Cenozoic tectonic evolution of the Alto Tunuyán foreland basin above the transition zone between the flat and normal subduction segment (33°30′–34°S), western Argentina

The Alto Tunuyán basin is a Neogene foreland basin located between Cordillera Principal and Cordillera Frontal, from 33°30′ to 34°00′ south latitude. At this latitude, the feature that characterizes the subduction geometry beneath the Andean Cordillera is a transition in the slab dip from nearly horizontal, north of 33°S, to normal dip, south of 34°S. This particular tectonic setting apparently controlled the Neogene tectonic history of the area. The Neogene sedimentary infill of the basin is represented by the Tunuyán Conglomerate and the Palomares, Butaló, and Papal formations. Thrusting and uplift of the Cordillera Principal began during the early Miocene. Deformation and uplift of the volcanic arc, located on the western part of the thrust belt, produced the sediment source for the lower 200 m of the Tunuyán Conglomerate. As deformation migrated progressively eastward during middle Miocene times, it involved the underlying Mesozoic sequences, the erosion of which provided the material accumulated in the rest of the Tunuyán Conglomerate. The Palomares Formation unconformably overlying the former unit reflects the uplift of Cordillera Frontal. Deposition of the Butaló and Papal formations over the partially deformed broken foreland basin reflects accumulation during a period of tectonic quiescence and low rate of erosion in the eastern part of Cordillera Principal and the western part of Cordillera Frontal. The basement uplift of Cordillera Frontal generated a sticking point that prevented the propagation of the thrust belt toward the foreland. Consequently, out-of-sequence thrusts developed in the Cordillera Principal and the basin was partially cannibalized.