Quaternary Deformation in the Neuquen Basin, Explained by the Interaction Between Mantle Dynamics and Tectonics

Quaternary deformations described in the retro-arc region at the latitudes of the Neuquen Basin can be divided into two main groups: a northern group characterized by Quaternary deformation zones concentrated near the main topographic breaks of different morphostructural systems, and a second group located in the southern Neuquen Basin distinguished by disconnected, sparced and noncontinuous Quaternary deformational zones. In the northern Neuquen Basin, evidence of active deformation is associated with the Frontal Cordillera (33 degrees-34 degrees S); while in the foreland area, young deformations concentrate in the San Rafael Block. In the southern Neuquen Basin, awestern deformational belt constitutes the continuation to the north of an intra-arc fault system associated with dip- and strike-slip displacements in a strain-partitioned regime (Liquine-Ofqui fault system). At these latitudes, to the east, isolated evidence of Quaternary deformation, regional uplift and development of non-equilibrated fluvial profiles are recognized in the Tromen and Auca Mahuida volcanic plateaux and sierra de Cara Cura-sierra de Reyes area. These systems are short and unconnected and have been explained through an intricate pattern of asthenospheric anomalies evidenced from magnetotelluric data. These mantle anomalies could be related to the tearing of the subducted Nazca plate at depth evidenced by seismic-tomographic data. We therefore suggest that the thermally weakened crust at the southern Neuquen Basin latitudes could be the main control responsible for focalizing contractional, extensional and transpressional deformations in isolated mountain systems.