Oblique-slip tectonics in an active volcanic chain: A case study from the Southern Andes

Abstract

Oblique-slip tectonics in the intra-arc region of the Southern Andes accommodates heterogeneous deformation derived from plate convergence during the Pliocene and Quaternary. Long-term mechanical interaction between Andean transverse faults (i.e. NW-striking sinistral faults) and margin-parallel faults (i.e. NNE-striking faults) results in linked transtensional fault damage zones that facilitate structural conditions for the migration and emplacement of geofluids in the upper crust. We investigated the architecture of pre-eruptive units and the nature of faulting at the Tatara–San-Pedro–Pellado volcanic complex in the Southern Andes. Here, oblique-slip faulting crosscuts Miocene folded strata and granitoids. Our main results suggest that Quaternary volcanism and an associated geothermal systems developed on top of an ENE-oriented structural anisotropy defined by hundreds of faults and dikes interacting in a ca. 9 km long and 4 km wide rock volume, named the Tatara Damage Zone. Deformation in this domain is characterized by ENE- to WNW-striking transtensional oblique-slip faults flanked by (1) the seismically active NS-striking (dextral) Melado Fault to the west, (2) discrete NS- to ENE-striking dextral splay faults to the east and (3) the sinistral NW-striking Los Cóndores Fault to the north-east, which is reported for the first time in this work. The latter fault represents an excellent example of a long-lived Andean Transverse Fault. Furthermore, we suggest that the Los Cóndores Fault accommodates a margin-oblique slip component of bulk transpressional deformation. We demonstrate that Pliocene–Quaternary intra-arc oblique faulting developed after pre-Late Miocene compressional tectonics, and that this oblique faulting constrains the geometry of permeable pathways for the flow, emplacement, and eruption of quaternary geofluids. Furthermore, we evaluated the stress field for a discrete volcanic complex and provided key elements to better understand the role of Andean Transverse Faults in the spatial organization of Quaternary arc volcanism and geothermal systems in the Southern Andes.