Compressional tectonics and volcanism: the Miocene-Quaternary evolution of the Western Cordillera (24–26°S), Central Andes

Volcanism in compressional tectonic settings presents several unclear relations, especially between faulting, volcano locations, and local stress fields. The Central Andes comprise one of the most important volcanic provinces in the world, where these relations can be studied. We investigate the Miocene-Quaternary faulting and the tectonic stress evolution of the Western Cordillera of Chile, between 24 and 26°S, and how they dictate the orientation of magma feeding fractures, to understand the relations between deformation and volcanism. We calculated 68 new stress tensors from faults of recognized age and reconstructed magma paths by analyzing the morphostructural characteristics of 130 monogenetic and polygenetic volcanoes of known age. Moreover, we integrated the database with previously published data from the Western Cordillera to carry out a regional comparison. Results allow us to recognize three main volcano-tectonic events. The oldest occurred in the Early Miocene and was characterized by an E-W greatest principal stress (σ1) expressed by N-S-striking reverse faults and NW–SE left-lateral strike-slip faults. Volcanoes belonging to this stage show morphometric characteristics that indicate dominant N-S magma feeding systems. The second event, active during the Upper Miocene-Pliocene, was characterized by NW–SE to NNW-SSE σ1, WNW-ESE right-lateral strike-slip faults, and NW–SE preferential direction of volcanic feeding systems. The last event was active in the Upper Pliocene–Pleistocene, mainly in the northern part of the study area, with N-S to NE-SW normal and right-lateral strike-slip faults with NNE-SSW-trending least principal stress (σ3). Volcanism in this stage is characterized by NW–SE and N-S magma feeding systems. Our results suggest that volcano distribution has been mainly controlled by variations of the stress field related to the growth and collapse of the Puna Plateau. Magma emplacement was mainly guided by fractures parallel to the compression direction, irrespectively of the horizontal stress being σ3 or the intermediate principal stress σ2. Anyway, magma emplacement occurred also through fractures oblique to σ1, along strike-slip faults, or by exploitation of inherited weak structures, such as reverse faults.