| Project/Area Number |
10041121
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| Research Category |
Grant-in-Aid for Scientific Research (B).
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
地球化学
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| Research Institution | OKAYAMA UNIVERSITY |
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Principal Investigator |
KUSAKABE Minoru Institute for Study of the Earth's Interior, Okayama University, Professor, 固体地球研究センター, 教授 (20015770)
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| Co-Investigator(Kenkyū-buntansha) |
OHBA Takeshi Kusatsu-Shirane Volcano Observatory, Tokyo Institute of Technology, Associate Professor, 草津白根火山観測所, 助教授 (60203915)
NAGAO Kesuke Graduate School of Sciences, University of Tokyo, Professor, 理学部, 教授 (40131619)
GREG Tanyile IRGM(Cameroon), 研究員
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| Project Period (FY) |
1998 – 1999
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| Project Status |
Completed (Fiscal Year 1999)
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| Budget Amount *help |
¥9,000,000 (Direct Cost: ¥9,000,000)
Fiscal Year 1999: ¥3,800,000 (Direct Cost: ¥3,800,000)
Fiscal Year 1998: ¥5,200,000 (Direct Cost: ¥5,200,000)
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| Keywords | Cameroon Volcanic Line / Lake Nyos / Carbon dioxide / Rare gas isotopic compositions / K-Ar ages / Volcanic rocks / Mantle xenoliths / Geochemical heterogeneity / 炭素同位体比 |
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| Research Abstract |
The Cameroon Volcanic Line (CVL) is a 1600 km long, linear chain of volcanoes that trends in NE-SW direction across Cameroon, West Africa. CVL hosts numerous crater lakes that include notorious Lakes Nyos and Monoun for their gas disasters in 1986 and 1984. Scientific surveys after the disasters indicate that both lakes contain a huge amount of magmatic COィイD22ィエD2 in their bottom waters and are considered to have a high potential to explode again due to continuous supply of COィイD22ィエD2 through the lake bottom. Many soda springs occur along CVL.
The purposes of this study are two fold : To obtain the current physico-chemical situations of these gassy lakes, and to understand the geochemical features of CVL magmas. To this end, the following field and laboratory work was undertaken ; (1) determination of COィイD22ィエD2 profiles and isotopic compositions of rare gases dissloved in the lakes, (2) systematic sampling of soda springs along southern part of CVL to characterize their chemistry and rare gas isotopic compositions, and (3) systematic sampling of volcanic rocks and mantle xenoliths for their K-1r ages, chemical compositions and rare gas elemental/isotopic compositions.
The results are : (1) The COィイD22ィエD2 concentration in these lakes is steadily increasing, (2) The COィイD22ィエD2 originates from mantle, (3) Volcanism of CVL took place during Pleistocene-Holocene along the whole CVL, and (4) the upper mantle beneath CVL is geochemically heterogeneous with respect to (U+Th)/ィイD13ィエD1He rations with the highest ratio occurring at present ocean-continent boundary. The last interpretation is based on a clear observation that ィイD13ィエD1He/ィイD14ィエD1He ratios of phenocrysts and xenoliths from volcanic rocks of this region are definitely lower than those from the other regions.
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