Volcano-Tectonic-Geothermal Domains on the Southern Andes Volcanic Zone

Abstract

The interplay between tectonics and volcanism creates the conditions to form geothermal systems and controls the fluid chemistry evolution. The Southern Andes volcanic zone (SVZ) is one of the best natural laboratories to address such interplay because of the occurrence of numerous geothermal areas, recent seismic activity generated by regional fault systems, and intense volcanic activity. In this study, we integrate structural analysis at regional and local scale of active geothermal areas, with geochemical analysis of hydrothermal fluids, to define the development of magmatic-tectonic-hydrothermal domains. In the SVZ, volcanism is strongly controlled by the Liquiñe-Ofqui Fault System (LOFS), an intra-arc, strike-slip fault, and by the Andean Transverse Faults, a set of transpressive NW-striking faults. We identify two end-members on the magmatic-tectonic-hydrothermal domains. The Liquiñe–Ofqui fault system domain encompasses geothermal areas located either along the master or subsidiary faults. These are favorably orientated for shear and extension, respectively. In the LOFS domain, the geochemistry of hot spring discharges is controlled by interaction with the crystalline basement, and is characterized by low B/Cl. In marked contrast, the Andean Transverse Faults domain includes geothermal occurrences located on the flanks of volcanoes forming WNW-trending alignments; these systems are built over faults that promote the development of crustal magma reservoirs. Unlike the first domain, the fluid chemistry of these geothermal discharges is strongly controlled by volcanic host rocks, and is typified by higher B/Cl ratios. Helium, nitrogen and carbon isotope signatures in hydrothermal fluids complements major and trace analyses results and enlighten on variation due to fault systems intersections and the northern termination of the LOFS. Results from this study provide new insights towards efficient exploration strategies of geothermal resources in Southern Chile.