Decadal transition from quiescence to supereruption: petrologic investigation of the Lava Creek Tuff, Yellowstone Caldera, WY

The magmatic processes responsible for triggering nature’s most destructive eruptions and their associated timescales remain poorly understood. Yellowstone Caldera is a large silicic volcanic system that has had three supereruptions in its 2.1-Ma history, the most recent of which produced the Lava Creek Tuff (LCT) ca. 631 ka. Here we present a petrologic study of the phenocrysts, specifically feldspar and quartz, in LCT ash in order to investigate the timing and potential trigger leading to the LCT eruption. The LCT phenocrysts have resorbed cores, with crystal rims that record slightly elevated temperatures and enrichments in magmaphile elements, such as Ba and Sr in sanidine and Ti in quartz, compared to their crystal cores. Chemical data in conjunction with mineral thermometry, geobarometry, and rhyolite-MELTS modeling suggest the chemical signatures observed in crystal rims were most likely created by the injection of more juvenile silicic magma into the LCT sub-volcanic reservoir, followed by decompression-driven crystal growth. Geothermometry and barometry suggest post-rejuvenation, pre-eruptive temperatures and pressures of 790–815 °C and 80–150 MPa for the LCT magma source. Diffusion modeling utilizing Ba and Sr in sanidine and Ti in quartz in conjunction with crystal growth rates yield conservative estimates of decades to years between rejuvenation and eruption. Thus, we propose rejuvenation as the most likely mechanism to produce the overpressure required to trigger the LCT supereruption in less than a decade.