Crustal Structure of the Camamu‐Almada Margin Along the Northeastern Rift Segment of Brazil From an Integration of Deep‐Penetration Seismic Reflection Profiles, Refraction, and Gravity Modeling

Abstract

AbstractThe Camamu‐Almada segment of the northeastern Brazil rifted‐passive margin covers an area of 22,000 km2 and includes: (a) thin to ultra‐thin metamorphic continental crust; (b) a transitional zone of unknown composition; and (c) Albian and younger oceanic crust. We investigate the structural‐magmatic evolution of the region by interpreting 19,000 line km of two‐dimensional reflection seismic data, 105 offshore well logs, and 15 seismic refraction stations. Interpretation of these data suggests that the 100 km‐wide rifted zone is structurally complex and composed of at least three discrete crustal blocks: (a) 10–40 km‐wide and 4–6 km‐thick zones of hyperextended continental and possibly unroofed lower continental crust with an average density of 2.88 g/cc; (b) two 20 km‐wide sub‐circular zones of exhumed mantle with an average density of 3.1 g/cc; and (c) 40–60 km‐wide and 6–7 km‐thick proto‐oceanic crust that formed in situ. These blocks are similar in thickness and composition to rifted zones described by previous workers along its conjugate margin in Gabon, West Africa, and on the rifted‐passive margin of the western Mediterranean.