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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. Key Points: We present results of a teleseismic tomography study at Laguna del Maule volcanic field, ChileAn upper‐crustal magma reservoir of several hundred cubic kilometers is identified and characterizedFindings complement independent geophysical and petrologic observations and reveal a transcrustal magmatic system at LdMVF [ABSTRACT FROM AUTHOR]

The Laguna del Maule volcanic field (LdMVF) in Chile, a rapidly inflating silicic volcanic system without historical eruption, is intersected by active regional faults. The LdMVF provides an opportunity to observe how faults influence, accommodate, or are driven by an actively deforming large silicic system. Here we use Compressed High Intensity Radar Pulse (CHIRP) acoustic reflection data to map the fault network in sediments captured within the eponymous lake at the LdMVF and combine our fault maps with the volcanic history, earthquake locations, focal mechanisms, and lacustrine magnetic data to interpret how faults and magmatism interact. Our seismic data image dominantly dip‐slip faults forming grabens within the lake, subparallel to regional faults. No indications exist in the seismic data to suggest that fault patterns were created by the volcanic system, either ring or radial faults. Fault strikes interpreted from seismic and magnetic data are consistent with mapped dike and fault orientations on land. We therefore interpret that active faults at the LdMVF are tectonic rather than volcanic in origin, forming a transtensional zone that hosts the magmatic system. However, vertical motion along a NS‐striking fault near the center of uplift suggests trapdoor‐style faulting above the volcanic center in which tectonic faults are reactivated to accommodate magmatic inflation and overlying deformation. Magnetic anomalies follow regional faults, suggesting that faults also provide migration pathways. Depositional patterns indicate a prior episode of uplift followed by quiescence, indicating that significant magmatically related uplift at the LdMVF can occur without an associated major eruption. Key Points: Active normal faults subparallel to regional faults are imaged in the upper 20 m of lake sediments in the Laguna del Maule volcanic fieldGrabens within the lake are on trend with magnetic lineations and faults mapped on land, consistent with normal offset focal mechanismsFault‐facilitated localized doming and venting are present near the center of magmatic inflation [ABSTRACT FROM AUTHOR]