Supersized and Speedy: The Timing and Initiation of the Lava Creek Tuff Supereruption, Yellowstone Caldera

Abstract:

Yellowstone caldera is infamous for its three past supereruptions including the most recent that erupted ~631,000 years ago and deposited >1000 km³ of rhyolite ash across the contiguous US, known as the Lava Creek Tuff (LCT). Despite Yellowstone’s present-day activity and hazard potential, the mechanisms and timing responsible for eruption initiation at Yellowstone are largely unknown, which have important implications for hazard mitigation and planning. This study examines LCT fallout ash by combining nano-scale chemical measurements with mineral thermometry, diffusion chronometry, and rhyolite-MELTS modeling to reconstruct the life history of the LCT magmatic system prior to its most recent supereruption. Sanidine and quartz phenocrysts are reversely zoned and rich in Ba and Sr (in the case of sanidine) and Ti (in the case of quartz) relative to their interiors. Phenocryst interiors display a variety of zoning patterns suggesting variable recorded histories. Sanidine and quartz rims appear to be co-saturated based on rhyolite-MELTS modeling, crystal textures, and sanidine-liquid and Ti-in-quartz thermometry results that yield temperatures within error of each other of ~815ºC. Rhyolite-MELTS modeling at the conditions recorded in the crystal rims show that the bulk LCT system was dominantly liquid at the time of their formation, suggesting magma viscosities capable of mobilization at this time. When considering the possible mechanisms capable of producing this crystal record, our data suggest a rejuvenation of relatively juvenile rhyolitic magma perturbed the LCT magmatic system and initiated ascent leading to decompression-related rim growth. Ba-, Sr-, and newly determined Mg-in-sanidine, in addition to Ti-in-quartz diffusion chronometry and crystal growth rates all suggest rejuvenation occurred and initiated the LCT supereruption relatively quickly, over timescales as short as a few months.