The large‐scale surface uplift in the Altiplano‐Puna region of Bolivia: A parametric study of source characteristics and crustal rheology using finite element analysis

Abstract

[1] This paper focuses on the driving mechanism behind a 70 km wide region of ground uplift centered on Uturuncu volcano, in the Altiplano-Puna region of southern Bolivia. We present a series of forward models using finite element analysis to simultaneously test for first-order parameters that help constrain a viable model for the observed maximum line of sight uplift rate of 1-2 cm/yr between 1992 and 2006. Stresses from pressure sources with finite geometries are solved numerically, accounting for both homogeneous and heterogeneous mechanical rock properties in elastic and viscoelastic rheologies. Crustal heterogeneity is constrained by seismic velocity data that indicate the presence of a large low-velocity zone, the AltiplanoPuna magma body, at depths of~17 km below the surface. A viscoelastic rheology is employed to account for time-dependent deformation and an inelastic crust. Comparing homogeneous and heterogeneous models demonstrates the significant impact of a mechanically weak, source-depth layer, which alters surface displacement patterns by buffering subsurface deformation. Elastic model results guide the source parameters tested in the viscoelastic models and demonstrate a range of possible causative source geometries. Our preferred model suggests that pressurization of a magma source extending upward from the Altiplano-Puna magma body is causing the observed surface uplift and alludes to a continued increase in this pressure to explain both the spatial and temporal patterns. We also demonstrate how a pressure-time function plays a first-order role in explaining the observed temporal deformation pattern. Hickey, J., J. Gottsmann, and R. del Potro (2013), The large-scale surface uplift in the Altiplano-Puna region of Bolivia: A parametric study of source characteristics and crustal rheology using finite element analysis, Geochem.

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

“…Required mean amplitudes of excess pressurization to explain the available geodetic time series are very small (<0.006 MPa/yr). The pressure changes are significantly lower than those calculated in earlier models (Pritchard and Simons, 2002;Hickey et al, 2013). This difference is due to several factors: in increasing order of significance, (1) the invoked mechanical heterogeneity in physical properties of the crust, (2) the thermally controlled time-dependent stress relaxation, (3) the size and configuration of the reservoirs, and (4) the invoked bulge above the APMB.…”

“…1). Several explanations have been proposed for the deformation anomaly, including the pressurization of subsurface cavities (as a proxy for magma reservoirs) located at various crustal depths above, within, and below the APMB, and complex interactions between multiple magmatic systems located at upper to lower crustal levels (Pritchard and Simons, 2002;Sparks et al, 2008;Hickey et al, 2013). Alternatively, Fialko and Pearse (2012) proposed the ascent of a magmatic diapir from the APMB to explain a broad moat of relative ground subsidence surrounding a central area of ground uplift (Figs.…”

Time-dependent deformation of Uturuncu volcano, Bolivia, constrained by GPS and InSAR measurements and implications for source models

“…Henderson and Pritchard | Time-dependent deformation of Uturuncu volcano GEOSPHERE | Volume 13 | Number 6 decades due to increasing reservoir pressurization (e.g., Pritchard and Simons, 2004;Hickey et al, 2013) or buoyant diapiric ascent (Fialko and Pearse, 2012;del Potro et al, 2013).…”

“…Considering the evidence for mid-crustal melt, observed deformation at Uturuncu was previously hypothesized to be caused by magmatic intrusion into or out of the APMB (e.g., Pritchard and Simons, 2004;Hickey et al, 2013).…”

Remote sensing of volcanoes and volcanic processes: integrating observation and modelling – introduction

“…Biggs et al 2009). However, subsurface structures and the thermal influence of the magma system itself may introduce complexities that may bias the model results (Hickey et al 2013). Such influences are best investigated using Finite Element Analysis but the high computational requirements and huge number of parameters means that full testing of the parameter space, error estimates and non-unique solutions are challenging.…”