Monitoring Magma Differentiation Through Crystal Isotope Stratigraphy

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9526903 Davidson The details of differentiation (melting, fractional crystallization, magma mixing and contamination) in a given magma system are commonly difficult to decipher. One particularly useful tool in identifying open system processes is the use of isotopic ratios. Interaction between isotopically diverse components modifies the isotopic compositions of resulting differentiates, but bulk analyses of the rocks typically fail to identify the end members involved. If vestiges of these components retain their physical identity (early-formed crystals from magmas that have subsequently hybridized, xenocrysts from assimilants, etc.) then they may also retain their original isotopic compositions. Complications arise from the for continued - if not constant - growth phases through complex differentiation scenarios. In principle, much of the evolutionary history of a magma system is locked into phases crystallizing from it. Determining isotopic variations within these phases may help elucidate such histories, particularly when integrated with spatially correlated major and trace element data. The P.I.s propose to improve on methods to perform such analyses, and outline some specific studies that may illustrate its potential.