Experimental Studies of Garnet-Melt Trace Element Partitioning

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Understanding how the compositions of garnet and coexisting silicate melt influence partitioning of trace elements is critical for understanding mantle evolution in terrestrial planetary interiors. Garnet is one of the two most important minerals (along with clinopyroxene) for fractionating trace elements during upper mantle melting and crystallization. However, no model exists that predicts how these fractionations evolve as a function of pressure, temperature, and composition at pressures exceeding 4 Gpa, severely hampering development of petrogenetic models of large-scale differentiation processes through melting in planetary mantles. This experimental program is designed to investigate critical controls on garnet-melt trace element partitioning at high pressure. Some of the elements to be studied (e. g. Sm, Nd, Lu, Hf, Th) define the behavior of isotopic systems of fundamental importance in unraveling the evolution of planetary interiors. The project builds on recent experimental and theoretical work that has revealed important factors affecting partitioning between garnet and anhydrous melt, including the roles of the elements iron and titanium and the garnet's majorite and grossular contents. We seek to acquire the data needed to understand fully the interrelationships between these compositional controls on garnet-melt partitioning.