Lithospheric heating by crustal thickening: a possible origin of the Parnaíba Basin

The subsidence of basins formed by extension is now quite well understood. But that of cratonic basins is not, though a variety of models have been proposed. This volume is concerned with the structure and evolution of one such basin, the Parnaíba basin in NE Brazil. At the moment probably more is known about this basin than about any other cratonic basin. A long deep seismic reflection profile across the basin shows no evidence of extension, or of structural control by the underlying basement. Backstripping of two wells in the basin show that the time scales for their subsidence are 68 and 74 Ma. We show that these observations are consistent with a thermal model for the formation of the basin, where the thermal disturbance results from the emplacement and removal of a crustal layer whose thickness is 35–40 km, and not from extension. Such a layer is presently being emplaced as a gravity current on the thick lithosphere of northern India as Tibet flows southwards. Such currents and cratonic basins have similar circular shapes. This model is not incompatible with the relevant geological observations. It may be possible to test its predictions by careful study of the growth of metamorphic minerals.