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 ignimbrite- forming eruptions during the past several million years and currently hosts the world's largest zone of silicic partial melt in the form of the Altiplano- 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 large-scale surface uplift that have been found to represent ongoing movement of magmatic fluids in the middle to upper crust. The locations 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 deformation, 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 resistivity, 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.
Geography, Geology, and Planning
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Pritchard, M. E., S. L. De Silva, G. Michelfelder, George Zandt, Stephen R. McNutt, J. Gottsmann, M. E. West et al. "Synthesis: PLUTONS: Investigating the relationship between pluton growth and volcanism in the Central Andes." Geosphere 14, no. 3 (2018): 954-982.