| 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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| Project Status |
Completed (Fiscal Year 2000)
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| Budget Amount *help |
¥4,000,000 (Direct Cost: ¥4,000,000)
Fiscal Year 2000: ¥900,000 (Direct Cost: ¥900,000)
Fiscal Year 1999: ¥3,100,000 (Direct Cost: ¥3,100,000)
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| Keywords | Cretaceous / Felsic igneous rocks / Petrochemistry / Ridge / Sr and Nd isotopes / Adakite / MORB / Granites / 西南日本 / 第三紀 / 火成活動 / Sr・Nd同位体比 / 酸性岩 / 地球化学 |
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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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