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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The Altiplano-Puna Volcanic Complex of the Central Andes is host to an ~150-km-wide, quasi-circular ground deformation anomaly centered on Uturuncu volcano (Bolivia). The precise onset and duration of this deformation is unclear, but geomorphologic studies bracket its initiation at less than a few hundred years ago. Here we report on the deformation history over an ~50 yr period by deriving orthometric height changes from leveling and global navigation satellite system (GNSS) observations at 53 benchmarks along a regional leveling line that crosses the deformation anomaly. The comparison of interferometric synthetic aperture radar (InSAR) line-of-sight (LOS) displacements and LOS-projected orthometric ground velocities in a common reference frame reveal central uplift extending to ~35 km from Uturuncu at a maximum orthometric rate of 1.2 cm yr-1 , and peripheral subsidence at a maximum rate of 0.3 cm yr-1 to ~60 km from Uturuncu. This pattern is consistent with the spatial extent and average rate of deformation observed by InSAR. Our interpretation of the data is that long-wavelength ground uplift at Uturuncu has likely occurred at a quasi-constant rate for at least half of a century. This study bridges the observational time spans between modern satellite geodetic observations (up to a few decades) and geomorphological observations (a few centuries and longer) of the recent deformation history of the continental crust in the Central Andes and adds to a select group of case studies of quantifiable long-term volcano deformation worldwide.

S U M M A R YMeasurements of ground deformation can be used to identify and interpret geophysical processes occurring at volcanoes. Most studies rely on a single geodetic technique, or fit a geophysical model to the results of multiple geodetic techniques. Here we present a methodology that combines GPS, Total Station measurements and InSAR into a single reference frame to produce an integrated 3-D geodetic velocity surface without any prior geophysical assumptions. The methodology consists of five steps: design of the network, acquisition and processing of the data, spatial integration of the measurements, time series computation and finally the integration of spatial and temporal measurements. The most significant improvements of this method are (1) the reduction of the required field time, (2) the unambiguous detection of outliers, (3) an increased measurement accuracy and (4) the construction of a 3-D geodetic velocity field. We apply this methodology to ongoing motion on Arenal's western flank. Integration of multiple measurement techniques at Arenal volcano revealed a deformation field that is more complex than that described by individual geodetic techniques, yet remains consistent with previous studies. This approach can be applied to volcano monitoring worldwide and has the potential to be extended to incorporate other geodetic techniques and to study transient deformation.