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

我们利用稀有气体同位素比值和Ar-Ar测年对壳幔物质的循环演化进行了研究，获得了如下结果：东西伯利亚锡霍特阿林地区部分地幔包体的3He/4He比值低于大气值。基于橄榄石和辉石晶体中CO2包裹体的显微拉曼光谱分析，我们发展了一种评估CO2捕获压力的方法。利用该方法可以估算锡霍特阿林岩样的圈闭压力，测得的圈闭压力为0.96~1.04 Gpa，对应深度约30公里。由此推测，古老的俯冲地壳物质可能影响了3He/4He比值，也可能影响了东西伯利亚大陆之下的微量元素组成。此外，对霍罗曼橄榄岩杂岩中的金云母进行了Ar-Ar测年，测得其Ar-Ar年龄约为21 Ma，具有超额40Ar的特征。这表明金云母可能是在大气成分通过水在一定程度上影响的深度二次形成的。另一方面，从洛伊希火山区潜水器采集的玻璃样品的惰性气体分析表明，洋壳物质的影响。留尼汪岛和毛里求斯群岛样品的稀有气体分析表明，与来自留尼汪岛和留尼汪岛的较老样品相比，毛里求斯岛上小于1 mA的样品的3He/4He比值较低。这似乎表明了热点型大洋岛的演化趋势。

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.