Understanding the Geodynamic Role of Structural Elements and their Influence on (Paleo)Fluid Flow at the Licancura Geothermal Field, northern Chile

The southern part of the Central Andean Volcanic Zone, undergoing compression arising from the plate convergence, hosts a series of potential geothermal fields. Regional surveys suggest a genetic link between arc-parallel and arc-oblique structural elements (e.g. cataclasites, hydrothermal breccia, fault veins and veins) and mineral alteration patterns. Remote sensing analyses of the Licancura-Camiña area show a strong mineral alteration pattern, most probably resulting from an increased heat and fluid flow. We carried a detailed field survey and log the orientation, kinematics and associated mineral species for a variety of structural elements, aiming to stablish a relation between types of structural elements, stress fields, and mineral occurrences in the development of a geothermal field. In the field at Licancura, NW- and NNE-to-NE-striking structural elements display right- and left-lateral, and thrust displacements as they cut Miocene-Pliocene(?) volcaniclastic rocks. Structural elements show evidence of fluid emplacement as particular hydrothermal mineral assemblages (i.e. epidote) are part of the matrix or the filling material. Estimation of stress fields indicates three different regimes. The obtained strike-slip transpressional solution likely represents the accommodation of the shear component of the far-stress field imposed by the plate convergence. Reverse stress field solutions indicate NE- and NNW-trending compression and subvertical tension, likely due to plate convergence and local accommodation, respectively. The common NE-trending orientation of the s1 axis for the strike-slip and one of the reverse stress field solutions argues that some NW-striking thrust faults may be reactivated former strike-slip faults. Multiple statistical clustering of the poles to veins is consistent with orientation clusters defined by mineral associations. Estimations of the orientation of the s3 axes from vein clusters are consistent with those obtained from shear-related structural elements. Common solutions argue for a direct relation between specific mineral hydrothermal assemblages and particular stress field regimes, on where the driving pressures for the different set of veins vary between 1% and 30% of the differential stress at the time of fracturing and fluid emplacement.