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Geochemical investigations on a contribution of a hot-plume to the volcaric activities in Canary islands.

热羽对加那利群岛火山活动贡献的地球化学调查。

基本信息

批准号：
09440189
负责人：
NAKAI Shun'ichi
金额：
$ 5.38万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 1998
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-09440189/
关键词：
Helium isotop ratio Canary Islands hot plume lower mantle trace element abundance Ph isorope ratio

项目摘要

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.

加那利群岛火山活动的起源是有争议的。一组将这些活动归因于与热点有关的火山活动，另一组将其归因于裂谷火山活动。本研究旨在利用氦同位素对矿床成因进行地球化学制约。它是探测下地幔物质最有力的同位素示踪剂。我们分析了氦同位素比值的橄榄石和单斜辉石从火山岩收集在四个岛屿，兰萨罗特岛。特内里费，耶罗。和La Patina的全融合气体提取。橄榄石的^3He/^3He同位素比值为6.5 ~ 7.0 R/Ra。(Ra代表空气的^3He/^3He同位素比）。在同位素变异或N盖-洋脊玄武岩中，因此，我们不能检测到下地幔起源的氦。这可能是由于分析的样品数量较少所致。或者也释放放射性氦的熔化提取方法。我们正在改进惰性气体质谱仪的探测器系统，以便能够通过破碎提取方法分析少量的氦，这种方法释放出很少的放射性成因^3He。在我们换了探测器之后。为了将固体元素的丰度和同位素信息与氦同位素比值进行比较，自1997年6月加入地震研究所以来，我们还致力于通过ICP-MS和同位素分析的同位素分离方法建立痕量元素分析方法。目前已成功地建立了多种微量元素的分析方法，归纳了稀土、铀、钍等微量元素的分析方法。采用电感耦合等离子体质谱法对碱金属和碱土金属元素进行了分析，分析精度优于5%。PB.铀和钍来自岩石样本。我们将开始对加那利群岛的岩石样本进行同位素和元素分析。