地幔流体与地球的放气作用  

MANTLE FLUID AND EARTH DEGASSING

作　　者：朱永峰[1] 

机构地区：[1]北京大学地质学系

出　　处：《地学前缘》1998年第A08期71-75,共5页Earth Science Frontiers

基　　金：北京大学自然科学基金

摘　　要：地幔流体的形成、聚集和渗透是引起地幔交代作用的主要营力。地幔交代作用发育的强弱决定着所生成岩浆的碱性程度。地幔流体和部分熔融体高度富集不相容元素，它们与亏损地幔的相互作用可以使后者发生ＬＲＥＥ和不相容元素的局部富集。通过板块俯冲作用使地球表层的ＣＯ２进入地幔，参加地球的碳循环。热点岩浆来源的ＣＯ２中含有部分循环的ＣＯ２，而大洋中脊玄武岩中的ＣＯ２主要是原始地球的ＣＯ２。携带ＣＨ４和Ｈ２Ｏ的流体渗透至被俯冲带带入地幔的物质，使碳酸盐化的榴辉岩还原而形成含金刚石的榴辉岩和富水流体，并诱发局部熔融，所形成的熔体以火山喷发的形式上升到地表。地幔岩石中含有大量的流体，它们主要以流体包裹体的形式存在于地幔矿物中。几乎在所有的上地幔环境下形成的矿物中均找到了流体包裹体。包裹体内流体的成分主要是ＣＯ２，ＣＨ４，Ｈ２Ｏ及少量Ｈ２，Ｎ２等。The Earth differentiates more and more strongly during its degassing, the main forms of the Earth degassing are volcanic/magmatic processes. There are a lot of fluids presented in the mantle rocks, which mainly in the form of fluid inclusion. Almost all minerals formed in the mantle conditions contain fluid inclusions. Such fluid is mainly consisted of CO 2,CH 4,H 2O, H 2, and N 2 etc. Kimberlite magma is generated during the reaction process between the mantle rocks and the mantle fluids. Both the mantle fluids and the melts generated by partial melting of the mantle rocks are greatly enriched in incompatible elements, when such fluids and melts react with the depleted mantle, the incompatible elements and LREE will be concentrated in the depleted mantle locally. CO 2 in the shallow part of the Earth can be transported into the Earth′s deep part during plate subduction and participates in the Earth′s carbon circulation. Some CO 2 from the hot spot magma are originated from such re circulating carbon, otherwise, CO 2 from MORB is originated mainly from the primary Earth. The CH 4+H 2O fluid in the mantle, which is infiltrated into the crust matter and the later is transported into the mantle during subduction, makes the carbonated eclogite to be reduced and form diamond bearing eclo￣gite and water rich fluid, and finally induces partial melting of the mantle rocks. The generated melt may come to the Earth surface by means of volcanic eruption.

关 键 词：地球 地幔流体 放气作用 岩浆活动 

分 类 号：P312[天文地球—固体地球物理学] P183[天文地球—地球物理学]