A Thermo-Compositional Model of the Cratonic Lithosphere of South America

Abstract

New seismic data on the crust and upper mantle of South America have recently become available and describe its deep structure with unprecedented resolution. Here, seismic data are combined with gravity data and mineral physics constraints to develop self-consistent models of the temperature, composition, and density of the South American lithospheric and sub-lithospheric upper mantle. A new model of the crustal structure was developed, including sediment and average crustal density and depth to the Moho. This crustal model was used to correct the gravity field and obtain the residual topography. Then, an initial temperature model, derived from seismic tomography and mineral physics, was improved through an iterative process based on the joint inversion of gravity and residual topography. The results reveal deep cratonic roots present under wide parts of the Amazon, São Francisco, and Paranapanema Cratons, but not under the Rio de la Plata and Parnaíba Cratons. These cratons probably never developed lithospheric roots or were rejuvenated during subsequent tectonic events. We hypothesize that the root of the northwestern Amazon craton was removed by upwelling of hot mantle material under the Guyana highlands. Temperature and density anomalies evident beneath the São Francisco Craton appear to be connected with those of the Paranapanema Craton, which could indicate a westward shift of its root. Depletion south of the Paranapanema Craton probably denotes remnants of a previously larger craton that was rejuvenated by the upwelling of hot mantle material leading to emplacement of the Paraná Flood Basalts.