Multiple, Coeval Silicic Magma Storage Domains Beneath the Laguna Del Maule Volcanic Field Inferred From Gravity Investigations

The rhyolite-producing Laguna del Maule volcanic field (LdMVF), Chile, has had numerous post-glacial eruptions that produced large explosions and voluminous lava flows. During the Holocene similar to 60 m of surface uplift is recorded by paleo-shorelines of the fresh-water Laguna del Maule, with an inflation source near the Barrancas volcanic complex. Rhyolites from the Barrancas complex erupted over similar to 14 ka including some of the youngest (1.4 +/- 0.6 ka) lava flows in the field. New gravity data collected on the Barrancas complex reveals a residual gravity low (-6 mGal, "Barrancas anomaly") that is distinct from the pronounced gravity low (-19 mGal; "Lake anomaly") associated with present-day ground uplift to the northwest. Three-dimensional inversion of the Barrancas anomaly indicates the presence of a magma body with a maximum density contrast with the host rock of -250 kg/m(3) centered at a depth of similar to 3 km below surface. Nearby Miocene high-silica granites represent frozen remnants of highly evolved rhyolitic magma. Comparison of the densities measured from samples of these plutons with the geophysical model densities, and integration of thermodynamic modeling of silicic melt evolution, provide constraints on our interpretation. We propose a magma body, containing <30% melt phase and low volatile content, exists beneath Barrancas. The Barrancas and Lake gravity lows represent magma in different physical states, associated with past and present-day storage beneath LdMVF. The gravity model mirrors geochemical observations which independently indicate that at least two distinct rhyolites were generated and stored as discrete magma bodies within the broader LdMVF.