Long-lived crustal damage zones associated with fault intersections in the high Andes of Central Chile

Abstract

Long-lived, high-angle fault systems constitute high-permeability zones that can localize the upward flow of hydrothermal fluids and magma throughout the upper crust. Intersections of these types of structures can develop complex interference patterns, which constitute volumes of damaged rock (networks of small-scale faults and fractures) where permeability may be significantly enhanced. This is relevant for understanding regional-scale structural controls on the emplacement of hydrothermal mineral deposits and volcanic centers, and also on the distribution of areas of active upper-crustal seismicity. In the high Andes of central Chile, regional-scale geophysical (magnetic, gravimetric, seismic) and structural datasets demonstrate that the architecture of this Andean segment is defined by NW- and NE-striking fault systems, oblique to the N-S trend of the magmatic arc. Fault systems with the same orientations are well developed in the basement of the Andes. The intersections of conjugate arc-oblique faults constitute the site of emplacement of Neogene intrusive complexes and giant porphyry Cu-Mo deposits, and define the location of major clusters of upper-crustal earthquakes and active volcanic centers, suggesting that these fault systems are still being reactivated under the current stress regime. A proper identification of one-dimensional, lithospheric-scale high-permeability zones located at the intersections of high-angle, arc-transverse fault systems could be the key to understanding problems such as the structural controls on magmatic and hydrothermal activity and the patterns of upper-crustal seismicity in the high Andes and similar orogenic belts

Reactivation of Fault Systems by Compartmentalized Hydrothermal Fluids in the Southern Andes Revealed by Magnetotelluric and Seismic Data

“…This tectonohydrothermal environment has been observed in different regions of the Andes, where the intersections of major NNE thrust faults and ATF are hosts to giant ore‐porphyry deposits (Figure 1) (e.g., Chernicoff et al, 2002; Cox, 2005; Curewitz & Karson, 1997; Piquer et al, 2019; Rowland & Simmons, 2012; Sillitoe, 1997; Veloso et al, 2019). These points of intersection have also been deduced to impact geothermal reservoir development (Perez‐Flores et al, 2017; Sanchez et al, 2013).…”

“…As discussed in section 2, these structures are considered discrete, reactivated, pre‐Andean faults, which exert a fundamental control in the location and development of volcanic features. They are enigmatic as their orientation with respect to the regional stress field makes them unfavorable to transport magma through the lithosphere (Cembrano & Lara, 2009; Chernicoff et al, 2002; Piquer et al, 2019; Sielfeld et al, 2019). The seismicity of Cls1 does not extend to the surface nor is there any surface expression of the structure, which supports the hypothesis that the ATF domain is contained within the basement lithology, and that they are of Pre‐Andean origin (Cembrano & Lara, 2009).…”

“…The intersection of major NNE oriented fault systems and the potentially blind, discrete WNW trending ATF domains occur across all latitudes of the Andes, showing an along‐strike spatial control of major mineral deposits (Katz, 1971; Sillitoe, 1997). Sillitoe (1997) and Piquer et al (2019) suggested that hydrothermal minerals related to porphyry copper deposits of central Chile are formed at such intersections. As the surface expressions of the ATF are limited to a few scarce outcrops (Lara et al, 2004; Perez‐Flores et al, 2016), they are mostly inferred from kilometer‐scale topographic lineaments (Cembrano & Lara, 2009; Giambiagi et al, 2019; Moreno, 1976; Piquer et al, 2016), major magnetic anomalies (Yáñez et al, 1998), and alignment of seismicity and volcanic morphological features (Aron et al, 2015; Lara et al, 2004; Sielfeld et al, 2017).…”

“…For example, a prominent geothermal reservoir found at the western flank of the Tinguiririca volcanic complex has been considered for geothermal energy exploitation (Aravena et al, 2016; Benavente et al, 2016; Clavero et al, 2011; Pritchard et al, 2013). Furthermore, the PPVC, which has been episodically on yellow alert due to degassing and ash expulsion events since 2011 (Aguilera et al, 2016; GVP, 2020), demonstrates a NNE strike alignment of eruptive vents and proximal geothermal springs along the major El Fierro Fault System (EFFS) that outcrops within the field area (Giambiagi et al, 2019; Mescua et al, 2013; Pavez et al, 2016; Piquer et al, 2019). The region of the SVZ is of particular interest due to the presence of both convergent margin‐parallel fold‐thrust belt systems such as the EFFS, and margin‐oblique WNW and ENE trending features, referred to as Andean Transverse Faults (ATF) (Cembrano & Lara, 2009; Katz, 1971).…”

Shallow Anatomy of the San Ramón Fault (Chile) Constrained by Geophysical Methods: Implications for its Role in the Andean Deformation

“…Escape‐tectonic behavior has been documented during the early Miocene (14 Ma) at 30°S, 300 km to the north of the study area (Giambiagi et al, 2017). Other evidences of Pliocene‐Quaternary strike‐slip deformation are found in the NE‐SW dextral and WNW‐ESE sinistral strike‐slip faults observed at the El Teniente porphyry copper deposits (~34°S) (i.e., Garrido et al, 1994; Piquer et al, 2016, 2019). Additionally, N37°E compression during the Quaternary (Lavenu & Cembrano, 2008) and strike‐slip focal mechanisms (Barrientos et al, 2004) in the Main Cordillera, to the east of the study area, consistently show a component of strike‐slip motion in the observed seismicity.…”