Reativações rúpteis de zonas de cisalhamento Pré-cambrianas na margem continental atlântica: bacias Sergipe-Alagoas e Pernambuco

Abstract

In this research, we investigated the role of Precambrian shear zones in the formation of the Ascension and Fernando Poo fracture zones during the South Atlantic Ocean opening and the brittle reactivation of rift and postrift faults in the onshore portion of the Sergipe-Alagoas and Pernambuco basins, northeastern Brazil. We combine and interpret a dataset of aeromagnetic and topographic data, associated with a few reflection seismic and borehole data, to analyze how the Precambrian shear zones may have influenced the evolution of the Atlantic continental margin of Brazil. Our results indicate that the in the crystalline basement, the magnetic lineaments are correlated with ductile structures as shear zones, and the continuity of these lineaments towards the continent-ocean boundary is interpreted as the shear zones below the sedimentary cover of the basins. We document that the shear zones and the oceanic fracture zones have a geometric connection. The São Miguel do Aleixo and Pernambuco shear zones acted as zones of weakness controlling the location of the transform faults that evolved into the Ascension and Fernando Poo fracture zones, respectively, during the Pangea breakup. Our model suggests that the formation of the transform faults/fracture zones influenced by the shear zones occurred in the earlier stages of the ocean opening, indicating that the transform faults/fracture zones formed after the opening were probably related to the thermal subsidence stage. Furthermore, we document the following phases of basement reactivation: (1) the opening of the South Atlantic Ocean in the Early Cretaceous under an extensional stress regime and (2) tectonic inversion induced by the Mid-Atlantic Ridge push and the Andean Cordillera rise in the Neogene-Quaternary under a predominantly strike-slip stress regime. During the rift phase, the shear zone reactivations controlled the locations and architectures of the rifts. They acted as zones of weakness and were reactivated as normal faults. The reactivation was still active during the strike-slip regime at the thermal subsidence stage of the basins and was responsible for the development of compressional structures. The reverse faulting and related folding pattern indicate tectonic inversion in the Late Cretaceous-Cenozoic. These late structures are consistent with the present-day stress field, indicating that tectonic inversion is an active phase of the Brazilian margin.