Effects of major fault zones on geothermal reservoirs – a case study at Villarrica Volcano, southern Chile

Abstract

Near Villarrica volcano, located in southern Chile, a high number of thermal springs indicate moderate geothermal activity with reservoir temperatures between 80 and 140 °C. Although being one of the most active volcanoes in Chile, high temperature geothermal manifestations are not observed. Moreover, the area is characterized by a complex tectonic pattern of two major fault zones intersecting each other.
Geochemical analysis disclose meteoric origin of the water with contributions >60 yrs and recent rain water. Local circulation patterns are characterised by low reservoir temperatures and low dilution along the LOFS and moderate reservoir temperatures and a higher amount of dilution away from the fault zones. A deep water component has not been detected. Strontium isotopy indicates equilibrium between thewater and surrounding rock.
Geophysical data indicate mid- and upper crustal conductors that can be attributed to major fault zones. A connection between the structures in the different crustal levels cannot be excluded from geophysical measurements, but geochemical data point to a barrier between deep and meteoric fluids. We can conclude that the active faults govern the geothermal system by controlling the fluid movements in local small-scale circulation pattern.