New constraints on the nature and composition of the São Paulo Plateau, Santos Basin: Magmatic, continental or hybrid crust?

The São Paulo Plateau (SPP), located in the Santos segment of the southeastern (SE) Brazilian margin underlying thick Cretaceous to Recent sediments, is an enigmatic feature with disputed crustal composition. Proposed crustal types include thinned continental crust, thick magmatic crust, and hybrid crust consisting of continental crust and magmatic addition. We use combined analysis of mainly geophysical datasets to investigate the crustal basement thickness and crustal type of the SPP, and the variation in timing of its rifting and magmatic addition. 2D and 3D combined analysis of deep seismic reflection and gravity anomaly data has been used to determine Moho depth, crustal thickness and basement density variation. Flexural back-stripping has been used to map sediment-corrected residual depth anomaly (RDA). A combination of observations of crustal thickness from gravity inversion, magnetic anomalies reduced to the pole, basement density from gravity-seismic joint-inversion, and RDA have been used together to distinguish and identify crustal basement types. Using these approaches, we show the distribution and coexistence of continental, hybrid and magmatic crust, as well as possible exhumed mantle in the Santos Basin.

In addition, 2D and 3D post-breakup subsidence modelling consisting of flexural back-stripping, decompaction and reverse thermal subsidence modelling has been used to determine the palaeo-datum of base and top salt at the time of salt formation. This salt palaeo-datum modelling is used to distinguish syn-tectonic from post-tectonic salt and to investigate the contrasting consequences of magmatic versus thinned continental crust on the palaeo-bathymetry of Aptian salt deposition. We show that the distribution of post-tectonic salt primarily corresponds to that of continental crust thinned by widespread early Aptian rifting while syn-tectonic salt locations correspond to that of magmatic crust extended by late Aptian rifting.