From São Francisco Craton to Jacuipe basin, passing trough the South Tucano and Recôncavo grabens: New insights from wide-angle-MCS data.

The structure and nature of the crust underlying the Northeast Brazilian margins have been investigated based on the interpretation of 12 wide-angle seismic profiles acquired during the SALSA (Sergipe ALagoas Seismic Acquisition) experiment in 2014. In this study, we present the coincident analyses of 2 marine seismic reflection and refraction data, SL07 and SL 08, that have been acquired using 15 and 13 ocean-bottom-seismometers along each profile, offshore the Jacuipe Basin. The SL07 has a 270-km long inland continuation with 46 land-seismic-stations crossing the South Tucano and Reconcavo Basins. Wide-angle seismic forward modellings reveal a narrow necking zone, an intermediate domain with anomalously high crustal velocities interpreted as intruded lower continental crust, and a sharp continent to ocean transition zone, greatly different from the adjacent segments (see companion paper of Evain et al., 2023). Below the Tucano half-grabens, the Moho shows no rise, displaying a flat reflector throughout the landward part of the profile. The high seismic velocities areas in the lower continental crust are interpreted as intrusions that provide an overloading allowing the necessary subsidence for the deposition of the thick sedimentary sequences. Together with the recent information obtained by the analysis of continental basins and aborted rifts, and similar wide-angle experiments on other margins and geodynamic contexts, we propose new paradigm for the thinning process which confirms the crucial role of the lower continental crust and its relation with the upper mantle. We postulate a phase of overloading of the lower continental crust, an exhumation phase of the lower continental crust, and a phase of proto-oceanic crust which involved the lower continental crust and the upper mantle, before the emplacement of a more typical oceanic crust. • This study is part of the SALSA project (S ergipe AL agoas S eismic A cquisition), led by IFREMER (France) and Petrobras (Brazil). • This article focuses on two E-W profiles offshore the Jacuipe Basin, crossing onland the South Tucano and Reconcavo Basin. • Below Tucano half-grabbens, the moho shows no rise, displaying a flat reflector throughout the landward part of the profile. • Offshore, a strong E-W-segmentation is described with a very abrupt thinning and a sharp continent ocean-boundary, greatly different from the adjacent segments • The intermediate domain has anomalously high crustal velocities ans is interpreted as intruded lower continental crust. • The lower continental crust and its interactions with the mantle play a crucial role, giving rise to a new paradigm. • 3 phases implying the lower continental crust are described : overloading and subsidence, exhumation, proto-oceanic crust. [ABSTRACT FROM AUTHOR]