ON ISOSTASY AT THE EQUATORIAL MARGIN OF BRAZIL

Ulisses T. Mello and André A. Bender
Petrobrás Research Center, Cidade Universitária, Qd 7, Ilha do Fundão, Rio de Janeiro, RJ, CEP 21910, Brazil.

Abstract

The cross-spectral method of studying isostasy was applied to profiles of free-air gravity anomalies and topography from the equatorial continental margin of Brazil. The experimental isostatic response function, or admittance, deduced in this study is compared with theoretical admittance functions predicted by a local and regional compensation mechanism. The results show that the most appropriate isostatic mechanism for this area is one in which the topography is not locally compensated. but regionally compensated by flexure of the lithosphere. Therefore, the topographic loads may be partially supported by the flexural elastic rigidity of the lithosphere. This study suggests that the effective elastic thickness of Eastern equatorial margin of Brazil is 5-10 km. Subsurface load may be present in the Pará-Maranhão region.