Visualizing preferential magmatic and geothermal fluid pathways via electric conductivity at Villarrica Volcano, S-Chile

Abstract

Preferential fluid pathways along regional fault systems are crucial for the spatial localization of volcanic and geothermal manifestations. Differences in electric properties of fluids and hydrothermal alteration products against the unaltered matrix allow for visualization of such pathways. Unfavorable geometry for 2-D inversion resulting from the fluid pathways in regional faults often being aligned along the geo-electric strike can be overcome by using 3D inversion of magnetotelluric data. For a section in the 1400 km long Liquifie-Ofqui Fault System (LOFS), we demonstrate the potential of 3-D inversion of magnetotelluric data for visualization of fluid pathways. Six out of eight electric resistivity anomalies at intermediate depth are connected to volcanic or geothermal surface manifestations. Deep and highly conductive anomalies are detected in the vicinity of the volcanic chain and where the LOFS is crosscut by a fault that belongs to the Andean transversal fault system. The anomaly related to the fault crossing reveals a vertical pathway extending to the surface. Phase tensor analyses indicate a structural origin of the latter anomaly that may be connected to a line of volcanic cones that occurs in the NE of the Villarrica Volcano.