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Early Cretaceous Rifting in Northeast Brazil: Chronology, Basin Geometry and Tectonics
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 3rd International Congress of the Brazilian Geophysical Society, Nov 1993, cp-324-00242
Abstract
The intracontinental rift basins of northeast Brazil constrain the chronology of breaking up the Gondowanaland between Brazil and West Africa. Besides constraining the timing of rifting, the basins demonstrate that during early stages of rifting, diffuse intraplate deformation may accommodate regional extension, as illustrated by the widespread distribution of rift basins, up to 600 km westwards from the actual passive margin. The basin distribution and geometry were basically controlled by the previous basement structural framework and by rifting kinematics, related to the spatial interaction between the Southern and Equatorial branches of the South Atlantic rift system. The northeast Brazilian rift basins show clear chronologie and tectonic links to progressive deformation that migrated, from south to north, in the Southern branch. Three syn-rift stages are associated with the rift evolution of the Southern branch, distinguished based upon the structural style and basin-fill characteristics. The main rift stage took pIace during the Neocomian-early Barremian Time, with the development of three main rift valleys: (1) the Gabon-Sergipe Alagoas trend (GSA),(2) the Reconcavo-Tucano-Iatoba trend (RTJ),and (3) the Carirl-Potiguar trend (CP).The influence of preeristing crustal weakness, a Proterozoic heritage, is demonstrated by the megashear zones of the Pernanbuco (Brazil) and Ngaundere (Africa), which behav~d like a huge accommodation zone, balancing ertensionat deformation along the RTJ e GSA trends with simultaneous enenslon along the CPtrend. The basins are typically 20-45 km wide, controlled by NESW trending normal faults, roughly perpendicular to the main extension direction. A major change in rifting kinematics occurred during the Neocomian when early rifting deformation developed in the eastern equatorial domain, meanwhile the CP trend was aborted, and the southern branch had the main stretching phase. During the Aptian, rifting occurred throughout the Equatorial branch and Benue trough (Africa), while a transitional eyaporitic sequence developed in the Southern branch (GSA),-and the RTJ trend was aborted. An Albian-Cenozoic marine drift megasequence overlies the northeast Brazilian rift basins eccept by the RTJ trend and some of the CP basins.