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Characteristics and origin of the magma generated in the fore-arc and accretionary regions

Research Project

Project/Area Number 06640583
Research Category

Grant-in-Aid for Scientific Research (C)

Allocation TypeSingle-year Grants
Section一般
Research Field Geology
Research InstitutionOkayama University

Principal Investigator

HONMA Hiroji  Okayama University, Institute for Study of the Earth's Interior, Prof., 固体地球研究センター, 教授 (70033131)

Co-Investigator(Kenkyū-buntansha) KAGAMI Hiroo  Okayama University, Institute for Study of the Earhth's Interior, Ass.Prof., 固体地球研究センター, 助教授 (20108179)
Project Period (FY) 1994 – 1996
Project Status Completed (Fiscal Year 1996)
Budget Amount *help
¥2,100,000 (Direct Cost: ¥2,100,000)
Fiscal Year 1996: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1995: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1994: ¥900,000 (Direct Cost: ¥900,000)
Keywordsfore-arc region / accretionary body / igneous activity / basalt magma / strontium isotope / granitoids of the Outer zone / neodimium isotope / oxygen isotope / 前弧部 / 玄武岩 / 花崗岩 / ストロンチウム / ネオジム / 同位体
Research Abstract

Sixty samples of granitoids, sedimentary rocks and xenoliths from Kii, Shikoku, Kyushu and Yakushima in the Outer zone of Southwest Japan and twenty-two samples of rocks of the olivine basalt-dolerite-olivine gabbro-granophyre-rhyolite association from Shionomisaki in the fore-arc region have been analyzed for majro elements, Rb-, Sr-, Nd, Sm- concentrations, and oxygen-, Sr- and Nd-isotope rations. Specific features of the mantle-derived magma and its behaviors in the crust and the genesis of per-aluminous granitoids were quantitatively discussed.
(1) The basaltic magma generated in the mantle beneath the fore-arc region has characteristic MORB-type chemical and isotopic features that are distinctly different from common arc magmas'. This depends to the specific tectonic positio of the fore-arc region where the slab-derived component cannot incorporate to the genesis of original baslt magmas. (2) The Sr-Nd systematic of the basalt-rhyolite association of Shionomisaki well fits to the b … More ulk-mixing model of the olivine basalt-average Shimanto sedimentary rock end-members, indicating that the MORB-type magma uprised to the accretionary part could derived isotopically much evolved acid magma by reaction with sedimentary rocks which proceeded simultaneously to the crystallization of the magma.
(3) Detailed studies of the chemical and isotopic change in each granite body and suite clearly discriminate the process of changing granitoid magma mass during uprise, crystallization and intrusion in the upper crust and the process of generation of varying parental granodioritic magmas in the depth. (4) The isotopic variation in granitoids is principally due to the local variation and internal heterogeneity of the parent granite magma mass, and its Sr-Nd isotopic systematics perfectly fits to the two-step two-component mixing model. This includes that the parental granite magma has been formed by 'mixing' of the mantle-derived arc magma and sedimentary rocks of the Shimanto Super Group.
(5) The parental granitoid magmas should be generated by the reaction, including melting and assismilation, of mantle-derived magma with lower crustal rocks, and their chemical and isotopic features should principally controlled by the degree of contribution and nature of lower-crust substances. The per-aluminous granitoids like those of the Outer zone of Southwest Japan can only generated in the young accretionary regions where only the sedimentary rocks can be incorporated in the process of generation of parental granite magma. Less

Report

(4 results)
  • 1996 Annual Research Report   Final Research Report Summary
  • 1995 Annual Research Report
  • 1994 Annual Research Report
  • Research Products

    (7 results)

All Other

All Publications (7 results)

  • [Publications] 本間弘次: "変動帯(領家帯)花崗岩の形成過程:特に酸素及びストロンチウム同位体の挙動について" 月間 地球. 特別号No.16. 99-106 (1996)

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      1996 Final Research Report Summary
  • [Publications] Honma.H.: "High ammonium contents in the 3800 Ma Isua supracrustal rocks,central West Greenland" Geochimica et Cosmochimica Acta. 80. 2173-2178 (1996)

    • Description
      「研究成果報告書概要(和文)」より
    • Related Report
      1996 Final Research Report Summary
  • [Publications] HONMA,Hiroji: "Genesis of granitoids in the mobile belt (the Ryoke belt) : with special refernce to the oxygen and strontium isotopic behaviors." Monthly 'The Earth', Spec.Vol.16. 99-106 (1996)

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      1996 Final Research Report Summary
  • [Publications] HONMA,Hiroji: "High ammonium contents in the 3800 Ma Isua supracrustal rocks, central West Greenland." Geochim.Cosmochim.Acta. Vol.60 No.12. 2173-2178 (1996)

    • Description
      「研究成果報告書概要(欧文)」より
    • Related Report
      1996 Final Research Report Summary
  • [Publications] 本間弘次: "変動帯(領家帯)花崗岩の形成過程:特に酸素及びストロンチウム同位体の挙動について" 月間地球. 特別号No.16. 99-106 (1996)

    • Related Report
      1996 Annual Research Report
  • [Publications] Honma,H.: "High ammonium contents in the 3800 Ma Isua supracrustal rocks. central West Greenland" Geochimica Cosmochimica Acta. 60・12. 2173-2178 (1996)

    • Related Report
      1996 Annual Research Report
  • [Publications] 本間弘次: "High ammonium contents in the 3800 Ma Isua supracrustal rocks,central West Greenland" Geochimica et Cosmochimica Acta. 60(出版受理、1996、2.27). (1996)

    • Related Report
      1995 Annual Research Report

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Published: 1994-04-01   Modified: 2016-04-21  

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