Temporal and spatial relationships of thick- and thin-skinned deformation: A case study from the Malargüe fold-and-thrust belt, southern Central Andes

In this paper we analyse two end-member models of temporal and spatial interactions between thick- and thin-skinned structures in a thrust front with pre-existing rift structures. In the most commonly accepted model, a hinterland-to-foreland sequence of inversion of pre-existing normal faults is proposed. As a result, the emplacement of shallow thrust sheets in the sedimentary cover occurs before the basement inversion in the foreland. In the other model, basin inversion occurs early in the deformation history of the external part of a fold-and-thrust belt, as the result of a foreland-to-hinterland sequence of inversion. The Malargüe fold-and-thrust belt (34-36°S) formed in response to compression of the Mesozoic Neuquén basin during Neogene to Pleistocene times. Integrating detailed structural data from the northern part of this belt with new Ar/Ar dating, we propose a revised kinematic model of thick- and thin-skinned interaction and define the temporal-spatial evolution of the belt. Comparison of the timing of deformation in the thick- and thin-skinned areas strongly supports the hypothesis that the reactivation of normal faults was coeval with the insertion of shallow detachments and low-angle thrusting along the migrating front of the thrust belt and occurred from the foreland to the hinterland. Detachments occur at several stratigraphic horizons, including a deep basement decóllement related to the basement-involved thrusting and shallow detachments located within the Jurassic and Cretaceous beds. These shallow and deep detachments were coeval producing simultaneous development of thrusts during the complex deformation of the thrust front between 15 and 8 Ma.