| Project/Area Number |
17K05706
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Multi-year Fund |
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| Section | 一般 |
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| Research Field |
Petrology/Mineralogy/Economic geology
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| Research Institution | Okayama University |
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Principal Investigator |
Ota Tsutomu 岡山大学, 惑星物質研究所, 助手 (80379817)
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| Project Period (FY) |
2017-04-01 – 2020-03-31
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| Project Status |
Completed (Fiscal Year 2019)
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| Budget Amount *help |
¥4,420,000 (Direct Cost: ¥3,400,000、Indirect Cost: ¥1,020,000)
Fiscal Year 2019: ¥1,560,000 (Direct Cost: ¥1,200,000、Indirect Cost: ¥360,000)
Fiscal Year 2018: ¥1,300,000 (Direct Cost: ¥1,000,000、Indirect Cost: ¥300,000)
Fiscal Year 2017: ¥1,560,000 (Direct Cost: ¥1,200,000、Indirect Cost: ¥360,000)
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| Keywords | リチウム同位体 / 水流体 / カンラン岩 / マントル内物質循環 / 二次イオン質量分析計 / リチウム / 流体 / マントル / 岩石・鉱物・鉱床学 / 地殻・マントル物質 |
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| Outline of Final Research Achievements |
The present study focused distributions of hydrogen and fluid-mobile elements including lithium isotopes in orogenic peridotites of the Horoman massif, Japan, to estimate spaciotemporal scales of mantle heterogeneity on light elements. The analytical results on the samples collected at various scales from kilometer (an entire massif) through meter (an outcrop) to submillimeter (a mineral) produced the following outcomes.
The Horoman peridotites were partly affected at 150 Ma by a subduction-zone fluid. However in the core of the massif, they have retained geochemical characteristics derived from sub-seafloor hydrothermal alteration at 1 Ga. The hydrogen abundances are more than 10-times higher than those of a typical residual mantle. The presence of the Horoman massif suggests that ancient oceanic mantle domains formed by sub-seafloor hydrothermal alteration could have survived in the mantle for at least 1 Gy, and have influenced to dynamics and chemical evolution of the mantle.
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| Academic Significance and Societal Importance of the Research Achievements |
水素のような軽元素は，地球マントルの高温高圧条件下では容易に拡散・均質化すると考えられるが，そのような含水（素）物質の質量や滞留時間といった情報を，地震学の間接的手法で得るのは難しい．
本研究では，地質学的・地球化学的手法を用いて，幌満カンラン岩体が典型的なマントルカンラン岩の十倍もの水流体を保持していること，岩体内部のキロメートル規模の領域には約十億年前の水流体が保持されていた可能性があることを示した．マントル物質の物性は，含水量によって大きく変化するため，幌満岩体のような含水物質によるマントル内不均質の時空間的情報は，マントルのダイナミクスや化学進化を理解する上で重要な知見である．
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