Study of Exotic Mantle Xenoliths

在我们对岩石类型、矿物学、化学和现代地幔的不均匀程度的认识上，仍然存在着显著的差距；随着追踪地球深处演化的努力被推后，这些数据变得更加模糊。追溯这段历史的一种方法是研究包含在爆炸驱动的含钻石火山中的意外包裹体。钻石产于古(3Ga)大陆克拉通的根带、过渡带(410-660公里)和下地幔(660公里)。捕虏体和钻石是沿着这些非凡的火山管道的样品，为了解地球深部提供了唯一的直接地质窗口。这项提案中概述的研究将集中在来自西非和卡阿瓦尔克拉通的含钻石金伯利岩中携带的奇异捕虏体的特定套装。一些包体来自超深(300公里)，是迄今发现的最深的岩石，提供了进入过渡带的前所未有的矿物和地球化学信息；另一些包体(榴辉岩)被选择来评价这些岩石是古代(3Ga)大陆地壳提取的地幔残留物还是俯冲洋底再循环的产物。对第三套包体的研究将制约熔体渗流、熔体提取的地球化学以及地幔中橄榄岩的交代模式。这些研究的结果有望为地幔的岩石化学提供新的见解。

9805091HaggertySignificant gaps remain in our knowledge of rock types, mineralogy, chemistry and the degree of heterogeneity in the modern mantle; and the data are more obscure as efforts to trace the evolution of the deep Earth are pushed back in time. One method of tracing this history is from the study of accidental inclusions incorporated into explosively driven diamondiferous volcanoes. Diamonds are generated in the root zones of ancient (3 Ga) continental cratons, in the transition zone (410-660 km) and in the lower mantle (660 km). Xenoliths and diamonds that are samples along the conduits of these extraordinary volcanoes provide the only direct geological window to the Earth's deep interior. The research outlined in this proposal will focus on specific suites of exotic xenoliths entrained in diamondiferous kimberlites from the West Africa and Kaapvaal Cratons. Some xenoliths are of ultradeep (300 km) origin, are the deepest rocks yet recognized, and provide unprecedented mineral and geochemical information that reaches into the transition zone; other xenoliths (eclogites) are selected to evaluate whether these rocks are mantle residues from extraction of ancient (3 Ga) continental crust or are the products of recycling of subducted oceanic floor. The study of a third suite of xenoliths will constrain the geochemistry of melt percolation, melt extraction and models for metasomatism of peridotites in the mantle. The results of these studies are expected to yield new insights to the petrochemistry of the Earth's mantle.