地幔脱气作用和大气圈惰性气体形成与演化  

MANTLE DEGASSING AND NOBLE GAS EVOLUTION IN THE ATMOSPHERE

作　　者：朱岳年[1] 许多[1] 张友学 

机构地区：[1]石油大学油气资源与环境地质研究所

出　　处：《地学前缘》1998年第A08期165-174,共10页Earth Science Frontiers

基　　金：石油大学科研基金;霍英东青年教师基金

摘　　要：惰性气体同位素地球化学是研究地幔脱气作用和地球大气形成与演化的有效工具。根据惰性气体提供的信息，地球大气圈中惰性气体主要由地幔脱气形成。地球有三个截然不同的惰性气体储集库：ＭＯＲＢ（洋中脊玄武岩）型地幔（大量脱了气的地幔），Ｌｏｉｈｉ（夏威夷洛尹黑海山）型地幔（少量脱了气的地幔），和大气圈＋海洋＋大陆地壳。为了探索这三个气体储集库之间的联系，国外学者已建立了三种地幔脱气模式：①整体脱气（ＢＤ）模式，②溶解度控制脱气（ＳＣＤ）模式，和③稳定态脱气（ＳＳＤ）模式。其中ＳＣＤ模式能较好地解释各储集库中惰性气体同位素体系特征。ＳＣＤ模式认为地幔中各种气体的脱出程度和脱出历史不完全相同，主要受气体在硅酸盐熔体中的溶解度所控制，因而认为地球大气中的各种气体的演化史也不完全相同。从地球形成时算起，大气中惰性气体主要形成和演化的平均时间分别为：１３０Ｘｅ为（２１±７）Ｍａ，３６Ａｒ为（５６±１９）Ｍａ，３Ｈｅ为（３１０±１２０）Ｍａ，４０Ａｒ为１５００Ｍａ，４Ｈｅ为８００Ｍａ。Noble gas isotopic geochemistry is a useful tool for studying on mantle degassing and evolution of the Earth′s atmosphere. Based on information from noble gas, noble gases in the atmosphere are originated from mantle degassing. The Earth is often divided into three reservoirs: MORB mantle (the more degassed mantle), Loihi mantle (the less degassed mantle), and the atmosphere plus ocean and continental crust. In order to predict the reason of the different noble gas isotopic systems in the three reservoirs, three kinds of mantle degassing models have been constructed: (1) bulk degassing(BD), (2) solubility controlled degassing(SCD) and (3) steady state degassing(SSD) models. Among the models, the noble gas systems are more consistent with the SCD model than the BD and SSD models. The SCD model predicts that the degree of degassing of each gas is controlled by its solubility, and different gases have different degassing history. That means different gases in the atmosphere have different evolution history. The mean time of degassing, measured from the formation of Earth, is (21±7)Ma for 130 Xe,(56±19)Ma for 36 Ar,(310±120)Ma for 3He, 1500Ma for 40 Ar and 800Ma for 4He.

关 键 词：惰性气体 同位素比值 地幔脱气作用 大气演化 

分 类 号：P593[天文地球—地球化学]