Correlation of erupted plutonic clasts and volcanic deposits from Newberry Volcano, Oregon

Magmatic plumbing systems of Quaternary volcanoes are poorly understood due to insufficient uplift and erosion required to expose the intrusive complex. These intrusive bodies remained in the plumbing system for longer timescales than the eruptive melt, and thus, are more extensive recorders of subvolcanic processes. We have investigated several erupted plutonic clasts (EPC) and hydrothermal drill cuttings collected within the Newberry Volcano, OR region to understand more about the plumbing system. This study uses the EPC ages to link the intrusive rocks inferred to be representative of the Newberry magmatic plumbing system, and to discern a systematic relationship with volcanism. SHRIMP U-Th disequilibrium and U-Pb zircon ages were analyzed from five EPCs and two granitoid drill cuttings from separate hydrothermal wells. All samples have unimodal ages; four EPCs have isochron ages ranging from 136-158 ka, and the other has a weighted average of -291 ka. The two drill cutting samples record ages ~ 386 ka, and the other -1.9 Ma, the latter interpreted to be a pre-Newberry intrusion. Cogenetic zircons briefly crystallized during periods of rhyolitic volcanism, suggesting that silicic reservoirs are short-lived, and rhyolitic melts erupt soon after they are produced. Coeval granitoids and rhyolites that have similar bulk rock compositions are interpreted to be cumulate equivalents of the pre-erupted rhyolites, while granitoids that are slightly more mafic are complements to the rhyolites. Zircons from each granitoid record distinct chemical signatures, suggesting that Newberry is an intricate network of contemporaneous melt bodies that crystallize these sidewall cumulates and may form zoned magma chambers. Cumulates form through efficient crystal-liquid separation processes, felsic liquids are extracted from the crystal-rich residuals and generate silicic magmas in the reservoir; these mechanisms are common amongst extensional systems such as Newberry Volcano.