Relative contributions of tectonics and dynamic topography to the Mesozoic-Cenozoic subsidence of southern Patagonia

Abstract

Sedimentary basins result from a complex interaction between mantle, crustal and surficial erosional-driven processes, which act at different time and spatial scales. While shortening and crustal loading drive flexural subsidence toward the foreland, stretching produces normal faulting and graben depocenters. In this contribution we analyze the Mesozoic-Cenozoic subsidence history of southern Patagonia, using backstripping from sixty eight oil well data and outcrops, distributed in the Santa Cruz and Chubut provinces, Argentina, in the Golfo San Jorge and Austral basins. These data are compared with three flexural analyses from six regional balanced cross sections along the southern Patagonian Cordillera, a stretching-thermal model (McKenzie)assuming lateral extension changes, five dynamic topography models localized in the core of the basins and a paleotopographic analysis derived from a paleolithospheric thickness approach (basalt geochemistry). The comparison between stratigraphic observations (backstripping in this case)and subsidence models provide us a residual subsidence value in southern Patagonia. These values are compared with dynamic topography and paleotopographic computations. No additional subcrustal forces are needed to explain the sedimentary accommodation during the Jurassic-early Cretaceous (extensional basin stage). However, from the late Cretaceous to the early Neogene, the foreland stages do require additional processes to account for the subsidence or uplift events. We reassert, like in our previous contributions, that subcrustal forces (lithospheric mantle thickness changes and asthenospheric flows)worked together with flexural accommodation to create a sedimentary basin, occasionally provoking drastic paleoenvironmental and landscape changes.