Change of structure and physical features of aqueous fluids in subduction zones
| Project/Area Number |
17540397
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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 |
Solid earth and planetary physics
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| Research Institution | Kyoto University |
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Principal Investigator |
KAWAMOTO Tatsuhiko Kyoto University, Graduate School of Science, Assistant Professor, 理学研究科, 助手 (00303800)
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| Co-Investigator(Kenkyū-buntansha) |
FURUKAWA Yoshitsugu Kyoto University, Graduate School of Science, Associate Professor, 理学研究科, 助教授 (80222272)
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| Project Period (FY) |
2005 – 2006
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| Project Status |
Completed (Fiscal Year 2006)
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| Budget Amount *help |
¥2,700,000 (Direct Cost: ¥2,700,000)
Fiscal Year 2006: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 2005: ¥1,900,000 (Direct Cost: ¥1,900,000)
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| Keywords | magma / aqueous fluid / mantle / solution / hydrogen bond / high pressure / mantle wedge / subduction zone / 構造解析 / 高温度 / 臨界現象 / 放射光X線 |
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| Research Abstract |
Silicate components dissolved in aqueous fluids in mantle change their chemistry from andesitic at 1-2 GPa to peridotitic at 3 GPa. We show direct observations of unmixing and mixing between aqueous fluid and a high-magnesian andesite and between aqueous fluid and an oceanic sediment by use of synchrotron X-ray radiography with multi-anvil type high-T and high-P apparatus at SPring-8. We observed aqueous fluid and a high-Mg andesitic (HMA) melt coexisting in pressures lower than 2.7 GPa. While above 2.8 GPa, we observed only one fluid phase, suggesting that the HMA and aqueous fluids are completely mixing and become supercritical. In addition to the HMA, we determined a critical endpoint between an oceanic sediment and aqueous fluid, which is located at around 2.6 GPa. We found a second critical endpoint between aqueous fluids and a peridotitic/ a MORB melt at 3.8/ 3.0 GPa, respectively. Based on these available data, we suggest that slab-derived fluids should be under supercritical conditions at the downgoing slabs beneath the volcanic arcs (3-6 GPa). This means a continuous change from aqueous fluids to hydrous melts at the base of mantle wedge. Whether the slab-derived fluids have chemical characteristics like a partial melt or an aqueous fluid depends on the temperature; slab derived-supercritical fluids in relatively warm regions can dissolve more silicate components than slab derived-supercritical fluids in relatively cold regions. The melt-like supercritical fluid formed at the base of the warm mantle wedge will separate into a melt phase and a fluid phase, which may result in double-magmatism, for example, coexisting of adakite rocks and common island-arc rocks or HMA and basalt.
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Report
(3 results)
Research Products
(8 results)
