Thermomechanical modeling of the Altiplano-Puna deformation anomaly: Multiparameter insights into magma mush reorganization

Abstract

A 150-km-wide ground deformation anomaly in the Altiplano-Puna vol­canic complex (APVC) of the Central Andes, with uplift centered on Uturuncu volcano and peripheral subsidence, alludes to complex subsurface stress changes. In particular, the role of a large, geophysically anomalous and partially molten reservoir (the Altiplano-Puna magma body, APMB), located ∼ 20 km beneath the deforming surface, is still poorly understood. To explain the observed spatiotemporal ground deformation pattern, we integrate geophysical and petrological data and develop a numerical model that accounts for a mechanically heterogeneous and viscoelastic crust. Best-fit models ­imply subsurface stress changes due to the episodic reorganization of an interconnected vertically extended mid-crustal plumbing system composed of the APMB and a domed bulge and column structure. Measured gravity-height gradient data point toward low-density fluid migration as the dominant process behind these stress changes. We calculate a mean annual flux of ∼ 2 × 10 7 m 3 of water-rich andesitic melt and/or magmatic water from the APMB into the bulge and column structure accompanied by modest pressure changes of 100 yr) residual deformation at Uturuncu. Episodic mush reorganization may be a ubiquitous characteristic of the magmatic evolution of the APVC.