| Project/Area Number |
17540452
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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 |
Petrology/Mineralogy/Science of ore deposit
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| Research Institution | University of Tsukuba |
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Principal Investigator |
KUROSAWA Masanori University of Tsukuba, Graduate School of Life and Environmental Sciences, Assistant professor (50272141)
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| Co-Investigator(Kenkyū-buntansha) |
ANMA Ryo University of Tsukuba, Graduate School of Life and Environmental Sciences, Assistant professor (70311595)
KOMATSUBARA Tetsuro University of Tsukuba, Graduate School of pure and Applied Sciences, Assistant professor (10195852)
SASA Kimikazu University of Tsukuba, Graduate School of pure and Applied Sciences, Assistant professor (20312796)
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| Project Period (FY) |
2005 – 2007
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| Project Status |
Completed (Fiscal Year 2007)
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| Budget Amount *help |
¥3,650,000 (Direct Cost: ¥3,500,000、Indirect Cost: ¥150,000)
Fiscal Year 2007: ¥650,000 (Direct Cost: ¥500,000、Indirect Cost: ¥150,000)
Fiscal Year 2006: ¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 2005: ¥1,600,000 (Direct Cost: ¥1,600,000)
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| Keywords | hydrogen / magma / melt inclusion / ion beam / water / ERDA / lzu / Fossa magna |
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| Research Abstract |
Chromian diopside megacrysts, a few cm in size, are often found in basalt and basaltic andesite dykes and tholeiitic basalt at a Miocene collision zone of the Izu-Bonin arc, central Japan. The diopside megacrysts occur from only dykes and lavas in sea-floor volcanic rocks of the Miocene age (6 Ma to 16 Ma) and are thought to be an early crystallization product of tholeiitic basalt at a shallower upper-mantle region, taking into account the low sodium and aluminum contents. The diopsides are also characterized by a large amount of melt inclusions. Thus, we have determined hydrogen contents of melt inclusions in the diopside megacrysts by a newly developed analytical method, Elastic Recoil Coincidence Spectroscopy (ERCS), to examine a water condition in the shallower mantle related to a young Arc-Arc collision zone. The megacryst samples were collected from basalt and basaltic andesite dykes and basaltic pillow lavas in the Tanzawa, the Misaka, and the Kushigata-yama mountains and the Fuji-gawa area at the collision zone of the Izu-Bonin arc. Water contents of the melt inclusions were 3 to 4 wt. %H2O. The contents are higher than the previous values of melt inclusions and quenched glasses in basalts and basaltic andesites from arcs and back-arc basins, indicating a large supply of water into the shallower upper-mantle region at the formation of the megacrysts. A restricted occurrence of the megacrysts from the 6 Ma to 16 Ma volcanic rocks also indicates the water supply event at that time. The water supply could be related to the collision of the Izu-Bonin arc.
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