Characterization of the geothermal anomaly associated with the pre-andean reverse fault of Calientes, South of Peru: a multi-disciplinary approach.

In Peru, energy production is more than 75 % dominated by hydrocarbons (IEA, 2018) while at the same time, the Andes forearc is in a full demographic and economic development. However, the geothermal potential associated with reverse fault in the mountain range forearcs remains poorly studied compared to normal faults.  It is then essential to evaluate the geothermal potential associated with the Andes forearc thrust faults, in considering the environmental risks associated.

The hydrothermal system associated with the Sama-Calientes fault, near the city of Tacna South of Peru (18°S) is a suitable field site to experiment how integrated studies could provide an exploration diagnostic. The Calientes hot springs (42-44°C) emerge on the Sama-Calientes fault, an active thrust which delimits the border between the Andes and the north extension of the Atacama Desert. With an integrated study of the hydrothermal fluids and gas geochemistry, XRD composition of the hydrothermal deposits and veins, structural geology, and 3D numerical modeling with COMSOL Multiphysics, we propose to characterize the thermal anomaly associated with the Calientes springs and faults, putting them in perspective with the other hydrothermal springs in the region. Preliminary results indicated that hydraulic breccia, veins, and concretions around the Calientes springs and faults are mainly composed of calcite, contrarily to the other hot springs sites inside the Andes (excepted the Ticaco hot springs). Free and dissolved gas of the springs associated with the high Andean volcanoes (Casiri, Yucamani, Tacora) are mainly composed of CO₂ (90-100%), while those associated with the pre-andean faults (Sama-Calientes, Incapuquio) are mainly composed of N₂ (60-100%). Volcanic-associated springs show high sulfate concentrations (48-54 mmol/L) compared to fault-associated springs (3-25 mmol/L).  A simple 3D numerical model with a surface DEM and a homogenous permeability indicates that the topography-driven flow lines contributing to the Calientes springs would come from the Tacora volcano, 40 km north-east of Calientes. More investigation will precise the organization of the hydrothermal cells and the associated thermal anomalies. This work will also contribute to understand the role of hydrothermal fluids in subduction zones and especially on seismogenic reverse fault dynamics.