Crustal detachment during South Atlantic rifting and formation of Tucano—Gabon basin system

Abstract

A series of major sedimentary basins of Mesozoic to Tertiary age are associated with the Brazilian continental margin between 8° and 14° S (Fig. 1). This passive continental margin formed when Africa and South America split apart with the initiation of seafloor spreading in the Aptian/Albian³. The offshore basins which border the continental margins on both sides of the Atlantic show evidence of both rifting and crustal attenuation before break-up and thermal subsidence after it. In contrast, a combined stratigraphical and gravity study of the Brazilian onshore basins, which are separated from the offshore basins by a northward-widening strip of Precambrian, suggests that up to 7 km of non-marine sediments were deposited during the rifting stage of the South Atlantic, with no apparent extension of the lower crust beneath these basins and no subsequent thermal subsidence. A mechanism for the linked development of these onshore and offshore basins is proposed here along the lines suggested by Wernicke^4,5, in which upper crustal extension in the onshore region is connected to, and balanced against, deeper lithospheric extension beneath the incipient passive margin by intracrustal detachments.