Collaborative Research: RUI: Probing Caldera-Forming Magmatism: Crystal Accumulation in Large, Upper Crustal Silicic Magma Chambers

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The next volcanic super-eruption will have global consequences for humanity. During one of these large eruptions, the explosive potential and the amount of lava and ash erupted are largely controlled by what happens in shallow magma reservoirs in Earth's crust. This project combines the study of frozen magma reservoirs trapped below-ground - plutons - with their associated above-ground volcanic rocks for two ancient super-volcanoes: the Lake City Caldera, Southern Rocky Mountain Volcanic Field in Colorado and the Turkey Creek Caldera in Arizona. The results of this study will provide unprecedented insight into processes occurring within shallow magma reservoirs that lead to super-eruptions, and ultimately will be applied to predict the behavior of potentially extremely hazardous active volcanic regions such as the Taupo Volcanic Zone, the Bay of Naples, and the Aegean Arc. The hypothesis being tested is that the plutonic porphyries in both the Lake City Caldera and the Turkey Creek Caldera are the quenched magma reservoirs remaining in the crust following caldera collapse. If this hypothesis is confirmed, these porphyries provide a unique snapshot of the evolution and post-eruptive conditions of the mushy rootzone associated with a super-eruption. The methods that will be applied to the volcanic and plutonic lithologies are: (1) detailed field mapping of the plutonic porphyries and field sampling of the volcanic units, (2) geochemical characterization of all units, (3) quantitative investigation of primary and accessory crystals in all units using electron microprobe analysis (EPMA), laser ablation inductively coupled mass spectrometry (LA-ICP-MS), and electron backscattered diffraction (EBSD), and (4) high resolution U-Pb dating and trace element analysis of zircons (CA-TIMS-TEA) in selected lithologies. This multi-analytical approach to the sub-volcanic intrusions and overlying silicic volcanic units is applied to establish the genetic relationship between the large, zoned ignimbrites and their plutonic roots, and to unravel the processes involved in chemical differentiation of large silicic magma chambers.