Gravimetric Study Of The Rio Grande Rise

Abstract

Within the South Atlantic oceanic basin, along the southeastern Brazilian continental margin, is located one of the largest bathymetric features of the Atlantic, the Rio Grande Rise. It is the scope of this work to map the Rio Grande Rise and the Rio Grande Rise rift by which it is cut. The Rio Grande Rise rift can be related to the Southern Cross gravity anomaly, a large NW-SE gravity anomaly found in the South Atlantic, associated to an Eocene deformational event (Sousa, 1991). According to Sousa, the Southern Cross gravity anomaly is a fracture zone. A better understanding of this deformational event has been achieved by revisiting the Southern Cross gravity anomaly with improved gravimetric data. The Southern Cross gravity anomaly appears as a combination of the gravimetric effects of the Rio Grande Rise rift and various seamounts, including the Jean-Charcot seamounts (Aguiar, 1997). We used free-air gravity anomalies obtained from altimetric data of the Geosat-GM satellite to calculate the horizontal gradient of the free-air gravity anomalies. The horizontal gradient was then used in conjunction with the free-air gravity anomalies to map the main bathymetric features in the area, establishing the relationship between the Rio Grande Rise rift, the Southern Cross Deformational event, the Jean-Charcot seamounts and the fracture zones in the area.