Partial Melting of Carbonated Peridotite and Eclogite in the Upper Mantle

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EAR-0310142Marc Hirschmann Small amounts of carbonate melt in the upper mantle are believed to have significant geochemical and geophysical consequences, but little is known about the depth of formation or the compositions of these melts. Decarbonation of peridotite during upwelling beneath ridges influences the rate of mantle degassing and the geophysical properties of the deepest parts of mid-ocean ridge basalt source regions. Partial melting of carbonated eclogite may be a key step in global deep cycling of carbon and may be the source of some carbonatites. This project is to determine melting relations of natural carbonated peridotite and eclogite at conditions of melting beneath oceanic ridges. Iterative experiments will be conducted in a multi-anvil device at pressures between 5 and 10 GPa. They will determine solidi locations for carbonated peridotite and eclogite and near-solidus major element compositions of partial melts. They will also provide the first data on partitioning of key trace elements (U, Th, Pb, Rb, Sr, K, Na, HFSE, REE) between carbonate liquids and residual minerals at pressures similar to those where such melts form in the convecting mantle.