MESOZOIC SOUTH-ATLANTIC OCEAN AND EVOLUTION OF ITS CONTINENTAL MARGINS

Gravity and magnetic anomalies bordering the continental margins of the S S Atlantic Ocean are compared, in detail, on conjugate sides of the ridge crest, and a model for the boundary between oceanic and continental basement is given. The area of study includes the predominantly sheared margins of the Agulhas-Falkland fracture zone, and the rifted margins of Argentina and S Africa S of the Rio Grande Rise and Walvis Ridge, respectively. These margins have associated with them, for the most part, linear magnetic anomalies that can be modeled as edge effect anomalies separating oceanic from continental basement. Coincident with the magnetic anomalies are gradients in the isostatic gravity anomaly. We have taken the location of these geophysical lineaments on the African margin and rotated them clockwise to fit the anomalies on the Argentine margin. This fit, which gives us a new pole of total closing for the S Atlantic Ocean, obviates, for the most part, the gaps and overlaps observed in other reconstructions. The improved fit thereby suggests rigid plate behavior and minimum stretching of continental crust during the early opening of the S S Atlantic Ocean.-Authors