Imaging exhumed continental and proto-oceanic crusts in the Camamu triple junction, Brazil

• Published in: Journal of South American earth sciences Vol. 126; p. 104336
• Main Authors: Loureiro, Afonso, Afilhado, Alexandra, Schnürle, Philippe, Evain, Mikael, Dias, Nuno A., Klingelhöfer, Frauke, Gallais, Flora, Pinheiro, João Marcelo, Soares, José Eduardo, Fuck, Reinhardt, Cupertino, J.A., Viana, Adriano, Corela, Carlos, Moulin, Maryline, Aslanian, Daniel
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-06-2023; Elsevier
• Subjects: Camamu triple poin; Cretaceous breakup; Crustal structure; Exhumed lower continental crust; NE Brazil; Passive margins; PSDM; SALSA; Sciences of the Universe; South atlantic ocean; Wide-angle refraction seismic; OBS; CEB; Wide-angle refraction seismic; PSDM; RTJ; Camamu triple poin; Crustal structure; JAC; Exhumed lower continental crust; NE Brazil; South atlantic ocean; TMAZ; RMO; Passive margins; SALSA; MCS; Cretaceous breakup
• ISSN: 0895-9811; 1873-0647
• DOI: 10.1016/j.jsames.2023.104336

During the SALSA experiment, in 2014, twelve combined wide-angle refraction and coincident multi-channel seismic profiles were acquired in the Jequitinhonha-Almada-Camamu, Jacuípe, and Sergipe-Alagoas basins, NE Brazil. Profile SL09 images the Almada-Camamu basin and the São Francisco craton, with 18 four-channel ocean-bottom seismometers and 22 land stations. The datasets were forward modelled and combined with pre-stack depth migration to increase the horizontal resolution of the velocity models.
Our results show that sediment thickness varies between 3.8 km in the oceanward part of the profile, 4.3 km in the Almada basin and 6.5 km in the Camamu basin. Crustal thickness at the north-western edge of the profile is of around 40 km, with velocity gradients indicating a continental origin.
The Camamu basin, which corresponds to the triple junction between the aborted N–S oriented Tucano rift, the SW-NE oriented Jacuipe-Sergipe-Alagoas branch, and the N–S Jequitinhonha-Almada branch, presents two crustal layers: a very thin upper layer, about 1.5 km thick, which increases seawards to 3 km in the Almada basin, and an higher velocity (HV) layer (6.8–7.2 km/s) about 4 km thick. This lower layer gradually disappears in the Almada basin. At the south-eastern edge of the profile, the resolution is lower but the thickness of the crust seems to increase up to 5 km. Deep wide-angle reflections indicate upper mantle stratification.
Crustal organisation and P-wave propagation velocities in the Almada and Camamu basins indicate a transitional crust domain of exhumed continental crust affinity. In the Camamu triple junction and beneath this thin exhumed continental crust, the HV layer may probably reflect intruded materials. No exhumed upper mantle is observed along the entire profile. The easternmost part of the profile may correspond to a proto-oceanic crust. Typical oceanic crust is never imaged along the 260 km-long offshore profile.
•The transitional domain in the Almada and Camamu basins has exhumed continental crust affinity.•The distal basin may correspond to a proto-oceanic domain.•Typical oceanic crust in not imaged on profile SL09.•Necking occurs within 60 km.