Basement control and transfer tectonics in the Recôncavo-Tucano- Jatobá rift, Northeast Brazil

Abstract

The Reôncavo-Tucano-Jatobá rift consists of a series of asymmetric grabens which are separated by basement highs and transfer faults. Opening of the rift took place in a NW direction oblique to the N-S rift trend. Well defined transfer faults parallel the opening direction. They were responsible both for offsetting en-echelon depocenters in the Tucano and Reci3ncavo basins and for switching of the asymmetry of half-grabens across the Vaza-Barris fault zone. The transfer faults show characteristic features such as change of movement sense along strike and with time, and “cactus-shaped” fault structures as well as flower structures in cross section. The sigmoidal plan-form of the rift is probably due to faulting following preexisting weaknesses through a complex mosaic of basement blocks. Basement anisotropy is thought to have controlled the asymmetry of the half-grabens and the localisation of the Vaza-Barris transfer. A 2° anticlockwise rigid rotation of the East Brazilian Microplate relative to the São Francisco Craton around a pole located near the eastern termination of the Jatoba Graben describes the calculated 20% extension in the South Tucano and Re&ncavo grabens, the oblique northwestward opening, and the eastward shallowing of the Jatoba Graben. Gravity modelling suggests important crustal thinning, locally up to 458, below the rift. Mantle upwarping is localized near the faulted margin of the rift. With localized thinning in a 100 km wide basin during a 20 Ma rifting event, lateral, as well as vertical heat conduction would be important and may account for the absence of a post-rift thermal subsidence phase.