268-10 Petrogenesis of the South Twin Complex, Utah: Zircon Evidence for a Shallow, Interconnected Reservoir

Session: Old and the New, Long and the Short: Perspectives on Integration of Timescales of Magmatic Processes: Special Session Related to MGPV Awards to Madison Myers and Anita Grunder (Posters)

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Zircon is an indispensable mineral in igneous petrochronology, as it is a passive recorder of geochemical information that can be used to determine magma differentiation and the timescales of crystallization. Constraining these processes is important in unraveling the petrogenesis of complex silicic volcanic systems. The Black Rock Desert (BRD) volcanic field in Utah, situated along the eastern margin of the extended Basin and Range Province, has erupted predominantly basalts, but contains an isolated, smaller volume of rhyolites dubbed the South Twin Complex (STC). Although spatially distinct, these rhyolitic units (North Twin, South Twin, Mid Dome, Coyote Hills, and Cudahy Mine) have temporal and genetic relationships which remain debated. To determine the magmatic architecture and understand the petrogenesis within the STC, this work uses zircon trace element concentrations, Ti-in-zircon thermometry, and high precision 40Ar/39Ar dates to model fractional crystallization processes. Results show that these ~2.4 Ma eruptions have strikingly similar chemistries and zircon crystallization temperatures, along with average fractional crystallization percentages between 50 and 60%. Zircon morphology also remains internally consistent within each unit, but varies between units. These data and observations point to a complex model, where the STC is a product of multiple discrete magma chambers linked to a shared parental magmatic source, rather than one single zoned chamber as suggested in previous literature. The integrated approach used for the BRD offers a framework for interpreting complex silicic systems worldwide, demonstrating how seemingly disparate rhyolitic eruptions can be genetically linked through a shared magmatic source, yet stored and evolved in spatially distinct reservoirs. This insight challenges traditional, single storage models, further enhancing our understanding of magma evolution.  

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7291

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