The Role of Active Crustal Faults in Geothermal Systems in Volcanic Areas: A Case Study of Southern Chile by Magnetotelluric Method

• Main Author: Pavez Moreno, Maximiliano Alejandro
• Other Authors: Kohl, Thomas, Tezkan, Bülent
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: KIT-Bibliothek, Karlsruhe 2023
• Subjects: Volcanoes; Magnetotellurics; Electrical structures; Magmatism; Crustal reservoir; Crustal faulting; Fluid pathways; ddc:600; Technology; info:eu-repo/classification/ddc/600; Antarctic; Antarc*
• Online Access: https://publikationen.bibliothek.kit.edu/1000164403; https://publikationen.bibliothek.kit.edu/1000164403/151693669; https://doi.org/10.5445/IR/1000164403

The Andean magmatic arc results from the on-going subduction of the Nazca and Antarctic beneath the South American Plates. The most active volcanoes in the Andes are concentrated in the Southern Volcanic Zone (SVZ) which extends from 33 to 46°S. This zone is characterized by the NNE-striking Liquiñe-Ofqui Fault Systems (LOFS), which extends over 1400 km and is offset by a group of NW-striking so-called Andean transverse faults (ATF). Preferential fluid pathways along these regional fault systems are crucial for the spatial localization of surface manifestations in the Andean magmatic arc. Ranging from volcanoes to thermal springs, they represent the geothermal spectrum from high- to low temperature geothermal systems in this area. Both, magmatic (melt) and geothermal fluids, are linked to comparatively high electrical conductivity and thus, prone to electromagnetic exploration. Given the depth of occurrence, here, we use magnetotelluric methods to develop flow concepts for both, low- and high temperature, fault-driven geothermal systems in volcanic areas. The low-and high-temperature systems of the Pucón/Villarrica area including 29 thermal springs (geochemical temperature estimations ranging from 84 to 184°C) and the Tolhuaca area including geothermal wells with temperature between 160 and 300°C, respectively, are considered representative examples. To identify the three-dimensional (3-D) effects generated by preferential fluid pathways in areas of interference between active cortical faults and volcanism surrounding the Pucón/Villarrica area, we used 31 broadband MT (BB-MT) stations deployed along E-W and N-S oriented profiles, intersecting the major fault systems. The 3-D inversion reveals eight electrical resistivity anomalies, which may be related to fluid pathways. Six of these anomalies are localized at a shallow-crustal level (<2 km) and are linked to volcanic or geothermal manifestations at the surface. Their connection to the surface is evident in the fault-related system, where the intersection of ...