2003 Fiscal Year Final Research Report Summary
Geochemical and geochronological examination on Mesozoic continental lithosphere beneath SW Japan
| Project/Area Number |
14540425
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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, Geoscience, Professor, 総合理工学部, 教授 (80032639)
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| Project Period (FY) |
2002 – 2003
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| Keywords | Chugoku district / Cretaceous / Magmatism / Crust / Mantle / geochemistry / Sr isotope / Nd isotope |
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| Research Abstract |
Felsic magmatism in SW Japan took place in a wide area from the Ryoke Belt to the San'in Belt during the late Cretaceous (from 100 Ma to 80 Ma). After that width of the magmatic zone became narrow, and the early Paleocene magmatism occurred only in the San'in Belt. Eocene and Oligocene magmatism occurred in more restricted area in the San'in Belt. Igneous rocks in the Ryoke and southern part of the Sanyo Belts show contrasting geochemical characteristic to those of the San'in Belt. This may be explained by subduction of the Kula-Pacific ridge.
The former have high initial Sr and low Nd isotope ratios, whereas the latter show low initial Sr and high Nd isotope ratios. Mixing and assimilation fractional crystallization model calculations indicate that this geochemical difference, between the igneous rocks in both belts cannot be ascribed to difference in the degree of contamination of the magma with upper crustal materials. This could be attributed to geochemical difference in the source of the magmas in both belts. A small continental blocks with enriched mantle similar to EMII must have existed beneath the Ryoke and southern part of the Sanyo Belts during the late Cretaceous. Eocene and Oligocene igneous rocks in the San'in Belt show more depleted nature than the Cretaceous and Paleocene igneous rocks, suggesting that depleted asthenospheric materials injected into the mantle beneath the San'in Belt in the Eocene.
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Research Products
(8 results)
