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 Wernicke4,5, 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.