Multiple, coeval silicic magma storage domains beneath the Laguna Del
Maule volcanic field inferred from gravity investigations
Abstract
The rhyolite-producing Laguna del Maule volcanic field (LdMVF) records
magma-induced surface inflation rates of ~ 25 cm/year
since 2007. During the Holocene, ~60 meters of
cumulative surface uplift is recorded by paleoshorelines of the Laguna
del Maule, located on the southeast edge of the LdMVF (Chile-Argentina
border) near the Barrancas volcanic complex. Rhyolites from the
Barrancas complex erupted over ~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 Bouguer low (-6 mGal,
Barrancas anomaly) that is distinct from the pronounced gravity low (-19
mGal; Lake anomaly) associated with present-day deformation and magma
intrusion to the north. Three-dimensional inversion of the Barrancas
anomaly indicates the presence of a magma body with a maximum density
contrast of -250 kg/m3 centered at a depth of
~ 3 km below surface. Comparison of model densities with
measured densities from nearby silicic plutons suggest that a magma
body, containing < 30 % melt phase and a low volatile
content, exists beneath the Barrancas complex. The Barrancas and Lake
gravity lows represent magma in different physical states, associated
with past and present-day storage beneath the LdMVF. The gravity model
mirrors existing geochemical observations which independently indicate
that at least two distinct rhyolites were generated and stored as
discrete magma bodies within the broader LdMVF. Small temperature
changes of these discrete bodies could reverse crystallization and
viscous lock-up and propel magma toward a crystal-poor eruptible state.