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2001 Fiscal Year Final Research Report Summary

Development of age determination method using U-Th isotope disequilibrium for the prediction of volcanic eruption

Research Project

Project/Area Number 11554021
Research Category

Grant-in-Aid for Scientific Research (B)

Allocation TypeSingle-year Grants
Section展開研究
Research Field Petrology/Mineralogy/Science of ore deposit
Research InstitutionOKAYAMA UNIVERSITY

Principal Investigator

NAKAMURA Eizo  Institute for Study of the Earth's Interior, Okayama University Professor, 固体地球研究センター, 教授 (80201672)

Co-Investigator(Kenkyū-buntansha) MORIGUTI Takuya  Institute for Study of the Earth's Interior, Okayama University Assistant Professor, 固体地球研究センター, 助手 (70304342)
MAKISHIMA Akio  Institute for Study of the Earth's Interior, Okayama University Associate Professor, 固体地球研究センター, 助教授 (70219301)
Project Period (FY) 1999 – 2001
KeywordsU-Th isotope disequilibrium / Th-Ra isotope disequilibrium / Magma process / Miyakejima / Isochron / TIMS / Analytical precision / Half-life
Research Abstract

In order to estimate the time scale of magma processes beneath island arc, we have developed new chimerical separation methods and highly precise isotope analyses for U, Th and Ra. These techniques were first applied to lavas from Miyakejima Island together with comprehensive petrological and geochemical investigations using major and trace element compositions and B-Sr-Nd-Pb isotopic compositions. The inferred genesis and transportation mechanism of magma with subduction component derived from descending slab in the wedge mantle beneath Miyakejima is summarized as follows:
^<238>U-^<230>Th disequilibrium observed in Miyakejima lavas with large 238U excess implies metasomatism of depleted mantle by fluid-related processes, as also suggested by the trace element and B-Sr-Nd-Pb isotope systematics. In the equiline diagram, trends observed in Stages 1 and 2 indicate two different isochrones with common initial ^<230>Th/^<232>Th ratios. The interval of individual fluid-release is obtained a … More s 15 kyr between Stages 1 and 2, and 3 kyr between Stages 2 and 3. ^<226>Ra-^<230>Th disequilibrium observed in some lavas suggests that the minimum interval of the fluid-release is approximately 1 kyr, indicating that the fluid-release and subsequent melt generation in the wedge mantle are episodic events intermittently occurring within 1-15 kyr. The ^<226>Ra-^<230>Th disequilibrium constraints the ascending rate of slab components as >45 m/yr, leading to the existence of crack in the wedge mantle. In contrast, Stages 3 and 4 samples depict a mixing trend in the equiline diagram between old andesitic magma and newly injected primitive magma. The involvement of primitive magma generally decreases from Stage 3 towards present, implying that primitive magma system is nearly closed system. Residence time of the differentiated magma in the crust is approximately 10 kyr, which is factor of two longer than theoretically obtained result. This may be due to the continuous heat supply from neighboring magma injection. Less

  • Research Products

    (12 results)

All Other

All Publications (12 results)

  • [Publications] Yokoyama, T., Makishima, A.Nakamura, E.: "Separation of thorium and uranium from silicate rock samples using two commercial extraction chromatographic resins"Analytical chemistry. 71. 135-141 (1999)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] Yokoyama, T., Makishima, A.Nakamura, E.: "Evaluation of the coprecipitation of incompatible elements with fluoride during silicate rock dissolution by acid digestion"Chemical Geology. 157. 175-187 (1999)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] Yokoyama, T., Makishima, A., Nakamura, E.: "Precise analysis of 234U/238U ratio using UO^<2+> ion with thermal ionization mass spectrometry for natural samples"Chemical Geology. 181. 1-12 (2001)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] Kobayashi, K., Nakamura, E.: "Geochemical evolution of Akagi Volcano, Northeast Japan"Journal of Petrology. 42. 2303-2331 (2001)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] Makishima, A., Nakamura, E.: "Determination of total sulfur at mgg-1 levels in geological materials by oxidation of sulfur into sulfate …"Analytical chemistry. 73. 2547-2553 (2001)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] Yokoyama, T., Nakamura, E.: "Precise determination of ferrous iron in silicate rocks"Geochimica et Cosumochimica Acta. 66. 1085-1093 (2002)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] Yokoyama, T., Makishima, A. and Nakamura, E.: "Separation of thorium and uranium from silicate rock samples using two commercial extraction chromatographic resins,"Anal. Chem. 71. 135-141 (1999)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] Yokoyama, T., Makishima, A. and Nakamura, E.: "Evaluation of the coprecipitation of incompatible trace elements with fluoride during silicate rock dissolution by acid digestion."Chem. Geol.. 157. 175-187 (1999)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] Yokoyama, T., Makishima, A. and Nakamura, E.: "Precise analysis of 234U/238U ratio using UO2+ ion with thermal ionization mass spectrometry for natural samples."Chem. Geol.. 181. 1-12 (2001)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] Kobayashi, K. and Nakamura, E., Geochemical Evolution of Akagi Volcano: "Northeast Japan: Implications for Interaction between Island Arc Magma and Lower Crust, and Generation of Isotopically"J. Petrol.. 42. 2303-2331 (2001)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] Makishima, A. and Nakamura, E.: "Determination of total sulfur at mg g-1 levels in geological materials by oxidation of sulfur into sulfate with in situ generation of bromine using isotope dilution high resolution"Anal. Chem.. 73. 2547-2553 (2001)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] Yokoyama, T. and Nakamura, E.: "Precise determination of ferrous iron in silicate rocks."Geochim. Cosmochim. Acta. 66. 1085-1093 (2002)

    • Description
      「研究成果報告書概要(欧文)」より

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Published: 2003-09-17  

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