| Project/Area Number |
09640536
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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 | Hokkaido University of Education |
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Principal Investigator |
OKAMURA Satoshi Hokkaido University of Education, Sapporo, Campus, Associate, Professor, 教育学部・札幌校, 助教授 (40175261)
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| Project Period (FY) |
1997 – 1998
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| Project Status |
Completed (Fiscal Year 1998)
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| Budget Amount *help |
¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 1998: ¥600,000 (Direct Cost: ¥600,000)
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| Keywords | arc-arc junction / opening of Okhotsk sea / dextral strike-slip fault / bimodal volcanism / arc volcanism / Neogene / Hokkaido / 大陸下リソスフェア / 島弧会合テクトニクス / 千島弧火山 / 島弧火山 / エンリッチマントル / 枯渇マントル / Sr同位体比 / Nd同位体比 |
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| Research Abstract |
K-Ar ages and chemical compositions of the Cenozoic volcanic rocks from Hamamasu district, western margin of central Hokkaido are determined to obtain constraints on the tectono-magmatic evolution of the Hokkaido located at a junction between the Kuril and Northeast Honshu arcs. The early to late Miocene (19 -8 Ma) volcanic rocks have more enriched isotopic ratios and lower Zr/Nb ratios. The early Miocene volcanism along the western margin of central Hokkaido including Hamamasu district from Rebun island to off the coast of Tomakomai is characterized by the bimodal volcanic rocks. We propose that the volcanism may have been related to the collision between the Eurasian Plate and the Okhotsk Plate, followed by the dextral strike-slip faulting associated with the formation of the Kuril Basin. The lack of correlation between relative enriched basalts from Hokkaido and depleted basalts from Sakhalin and Sikhote-Alin suggests that the source of the former basalts has not a significant contribution from an asthenosphere.
The Pliocene magmatism comprising both andesitic polygenetic and basaltic monogenetic volcanoes, have more depleted geochemical features. The temporal geochemical trends from 19 Ma to 2 Ma in volcanic rocks from Hamamasu suggest that there was a change in magma source from the lithosphere to the depleted asthenosphere as the collision progressed. It may be inferred that the Pliocene volcanism occurred under extensional stress field resulted from the oblique subduction of the Pacific Plate after the opening of the Japan Sea and Okhotsk Sea.
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