Trace Element Distribution Within, Between, and Among Metamorphic Minerals

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SpearEAR-0106738 This proposal is to develop trace element partitioning as a tool to assist petrologists in the task of deciphering the metamorphic history of a terrane, and to apply this tool to further our understanding of Earth history. Detailed studies will be carried out on metapelites that have undergone partial melting (anatexis) and rocks that have undergone high P/T metamorphism in order to characterize fully the trace element zoning and partitioning in major and accessory phases. An empirical calibration of a monazite-xenotime thermometer will be augmented and enhanced to include the influence of HREE, Th and U on monazite YPO4 content, and procedures developed for the application of this thermometer to yield meaningful results. Two additional thermometers, YAG-xenotime and YAG-monazite, will be similarly enhanced so that they are applicable over a wide range of conditions. Additional new, empirical thermometers based on yttrium partitioning between garnet and accessory minerals at high pressures will be explored Thermodynamic models of whole rock reactions and mineral composition variation will be developed to place accessory mineral paragenesis on a firm theoretical footing. The models will be used to make predictions about the involvement of accessory minerals in major phase reactions, and in the interpretation of natural parageneses observed in the study suites.