Shallow intrusion imaged by gravimetry records transient magma storage at the Laguna del Maule volcanic field, Chile

Abstract

The Laguna del Maule volcanic field, Southern Andean Volcanic Zone, Chile, is a geological exemplar for investigating magma storage at shallow crustal levels. The high volume of eruptive products in combination with an active, shallow magmatic system allow for multi-disciplinary investigations into storage depths, longevity, and eruptibility of magma. New Bouguer gravity data from near the Cari Launa lava flows is combined with earlier gravity surveys to reveal a −7 mGal gravity anomaly. Inverse and frequentist probability models resolve the source of the gravity anomaly to be a ∼2100–2300 kg/m³ density body, with the top and bottom of the body located at ∼250–2500 m below the ground surface, respectively. Forward models are used to test alternative geologic models for the source of the anomaly. Together, these models suggest that the observed gravity anomaly is best described by a shallow intrusion centered at ∼1000 m depth. The Cari Launa intrusion represents transient magma storage, in which shallowly emplaced magma rapidly cooled and degassed rather than erupted.