Magma storage and evolution of the most recent effusive and explosive eruptions from Yellowstone Caldera

Between 70 and 175 ka, over 350 km 3 of high-silica rhyolite magma erupted both effusively and explosively from within the Yellowstone Caldera. Phenocrysts in all studied lavas and tuffs are remarkably homogenous at the crystal, eruption, and caldera-scale, and yield QUILF temperatures of 750 ± 25 °C. Phase equilibrium experiments replicate the observed phenocryst assemblage at those temperatures and suggest that the magmas were all stored in the upper crust. Quartz-hosted glass inclusions contain 1.0–2.5 % H 2 O and 50–600 ppm CO 2 , but some units are relatively rich in CO 2 (300–600 ppm) and some are CO 2 -poor (50–200 ppm). The CO 2 -rich magmas were stored at 90–150 MPa and contained a fluid that was 60–75 mol% CO 2 . CO 2 -poor magmas were stored at 50–70 MPa, with a more H 2 O-rich fluid ( X CO 2 = 40–60 %). Storage pressures and volatiles do not correlate with eruption age, volume, or style. Trace-element contents in glass inclusions and host matrix glass preserve a systematic evolution produced by crystal fractionation, estimated to range from 36 ± 12 to 52 ± 12 wt%. Because the erupted products contain