1998 Fiscal Year Final Research Report Summary
Geochemical evolution of thelower crust and upper mantle beneath SW Japan.
| Project/Area Number |
09640545
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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, Department of Science and Technology, Professor, 総合理工学部, 教授 (80032639)
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| Project Period (FY) |
1997 – 1998
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| Keywords | Southwest Japan / Mesozoic-Cretaceous / Tertiary / Basic rocks / Acidic rocks / Sr・Nd isotopes / magmatism / mantle |
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| Research Abstract |
Objective of this research was to understand geochemical evolution of the lower crust and upper mantle beneath SW Japan since the Jurassic. As many geochemical and Sr and Nd isotope data have been reported for felsic rocks, We examined geochemistry and Sr and Nd isotope ratios of mafic to intermediate igneous rocks of the Jurassic to Tertiary in SW Japan. Our data indicate that upper mantle beneath the San-in and San-yo Belts had been changed to more depleted nature since the Jurassic, although the upper mantle beneath the San-yo Belt was more isotopically enriched than that beneath the San-in Belt during the Cretaceous. It is suggested that the upper mantle beneath the San-in Zone changed to depleted nature after the Miocene. Although it has been suggested by some researchers that voluminous Cretaceous magmatism in SW Japan were caused by subduction of the Kula-Pacific Ridge, clear geochemical evidences to support such a suggestion have not been obtained in this study. I am now examining early Cretaceous intermediate igneous rocks in San-yo Belt, because they have relatively higher Sr contents and low Sr initial isotope ratios than late Cretaceous igneous rocks. There is a possibility that these rocks were derived by partial melting of the subducting slab.
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