复杂橄榄岩捕虏体:反演岩石圈演化过程的罕见而重要的样品

地幔和／或下地壳中存在2类“复杂”橄榄岩捕虏体:一类为“混杂”,即“polymict”橄榄岩捕虏体;另一类为相对常见的“复合”,即“composite”橄榄岩捕虏体．复合橄榄岩捕虏体通常由橄榄岩和辉石岩／麻粒岩或由橄榄岩夹辉石岩脉2部分或多部分组成．岩相学上易于辨认,有时手标本上即可辨认．而混杂橄榄岩捕虏体为各种橄榄岩和／或辉石岩来源的矿物和熔体混杂在一起组成的构造岩,岩相学上很难辨认,只有通过矿物组成分析来判断．混杂橄榄岩捕虏体仅见于南非Kaapvaal 克拉通金伯利岩岩管中,该类捕虏体来源于地幔塑性剪切带,记录了流／熔体参与下的地幔变形和交代作用的全过程．复合橄榄岩捕虏体较常见,出现在全球各类玄武岩和金伯利岩中．复合橄榄岩捕虏体有多种成因,如地幔变形、壳幔过渡带样品、交代作用和堆积成因等等．这些复合橄榄岩捕虏体同样记录了岩石圈地幔和／或下地壳交代作用／改造过程的中间状态．因此,这些罕见而重要的复杂橄榄岩捕虏体为大陆岩石圈动力学演化过程提供了最直接的样品．

Complex Peridotitic Xenoliths: Rare and Important Samples for Understanding the Lithospheric Evolution

Two types of "complex" peridotitic xenoliths exist in the earth mantle and/or lower crust: "polymict" peridotitic xenoliths and "composite" peridotitic xenoliths. Composite peridotitic xenoliths usually comprise two or more components of peridotite and pyroxenite/granulite or of peridotite with pyroxenite veins and can be easily identified in petrography, sometimes in hand samples. But the polymict peridotitic xenoliths are tectonites composed of minerals from various peridotites and/or pyroxenites and melts and brought together by mantle shear zone and difficult to identify in petrography, they must be classified by compositional analyses of constituent minerals. Polymict peridotitic xenoliths have only been found in kim-berlite pipes from the Kaapvaal craton, South Africa so far. These polymict peridotitic xenoliths originated from the mantle shear zone and recorded the whole evolutionary processes of fluid/melt-assisted mantle deformation and metasomatism. Composite peridotitic xenoliths are relatively common and occur in global basalts and kimberlites of all kinds. Composite peridol-itic xenoliths have a variety of origins such as mantle deformation, crust-mantle transitional zone sampling, metasomatism and accumulates, etc. . These composite peridotitic xenoliths also record the intermediate stage of metasomatism and modification processes of the lithospheric mantle and/or lower crust. Therefore, these rare and important complex peridotitic xenoliths provide the most direct samples for the geodynamic evolution of the continental lithosphere.