Abstract

With substantial postglacial rhyolite eruptions and ongoing rapid uplift, the Laguna del Maule volcanic field in the southern Andes provides an exceptional opportunity to study the dynamics of an active silicic magmatic system. Using 4,093 P arrivals from 137 distant earthquakes recorded by 44 local stations over ∼2.25 years, we conduct teleseismic tomography to image the crustal structure down to 40 km below the volcanic field. A prominent low-velocity body at depths between ∼0 and 12 km below sea level (b.s.l.), characterized by a volume of ∼500 km3 and a peak anomaly of −400 m/s (∼9%), overlaps the location of the upper-crustal magma reservoir detected in recent gravity and surface wave tomography studies. Its estimated average P wave velocity of ∼4.6 km/s corresponds to an average melt fraction of about 14% and a melt volume of ∼70 km3. Petrologic observations are also consistent with generation and storage of rhyolitic melts at depths corresponding to the anomalous zone. Moreover, the tomographic results support a lower crust zone of MASH (melting, assimilation, storage, and homogenization) from a depth of ∼25 km to the base of the model, which likely reflects a deep crustal source of magma that contributes to and incubates the shallow silicic reservoir.