The Central Andes is a key global location to study the enigmatic relation between volcanism and plutonism because it has been the site of large ignim briteforming eruptions during the past several million years and currently hosts the world's largest zone of silicic partial melt in the form of the Alti plano Puna Magma (or Mush) Body (APMB) and the Southern Puna Magma Body (SPMB). In this themed issue, results from the recently completed PLUTONS project are synthesized. This project focused an interdisciplinary study on two regions of largescale surface uplift that have been found to represent ongoing movement of magmatic fluids in the middle to upper crust. The loca tions are Uturuncu in Bolivia near the center of the APMB and Lazufre on the Chile Argentina border, on the edge of the SPMB. These studies use a suite of geological, geochemical, geophysical (seismology, gravity, surface defor ma tion, and electromagnetic methods), petrological, and geomorphological techniques with numerical modeling to infer the subsurface distribution, quantity, and movements of magmatic fluids, as well as the past history of eruptions. Both Uturuncu and Lazufre show separate geophysical anomalies in the upper, middle, and lower crust (e.g., low seismic velocity, low resistiv ity, etc.) indicating multiple distinct reservoirs of magma and/or hydrothermal fluids with different physical properties. The characteristics of the geophysical anomalies differ somewhat depending on the technique used-reflecting the different sensitivity of each method to subsurface melt (or fluid) of different compositions, connectivity, and volatile content and highlight the need for integrated, multidisciplinary studies. While the PLUTONS project has led to significant progress, many unresolved issues remain and new questions have been raised.

The vertical transport of large volumes of silicic magma, which drives volcanic eruptions and the long‐term compositional evolution of the continental crust, is a highly debated problem. In recent years, dyking has been favored as the main ascent mechanism, but the structural connection between a distributed configuration of melt‐filled pores in the source region and shallow magma reservoirs remains unsolved. In the Central Andes, inversion of a new high‐resolution Bouguer anomaly data over the Altiplano‐Puna Magma Body (APMB) reveals ~15 km wide, vertically elongated, low‐density, 3D structures rooted at the top of the APMB at 20 km depth. We integrate our gravity inversion with the available geophysical, geological, and petrological observations, and in agreement with petrological/mechanical considerations propose that, in this region of the Andes, partially molten granitic bodies ascend diapirically through the hot ductile mid‐upper crust.

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[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.

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