Gravimetric Study Of The Rio Grande Rise

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