Non-equilibrium stable isotope partitioning in igneous processes?

Abstract

Studies of the stable isotope compositions of igneous rocks commonly assume that crystallization occurs under conditions of melt/solid equilibrium and that disequilibrium fractionations, when observed, reflect mixing processes. However, igneous phenocrysts commonly exhibit oscillatory, sector, and more complex zoning of major and trace elements that could be produced by diffusion-limited transport near the crystal/melt interface and/or by partitioning into structurally anomalous surface sites. And, melt-phase inter-diffusion is known to lead to gradients in stable isotope compositions. We look for evidence that stable isotope compositions of phenocrysts could reflect such disequilibrium during growth.

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