Effects of structural zonation on fluids circulation of the Copahue geothermal system

Abstract

The volcano-hosted geothermal system of Copahue is one of the most promising resources of renewable energy in Argentina. The associated geothermal field is bounded by a set of N60° trending normal faults to the north and by WNW-ESE trending faults to the south. This paper aims to review this first-order distribution of the structures, using previously published b-value data, and to explore the relationship between the local stress field, the superficial structural setting, the magmatic source, and the geothermal fluid flow paths related to the volcanic complex. The 2D dilation tendencies of the geomorphic lineaments is calculated, defining a structural domain with dilatant lineaments that agrees well with high b-values observed at shallow depths(2 km below the surface), and with the known extension of the geothermal field. A rough spatial correspondence is also observed between domains of unfavorable oriented to dilate lineaments and shallow low b-value areas, suggesting that these discontinuities inhibit the horizontal motion of fluids at the same structural level, and constraining the reservoir both to the northwest and to the southeast. b-value data unravels the potential magmatic plumbing system at depth, highlighting a major NW-elongated high b-value body centered at 5 km below surface, from Chancho-có hill towards the south of Maquinas fumaroles. It is coincident at surface with a high density of lineament intersections domain, which creates in depth an intense structural damage zone that may facilitate the ascent of magmatic fluids. The NW anomaly can be extrapolated to the western margin of the Caviahue lake, agreeing with the occurrence of volcano-tectonic seismic events and elevated heat flows reported in this area, and therefore suggesting the presence of the geothermal reservoir at depth. Vertical appendices branching from the b-value anomaly reach up to 3 km below Termas and Maquinitas fumaroles, outlining the possible bottom of the geothermal reservoir. The shallower one is interpreted as a blob of magma injected below the Copahue Village fault system, providing the main heat source. These findings contribute to the current understanding of the geothermal reservoir, its depth coverage and upflow zones, providing insights for future geophysical exploration stages.