Wide-angle seismic imaging of divergent and transform segments of the Pará-Maranhão-Barreirinhas-Ceará margin, NW Brazil.

The structure of the North-East equatorial Brazilian margin was investigated during the MAGIC (Margins of brAzil, Ghana and Ivory Coast) seismic wide-angle experiment. This study focuses on the MC5 profile, that spans NW-SE 720 km in length, from the São Paulo Double Fracture Zone to the Barreirinhas margin and continental Borborema province. Its main objective is to understand the fundamental processes which lead to the thinning and finally to the breakup of the continental crust in a specific context of a divergent pull-apart system with two strike-slip borders. The experiment was devised to obtain the 2D structure along this profiles from joint pre-stack depth migration of streamer data and travel-time inversion by forward modeling of 43 Ocean Bottom Seismometers and 21 Land Seismic Stations records. Along the MC5 wide-angle transect, 4 major sectors are identified: 1) the São Paulo Double Fracture Zone presenting a 4.5 km thick volcano-sedimentary Basin on top of a 5.5 km thick basement; 2) a volcanic alignment and intermediate domain SE-ward, formed by the 4.5 km thick Basin III; 3) the 7.5 km thick Basin II, and the 5.5 km thick Basin I composing the continental slope and shelf. While all the offshore basement remains about 6 km thick in the deep-sea domains, acoustic velocity evolves from two-layer 4.8–6 km/s and 6.1–6.8 km/s beneath Basin III to two-layer high velocity 6.1–6.8 km/s and 7.2–7.4 km/s beneath Basin II and I, The necking zone, forming the Parnaiba Platform and associated Piaui-Camocim and Ceará Basins, is 50 km wide; 4) the Médio Coreaú and Ceará Central thrust belt, where the un-thinned continental crust thickness reaches 32 km. Finally, a schematic kinematic reconstruction that satisfies these observation is argumented. • The MAGIC (Margins of brAzil, Ghana and Ivory Coast) wide-angle experiment. • The North-East equatorial Brazilian margin. • A 50 km wide necking zone. • The exhumed lower continental crust. • A trapped piece of African exhumed lower continental crust. [ABSTRACT FROM AUTHOR]