SGER: Reconciling U-series Ages of Major and Accessory Phases

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Understanding the dynamics of crustal magma systems requires knowledge of the types of of processes that lead to chemical changes and the timescales of such processes. This award will explore a novel approach to unravel why crystal ages that are obtained using U-series isotopic compositions of different mineral phases (accessory versus major phases) tend to yield discrepant ages. As part of the research plan, the investigators will measure a comprehensive suite of U-series crystal ages (i.e., in situ 238U-230Th ages in zircon and 226Ra-230Th and 238U-230Th ages in bulk separates of both major phases and zircon) in samples from rhyodacite domes at South Sister Volcano, Oregon Cascades, and rhyolite domes of the Tarawera volcanic complex, New Zealand. This one year of exploratory research will allow them to address the core question of the temporal relationship between major and accessory phase crystallization, while simultaneously laying the foundation for further work. The results of this exploratory project could have immediate and significant impact on the field because they will provide a much stronger context for interpretation of the growing body of age data for zircon and major phases; understanding the extent to which major and accessory phases are recording the same magmatic events is critical in order to make generalizations about how magma systems work from the studies of disparate systems that have been conducted to date.