Crustal Structure and Tectonic Evolution of the Potiguar Basin--Northeast Brazil

MATOS, RENATO M. D., Cornell University/Petrobras, Ithaca, NY

The combined analysis of potential field and seismic reflection data suggest that the Potiguar basin of northeast Brazil developed as a consequence of northwest-southeast extension, resolved in the upper crust by hanging-wall block rotation along a system of linked faults. This extension developed during the Early Cretaceous rifting associated with the separation of South America and Africa. The basic basin architecture includes two main parallel northeast-trending half-grabens (Umbuzeiro and Boa Vista) separated by intervening basement highs and northwest-trending transfer faults. A three-dimensional crustal-scale model of the basin was generated by combining deep and shallow seismic reflection data, borehole and outcrop information, and potential field data.

The deep seismic profiles reveal a highly reflective crust underlain by a high-amplitude reflection Moho around 10 seconds (roughly 30 km depth). The crustal reflectivity seems to be directly associated with the highly deformed Proterozoic terranes observed in outcrop around the basin. Moreover, it seems that the basin-bounding normal faults (Carnaubais and Quixaba fault systems) terminate at a mid-crustal detachment surface, suggesting that the basin architecture is mainly controlled by two parallel listric normal fault zones that follow pre-existing upper crustal weaknesses, partially reactivated during the main rift episode (Neocomian). Whereas the pre-existing northeast-trending planar fabrics within the basement (schistosities, gneissosity, and shear zones) apparently controlled he main normal faults, internal conjugate and synthetic transfer faults are probably related to major discontinuities in basement rock fabrics. Seismic reflection data, together with gravity and magnetic modeling, show that the basin architecture is directly related to a linked system of northeast-trending listric normal faults and a mid-crustal detachment surface.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)