Geoelectrical characterization of Socompa lagoon area in the Andean Central Volcanic Zone from 3-D audiomagnetotelluric inversion

Abstract

The Socompa stratovolcano is located in the Andean Central Volcanic Zone, where active volcanism turns it into an area of interest for geothermal resources. In the surroundings of the volcano, the Socompa Geothermal Prospect was carried out looking for thermal manifestations related to an active geothermal system. The results of these preliminary studies are not conclusive. Here we present a geoelectrical model from a 3-D inversion of audiomagnetotelluric data acquired in an area of 16 km2. It covers the topographic low where the Socompa lagoon and the thermal springs are located, in order to determine the reservoir of circulating geothermal waters. The most distinctive feature determined by the 3-D model is a high conductive layer (less than 10 Ωm) at a depth of about 400–500 m and at least 200 m thick. Due to the environment and the depth to which the conductive layer is found, there is more than one possibility to explain its presence. It could be due to a deep saline aquifer that would be hosting the circulating waters. But since the low topography could coincide with a cryptic caldera of Miocene - Pliocene(?) age, the high conductivity layer could also be explained by the presence of a clay cap developed during the period of activity. From the inversion of the audiomagnetotelluric data it was possible to carry out a geoelectrical characterization of the upper units present in the study area, as well as to delimit, in a first approximation, the depth to which the hydrothermal reservoir would be found.