NdI (0.51286-0.51310). Early Miocene basaltic rocks are also characterized by higher abundances of HFSE and LREE, and higher Zr/Y compared to Middle Miocene and Pliocene basaltic rocks. The geochemical features of Early Miocene basaltic rocks are almost identical to those of basaltic rocks found in continental rift zones, such as the Rio Grande rift. The different geochemical signatures of Early and Middle Miocene basaltic rocks can be ascribed to the geochemical differences in the mantle source. Apart from andesitic rocks of the Kakuda area, most of Early and Middle Miocene intermediate to felsic volcanic rocks from the Niigata region show significantly higher SrI values (0.70673-0.70773) and lower NdI values (0.51234-0.51254) than Early Miocene basaltic rocks, indicating a lower crustal origin for these more felsic volcanic rocks.

    DOI: 10.1016/j.lithos.2005.06.001

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  • Compositional continuity and discontinuity in the Horoman peridotite, Japan, and its implication for melt extraction processes in partially molten upper mantle 査読

    M Obata, E Takazawa

    JOURNAL OF PETROLOGY45 ( 2 ) 223 - 234   2004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:OXFORD UNIV PRESS  

    A hypothetical model is proposed to explain the origin of compositional discontinuities in the layering observed in orogenic lherzolites. The observed collinearity of the whole-rock peridotite compositions is best explained in terms of partial melting and melt segregation. The presence of chemical discontinuities implies that melt segregation includes an abrupt and discontinuous process. A kg concept in the model is the topological transformation of melt geometry in partially molten rocks responding to the equality and inequality of the fluid pressure and solid pressure, which may be realized in a gravitational field. It is emphasized that the percolation threshold is a critical boundary, beyond which a rapid microstructural change occurs in response to the change of local fluid pressure, thus causing a rapid increase of permeability. The model implies that the mode of melting is closer to batch melting than to fractional melting in the upper mantle.

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  • Geochemistry and origin of the basal lherzolites from the northern Oman ophiolite (northern Fizh block) 査読

    E Takazawa, T Okayasu, K Satoh

    GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS4   2003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:AMER GEOPHYSICAL UNION  

    [1] Abundances of major and trace elements in whole rocks and minerals in lherzolites and harzburgites from the northern Oman ophiolite are used to understand the mantle processes creating compositional variation in oceanic lithospheric mantle. Detailed mapping shows that lherzolites occur near the base of a mantle section in the northern Fizh block. Geochemical analyses identify two types of basal lherzolite. The first type (Type I lherzolite) displays porphyroclastic microstructure and occurs sporadically in the basal mylonite zone. Whole rock and clinopyroxene are highly depleted in incompatible elements such as Na, Ti, Zr, and rare earth elements (REE). The chondrite-normalized patterns of Type I lherzolites show steep slopes from heavy REE (HREE) to light REE (LREE) that are ascribed to melt extraction, up to 12-18%, from a source containing a small amount of garnet. The chondrite-normalized patterns have slight enrichment in LREE relative to the patterns expected for residues of partial melting thereby indicating reaction with a LREE-enriched melt or fluid at a low melt/rock ratio. The second type (Type II lherzolite) shows mylonitic microstructure and only occurs at the contact between the mantle section and the metamorphic sole. Abundances of incompatible elements in whole rocks and clinopyroxenes are greater than those of Type I lherzolites, and clinopyroxenes in Type II lherzolites have high Na(2)O contents (&gt; 1 wt.%). To a first approximation, the high Na content of clinopyroxenes and whole rocks and the LREE-depleted, chondrite-normalized whole rock REE patterns are consistent with Type II lherzolite being in equilibrium with a midocean ridge basalt (MORB)-type melt at relatively high pressure (&gt; 2 GPa). However, the flatness of chondrite-normalized patterns for middle and heavy REE are inconsistent with residual garnet peridotite. The characteristics of Type II lherzolites are better explained by a mixing process in which residual peridotite was refertilized by addition of a LREE-depleted melt. The large compositional gradient near the basal thrust in the northern Fizh block may have recorded a transient state in which the degree of partial melting was progressively decreased as a result of reducing mantle temperature and upwelling rate. This scenario is consistent with the inferred failing ridge associated with a transform zone in the western side of the northern Fizh block proposed by Nicolas et al. [2000]. In the detachment stage of the Oman ophiolite, a small amount of ascending melt may have crystallized near the basal part of mantle section thereby forming Type II lherzolites. Basal lherzolites and their spatial chemical variations in the northern Fizh block may provide a key for understanding the processes of ridge segmentation and detachment at fast spreading ridges.

    DOI: 10.1029/2001GC000232

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  • Model of layering formation in a mantle peridotite (Horoman,Hokkaido, Japan) 査読

    Atsushi Toramaru, Eiichi Takazawa, Tomoaki Morishita, Kyoko Matsukage

    Earth and Planetary Science Letters185 ( 3/4 ) 299 - 313   2001年3月

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    The Horoman peridotite complex exhibits a conspicuous layered structure. It is found, from the geological and petrological survey, that the pattern of layering has three characteristics: symmetry, asymmetry (subtly collapsed symmetry) and scale invariance. Especially, symmetric and asymmetric patterns clearly recognized in the sequence of mafic layers at the Northern ridge of Apoi-dake peak, and at the Western ridge of Bozu-yama peak are noticeable. We present a simple mathematical model describing stretching (thinning) and folding during deformation that accounts for the three characteristics. The model quantitatively reproduces the slope in cumulative frequency distribution of the width of mafic layers and indicates that the frequency distribution is strongly influenced by the spatial strain contrast. Applying the model result to the observational data for mafic layers, it is found that the strain contrast approximately ranges several to 10 times between regions with the highest and the lowest strain rates. © 2001 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S0012-821X(00)00382-4

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  • Re-Os isotopes in the Horoman peridotite: Evidence for refertilization? 査読

    AE Saal, E Takazawa, FA Frey, N Shimizu, Hart, SR

    JOURNAL OF PETROLOGY42 ( 1 ) 25 - 37   2001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:OXFORD UNIV PRESS  

    Re-Os isotopic data for 20 samples from a well-characterized 140 m section across a layered sequence, ranging from plagioclase lherzolite through lherzolite to harzburgite, of the Horoman peridotite show: (1) a range in Os-187/Os-188 ratios (from 0.1158 to 0.1283) similar to that reported for other peridotitic massifs, thereby suggesting that the processes responsible for the Re-Os isotopic variation at the meter-scale and the whole-massif scale are similar; (2) that the Os isotopic ratio is controlled by the Re content through radiogenic ingrowth over a period of similar to0.9 Gy. The ultramafic and some of the mafic rocks (Type I layers)from the Horoman massif define an 'apparent age' of 1.12 +/- 0.24 Ga in the Re-OS isochron diagram, within error of the previously reported age of 833 +/- 78 Ma based on Sm-Nd isotopes. Although the Re-Os isotopic data do not define an isochron, the consistency of the similar to 900 Ma age defined by both isotopic systems suggests that this age has a geologic meaning and that mafic (Type I layers) and ultramafic rocks are genetically related, A plausible explanation for the genetic relationship between the mafic and ultramafic rocks, the meter-scale compositional variations from lherzolite to plagioclase lheriolite, the suprachondritic Re-187/Os-188 ratios in some fertile peridotites, and the oldest RE depletion model age of similar to1.86 Ga obtained for Horoman rocks is a refertilization process involving reaction of a mid-ocean ridge basalt-like magma with depleted lithospheric mantle at similar to 900 Ma.

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  • Whole rock compositional variations in an upper mantle peridotite (Horoman, Hokkaido, Japan): Are they consistent with a partial melting process? 査読

    E Takazawa, FA Frey, N Shimizu, M Obata

    GEOCHIMICA ET COSMOCHIMICA ACTA64 ( 4 ) 695 - 716   2000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:PERGAMON-ELSEVIER SCIENCE LTD  

    Whole rock major and trace element abundances of the Horoman peridotites were used to understand processes forming lithological and compositional variations in the upper mantle. Similar to other orogenic peridotites, Horoman peridotites range from fertile lherzolites (3 to 4% Al(2)O(3) and CaO) to depleted harzburgites (similar to 0.5% Al(2)O(3) and CaO). Abundances of major oxides and compatible to moderately incompatible elements vary systematically with variations in MgO content. Such trends are commonly interpreted as indicating that the peridotites formed as residues from varying degrees of partial melting. The fertile end of these trends coincides with estimates of primitive mantle composition. Because of a mismatch between experimental melting trends for spinel peridotite, especially the Na(2)O-MgO trend, the compositional variations of Horoman peridotites are not consistent with formation as residues from partial melting of spinel peridotite. Non-Linear trends in minor and trace element versus major element abundance diagrams also preclude a two-component mixing model. Recent melting experiments on garnet peridotite demonstrate that at 3 GPa the near-solidus peridotite has a large amount of subcalcic clinopyroxene (ca. 27%) coexisting with small amount of garnet (ca. 2%). Residues from polybaric melting of such garnet peridotite are consistent with the abundance variations of major and moderately incompatible elements, such as Na and heavy rare-earth elements, in the Horoman peridotites. A similar conclusion is applicable to other orogenic peridotites such as the Ronda peridotite because their major element compositional variations are similar to the Horoman peridotite. Copyright (C) 2000 Elsevier Science Ltd.

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  • 新潟-福島県境付近の奥只見地域から産出したペルム紀腕足類とその構造地質学的意義 査読

    田沢 純一, 安藤 勧, 古橋 慎矢, 古田 梢, 岡安 冬恵, 志村 俊昭, 高澤 栄一, 立石 雅昭, 渡辺 諭, 山本 和美, 山本 亮, 豊島 剛志, 大河内 誠

    地質学雑誌105 ( 10 ) 729 - 732   1999年10月

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    記述言語:日本語   掲載種別:研究論文(学術雑誌)   出版者・発行元:日本地質学会  

    The following four brachiopod species are newly recognized from the Okutadami area, central Japan : Anemonaria sp., Yakovlevia sp., Spiriferella sp. and Attenuatella sp. These brachiopods indicate a late Middle Permian (Midian) in age. The Okutadami fauna, consisting of both the Boreal- and Bipolar-type genera, is the first documented Permian Boreal brachiopod fauna in Japan. The occurrence of the Boreal brachiopod fauna from the Okutadami area suggests that the fossil-bearing rocks were formed at the northern-most part of Japan in the Permian time.

    DOI: 10.5575/geosoc.105.729

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  • Non-chondritic platinum-group element ratios in oceanic mantle lithosphere: petrogenetic signature of melt percolation? 査読

    M Rehkamper, AN Halliday, J Alt, JG Fitton, J Zipfel, E Takazawa

    EARTH AND PLANETARY SCIENCE LETTERS172 ( 1-2 ) 65 - 81   1999年10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 SCIENCE BV  

    The concentrations of the platinum-group elements (PGE) Ir, Ru, Pt and Pd were determined in 11 abyssal peridotites from ODP Sites 895 and 920, as well in six ultramafic rocks from the Horoman peridotite body, Japan, which is generally thought to represent former asthenospheric mantle. Individual oceanic peridotites from ODP drill cores are characterized by variable absolute and relative PGE abundances, but the average PGE concentrations of both ODP suites are very similar. This indicates that the distribution of the noble metals in the mantle is characterized by small-scale heterogeneity and large-scale homogeneity. The mean Ru/Ir and Pt/Ir ratios of all ODP peridotites are within 15% and 3%, respectively, of CI-chondritic values. These results are consistent with models that advocate that a late veneer of chondritic material provided the present PGE budget of the silicate Earth. The data are not reconcilable with the addition of a significant amount of differentiated outer core material to the upper mantle. Furthermore, the results of petrogenetic model calculations indicate that the addition of sulfides derived from percolating magmas may be responsible for the variable and generally suprachondritic Pd/Ir ratios observed in abyssal peridotites. Ultramafic rocks from the Horoman peridotite have PGE signatures distinct from abyssal peridotites: Pt/Ir and Pd/Ir are correlated with lithophile element concentrations such that the most fertile Iherzolites are characterized by non-primitive PGE ratios. This indicates that processes more complex than simple in-situ melt extraction are required to produce the geochemical systematics, if the Horoman peridotite formed from asthenospheric mantle with chondritic relative PGE abundances. In this case, the PGE results can be explained by melt depletion accompanied or followed by mixing of depleted residues with sulfides, with or without the addition of basaltic melt. (C) 1999 Elsevier Science B.V. All rights reserved.

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  • Polybaric petrogenesis of mafic layers in the Horoman peridotite complex, Japan 査読

    E. Takazawa, F. A. Frey, N. Shimizu, A. Saal, M. Obata

    Journal of Petrology40 ( 12 ) 1827 - 1851   1999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:Oxford University Press  

    Two major types of mafic granulite layers occur within the Horoman peridotite, an 8 km x 10 km x 3 km orogenic lherzolite exposed in the high-T and low-P Hidaka metamorphic belt of Hokkaido, Japan. The mineral assemblages and textures of these layers reflect subsolidus reactions occurring during uplift from the upper mantle to the crust. Nevertheless, their whole-rock compositions can be used to infer the primary mineralogy of these layers, and a genetic relationship to melts geochemically similar to mid-ocean ridge basalts (MORB). The intralayer compositional variation of Type I layers (Al-Ti augite type mafic granulites) shows that the centers formed as garnet clinopyroxenites in equilibrium with an incompatible element depleted melt that crystallized to form the margins. In contrast, the Type II layers (Cr-diopside type mafic granulites) formed at relatively shallow depths and are much older, ~830 Ma, than the Type I garnet pyroxenites, which formed at ~80 Ma. The temporal sequence supports the hypothesis that the Horoman peridotite represents shallow MORB-related oceanic mantle that had subsided to deeper mantle depths before crustal emplacement.

    DOI: 10.1093/petroj/40.12.1827

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  • Collapsing carbon nanotubes and diamond formation under shock waves 査読

    Y. Q. Zhu, T. Sekine, T. Kobayashi, E. Takazawa, M. Terrones, H. Terrones

    Chemical Physics Letters287 ( 5-6 ) 689 - 693   1998年5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  

    In order to investigate the mechanical properties of carbon nanotubes, dynamic shock wave pressures (≤50 GPa) were applied on arc-discharge-generated carbon nanotubes containing polyhedral nanoparticles. High-resolution transmission electron microscopy (HRTEM) studies of the shock-recovered samples reveal that: (i) layers of the outer shells of the nanotubes break and transform into curled graphitic structures and (ii) the inner tube walls and bulk material display structural defects. Further X-ray powder diffraction and HRTEM analyses exhibit the presence of diamond nanocrystals which are produced after the shock-wave compression of polyhedral particles (present in the starting material).

    DOI: 10.1016/S0009-2614(98)00226-7

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  • Radiation temperatures of soda-lime glass in its shock-compressed liquid state 査読

    T. Kobayashi, T. Sekine, O. V. Fat'yanov, E. Takazawa, Q. Y. Zhu

    Journal of Applied Physics83 ( 3 ) 1711 - 1716   1998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 Institute of Physics Inc.  

    A radiation pyrometer in conjunction with a two-stage light gas gun has been used to measure shock temperatures of soda-lime glass in the pressure range 54-109 GPa. This pyrometer consists of two parts, i.e., an optical multichannel analyzer which measures the radiation spectrum over the visible range (∼450 nm window) and a four-channel photomultiplier tube system which records the time-varying behavior of shock temperatures. The measured radiation spectra are compared with the Planck function to estimate the shock temperatures and emissivities. Obtained spectra are well fit by the Planck function with moderate emissivities, indicating that relatively homogeneous thermal radiation is the main component of radiation. Obtained shock temperatures range from 2800 (100) to 5700 (300) K and they seem to represent shock temperatures of liquefied soda-lime glass (melt). The Hugoniot is well described by a linear relation, us = 0.14(21) + 1.92(5)up km/s. It is deduced that the radiation from liquids under shock compression, in contrast to the radiation from solids under shock compression, is more thermal and fits the Planck function well, even at lower temperatures. This is because the radiation spectrum of solids under compression often shows nonthermal radiation due to heterogeneous deformation, while the radiation spectrum of liquids under compression could not have such a nonthermal component. © 1995 American Institute of Physics.

    DOI: 10.1063/1.366889

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  • Shock-induced phase transitions among SiC polytypes 査読

    Y. Q. Zhu, T. Sekine, T. Kobayashi, E. Takazawa

    Journal of Materials Science33 ( 24 ) 5883 - 5890   1998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:Springer Netherlands  

    A series of recovery experiments was conducted using a propellant single-stage gun on starting materials of both α-SiC and β-S\\C. X-ray examination on the recovered samples indicated that obvious polytype transformations among 3C, 6H, and 15R took place. To the α-SiC starting material, 15R tends to increase and 6H tends to decrease, while a small amount of α-SiC form transforms to 3C type, along with increasing the shock temperature and pressure. X-ray diffraction analysis showed that the β-SiC polytype is transformed into rhombohedral forms. From results of both types of SiC samples, rhombohedral polytypes seem to be the favored shock modification. The effects of shock pressure and shock temperature and their heterogeneous distribution on these polytype transitions are discussed in detail. Analysis showed that these polytype transitions resulted from the stacking sequence changes of SiC atom layers. © 1998 Kluwer Academic Publishers.

    DOI: 10.1023/A:1004482922441

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  • Evolution of the Horoman Peridotite (Hokkaido, Japan): Implications from pyroxene compositions 査読

    E Takazawa, F Frey, N Shimizu, M Obata

    CHEMICAL GEOLOGY134 ( 1-3 ) 3 - 26   1996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:ELSEVIER SCIENCE BV  

    Processes occurring in the Earth's upper mantle are important in controlling evolution of the crust-mantle system. The effects of multiple igneous and metamorphic processes are recorded in upper-mantle peridotites, such as the Horoman Peridotite in Hokkaido, Japan. Geochemical studies of these peridotites and their minerals, combined with determination of the spatial geochemical variations, can be used to understand the sequence of processes that affected the peridotite. In this study we show that compositional zoning patterns of major and trace elements in clinopyroxene porphyroclasts reflect a sub-solidus, closed-system transition from garnet peridotite, equilibrated at 20-24 kbar and 1040-1160 degrees C, to plagioclase peridotite equilibrated at similar to 7 kbar and 850-950 degrees C. The preservation of compositionally zoned pyroxenes indicates that this transition was a relatively recent process that probably occurred as the Horoman Peridotite was emplaced into the Hidaka metamorphic belt, The clinopyroxene compositions also show that: (I) harzburgites and lherzolites reacted with a fluid/melt that resulted in relative enrichment of highly incompatible elements, such as the light rare-earth elements; and (2) this enrichment process preceded the sub-solidus breakdown of garnet.

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  • GEOCHEMICAL EVIDENCE FOR MELT MIGRATION AND REACTION IN THE UPPER MANTLE 査読

    E TAKAZAWA, FA FREY, N SHIMIZU, M OBATA, JL BODINIER

    NATURE359 ( 6390 ) 55 - 58   1992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:NATURE PUBLISHING GROUP  

    THE segregation of melts from the Earth's upper mantle into the crust is an important process in the chemical evolution of the crust-mantle system. The processes of melt formation and migration in the upper mantle are inadequately understood, but some important characteristics of these processes can be inferred from upper-mantle rocks exposed at the Earth's surface. The Horoman peridotite body in northern Japan is a layered upper-mantle rock. The major-element compositions of the layers are consistent with their formation as residues from varying extents of melting; however, abundances of rare-earth elements (REE) require additional processes to have occurred1, such as post-melting enrichment (metasomatism) resulting from reaction with a migrating fluid phase. We report here that chondrite-normalized REE patterns in clinopyroxenes show abrupt changes in slope, which vary with stratigraphic position and rock type. These data can be modelled by chromatographic fractionation as melts migrated through and interacted with peridotite, creating compositional heterogeneities in the upper mantle. In the Horoman peridotite these heterogeneities occur on a scale length of tens of metres.

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  • Compositional Variations within the Lower Layered Zone of the Horoman Peridotite, Hokkaido, Japan: Constraints on Models for Melt-Solid Segregation 査読

    Fred A. Frey, N. Shimizu, A. Leinbach, M. Obata, E. Takazawa

    JOURNAL OF PETROLOGY   211 - 227   1991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:OXFORD UNIV PRESS  

    The lower zone, similar to 2 km in thickness, of the similar to 8 km x 10 km Horoman peridotite is layered with several repetitive sequences of harzburgite-lherzolite-plagioclase lherzolite. Major and trace element abundances were determined in seven whole rocks and their minerals from a 200-m section that ranges from plagioclase lherzolite to harzburgite. The clinopyroxene- and plagioclase-rich (similar to 15-20%) lherzolites contain similar to 3-5-4% Al2O3, similar to 3-3-5% CaO, olivines of similar to Fo(89), and they have a relative light REE depletion, [(LREE)(N) similar to 06 and (HREE)(N) similar to 2 (N = chondrite-normalized)]. The variations in bulk-rock major element content and mineral composition from plagioclase lherzolite to harzburgite are consistent with control by melt-solid segregation. For example, a simple model of mixing between harzburgite, residual from partial melting, and a melt can explain most of the whole-rock compositional variations; i.e., abundances of major elements, compatible trace elements, and some incompatible trace elements. However, the whole-rock harzburgites and their constituent clinopyroxenes have anomalously high LREE/HREE ratios. These data require a more complex mantle process such as relative LREE enrichment caused by metasomatizing fluids. Evidence for a metasomatic process is the common occurrence of secondary phlogopite in some harzburgite layers (Arai & Takahashi, 1989).

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  • 上部白亜系湧別層群中のマンガンノジュール 査読

    榊原 正幸, 新井田 清信, 戸苅 賢二, 赤坂 正秀, 高澤 栄一, 後藤 芳彦, 芳川 雅子, 木村 学, 紀藤 典夫, 田近 淳, 加藤 孝幸, 戸田 英明

    地質学雑誌95 ( 3 ) 241 - 244   1989年

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書籍等出版物

  • マフィック岩を包有する不均質なマントルの部分融解に関する地質学的検証

    高澤, 栄一

    [高澤栄一]  2006年 

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    総ページ数:94p  

    CiNii Books

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MISC

  • モホ点描―超深部掘削で何がわかるのか?オマーンオフィオライト・サラヒ岩体マントルセクションの鉱物組成分布からみた海嶺‐島弧変遷プロセス

    高澤栄一, 春日良一, 山野井陽一

    月刊地球34 ( 4 ) 252 - 257   2012年4月

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    記述言語:日本語  

    J-GLOBAL

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  • モホ点描―超深部掘削で何がわかるのか?オマーンオフィオライト・フィズ岩体のマントルセクションに分布するダナイトの空間的な組成変動と成因について

    末武杏奈, 高澤栄一

    月刊地球34 ( 4 ) 247 - 251   2012年4月

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    記述言語:日本語  

    J-GLOBAL

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  • The MoHole: A Crustal Journey and Mantle Quest Workshop Report

    ILDEFONSE Benoît, ABE Natsue, BLACKMAN Donna K, CANALES J. Pablo, ISOZAKI Yoshio, KODAIRA Shuichi, MYERS Greg, NAKAMURA Kentaro, NEDIMOVIC Mladen, SKINNER Alesander, SEAMA Nobukazu, TAKAZAWA Eiichi, TEAGLE Damon A.H, TOMINAGA Masako, UMINO Susumu, WILSON Douglas S, YAMAO Masaoki

    Workshop Report1-67   2010年6月

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    記述言語:英語  

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  • Spatial variation of trace element abundances in clinopyroxenes from the layered orogenic lherzolite (Horoman peridotite, Japan): Implications for melt flow and reaction in the upper mantle

    E Takazawa, FA Frey, N Shimizu, M Obata, JL Bodinier

    GEOCHIMICA ET COSMOCHIMICA ACTA67 ( 18 ) A471 - A471   2003年9月

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    記述言語:英語   掲載種別:研究発表ペーパー・要旨(国際会議)   出版者・発行元:PERGAMON-ELSEVIER SCIENCE LTD  

    Web of Science

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  • 248 日高変成帯超苦鉄質岩類の岩石化学的性質

    新井田 清信, 高沢 栄一, 芳川 雅子

    日本地質学会学術大会講演要旨1988 ( 0 )   1988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  

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講演・口頭発表等

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共同研究・競争的資金等の研究

  • 中央海嶺と沈み込み帯における上部マントルの変質作用の実態解明

    研究課題/領域番号:20H02005  2020年04月 - 2025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)

    高澤 栄一, 野坂 俊夫, M Satish‐Kumar, 道林 克禎

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    担当区分:研究代表者 

    配分額:17550000円 ( 直接経費:13500000円 、 間接経費:4050000円 )

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  • 最上部マントルの構造とモホ面の形成過程の研究~海と陸からのアプローチ~

    研究課題/領域番号:16H06347  2016年05月 - 2021年03月

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

    道林 克禎, 小原 泰彦, 平内 健一, 田村 芳彦, 岡本 敦, 高澤 栄一

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    配分額:184210000円 ( 直接経費:141700000円 、 間接経費:42510000円 )

    本研究課題は最上部マントルの構造と地殻―マントル境界であるモホロビチッチ不連続面(モホ面)の形成過程を解明するために,小笠原・マリアナ海溝の海溝かんらん岩とアラビア半島オマーンオフィオライトかんらん岩について岩石構造組織の発達過程,弾性・電気伝導度・透水率等の物性測定,岩石水反応実験などの多角的アプローチから研究する.海と陸のかんらん岩の構造岩石学的特徴を比較検討して地球深部最上部マントルの発達過程とそれを支配する要因を考察するため,本研究課題では,海班,陸班,分析班の3班体制で研究を進めている.
    海班は,6月から7月に四国海盆の拡大軸周辺の海底調査を実施した.6月には研究支援船よこすかによるYK18-07航海として実施された潜水調査船しんかい6500による4回の潜航調査によって四国海盆の拡大軸周辺の岩石採取を実施した.7月には白鳳丸によるKH18-2航海として同海域のドレッジ調査による岩石採取を実施した.この2回の研究航海によってマドメガムリオンと名付けられた海底地形の概要が明らかとなった他,四国海盆ではじめて超苦鉄質岩の採取に成功した.これらの結果について,速報として12月に開催されたアメリカ地球物理学連合秋季大会において発表した.現在,論文準備中である.
    陸班と分析班は,ICDP国際オマーン掘削プロジェクトのちきゅうオマーン2018として昨年同様に7月5日から9月3日の約2ヶ月間に清水港に停泊中の地球深部探査船ちきゅうにおいて,前年度に掘削された約3200mの岩石コアの物性測定と1次記載を実施した.本研究課題の組織メンバーの多くが参加して多数の物性データと岩石基礎データを取得した.これらの結果について,速報として12月に開催された日本地質学会とアメリカ地球物理学連合秋季大会において発表した.

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  • オマーンオフィオライト陸上掘削による地殻-マントル境界の物性とモホ面の実態解明

    研究課題/領域番号:16H02742  2016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(A)  基盤研究(A)

    高澤 栄一, 道林 克禎, 小野 重明, 田村 芳彦, 阿部 なつ江, 森下 知晃

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    担当区分:研究代表者  資金種別:競争的資金

    配分額:45110000円 ( 直接経費:34700000円 、 間接経費:10410000円 )

    海洋プレートの化石であるオマーンオフィオライトの陸上掘削が国際陸上科学掘削計画 (ICDP)により平成28年度から実施されている。本研究はこのプロジェクトに参画し,オマーンオフィオライトのマントル-地殻境界相当層を貫く新たな掘削孔を提案・実行し,コア試料の岩石学・地球化学・構造地質学的解析から,地球科学の未解決問題であるモホ面の実態および地殻-マントル境界の構造と物理的特性を明らかにするものである。平成30年度は平成29年度に掘削された地殻ーマントル境界のはんれい岩とかんらん岩類,および,活動的変質帯の変かんらん岩類を地球深部探査船「ちきゅう」に輸送し,世界の最先端研究者と学生とともに,平成30年7月上旬から9月上旬にかけて船上の機材を利用して,岩石コアの記載と解析を行った。さらに,研究用コア試料を研究者間で分配した。
    地殻ーマントル境界を貫くCM1A孔は北方に60度傾斜する全長 404.15mのダイヤモンド掘削孔で,上部160mはかんらん石ガブロを主体とし,少量のトロクトライト,ウェルライト,ダナイトを挟む。160m以深は310mまでは塊状のダナイトが主体をなし,それ以深はハルツバージャイトへと変化する。150m厚に達するダナイト層は地殻-マントル遷移帯に相当し,少量のウェールライトとガブロを伴うほか,局所的に断層ガウジを伴う破砕帯が発達し,蛇紋岩化が著しいが,下部に向かうほど蛇紋岩化の程度が低くなる。マントル最上部では,ハルツバージャイト・ダナイト互層が発達する。
    CM1A孔の400 m北方に位置するCM2A孔(全長300m)は垂直孔で,下位からハルツバージャイト(31m),ハルツバージャイト・ダナイト互層(148m),地殻-マントル遷移帯(121m)からなる。地殻-マントル遷移帯の上面と下面の境界はほぼ南に30°傾斜していることが明らかになった。

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  • オマーンオフィオライトを用いたマントルウェッジの酸化還元状態の解析

    研究課題/領域番号:26610173  2014年04月 - 2017年03月

    日本学術振興会  科学研究費助成事業 挑戦的萌芽研究  挑戦的萌芽研究

    高澤 栄一, Satish-Kumar M, 赤坂 正秀

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    担当区分:研究代表者  資金種別:競争的資金

    配分額:3770000円 ( 直接経費:2900000円 、 間接経費:870000円 )

    北部オマーンオフィオライト・フィズマントルセクションをマントルウェッジのアナログとして酸素フガシティの分布を検討した。酸素フガシティの変化幅はFMQ-3.3から+1.8であり,地殻ーマントル境界(Moho)からマントルセクションの基底部に向かうにつれて低くなる。ダナイトはハルツバージャイトより酸化的である。スピネルの三価鉄/全鉄比をメスバウアー分光でさらに検証し調和的な結果を得た。V/Sc比,Zn/Fe比は酸素フガシティーとそれぞれ逆相関,正の相関を示し,酸化還元状態の変動下のフラックス溶融と調和的である。基底部は沈み込んだ還元的な堆積物由来のメルト/流体との反応の影響が考えられる。

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  • 初期島弧における海洋リソスフェアの再融解とボニナイトの生成に関する地質学的検証

    2007年04月 - 2010年03月

    日本学術振興会  科学研究費 基盤研究 (C) 

    高澤 栄一

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    担当区分:研究代表者  資金種別:競争的資金

    配分額:4550000円 ( 直接経費:3500000円 、 間接経費:1050000円 )

    オマーンオフィオライト北部に位置するフィズ岩体マントルセクションに分布するかんらん岩類と貫入岩類の構造と化学組成を分析し、中央海嶺における海洋リソスフェアの形成から海洋デタッチメントによる初期島弧での改変のプロセスを明らかにした。とくに融け残りかんらん岩の組成分布から海嶺セグメント構造が見いだされた。海嶺セグメント境界には高枯渇のハルツバージャイトとダナイトが分布し,海洋リソスフェアのデタッチメントに伴い,多量の流体が流動したことが明らかになった。

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  • 初期島弧における海洋リソスフェアの再融解とボニナイトの生成に関する地質学的検証

    研究課題/領域番号:19540478  2007年 - 2009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)

    高澤 栄一

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    配分額:4550000円 ( 直接経費:3500000円 、 間接経費:1050000円 )

    オマーンオフィオライト北部に位置するフィズ岩体マントルセクションに分布するかんらん岩類と貫入岩類の構造と化学組成を分析し、中央海嶺における海洋リソスフェアの形成から海洋デタッチメントによる初期島弧での改変のプロセスを明らかにした。とくに融け残りかんらん岩の組成分布から海嶺セグメント構造が見いだされた。海嶺セグメント境界には高枯渇のハルツバージャイトとダナイトが分布し,海洋リソスフェアのデタッチメントに伴い,多量の流体が流動したことが明らかになった。

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  • 地殻・マントル物質の精密解析による海洋プレート・オフィオライトの比較研究

    研究課題/領域番号:17340162  2005年 - 2007年

    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)

    宮下 純夫, 高澤 栄一, 前田 仁一郎

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    配分額:15700000円 ( 直接経費:14800000円 、 間接経費:900000円 )

    本研究ではマントルから地殻最上部の溶岩層まで系統的な研究を行い,以下のような成果を得た.オマーンオフィオライトのマントルの広域的地球化学的・鉱物組成マッピングから,高枯渇帯の存在が明らかになり,海嶺下における初生的な溶融プロセスや二次的な改変プロセスが明らかとなってきた.マントル-地殻境界の空間的変化の実体を解明するために,海嶺セグメント中心から末端部へ岩石柱状図を作成・比較した結果,セグメント中心部ほど流動が強くかつメルトの抽出が効率的に生じていたことが明らかになってきた.海洋下部地殻の形成プロセスの問に関しては,ガブロ層の基底部から上部へ向かって分化が進んで行くが,セグメント中心部では組成変化が小さいのに対し,中間部から末端部ではその変化が大きくなる傾向が明らかとなった.この事実はセグメント中心部ではよりガブロ氷河モデルに近く,中心部から離れるにしたがってガブロシートモデルに近い状況となっている事を示唆している.溶岩層に関しては,セグメント中心部付近では溶岩層が薄くイベント回数が多いのに対し,セグメント末端部では個々の溶岩層が厚くイベント回数が少ないといった系統的な変化が明らかとなった.また,セグメント末端部ではそのほぼ中間にアンバーが介在している事が発見された.これは大規模な重複海嶺における特徴的な地質現象を表している可能性があり,現在詳細な解析を進めている.
    超高速拡大海嶺で形成された海洋地殻であるIODP Hole 1256Dにおける研究では,ホールの深い部分での変成作用が輝石ホルンフェルス相に達していることや,一部で部分溶融が生じていることが記載岩石学から推定され,全岩化学組成の検討でも部分溶融が生じている事が示された.また,Hole 1256Dの玄武岩組成の特徴は,高速拡大海嶺のEPR玄武岩よりもやや不適合元素に枯渇している特徴がある事も明らかとなった.

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  • マフィック岩を包有する不均質なマントルの部分融解に関する地質学的検証

    2004年04月 - 2006年03月

    日本学術振興会  科学研究費 基盤研究 (C) 

    高澤 栄一

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    担当区分:研究代表者  資金種別:競争的資金

    配分額:3400000円 ( 直接経費:3400000円 )

    本研究では,幌満かんらん岩体に胚胎するマフィック岩の野外の産状と主成分・微量元素(希土類元素とHFS元素)の分布をセンチメートルオーダーで詳細に検討し、過去8千年前のアセノスフェアの上昇に伴い,幌満岩体のマフィック岩がどのように部分融解し、生成したメルトがどのように母岩のかんらん岩と反応したのか、一連のプロセスを明らかにした。

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  • マフィック岩を包有する不均質なマントルの部分融解に関する地質学的検証

    研究課題/領域番号:16540413  2004年 - 2005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)

    高澤 栄一

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    配分額:3400000円 ( 直接経費:3400000円 )

    本研究では,幌満かんらん岩体に胚胎するマフィック岩の野外の産状と主成分・微量元素(希土類元素とHFS元素)の分布をセンチメートルオーダーで詳細に検討し、過去8千年前のアセノスフェアの上昇に伴い,幌満岩体のマフィック岩がどのように部分融解し、生成したメルトがどのように母岩のかんらん岩と反応したのか、一連のプロセスを明らかにすることを第1の目的とした。
    本研究の結果、幌満かんらん岩体のType Iマフィックグラニュライトは約8千万年前に再溶融のイベントを経た可能性が明らかとなった。マフィックレイヤーの中心部はガーネット単斜輝岩に相当し、周縁部はそれと平衡にある未分化な玄武岩質メルトと推定される。両者とも幌満岩体の上昇過程で変成し、マフィックグラニュライトに変化したと考えられる。
    次に、海洋性マントルの部分融解による化学的不均質性の形成過程を検討するために、平成16年12月〜平成17年1月にかけて中東オマーンオフィオライトの現地調査を実施した。採取した試料を用いて詳細な鉱物化学組成の広域的分布を検討した結果、高枯渇度の領域は、海洋リソスフェリックマントルの再溶融の融け残りである可能性が判明した。これらは、マントルセクションを斜行する剪断帯に沿っており、剪断帯の形成に伴う流体の通過とそれに伴うマントルかんらん岩のソリダス温度の低下によって再溶融したものと考えられる。
    海洋性マントルの直接観察として、国際深海掘削計画第209次航海で得られたかんらん岩試料を用いて、海洋性マントルの不均質性とそれをもたらしたプロセスの検討も行った。ODP Leg 209は大西洋中央海嶺15°20″断裂帯を挟む北緯14°〜16°付近に露出するマントルかんらん岩をSite1268〜1275の8サイトで掘削した。Site1271,Hole Bから得られた岩石の鏡下組織と鉱物化学組成に基づき最上部マントルにおけるメルトの流動とメルト-マントル反応について考察した結果、Hole 1271Bのimpregnated dunite、カンラン石ガブロ/ガブロノーライト/トロクトライトが、ダナイトと苦鉄質メルトの混成岩として形成したことが明らかになった。

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  • アセノスフェアによるリソスフェアマントル改変プロセスの地質学的検証

    2003年04月 - 2005年03月

    日本学術振興会  科学研究費 基盤研究 (C) 

    高澤 栄一

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    担当区分:研究代表者  資金種別:競争的資金

    配分額:4100000円 ( 直接経費:4100000円 )

    大陸縁のリソスフェアマントルである北海道日高変成帯の幌満かんらん岩体と,海洋性リソスフェアマントルであるオマーンオフィオライトのマントルセクションを研究対象とし,リフト帯と中央海嶺などの伸張場でアセノスフェアマノトルの上昇に起因するリソスフェアマントルの削剥・改変過程の解読を行った。かんらん岩とその構成鉱物の希土頬元素をはじめとする微塵元素の空間分布をもとに,アセノスフェアの部分融解で発生した苦鉄質メルトが,リソスフェアマントルを通過する際に引き起こした一連の現象を定量的に明らかにした。

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  • アセノスフェアによるリソスフェアマントル改変プロセスの地質学的検証

    研究課題/領域番号:14540421  2002年 - 2003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)

    高澤 栄一

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    配分額:4100000円 ( 直接経費:4100000円 )

    本研究は,大陸縁のリソスフェアマントルである北海道日高変成帯の幌満かんらん岩体と,海洋性リソスフェアマントルであるオマーンオフィオライトのマントルセクションを研究対象とし,リフト帯と中央海嶺などの伸張場でアセノスフェアマノトルの上昇に起因するリソスフェアマントルの削剥・改変過程の解読を行った.とくに,かんらん岩とその構成鉱物の希土頬元素をはじめとする微塵元素の空間分布をもとに,アセノスフェアの部分融解で発生した苦鉄質メルトが,リソスフェアマントルを通過する際に引き起こした一連の現象を定量的に明らかにすることを目的とした.
    本研究の結果,幌満かんらん岩体では,140メートルの連続露頭の中に未分化マントルに匹敵するレルゾライトからメルトに枯掲したハルツバージャイトまで多岐にわたる岩相が存在し,さらに微量元素の分布は主成分元素以上に複雑なことが明らかになった。すなわち,造山帯レルゾライトが過去にアセノスフェアマントルによる様々な改変を受けてきたことを示している。一方、海洋性リソスフェアマントルは,造山帯レルゾライト岩体に比較して,組成不均質性に乏しい.オマーンオフィオライトのマントルセクションの約25x15kmの範囲内における組成変化は,幌満岩体における140mの中で認められた組成変化よりもはるかに小さい.幌満岩体の場合,希土類元素の分布は数センチ〜メートルオーダーで変化する.一方,オマ-ーンオフィオライトのマントルセクションにおける組成の均質性は中央海嶺下における部分融解によるMORB形成のプロセスの影響を色濃く残している.しかし,本研究によりオマーンオフィオライトのマントルセクションにも従来知れていなかった組成不均質性が存在することが明らかとなった.すなわち,海洋リソスフェアの再溶融とアセノスフェア起源のメルトによる再肥沃化がkm規模で生じた可能性が考えられる.

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  • かんらん岩からマントルプロセスを読む-新たな展開と第4回国際レルゾライト会議をめざして

    研究課題/領域番号:13894015  2001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)

    小畑 正明, 小澤 一仁, 新井田 清信, 荒井 章司, 高橋 奈津子, 高澤 栄一

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    配分額:3400000円 ( 直接経費:3400000円 )

    2001年7月21日から25日にわたって,北海道様似町の様似町公民館及びアポイ山荘会議室にてシンポジウム「かんらん岩とマントルプロセス」を開催した.本集会は2002年8-9月北海道様似町で開催予定の第4回国際ワークショップ「造山帯レルゾライトとマントルプロセス」に向けて国内の準備体制を強化し,国内の研究をより一層推進するためのものであった.21日,22日及び23日の夜間は室内講演会,討論会を行った.また23日,24日は幌満かんらん岩の野外地質巡検を実施した.全国の大学から教官21名,学生,院生11名の計32名が参加し,室内討論会では19編の口頭発表と7編のポスターの発表がなされた.カバーしたテーマは岩石学,構造地質学・実験岩石学・微量元素・同位体地球化学,地球物理学,など多方面にわたり,短期間であったが集中的な討議ができた.野外地質巡検では,2002年の本会議の時の巡検予定コースを実地に検討することで幌満かんらん岩の研究の最前線を野外で検証し知識を参加者間で共有する事ができた.25日は関係者で準備委員会を行い,様似町側と詳細な準備打ち合わせを行った.なお本シンポジウムで発表された講演の要旨は別に冊子にまとめ参加者,関係者に配布するべく3月現在準備中である.
    9月下旬には金沢において準備委員会を開催し,本会議のセカンドサーキュラーの骨子を作成,その後関係者間で協議を続けることにより,11月にセコンドサーキュラーを完成させweb上で公開するとともに,世界に配布した・またこの間海外の組織科学プログラムメンバーとも意見を交わし,会議のプロシーディングをJ.Petrolgyに出すこと,またそのゲストエディターのメンバーを決定し2002年の国際会議に向けて準備を大きく進めることができた.

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  • 海洋地殻-マントル系の生成と改編:オマーン・オフィオライトの例

    研究課題/領域番号:11691121  1999年 - 2000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)

    荒井 章司, 海野 進, 高澤 栄一, 宮下 純夫, 水田 敏夫, 増田 俊明, 石川 剛志

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    配分額:20000000円 ( 直接経費:20000000円 )

    1.上部マントルのかんらん岩の岩石学的・構造学的調査により,レールゾライトからハルツバーガイトに渡る広い岩相変化,組織の分布からみた変形履歴,鉱物の結晶構造の変化,マイロナイトの成因などが判明した.また白金族元素の濃集したクロミタイトが発見された.
    2.後期貫入岩体を3つのタイプに分類した.急冷相のピクライト玄武岩に伴うコマチアイト様超マフィック噴出岩が発見された.現在,その詳細な性格付けを急いでいる.
    3.海嶺のセグメント構造が斑れい岩層の変化から確定された.セグメント中心部の派生的なマグマ溜りの周辺部にノーライトが貫入し,岩脈群の一部が輝石グラニュライト相までの変成作用を受けている.またマグマ溜りルーフゾーンの構造と進化過程が判明した.
    4.上部溶岩の単斜輝石斑晶の化学組成を精密に測定し,3種類に分類し,各々の成因の概要を明らかにした.またボニナイトを発見した.さらに,オブダクション期に活動したサラヒ火山岩類について予察的なデータを得た.
    5.バチナ・コースト地域のグゼイン鉱床の生成環境の鉱床学的・地球化学的検討を行い,その詳細を明らかにした.すなわち,変質玄武岩中の緑泥石に熱水から亜鉛,ニッケルが選択的に固定し,鉱体ではこれらに成分に乏しくなった.また,オマーン・オフィオライトの熱水形成では水/岩石比が20程度で2〜4という理論値をはるかに上回っていることが明らかになった.
    6.玄武岩〜ドレライトの変成作用,特にプレーナイト-アクチノ閃石相内の温度構造を考察し,変成温度が層序的に下位に向かって上昇していることを確認した.
    7.メタモルフィックソールの剪断がNE-SW方向に起こり,上盤がSW方向に移動したことが分かった.マントルウェッジ直下から数十m以内で,塩基性角閃岩は,多様な流動形態を示すことがわかった.

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  • 本州弧,領家帯の基礎をつくった先白亜紀岩石の初生形成年代と形成環境

    研究課題/領域番号:10440139  1998年 - 2000年

    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)

    加々美 寛雄, 志村 俊昭, 高澤 栄一, 小林 健太, 田結庄 良昭, 豊島 剛志

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    配分額:13000000円 ( 直接経費:13000000円 )

    本研究をとおし領家帯を構成する岩石類から得られた年代をまとめる.(1)20〜18億年:この年代は堆積岩源変成岩類のdepleted mantleを用いたモデル年代,領家花崗岩類と苦鉄質岩類のinherited zirconのU-Pb年代,一部花崗岩類のモデル年代から得られ,地下深所に原生代岩石類が存在している事を示している.筑波山地には更に古い20億年代の岩石が存在している可能性がある.これらのデータは領家帯の基礎はその全域ではないにしろ大陸的特徴をもっている事を示唆している.(2)17.5〜16億年:この年代は堆積岩源変成岩と一部花崗岩類のモデル年代から得られた.しかしこの年代はinherited zirconからは未だ得られていない.この年代のもつ意味については今後の検討が必要である.(3)2.2〜1.9億年:苦鉄質岩類のSm-Nd全岩アイソクロン,鉱物アイソクロンから得られた年代で,これら苦鉄質岩類の活動年代を示している.活動時は大陸的環境下にあったものと考えられる.(4)1.7〜1.6億年:一部の苦鉄質岩のSm-Nd全岩アイソクロン,鉱物アイソクロンおよび花崗岩類のSm-Nd鉱物アイソクロンと花崗岩類のRb-Sr全岩アイソクロンから求められる.領家帯の一部の苦鉄質岩と花崗岩類はこの頃活動している.(5)1.25〜0.7億年:領家帯に産する苦鉄質岩類,苦鉄質〜中性岩脈類,花崗岩類について様々な方法によりこの範囲の年代が得られる.苦鉄質岩類の場合は花崗岩類の貫入による熱的影響を示すものであり,苦鉄質〜中性岩脈類と花崗岩類の場合は活動時期とその後の冷却史を示している.領家帯内における火成活動の時空変遷についてはYuhara et al.(2000)が詳しく論じている.なお後期白亜紀の火成活動は島弧あるいは大陸縁辺部的環境下にあった事がKagami et al.(1992)の研究から明らかとなっている.(5)の火成岩類と同位体的特徴の似た火成岩類は本州弧において領家帯以外にも広く分布している.この事は領家タイプの大陸性リソスフェアが本州弧の骨格をつくっている事を示している(加々美ほか,1999;2000).

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  • 海洋地殻生成のダイナミクス-オマーンオフィオライトを例として

    研究課題/領域番号:09041101  1997年 - 1998年

    日本学術振興会  科学研究費助成事業 国際学術研究  国際学術研究

    宮下 純夫, 高澤 栄一, 石川 剛志, 海野 進, 川幡 穂高, 荒井 章司, 石塚 英男

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    各研究グループごとに成果を要約する.マントルグループは,モホ漸移帯でのメルト-マントルの反応過程の解析とその地域的不均質性を明らかにした.また,川砂のスピネルの分析から,マントルが枯渇した特徴を有していることを明らかにした.広域的なマントルの岩相変化についても,次第に輪郭が明らかになりつつある.
    斑れい岩グループは,従来一連とされていた斑れい岩層を2つに区分した.そして,海嶺伝播に伴う地殻深部でのプロセスをモデル化した.また,海嶺セグメントの中心部を同定し,海嶺軸方向に沿ったマグマ組成変化を明らかにした.斑れい岩層の鉱物組成変化から,サイクリックユニットを同定するとともに,斜長石の逆累帯構造の解析から上部マントルからマグマチェンバーへのマグマプロセスの解明へと進みつつある.地殻上部グループは,シート状岩脈群の方向や岩脈の厚さについて広域的に解析し,数kmオーダーでの海嶺のセグメント構造の実体を初めて明らかにした.また,ダイクの幅が海嶺軸方向に沿って系統的な変化を示すことを見いだし,マントルや斑れい岩から推定されていより規模の大きなセグメント構造との対応関係を明らかにした.
    変質・地球化学グループは,変質鉱物組み合わせの変化,変質度合などについて記載し,変質条件と層序的位置との関係について検討を進めている.また,Sr同位体組成を用いて,海水が地殻のかなり深部まで到達していることを明らかにした.このほか,アレイユニットの地球化学的検討の結果,これらが極めて特異な性格を持っていることも判明してきた.
    構造グループは,オフィオライト基底部の変成岩について2方向の線構造を有するものや,全く線構造が見られない岩石も存在することなどを発見している.この過程で,線構造の認定方法という一般に広く用いられている研究手法自体の再検討をおこない,厳密に線構造を決定する方法も提唱している.

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