Structural analysis of the Planchón-Peteroa Volcanic Complex: Insights for the geothermal system

Abstract

The Planchon-Peteroa ́ Volcanic Complex (PPVC) is located in the Transitional Southern Volcanic Zone of the Andean Ridge. Structural control of the main NNE-striking El Fierro fault system (EFFS) over the volcanic activity has been commonly assumed, although a paucity of evidence remains. The aim of this paper is to explore the relationship between the local stress field, the superficial structural setting and the geothermal fluid flow paths related to the volcanic complex. To conduct the structural analysis, this work combines remote sensing determination of lineaments, recognition of fracture patterns, with the inversion of kinematic indicators on outcropscale faults, to finally evaluate the role of the local stress field over the 2D slip and dilation tendencies of the recognized structures. Mesoscale morphostructural lineaments present three main directions: ~E-W, ~NE-SW, and ~NW-SE. Major lineaments develop inflections, giving rise to left bends between the NW-SE to E-W along the strike, compartmentalized by ~ NNE trending lineaments. Strike-slip fault solutions with an ENE-WSW to NE-SW oriented shortening axis were obtained from fault-slip data analysis. The inversion of fault kinematic indicators constrains a Quaternary to recent strike-slip regime, with a ~ENE-WSW trending σ1, and a subvertical σ2. Under the defined local stress field, ~NE-SW and ~WNW-ESE oriented structures have high slip tendency, while those spanning from NE-SW to E-W are prone to dilate. Our analysis suggests that these transverse structures exert first-order controls on the location of Vergara Pass Hill, and Pen ̃on ́ River and Azufre River Valleys hydrothermal manifestations. It seems that intersection zones with submeridian structures, as EFFS, increase structural damage and facilitate hot fluid migration. Circulation would profit the most from ~ENE-WSW and ~NW-SE striking outcrop-scale faults and fractures associated with the damage zones.