| Abstract |
Geoelectrical surveys of the subsurface have been widely used to explore the internal structure of active fault-controlled geothermal systems, in which fault-fracture meshes, hydrothermal fluid flow and mineral precipitation may occur. Nevertheless, there are few applications of geoelectrical methods in exposed fault zones which could be used as a way to validate inferences based on electrical measurements, e.g. nature and occurrence of the fault core and damage zone. In this work, we correlate the results of outcrop scale structural mapping, X-ray crystal diffraction (XRD) and geoelectrical profiles in two very well exposed fault zones of the Liquiñe-Ofqui Fault System (LOFS) and the Andean Transverse Faults (ATF), Southern Andes. The LOFS is a Cenozoic intra-arc 1200 km-long, right-lateral structure that strikes NS to NE in its master faults and NE to EW in its subsidiary faults. The ATF constitute an active but older NW-striking family of morphotectonic lineaments, in which sinistral, sinistral-reverse and normal movement is recorded. Structural mapping and XRD sampling were conducted in two 22-m-long transects belonging to the previous structural features, where a 2D direct current in situ geoelectrical survey was carried out. The field installation considered electrodes installed in a vertical wall of rock, from which a plan view resistivity profile is obtained. The studied exposures of the LOFS and ATF have simple cores and their orientation is N83W/65S and N45W/60SW respectively. Asymmetric damage zones, where the hanging wall has more frequency of discontinuities than the footwall, can be observed. XRD analyses indicate that zeolites dominate hydrothermal mineralogy and seal the cores and damage zones. The cores, proportionally rich in zeolites, have higher conductivity (all values <200 ohm-m) than the damage zones (75% of values <500 ohm-m). Electrical results suggest a significant positive correlation between zeolite amount per area unit and rock conductivity, which is greater in the core and hanging wall with respect to the unaltered andesitic host rock. |