| Project/Area Number |
09440189
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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 | The University of Tokyo |
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Principal Investigator |
NAKAI Shun'ichi Univ.of Tokyo, Earthquike Res Inst., Assoc.Prof., 地震研究所, 助教授 (50188869)
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| Project Period (FY) |
1997 – 1998
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| Project Status |
Completed (Fiscal Year 1998)
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| Budget Amount *help |
¥8,400,000 (Direct Cost: ¥8,400,000)
Fiscal Year 1998: ¥900,000 (Direct Cost: ¥900,000)
Fiscal Year 1997: ¥7,500,000 (Direct Cost: ¥7,500,000)
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| Keywords | Helium isotop ratio / Canary Islands / hot plume / lower mantle / trace element abundance / Ph isorope ratio |
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| Research Abstract |
The origin of the volcanisms in Canary Islands is controversial. One group attribute the activities to a hot spot-related volcanism and another to a rift volcanism. This study aimed at to put geochemical constraints on the origin by using helium isotope. which is the most powerful isotopic tracer to detect lower mantle materials. We analyzed helium isotopic ratios of olivine and clinopyroxene separated from volcanic rocks collected at four islands, Lanzarote. Tenerife, Hierro. and La Patina by total fusion gas extraction. The ^3He/^3He isotope ratios of olivines ranged from 6.5 to 7.0 R/Ra. (Ra stands for ^3He/^3He isotope ratio of air). within the isotopic variations or N lid-Ocean Ridge Basalt, thus, we could not detect helium of lower mantle origin. That may result from small number of the samples analyzed. or the melting extraction method which releases also radiogenic helium. We are modifying a detector system of a noble gas mass spectrometer to enable analyze small amount of helium by crushing extraction methods which releases little radiogenic ^3He. After we change the detector. we will analyze more samples with crushing extraction.
We also worked on establishing trace clement analysis method by a ICP-MS and clement separation methods for isotope analysis since Nakai joined the Earthquake Research Institute in June of 1997 in order to compare abundance and isotopic information of solidelements with helium isotopic ratios. So far we have succeeded in establishing the analytical methods for many trace elements, inducing REE.U.Th. alkali and alkaline earth elements with precision better than 5% by the ICP-MS.We have started setting up chemical methods of extraction, preconcentration and separation of Sr. Nd. Pb. U and Th From rock samples. We are going to start isotopic and elemental analyses on rock samples from Canary Islands.
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