PROCESSES OF MAGMA EVOLUTION AND CRYSTAL RECYCLING RECORDED IN ZIRCON POPULATIONS OF LARGE VOLUME RHYOLITES IN THE WESTERN MOUNT BENNETT HILLS, CENTRAL SNAKE RIVER PLAIN, IDAHO, AND THE IMPLICATIONS FOR CONSTRAINING THE PRE- AND SYN-ERUPTIVE EVOLUTION OF SILICIC MAGMAS

The western Mount Bennett Hills region (WBH), situated along the northern margin of the central Snake River Plain, hosts a series of 10 large volume, high temperature rhyolite units of Miocene age. Due to a well-mapped volcanic stratigraphy, high magmatic productivity spanning several million years, and abundant zircon, the WBH rhyolites are ideal for studying how zircon populations record contrasting processes of magma evolution and crystal recycling through LA-ICPMS trace element analysis and chemical abrasion (CA) TIMS U/Pb geochronology. This presentation will illustrate this tandem analytical approach, whereby sectioned and polished zircon grains are imaged via cathodoluminescence, analyzed for a full suite of trace elements and low-precision U-Pb ages (±1 Ma) via LA-ICPMS, and then sampled from the mount for high-precision CA-TIMS U-Pb ages (± 10-20 ka). By linking growth history, geochemical variations, and precise ages, this tandem analytical approach will test whether the commonly observed span of zircon ages in such rhyolites is the product of crystal recycling from earlier eruptives. Preliminary results will be presented for four units of the younger Danskin Block rhyolites of the WBH, and used to interpret the fidelity of zircon crystals for constraining the duration and tempo of silicic magma differentiation, storage, and eruption.