Several independent gravity surveys were integrated to produce a gravity map of the northernmost portion of Northeast Brazil and its continental margin. At present, 37,435 gravity measure-ments were used (11,814 in land and 25,621 in sea), covering the area limited by longitudes 33° 30' W and 43° W and latitudes 2° 55' S and 7° 30' S, with an approximate density of 1 gravity station per 13 km2. The area has about 1,000 km (west-east direction) by 500 km (north-south direction) and covers the portion of the Borborema Province located north of the Patos Lineament, the easternmost portion of the Parnaíba basin, and the adjacent continental margin. The dominant long wavelength anomaly in the Bouguer anomaly map is an expressive gradient, grossly parallel to the continental margin, caused by the Moho uplift in the transition from the continental crust to the oceanic crust originated by the separation between South America and Africa. Medium to small wavelength anomalies are due to intracrustal heterogeneities such as different Precambrian crustal blocks, Brasiliano-age granites and Mesozoic sedimentary basins. Based on a flexural model for isostasy, a preliminar estimate was obtained of the relief of the crust-mantle interface using the topographic/bathymetric data. It was possible to delineate a zone of crustal thinning associated to the Cariri-Potiguar trend of Mesozoic intracontinental rift basins. Around the eastern border of the Parnaíba basin, a zone of relatively thick crust was also identified, possibly representing a collision suture during the Brasiliano Cycle. The isostatic residual anomaly map displays a complex pattern of anomalies, some of them implying expressive lateral density changes possibly associated with lithospheric scale shear zones and terrane sutures which make up the structural framework of the Borborema Province.
Gravimetry; Borborema Province; Crust-mantle Interface
