| Project/Area Number |
11640454
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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 | Ehime University |
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Principal Investigator |
SANO Sakae Ehime University, Faculty of Education, Associate Professor, 教育学部, 助教授 (10226037)
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| Co-Investigator(Kenkyū-buntansha) |
KIMURA Jun-ichi Shimane University, Faculty of Science and Technology, Associate Professor, 総合理工学部, 助教授 (30241730)
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| Project Period (FY) |
1999 – 2001
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| Project Status |
Completed (Fiscal Year 2001)
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| Budget Amount *help |
¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2001: ¥1,000,000 (Direct Cost: ¥1,000,000)
Fiscal Year 2000: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1999: ¥2,100,000 (Direct Cost: ¥2,100,000)
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| Keywords | ophiolite / ultramafic rock / mantle / trace element / geochemistry / dunite / harzburgite |
|---|
| Research Abstract |
The Red Hills peridotite body (RHP) in Dun Mountain ophiolite belt in South Island, New Zealand, is divided into two parts, a harzburgite dominant zone in thelower part (L-RHP) and a dunite dominant zone in the upper part (U-RHP). The L-RHP harzburgite is homogeneous except for a plagioclase-bearing variety in the uppermost part. In the U-RHP, clinopyroxene-bearing and plagioclase-bearing dunites and blocky harzburgites are observed in the common dunite matrix. It is supposed an interaction process on relatiotiships between the dunite and the U-RHP ranges from 87.0 to 92.5 while that in the L-RHP ranges from 90.5 to 93.0. Spinels in the U-RHP show a variation of 0.2 to 0.6 in Cr#, but have lower Mg# than those in the L-RHP. On Fo in olivine and Cr# in spinel, there is a good correlation which has been proposed as olivine-spinel mantle array, on rocks of the L-RHP, while mineral compositions of the U-RHP shift from the array to lower Fo side. Based on textures, modal compositions and ch
… More
emical compositions, the L-RHP corresponds to residual upper mantle beneath a mid-ocean ridge, and the U-RHP represents line mantle-crust transition zone. Chondrite-normalised REE patterns of the U-RHP clinopyroxene show a wide compositional range compared with those in the L-RHP clinopyroxene. The REE patterns of cpx- and pl-dunites in the U-RHP are strongly depleted in LREE relative to those of clinopyroxenes in other ophiolitic dunites. Inferred melt compositions from the clinopyroxenes are not consistent with erupted MORB compositions, but rather similar to those of ultra-depleted primary melts included in olivine phenocryst hosted in MORB. The possible mechanism for producing the ultra-depleted melt has been considered as critical melting at the shallowest level. The clinopyroxenes in the U-RHP dunites probably be precipitated during such melting process at shallow level mantle. Clinopyroxene REE patterns in the L-RHP harzburgites are strongly depleted in LREE〜MREE. The LREE concentration is rather lower than clinopyroxenes in normal oceanic peridotites. The strongly LREE-MREE depleted patterns of the clinopyroxenes in the L-RHP harzburgite could be explained by polybaric multiple melting processes through garnet-to spinel-stability fields. Less
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