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Investigation on recycling and evolution of crust and mantle materials based on noble gas isotope ratios and Ar-Ar dating

基于稀有气体同位素比值和Ar-Ar测年的壳幔物质循环与演化研究

基本信息

批准号：
12440145
负责人：
KANEOKA Ichiro
金额：
$ 9.6万
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：
2000
资助国家：
日本
起止时间：
2000 至 2002
项目状态：
已结题

项目摘要

We have performed the investigation on the recycling and evolution of crust and mantle materials based on noble gas isotope ratios and Ar-Ar dating in order to clarify the system and obtained the following results.We found 3He/4He ratios of less than the atmospheric value in some mantle xenoliths from Sikhote Alin area, east Siberia. Based on the micro-Raman spectroscopic analysis of CO2 inclusions in olivine and pyroxene crystals, we have developed a method to evaluate the trapping pressure of CO2. By using the method, wee could estimate the trapping pressure for Sikhote Alin samples, which indicated the pressure of 0.96〜1.04Gpa, corresponding to the depth of about 30km. From such information, it is inferred that old subducted crustal materials might have affected the 3He/4He ratios and probably also affected the trace element compositions underneath the east Siberian continent. Furthermore, Ar-Ar dating for phlogopite in Horoman Peridotite Complex indicates an Ar-Ar age of about 21Ma with a signature of the occurrence of excess 40Ar. It suggests that the phlogopite might have formed secondarily at a depth where the atmospheric component affected to some extent through water. On the other hand, noble gas analysis for glassy samples which were collected by submersibles from the Loihi Volcano area suggests the effect of oceanic crustal materials. Noble gas analysis for samples from Reunion and Mauritius Islands indicate the lowering of 3He/4He ratios for samples of less than 1Ma from Mauritius Island compared to those of older samples from the island and those of Reunion Island. This seems to indicate the evolutional trend of a hotspot type oceanic island.

为了阐明这一体系，我们利用稀有气体同位素比值和Ar-Ar定年研究了壳幔物质的再循环和演化，并取得了以下结果：在东西伯利亚SikhoteAlin地区的一些地幔包体中发现了低于大气值的~ 3 He/~ 4 He比值。基于橄榄石和辉石晶体中CO2包裹体的显微拉曼光谱分析，我们发展了一种估算CO2捕获压力的方法。利用该方法对SikhoteAlin样品的捕获压力进行了估算，结果为0.96 × 1.04Gpa，对应深度约30 km。根据这些信息，可以推断，古老的俯冲地壳物质可能影响了3 He/4 He比值，也可能影响了东西伯利亚大陆下的微量元素组成。霍罗曼橄榄岩杂岩中金云母的Ar-Ar年龄为21 Ma左右，具有40 Ar过量的特征。这表明金云母可能是在大气成分一定程度上通过水影响的深度上次生形成的。另一方面，对用潜水器从洛伊希火山地区收集的玻璃样品进行的惰性气体分析表明了海洋地壳物质的影响。从留尼汪岛和毛里求斯群岛的样品的稀有气体分析表明，从毛里求斯岛小于1 Ma的样品的3 He/4 He的比率相比，从岛上和留尼汪岛的老样品的降低。这似乎表明了热点型洋岛的演化趋势。