History of the northeast Brazilian rift system: kinematic implications for the break-up between Brazil and West Africa

Abstract

Abstract The record of diachronic rift stages and widespread crustal deformation within the Brazilian-West African rift basins indicates changes in plate tectonics regimes and associated stress fields during the opening of the South Atlantic. Similarly to the presently active East African Rift System, the intracontinental rift basins of northeast Brazil provide a good example of an ancient intracontinental rift zone. They illustrate the three-dimensional geometries of rift systems and the control exercised by the basement structural framework, as well as important chronostratigraphic data that constrain the break-up of Gondwanaland between Brazil and West Africa. The stepwise opening of the South Atlantic led to considerable deformation, recorded in northeast Brazil as magmatic and sedimentary events, and by at least three tectonic stages, Syn-rift I, II and III. The tectonic stages are defined in northeast Brazil by discrete episodes of half-graben formation distributed over three main rift axes: (1) the Gabon-Sergipe-Alagoas trend; (2) the Reconcavo-Tucano-Jatoba trend; (3) the Cariri-Potiguar trend. Extensional deformation commenced in the Late Jurassic-early Berriasian and culminated in the late Aptian, when oceanic crust began to be emplaced between northeast Brazil and West Africa. Rift propagation is a matter of debate in the Equatorial Atlantic. It is suggested that the break-up progressed from south to north in the southern South Atlantic (Southern Branch) and concurrently from east and west in the Equatorial Branch. The rifting has been dated as Early Cretaceous (Neocomian-Barremian time) in the Southern Branch, and younger (Aptian-Albian) in the Equatorial Branch Palaeontological data indicate that these two branches intersected between northeast Brazil and Cameroon, Africa. Numerous reconstructions of the opening history of the South Atlantic have been proposed. However, most of these models are based on partial observations or an incomplete understanding of the sedimentary and tectonic record, and have resulted in derivation of improbable regional stress fields. This paper provides a regional view of a series of intracontinental rift basins in northeast Brazil, emphasizing their differences and similarities, as well as the diachronism within the equatorial and the southern basins. These basins yield substantial chronostratigraphic data that constrain the temporal and spatial interaction of the rift phases, especially during the Neocomian. Palaeostress directions for the northeast Brazilian rift basins are, even with the best available data sets, difficult to determine because different tectonic regimes can result in similarly oriented rift basins, especially in the Borborema Province, northeast Brazil, where large Proterozoic shear zones determine the pre-rift tectonic framework. Examination of this region demonstrates the results of changes in the regional kinematic framework through time and the control exercised by the extensively deformed Proterozoic continental crust of rift geometries.