Crustal structure of the southeastern Brazilian margin, Campos Basin, from aeromagnetic data: New kinematic constraints

Abstract

The continental and adjacent marginal features along southeast Brazil were investigated, focusing on the basement structural relationships between onshore and offshore provinces. Lateral and vertical variations in the magnetic anomalies provided a good correlation with the regional tectonic features. The sin-rift dykes and faults are associated with the magnetic lineaments and lie sub parallel to the Precambrian N45E–S45W basement structure of the Ribeira Belt, but orthogonally to the Cabo Frio Tectonic Domain (CFTD) basement, implying that: (1) the upper portion of the continental crust was widely affected by Mesozoic extensional deformation; and (2) tectonic features related to the process of break up of the Gondwana at the CFTD were form regardless of the preexisting structural basement orientation being controlled by the stress orientation during the rift phase. The deep crustal structure (5 km depth) is characterized by NE–SW magnetic “provinces” related to the Ribeira Belt tectonic units, while deep suture zones are defined by magnetic lows. The offshore Campos structural framework is N30E–S30W oriented and resulted from a main WNW–ESE direction of extension in Early Cretaceous. Transfer zones are represented by NW–SE and E–W oriented discontinuities. A slight difference in orientation between onshore (N45E) and offshore (N30E) structural systems seems to reflect a re-orientation of stress during rifting. We proposed a kinematical model to explain the structural evolution of this portion of the margin, characterized by polyphase rifting, associated with the rotation of the South American plate. The Campos Magnetic High (CMH), an important tectonic feature of the Campos Basin corresponds to a wide area of high crustal magnetization. The CMH wass interpreted as a magmatic feature, mafic to ultramafic in composition that extends down to 14 km depth and constitutes an evidence of intense crustal extension at 60 km from the coast.