2000 Fiscal Year Final Research Report Summary
Elucidation of factors controlling spatial geochemical variation of Cretaceous igneous rocks in SW Japan and verification of the ridge subduction.
| Project/Area Number |
11640451
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Geology
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| Research Institution | Shimane University |
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Principal Investigator |
IIZUMI Shigeru Shimane University, Fac.Sci & Eng., Professor, 総合理工学部, 教授 (80032639)
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| Co-Investigator(Kenkyū-buntansha) |
AKASAKA Masahide Shimane University, Fac.Sci & Eng., Professor, 総合理工学部, 教授 (20202509)
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| Project Period (FY) |
1999 – 2000
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| Keywords | Cretaceous / Felsic igneous rocks / Petrochemistry / Ridge / Sr and Nd isotopes / Adakite / MORB / Granites |
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| Research Abstract |
Aims of this project are to elucidate the factors controlling spatial geochemical variation of the Cretaceous igneous rocks in SW Japan and to clarify relationship between this voluminous magmatism and ridge subduction at the eastern Eurasian continent during the Cretaceous. Geological and petrochemical studies have been carried out for early to middle Cretaceous igneous rocks in the San'yo Belt and also for some igneous rocks with unknown ages in the San'in Belt. The igneous rocks with ages ranging from 100 to 120 Ma in the San'yo belt have different geochemical and initial Sr and Nd isotope ratios from igneous rocks with younger ages in the same region. Some older igneous rocks in the San'yo Belt are characterized by high Sr and low Y contents, and also by lower initial Sr and higher initial Nd isotope ratios than the younger igneous rocks in the same region. These geochemical characteristics of the older igneous rocks are similar to the Archean high-Al TTD and Cenozoic adakite, indicating that the magmas were derived by partial melting of the subducted oceanic lithosphare. Those igneous rocks, however, are relatively enriched in Sr and Nd isotope ration, compared with MORB.Then, the magma derived from the subducted slab may have been contaminated with the overlying crustal materials. As these adakitic igneous rocks are frequently recognized in areas, where ridges was subducting, it is strongly suggested that the Kula-Pacific ridge was subducted beneath the eastern margin of the Eurasian continent during the Cretaceous.
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[Publications] Kagami, H., Kawano, Y., Ikawa, T., Ishioka, J., kagashima, S., Yuhara, M., Shuto, K., Iizumi, S.Imaoka, T., Owada, M., Osanai, Y.and Tainosho, T.: "Transition of space and time of Cretaceous to tertiary igneous activity and lower crust of Honshu Arc-Examination based on Rb-Sr whole rock isochron ages and Sr and Nd isotopes-."Mem.Geol.Soc.Japan. 53. 1-19 (1999)
Description
「研究成果報告書概要(欧文)」より
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[Publications] Kagami, H., Yuhara, M., Iizumi, S., Tainosho, Y., Owada, M., Ikeda, Y., Okano, O., Ochi, S., Hayama, Y.and Nureki, T.: "Continental basalts in the accretionary complexes of the South-west Japan Arc : Constrains from geochemical and Sr and Nd isotopic data of metadiabase."The Island Arc. 9. 3-20 (2000)
Description
「研究成果報告書概要(欧文)」より
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