Geochemical investigations on a contribution of a hot-plume to the volcaric activities in 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其成因进行地球化学约束。这是探测下地幔物质最有力的同位素示踪剂。我们分析了从兰萨罗特岛四个岛屿收集的火山岩中分离出的橄榄石和斜辉石的氦同位素比率。特内里费,陷入困境。和La Patina采用全融合气体提取。橄榄石的^3He/^3He同位素比值在6.5 ~ 7.0 R/Ra之间。（Ra代表空气的^3He/^3He同位素比率）。在N盖洋脊玄武岩的同位素变化中，我们无法探测到下地幔起源的氦。这可能是由于分析的样本数量较少。或者熔化提取法也会释放放射性氦。我们正在改进稀有气体质谱仪的探测系统，使其能够通过破碎提取方法分析少量的氦，这种方法释放很少的放射性氦。在我们换了探测器之后。我们将用破碎萃取法分析更多的样品。自Nakai于1997年6月加入地震研究所以来，我们还建立了ICP-MS微量元素分析方法和同位素分析元素分离方法，以比较固体元素与氦同位素比值的丰度和同位素信息。目前已成功建立了多种微量元素的分析方法，包括稀土元素、稀土元素、稀土元素等。用ICP-MS测定碱土和碱土元素，精密度优于5%。我们已经开始建立提取、富集和分离sr - Nd的化学方法。Pb。U和Th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。

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.