The Piuquencillo fault system: a long-lived, Andean-transverse fault system and its relationship with magmatic and hydrothermal activity

Abstract

Abstract. Lithospheric-scale fault systems control the large-scale permeability in the Earth's crust and lithospheric mantle, and its proper recognition is fundamental to understand the geometry and distribution of mineral deposits, volcanic and plutonic complexes and geothermal systems. However, their manifestations at the current surface can be very subtle, as in many cases they are oriented oblique to the current continental margin and to the axis of the magmatic arc; be partially obliterated by younger, arc-parallel faults; and also be covered by volcanic and sedimentary deposits, through which the fault might propagate vertically. The Piuquencillo fault system (PFS) is a proposed lithospheric-scale fault system, located in the Main Cordillera of central Chile. Here, we present the results of the first detailed field study of the PFS, based on structural data collected at 82 structural stations distributed across all the western Main Cordillera. The first published U–Pb zircon ages for the La Obra batholith, which is bounded to the south by the PFS but also affected by younger reactivations of it, were obtained. They yielded 20.79 ± 0.13 Ma (granodiorite) and 20.69 ± 0.07 Ma (monzogranite). Statistical analysis of fault-plane data shows that the presence of the PFS is reflected on a strong preferred NW to WNW strike, with variable dip directions, evident from the analysis of the total fault-plane population and also from individual segments of the PFS. In some segments, the presence of major NE- to ENE-striking faults which intersect the PFS is also reflected in the preferred orientation of fault planes. Preferred orientations of hydrothermal veins, breccias and dikes show that both the PFS and some ENE-striking faults were capable of channelling hydrothermal fluids and magma. Kinematic and dynamic analysis of fault-plane data reveals that most of the PFS was reactivated with sinistral ± reverse kinematics during the Neogene, under a strike-slip to transpressive regime with E- to ENE-trending shortening direction (σ1). Detailed kinematic and dynamic analyses were completed for various segments of the PFS and also for the different rock units affected by it. This study supports the concept that the PFS is a lithospheric-scale fault system, which strongly controlled deformation and the flow of magmas and hydrothermal fluids during the Neogene. The PFS forms part of a larger, margin-transverse structure, the Maipo deformation zone, a continental-scale discontinuity which cut across the entire Chilean continental margin and has been active at least since the Jurassic.

Anatomy of a high-silica eruption as observed by a local seismic network: the June 2011 Puyehue–Cordón Caulle event (southern Andes, Chile)

“…This system accommodates the dextral trench-parallel component of oblique convergence between Nazca and South American plates, and it is genetically linked to the Southern Volcanic Zone (SVZ) of the Andes (Cembrano and . The NW-oriented basement structure controlling the architecture of PCCVC belongs to the Andean Transverse Fault System (ATFS; Sanchez et al, 2013), a group of large basement structures segmenting the southern Andes that have been inherited since the Late Paleozoic (Piquer et al, 2021).…”

Rainfall-Induced Landslide Assessment under Different Precipitation Thresholds Using Remote Sensing Data: A Central Andes Case

“…Moreover, the marine and continental sedimentary units show a lower predisposition to landslide. In the Maipo basin, the lithologies show the impact of hydrothermal fluids [38,71]; in addition, at the regional scale, at least two deformation events are noted with evident folding and faulting on the rocky units of the zone [33][34][35]70], which, together with the climate action, are evidenced in the weak mechanical integrity of rocks [24]. The slopes of the valleys in the area expose a wide variety of unconsolidated deposits of diverse selection on the surface.…”

One decade of b-value variations from volcano-tectonic seismicity as an early indicator of episodes of crisis in a volcano: the case of Copahue, Southern Andes

“…The LOFS is characterized by a right lateral strike-slip regime that also controls the Quaternary volcanism (Cembrano et al, 2000;Cembrano Perasso and Lara, 2009). Shallow seismic activity has been documented along the LOFS (Haberland et al, 2006;Lange et al, 2008;Legrand et al, 2011;Sielfeld et al, 2019) (Cembrano Perasso and Lara, 2009;Sánchez et al, 2013;Maldonado et al, 2021), a NW-WNW striking arc-oblique longlived basement fault system linked to pre-Andean crustal weakness zone associated with Permian-Triassic tectonics (Piquer et al, 2021).…”