Combined thin-skinned and thick-skinned deformation in the central Andean foreland of northwestern Argentina

The Choromoro Basin, an intramontane structural depression in the foreland fold-and-thrust belt of the central Andes of northwestern Argentina, is underlain by Proterozoic-Recent sedimentary deposits, with Cretaceous-Paleogene and older rocks exposed along the margins and Neogene and Quaternary deposits exposed within it. The Cretaceous-Paleogene deposits represent part of an extensive rift system. Late Cenozoic Andean compression followed rifting and initiated the foreland basin stage of sedimentation. The Choromoro Basin developed in response to the fragmentation of the Andean foreland during the latest Cenozoic Andean orogeny. Regionally, the Choromoro Basin is located in an area dominated by a thick-skinned structural style of deformation, which is marked by high-angle, eastward-verging reverse faults rooted in a mid-crustal detachment that uplifted the basement blocks that bound the basin along its western and eastern margins. Faulting is associated with eastward-verging folds that involve the basement rocks and overlying Cretaceous-Neogene sedimentary strata. In contrast, Neogene beds in the Choromoro Basin show a thin-skinned structural style of deformation with an eastward-verging, imbricated thrust system and associated folds related to a shallow detachment located at approximately 2.5-3 km depth in the Cenozoic succession. The superposition in space and time of thick- and thin-skinned structural styles in the Choromoro Basin gives rise to a combined style of deformation. Several orogens, including the Andes, show the coeval development of thick- and thin-skinned structural styles, but they are spatially distributed in the orogen and foreland realms, respectively. In the Choromoro Basin, the thin-skinned deformation developed in an area dominated by thick-skinned deformation.