Characterization of Southern Peru hydrothermal systems: New perspectives for geothermal exploration along the Andean forearc

Abstract

This study provides a comprehensive characterization of various hydrothermal sys- tems in Southern Peru ranging from the faulted Precordillera’s steep topography up to the volcanic High Cordillera (>4000 m asl). The objective is to investigate thermal anoma- lies that may potentially serve as new geothermal resources.Our integrated approach com- bines: i) geochemistry from 14 hot springs sampled throughout the Tacna region, and ii) 3D numerical modeling of coupled groundwater and heat transfer considering topog- raphy and faults embedded in homogeneous permeability. Water and gas analysis indi- cates that the springs located near volcanoes discharge Na-K-Cl waters with high tem- peratures (>87°C), high Total Dissolved Solid concentrations (TDS >3452 mg/L), and free gases dominated by CO2 (>90 vol%). Springs located along the regional faults in the Precordillera discharge Ca-SO4 and Na-K-Cl waters with moderate temperatures (27- 53°C), intermediate TDS concentrations (464-2458 mg/L), radiocarbon ages between 1.4 and 7.9 kyr, and free gases dominated by N2 (>95 vol%). The Aruma springs, which are located at the transition between the High and the Precordillera, display intermediate characteristics. Numerical models accurately replicate the locations and temperatures of the fault-related springs only for permeable faults (>10 m), revealing the creation of 100-km long thermal plumes along faults, locally rising up the 150°C-isotherm to about ∼ 1000 m below the surface. This approach clearly distinguishes the spring origins, which are volcanic in High Cordillera and tectonic in Precordillera. Moreover, we highlight that steep topographic gradient and permeable reverse faults in the Andean forearc may gen- erate considerable thermal anomalies, opening perspectives for the geothermal exploration.