Regional evaluation of the Santos Basin, Brazil, using 2-D seismic and gravity / magnetic data has revealed a linear basement anomaly within the centre of the basin, extending NNE from a large igneous body to the western end of the Santos Fault. This feature coincides with an area of high thermal maturity within potential source rocks and with poor permeability due to intense cementation within clastic reservoirs, indicative of higher heat-flow. Structural reconstruction and modelling indicates a high degree of crustal thinning with raised heat-flows associated with this feature. Integration of the data over this feature with the structural reconstruction suggests it is either a failed break-up basin or an aborted sea-floor spreading centre, both of which could explain the observed geophysical and thermal anomalies. Plate tectonic reconstructions indicate the early South Atlantic sea-floor spreading centre ended at the Florianopolis Fracture Zone in the outer part of the Santos Basin. The linear anomaly in the Santos Basin appears to be a failed attempt to continue this centre north-eastwards towards the Brazilian coast line and was apparently abandoned early in its development. Subsequently, a successful spreading centre developed to the east, continuing the northwards opening of the South Atlantic Ocean.