The Volcanic Outer High of Campos Rifted Margin in Southeast Brazil: The structure and formation of SEMA

Abstract

The SEMA (South East Magnetic Anomaly) is a high amplitude magnetic lineament in the most distal part of the Campos Rifted Margin in Southeast Brazil. It runs continuously from south to north along 85 km reaching 500 nT in deep waters. The aim of this paper is to investigate the structure, stratigraphy and nature of the SEMA, and to discuss its significance for the evolution of the margin. Based on seismic, magnetic and gravity analysis, we interpret the SEMA as a volcanic outer high. Its formation was prior to the salt migration oceanwards, probably earlier to the breakup, constraining a time-relative formation in the Late Aptian - Early Albian. It is bounded by a basinward dipping, large-scale fault that created a huge depocenter continentwards. The Volcanic Outer High of the SEMA marks the transition to a distinct tectonostratigraphic compartment and salt domain, characterized by intense halokinesis, significant thinning and modification of the pre-salt sequences, and increasing presence of volcanic and intrusive rocks. It forms a long volcanic ridge in the external boundary of the Campos Rifted Margin, which may have influenced the paleo-circulation. Moreover, its understanding could provide new insights into the breakup process.