The role of tectonic inheritance in the development of a fold-thrust belt and superimposed rift : an example from the São Francisco basin, eastern Brazil.

Abstract

The Sao ̃ Francisco intracratonic basin, eastern Brazil, hosts multiple sedimentary successions younger than 1.8Ga that witnessed major plate reorganizations since its generation. During the Brasiliano/Pan-African Gondwana amalgamation, in the Ediacaran-Cambrian boundary, the western half of the basin was involved in the Brasília foreland fold-thrust belt, which propagated eastwards deforming its Proterozoic-Paleozoic strata. Lately, as the South Atlantic rift evolved giving rise to the Brazilian continental margin, the basin was affected by extensional tectonism leading to the development of the Cretaceous Abaet ́e half-graben. During this episode, elements related to a prominent structure of the Brasília foreland fold-thrust belt, the Joao ̃ Pinheiro fault, were reactivated controlling the graben architecture. Aiming to unravel the evolutionary history of the fault zone since its nucleation until its Cretaceous extensional reactivation, we conducted a structural investigation based on field, well-tied 2D seismic data, and paleostress analysis. Our study revealed that the fault represents an emergent ramp of the basal detachment of the Brasilia foreland fold-thrust belt. Formed under EW-oriented shortening, the structure exhibits a gentle recces-salient geometry in map view, which reflects variations in the detachment depth influenced by pre-orogenic rift structures. Trains of NS-trending chevron folds are abundant and their high symmetry and dominance are expressions of the control exerted by mechanical stratigraphy and low-friction

basal detachment. The superposed Abaet ́e half-graben developed under an extensional regime with a NE- trending maximum extension. Under this condition, a stratigraphic interface along the Joao ̃ Pinheiro fault

zone was reactivated giving rise to the graben border fault. NS- to NW-oriented preexisting bedding planes were activated as small normal faults. Although newly-formed faults are present, reactivation is the most effective mechanism of extension accommodation. Therefore, this study provides insights on the influence of tectonic inheritance on the architecture, deformation pattern, strain/stress partitioning and evolution of both extensional and compressional intracontinental systems.