3D gravity modelling of Colorado and Claromecó basins: new evidences for the evolution of the southwestern margin of Gondwana

Abstract

Although cratons have long been recognized as an important part of continental tectonic processes, we still have much to learn about their structural features and their relation to the genesis of basins, sedimentary thickness distributions, fold and thrust belts and surface processes. Contributing to a better knowledge of the crustal state and configuration of the southernmost part of the Rio de la Plata Craton, could shed light on the still controversial tectonic processes, which were responsible for the deformation of the southwestern margin of Gondwana during the Late Paleozoic. In particular, the deformation and uplift of the Sierras Australes, which are part of the Claromeco Basin (Buenos Aires, Argentina), would be closely related to the crustal structure of the southern limit of the Rio de la Plata Craton. Therefore, it is of crucial importance to investigate the possible existence of crustal heterogeneities underneath the Claromeco Basin, the Sierras Australes and the Colorado Basin, which can be related to structural features and weakness zones that could have played a major role in the tectonic evolution of the study area. For this purpose, we developed a 3D lithospheric-scale density model integrating various data, such as geological information, global gravity models, well data (thicknesses and lithologies), seismic tomography data (Moho depth), and pre-existing 3D density models of the Colorado Basin. Our model includes layers of sediments, crystalline crust and lithospheric mantle and therefore predicts the thickness variation of the upper and lower crust in the study area and of the main sedimentary sequences infilling the basins. Moreover, by analysing the model results, we propose a tentative location of the southern limit of the Rio de la Plata Craton and its possible tectonic relationship with transfer zones identified in the Atlantic platform southwards. Our results suggest that the southern boundary of the craton is located along the northernmost limit of the Colorado Basin, which is in contrast with the boundary proposed in previous works. Therefore, we propose that the Colorado Basin rifting process could have occurred along this weakness domain.