1989 Fiscal Year Final Research Report Summary
Behavior of trace elements concentrated at grain-boundaries during partial melting of Peridotites
| Project/Area Number |
63460053
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
鉱物学(含岩石・鉱床学)
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| Research Institution | Nagoya University |
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Principal Investigator |
SUZUKI Kazuhiro Nagoya University, School of Science, Associate Professor, 理学部, 助教授 (90111624)
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| Co-Investigator(Kenkyū-buntansha) |
ENAMI Masaki Nagoya University, School of Science, Assistant Professor, 理学部, 助手 (20168793)
SUWA Kanenori Nagoya University, School of Science, Professor, 理学部, 教授 (70022564)
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| Project Period (FY) |
1988 – 1989
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| Keywords | Grain-boundary / Magma / Partial melting / Trace element / Peridotite / Basalt / Incompatible element |
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| Research Abstract |
The distribution of the incompatible elements in mantle peridotites was examined by means of electron microprobe analysis, water leaching and in situ partial melting to explain the contents of potash and other incompatible elements in basaltic magmas. The mineral chemistry can hardly account for the chemistry of the parental peridotites. The enrichment of incompatible elements along grainboundaries is confirmed by the EPMA step analysis across boundaries of the constituent minerals. The boundary enrichment is demonstrated also by the EPMA analysis of the surfaces of the constituents before and after acid washing. AIKbeta emission spectrum of the surfaces suggests that atoms on mineral surfaces are less tightly bonded with surrounding atoms than those in minerals. ahd hence they are leached out easily. To estimate the amount of incompatible elements stored on the surfaces, elements were leached out through repeated washing of samples with deionized water at 20, 75 and 160ﾟC and the leac
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hing solutions were analyzed with an ion chromatographic analyzer. The accumulated amount of leached elements tends to become almost constant at each temperature, but increases with increase in temperature. The potash leached out from 1g sample at 160ﾟC amounts to 63.3-255mug, about 40-80 % of the whole-rock abundance. Thus, we find that most of the unaccountable elements in peridotites is stored on the grain-boundaries. The grain-boundary enrichment of potash and other incompatible elements should be particularly important in partial melting of peridotites. To examine this, chips of peridotites were heated at 1100-1370ﾟC in a gas-mixing furnace. Glass veins, 3-30 mum in width, are formed along grain-boundaries of the constituents at every temperatures. Glass makes up 4-8 vol.
% at 1300ﾟC, and shows a basaltic composition. This result leads us to a conclusion that the abundance of incompatible elements in the melt at the small degree of melting is governed mainly by the grain-boundaries, because the grain-boundaries can melt first. The present study demonstrates that basaltic magmas can be generated from kaersutite- and/or phlogopite-free mantle peridotites. Less
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[Publications] Iiyama, J.T. ( Suzuki, K., Akaogi, M., Nishiyama, T., Fujimoto, K. and Kato, Y.): "Material transfer during metamorphic process: Experimental approaches." Dynamic processes of material transport and transformation in the earth's interior, No. 4, 199-208, 1989.
Description
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