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Origin and Regional Variation of the Magma in the Ryukyu Arc-Back Arc System

Research Project

Project/Area Number 03640643
Research Category

Grant-in-Aid for General Scientific Research (C)

Allocation TypeSingle-year Grants
Research Field 地質学一般
Research InstitutionInstitute for Study of the Earth's Interior

Principal Investigator

HONMA Hiroji  Okayama Univ., Institute for Study of the Earth's Interior, Professor, 地球内部研究センター, 教授 (70033131)

Co-Investigator(Kenkyū-buntansha) NAKAMURA Eizo  Okayama Univ., Institute for Study of the Earth's Interior, Associate Professor, 地球内部研究センター, 助教授 (80201672)
KAGAMI Hiroo  Okayama Univ., Institute for Study of the Earth's Interior, Associate Professor, 地球内部研究センター, 助教授 (20108179)
Project Period (FY) 1991 – 1992
Project Status Completed (Fiscal Year 1992)
Budget Amount *help
¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 1992: ¥300,000 (Direct Cost: ¥300,000)
Fiscal Year 1991: ¥800,000 (Direct Cost: ¥800,000)
KeywordsRyukyu arc / Volcanic rocks / Trace element / Strontium isotope ratio / Neodymium isotope ratio / Magma genesis / Two-component mixing model / Alkaline rocks / 島弧マグマ / 微量元素組成 / ストロウンチウム同位体 / ネオジム同位体 / 琉球系火山岩 / 高苦土安山岩 / 黄尾礁 / アルカリ火山岩 / ストロンチウム同位体
Research Abstract

Contents of Rb, Sr, Nd and Sm and ^<87>Sr/^<86>Sr and ^<143>Nd/^<144>Nd ratios have been analyzed for Cenozoic volcanic rocks of the Ryukyu arc system. The distinctly low Sm contents and Sm/Nd ratios of hornblende-bearing rocks and the variation of Zr/Sr in rocks of the arc side with significantly low Zr/Sr ratios in relatively basic rocks clearly indicate the effects of the hornblende- and plagioclase-dominant fractionations, respectively, which most probably are related to crystallization differentiation of the magma. The Sr-Nd isotopic characteristics are best interpreted by the paired two-component mixing models, namely the 'source-mixing' and 'crustal-mixing' : (1)Strontium and Nd in the primary magmas consist mainly of the mixture derived from the MORB source-type peridotite and subducted sedimentary rocks. (2)Contribution of sedimentary components to the primary magma is distinctly lower in the back-arc side (27-30%). (3)Often magmas of both sides have been affected by considerable degree of isotopic modification by crustal materials during their evolution in the crust. (4)The ^<87>Sr/^<86>Sr and ^<143>Nd/^<144>Nd ratios also change with changing geological settings. (5)The high magnesian andesite has the high ^<143>Nd/^<144>Nd ratio compared to its ^<87>Sr/^<86>Sr ratio, and its primary magma should have originated from the different source material. (6)Alkaline basalts of the Obisyo characteristically have the isotopic signature of the plume-type basalts.
Both the Zr-Sr and Sm/Nd-SiO_2 systematics and their accordance with each other strongly support the hypothesis that the difference in the melting degree (increase from back-arc side towards the arc side) should be the main controlling factor for the chemical difference of the primary magmas between both sides.

Report

(3 results)
  • 1992 Annual Research Report   Final Research Report Summary
  • 1991 Annual Research Report
  • Research Products

    (7 results)

All Other

All Publications (7 results)

  • [Publications] HONMA,Hiroji: "Across-arc variation of Rb,Sr,Nd and Sm contents and ^<87>Sr/^<86>Sr and ^<143>Nd ^<144>Nd ratios in Quatemary volcanic rocks from the Satsunan Islands area of the Ryukyu arc,Southwest Japan." 地質学雑誌.

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      1992 Final Research Report Summary
  • [Publications] HONMA,Hiroji: "Chronological and areal variation of Sr and Nd isotope ratios in Cenozoic volcanic rocks of the Ryukyu arc system,Southwest Japan." Contr.Min.Petrol.

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      1992 Final Research Report Summary
  • [Publications] HONMA,Hiroji: "Rubidium,Sr,Nd and Sm contents and ^<87>Sr/^<86>Sr and ^<143>Nd ^<144>Nd ratios of Japanese sedimentary rocks." Geoche.J.

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      1992 Final Research Report Summary
  • [Publications] Hiroji Honma: "Across-arc variation of Rb, Sr, Nd and Sm contents and 87Sr/86Sr and 143Nd/144Nd ratios in Quaternary volcanic rocks from the Satsunan Islands area of the Ryukyu arc, Southwest Japan" Bull.Geol.Scoc.Japan.

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      1992 Final Research Report Summary
  • [Publications] Hiroji Honma: "Chronological and areal variation of Sr and Nd isotope ratios in Cenozoic volcanic rocks of the Rukyu arc system, Southwest Japan" Contr.Min.Petrol.

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      1992 Final Research Report Summary
  • [Publications] Hiroji Honma: "Rubidium, Sr, Nd and Sm contents and 87Sr/86Sr and 143Nd/144Nd ratios of Japanese sedimentary rocks." Geochem.J.

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      1992 Final Research Report Summary
  • [Publications] Hiroji Honma: Geochemical Journal. 25. 121-136 (1991)

    • Related Report
      1991 Annual Research Report

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Published: 1991-04-01   Modified: 2016-04-21  

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