Timescales and thermal evolution of large silicic magma reservoirs during an ignimbrite flare-up: perspectives from zircon

Abstract Four voluminous ignimbrites (150–500 km 3 ) erupted in rapid succession at 27 Ma the central San Juan caldera cluster, Colorado. To reconstruct timescales and thermal evolution of these magma reservoirs, we used zircon ID-TIMS U–Pb geochronology, LA-ICP-MS geochemistry, modeling, age crystallization modeling. Zircon geochronology reveals dispersed spectra all ignimbrites, with decreasing dispersion through time that term a ‘chimney sweeping’ event. whole-grain modeling suggests 2? spans represent approximately one-quarter total due to averaging effect whole-grain, individual ages, resulting 0.8–2.7 m.y. Thermal combined Ti-in-zircon temperatures indicates reservoirs were built over millions years relatively low magmatic vertical accretion rates (VARs) 2–5 × 10 –3 m y ?1 (2–5 –6 ?2 ), suggest such VARs characteristic assembly greater body. Though cannot unequivocally discern between caused by inheritance (xenocrystic or antecrystic) versus prolonged from same reservoir (autocrystic), our findings long-term input produced thermally mature upper crustal protracted timescales. Compiling ages large interpret longer subduction-related as result term, lower flux magmatism, shorter Snake River Plain higher magmatism.