Geological and geophysical evidences of the polyphase structural evolution of the Southern Precordillera (31°42′S-69°24′W), central-western Argentina

Abstract

The evolution of the western margin of South America comprised different tectonic regimes responsible of the present geological composition and structure of the Central Andes. Remote sensing, geological and geophysical data (aeromagnetic and seismological data) have been processed to understand the polyphase structural evolution of the Argentine Southern Precordillera. The outcrops exposed in the Sierra de Barreal (31°42′S-69°24′W) show evidences of a complex structural evolution related to the superposition of three orogenies from the Early Paleozoic to nowadays. The Chanic orogeny (Late Devonian) is characterized by two systems of non-coaxial ductile folds that affect Early Paleozoic rocks of the Ciénaga del Medio Group. The recognized rotation in the shortening direction (from NW-SE to ENE-WSW) is interpreted here as a result of a sinistral transpressive regime. The San Rafael orogeny (Early Permian) is represented by back-thrusts and blind faults associated to asymmetric folding that involves the deformation of Upper Carboniferous rocks (Majaditas Formation). Finally, the compressive Andean orogeny associated to the Pampean flat-slab subduction segment has been locally controlled by inherited pre-Andean anisotropies. This is evidenced by: 1-the structural style of western-southern Argentine Precordillera, which in the study area is represented by faulted blocks and top-to-west vergent back-thrusts; 2- NW-SE deflections and associated magnetic anomalies in the Argentine Precordillera fold-and-thrust belt; 3-neotectonic structures developed in a sinistral transpressive system; 4-the crustal seismicity associated to NW-SE trending structures with left-lateral component motion.