Tectonic and dynamic controls on the topography and subsidence of the Argentine Pampas: The role of the flat slab

Abstract

We analyze the Pampean foreland (the Pampas) along the modern flat-slab segment of the south-central Andes between 31° and 33° South latitude and to the east of the Argentine "flat-slab" province, using flexural and gravity studies and computations of dynamic topography. Bouguer anomalies and flexural analysis predict a foredeep of ~250. km width and a peripheral bulge amplitude of ~25. m, which match the regional morphologies of the modern Argentine Pampean Plain. However, these studies do not account for the subsurface Miocene-Quaternary basin preservation, represented by sedimentary thicknesses > 400 m and with depocenters > 400 km eastward with respect to flexural models. The discrepancy suggests that two mechanisms, acting at different wavelengths, influence the Argentine Pampas. The basin preservation is likely the result of a large-scale geodynamic forcing. Models of mantle flow, driven by realistic flat-slab subduction geometry and density contrasts, reproduce the depocenter location and the wavelength of subsidence as well as most of the remaining amplitude. Nonetheless, more sophisticated studies (e.g. considering lateral viscosity variations in the mantle wedge) might help reduce the dynamic amplitudes and better reproduce the observed geological record.