Thick lithosphere in NE Brazil: Implication for lithospheric stretching during South Atlantic opening

The Borborema province is a mobile belt that was established at the end of the Brasiliano orogeny (600±50 Ma) as a consequence of the collision among the West African, São Luiz, Congo-Kasai and São Francisco cratons. Its basement comprises vast blocks of Archean and Paleo-Proterozoic ages. The Borborema province is crossed by several mantle-scale shear faults, with eastward extension into Africa. During the opening of the South Atlantic, the Borborema Province played a key role, initially through extensional deformation that allowed the formation of several basins, and later acting as a lock during Albian times. Indeed, its northeasternmost portion at the contact between the South Atlantic and the Equatorial Atlantic was the last to split from Africa. It has been suggested that internal block rotation provided by the shear zones absorbed deformation, and that the final split from Africa provided the connection between the Equatorial and South Atlantic oceans only after thinning of the lithosphere and oceanic rifting. With the goal to study the resistivity structure at lithospheric depths of the Borborema Province, a 3D long- period MT survey was conducted in NE Brazil in 2016 and 2017. The 3D inversion model revealed an unexpectedly resistive, therefore thick lithosphere along the continental margin of the study area, narrowing towards the SW. This finding suggests that the current Borborema continental margin endured segmented extensional deformation during the opening of the South Atlantic Ocean, and that deformation probably focused on a narrow continental block currently offshore and in select internal areas.