Study of Exotic Mantle Xenoliths

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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.