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

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.


NE Brazil, South atlantic ocean, Passive margins, Camamu triple poin, Wide-angle refraction seismic, PSDM, Crustal structure, Cretaceous breakup, Exhumed lower continental crust, SALSA

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Fig. S25. Microseismicity detected by the SALSA land stations. Earthquakes and quarry blasts detected by analyzing the coherent signals (Vales et al., 2014) found in the spectrograms of the land ....
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Loureiro Afonso, Afilhado Alexandra, Schnürle Philippe, Evain Mikael, Dias Nuno A., Klingelhoefer Frauke, Gallais Flora, Pinheiro Joao Marcelo, Soares José Eduardo, Fuck Reinhardt, Cupertino J.A., Viana Adriano, Corela Carlos, Moulin Maryline, Aslanian Daniel, SALSA Team (2023). Imaging exhumed continental and proto-oceanic crusts in the Camamu triple junction, Brazil. Journal Of South American Earth Sciences. 126. 104336 (24p.).,

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