CONICET | Buscador de Institutos y Recursos Humanos

Both in continental collision and subduction-related orogens, different kinds of mega-detachments have been proposed to explain the horizontal shortening, crustal thickening and topographic uplift. In fold-and-thrust belts, these detachments have traditionally been located inside levels of mechanical anisotropies. These orogenic wedges thicken towards the hinterland, reaching depths located in the brittle-ductile transition. At an orogenic scale, these shear zones are not controlled by frictional sliding, but rather by temperature, composition, strain rate, and the stress field. While the synergies between crustal deformation, exhumation and sedimentation processes are well-known to a first order, it is challenging to evaluate the interplay between constructive deep mechanisms and the in-situ stress field. Two outstanding questions in the study of orogenic processes are: How does shallow structures in the foreland fold-and-thrust belt connect with ones in the hinterland under an evolving and changing stress field? How long can a detachment remain active during an orogenic event?To answer these questions, we use the Central Andes as a natural laboratory and construct kinematic-thermomechanical models for the last episode of crustal deformation and thickening. Our models show that a shallow, sub-horizontal megadetachment located at the shallowest brittle-ductile transition concentrates most of the horizontal crustal shortening between the fore-arc and the South American craton. We propose that, locally, a threshold in horizontal shortening and crustal thickening is achieved when the buoyancy force equals the horizontal force, and at this point, the mega-detachment deactivates, and the crustal root widens eastwards, in concert with ductile deformation in the lower crust and the generation of a new mega-detachment. Our working hypothesis is that, by studying changes in the paleo-stress fields along the arc region, together with the timing of uplift and exhumation of the morpho-structural units across the transects, we can constrain the timing of activation/deactivation of the detachments responsible for the Andean deformation. We suggest that a change in the stress field from compression to strike-slip regime can be used as a proxy for the deactivation of a mega-detachment.For this purpose, the temporal and spatial stress field variations is used as a parameter crucial to understanding the relationship between deep and shallow crustal deformation