Magnetotelluric evidence of deep source fluids from the Valle del Cura geothermal system, San Juan, Argentina

BARCELONA, HERNAN; FAVETTO, ALICIA; POMPOSIELLO, M. CRISTINA; PERI, VERÓNICA GISEL

Buenos Aires

Encuentro; XIV Giambiagi Winter School ?Applied and Environmental Geophysics?; 2012

Departamento de Física, Facultad de Ciencias Exactas y Naturales, UBA

The Valle del Cura morphotectonic province is located on the pampean flat slab subduction segment, characterized by the lack of actual volcanism. Usually, geothermal systems are related to volcanic activity, but at the Valle del Cura there are several active hyperthermal manifestations. The aim of our work was to study the source of the geothermal fluids by magnetotelluric (MT) and geological studies in order to prove the existence of a geothermal system linking the apparent isolated hot springs. The MT survey was focused in Los Despoblados, the most representative hot spring in the region. A total of 18 MT sites were located along two profiles with NE-SW strike. We used a broad band MT equipment (EMI MT24 from Geometrics) in order to obtain a frequency band from 0.1 s to 100 s. Robust analysis of the time series and dimensional and distortion analysis were performed before developing 2D-inversions. The models of resistivity distribution allowed us to determine clearly the lithostratigraphic column of Los Despoblados. Also, two conductive anomalies were observed. The data revealed that these anomalies rise from a tabular conductive anomaly at 7-8 km depth, just between the Paleozoic metasediments and the cretaceous volcanic rocks transition. Taking into account that structural framework is quite similar to all the hot springs, our results suggest that this kind of anomaly are present in many hot springs of the region, thus indicating similar hot source for deep fluids. This evidence probably is the first one who determined that the scattered hot springs are linked and may be part of a non-conventional geothermal system.