Structural analysis of the deformation front at the northern Agrio fold and thrust belt (37º40’S - 70ºW), Neuquén Basin

Abstract

Two balanced cross-sections, supported by surface and subsurface data, were built in the deformation front of the northern Agrio fold and thrust belt (~37º40’S). The Las Yeseras thrust system originated first order structures at depth, rising ~2.3 km the basement, by means of faults inserted on jurassic and cretaceous evaporites (Auquilco and Huitrín Formations) creating triangle zones. Second order folds in the sedimentary cover have ~4-5 km wavelengths and basal detachment on the Auquilco Formation. The Veta Neuquén and San Eduardo anticlines have west-vergence and N-S trend, while the Maitenes and Las Viseras anticlines have NNW trend, west and east vergence respectively, and both are transported by thrusts that cut their forelimbs. The possible presence of inherited normal faults in the basement would control the location, trend and vergence of thrust originating the Maitenes and Las Viseras anticlines. Third order folds have ~2.5 km wavelengths and a detachment on cretaceous shales (Pilmatué Member). Flexural slip folding of layers with different competence originated minor fold-accommodation thrusts in the limbs and hinges. Late Cretaceous-Oligocene sequences in the frontal syncline are displaced by three lístric normal faults, of NNW trend and dipping to the NW, that join to a decollement on the Huitrín Formation. This extensional system would be formed by gravitational gliding induced by the increasing slope caused by the uplift of the Dorso de los Chihuidos.