Decoding the state of stress and fluid pathways along the Andean Southern Volcanic Zone

Abstract

Decoding means decrypting a hidden message. Here, the encrypted messages are the state of stress, fluid pathways, and volcano tectonic processes occurring in volcanoes of the Andean Southern Volcanic Zone (SVZ). To decode these messages, we use earthquake focal mechanisms, fault slip data, and a Monte Carlo simulation that predicts potential pathways for magmatic and hydrothermal fluids. From this analysis, we propose that SVZ volcanoes have three end-member stress patterns: (i) Stress-A, a strike-slip regime coupled with the regional far-field tectonic stress; (ii) Stress-B, an extensional regime that may be promoted by volcanic edifice loading and upward pressure due to magma inflation occurring within the upper brittle-crust; and (iii) Stress-C, a local and transient fluid-driven stress rotated ~90 degrees from Stress-A. Notoriously, Stress-C pattern was observed in most volcanoes with historical eruptions. We propose that volcanoes presenting Stress-B are attractive geothermal targets, while Stress-C could be used as a predicting signal for impending eruptions.

The Andean Southern Volcanic Zone: a review on the legacy of the latest volcanic eruptions

“…While the NE-and ENE-trending volcanic structures are associated with tension fractures, extensional-shear fractures, or tail cracks, along with more primitive magmas erupted, the NW-trending, ATF-related volcanic structures can serve as transient magma pathways allowing the eruption of more evolved magmas (López-Escobar et al, 1995;Cembrano et al, 1996;Cembrano and Lara, 2009;Stanton-Yonge et al, 2016). The intersection of ATFs structures with LOFS structures are considered high-permeability and structural damage zones that may facilitate the emplacement of volcanic centres, hydrothermal systems, intrusive bodies, and Cu-Mo-Au ore deposits (Roquer et al, 2017;Piquer et al, 2019;Pearce et al, 2020;Vigide et al, 2020;Pérez-Estay et al, 2023). According to Lara et al (2008), LOFS master faults with visible vertical offsets display numerous small eruptive centres on top, probably formed after transient vertical adjustments, either by isostatic rebound or transpressional-induced uplift.…”

“…At least 150 geothermal zones exist in the SVZ around Holocene volcanoes. These zones, characterized by meteoric and magmatic fluid contribution, are hosted within subvolcanic volcano-sedimentary sequences and crystalline basement, and favoured by tectonic features such as the LOFS or the ATFs (Sánchez-Alfaro et al, 2015;Wrage et al, 2017;Daniele et al, 2020;Pérez-Estay et al, 2023). The most promising geothermal sites are located at Tinguiririca, Calabozos, Laguna del Maule, Nevados de Chillán, Domuyo, Copahue, Tolhuaca, Sierra Nevada, and the PCCVC (Lahsen et al, 2005(Lahsen et al, , 2010(Lahsen et al, , 2015Chiodini et al, 2014;Barcelona et al, 2021).…”