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- Imaging exhumed lower continental crust in the distal Jequitinhonha basin, BrazilPublication . Loureiro, Afonso; Schnürle, P.; Klingelhoefer, Frauke; Afilhado, Alexandra; Pinheiro, J.; Evain, Mikael; Gallais, F.; Dias, Nuno; Rabineau, Marina; Baltzer, A.; Benabdellouahed, M.; Soares, J.; Fuck, R.; Cupertino, J. A.; Viana, Adriano Roessler; Matias, Luis; Moulin, Maryline; Aslanian, D.; Morvan, L.; Mazé, J. P.; Pierre, D.; Roudaut-Pitel, M.; Rio, I.; Alves, D.; Júnior, P. Barros; Biari, Youssef; Corela, C.; Crozon, J.; Duarte, J. L.; Ducatel, C.; Falcão, C.; Fernagu, P.; Lima, M. Vinicius Aparecido Gomes de; Piver, D. Le; Mokeddem, Z.; Pelleau, P.; Rigoti, C.; Roest, W.; Roudaut, M.Twelve combined wide-angle refraction and coincident multi-channel seismic profiles were acquired in the Jequitinhonha-Camamu-Almada, Jacuípe, and Sergipe-Alagoas basins, NE Brazil, during the SALSA experiment in 2014. Profiles SL11 and SL12 image the Jequitinhonha basin, perpendicularly to the coast, with 15 and 11 four-channel ocean-bottom seismometers, respectively. Profile SL10 runs parallel to the coast, crossing profiles SL11 and SL12, imaging the proximal Jequitinhonha and Almada basins with 17 ocean-bottom seismometers. Forward modelling, combined with pre-stack depth migration to increase the horizontal resolution of the velocity models, indicates that sediment thickness varies between 3.3 km and 6.2 km in the distal basin. Crustal thickness at the western edge of the profiles is of around 20 km, with velocity gradients indicating a continental origin. It decreases to less than 5 km in the distal basin, with high seismic velocities and gradients, not compatible with normal oceanic crust nor exhumed upper mantle. Typical oceanic crust is never imaged along these about 200 km-long profiles and we propose that the transitional crust in the Jequitinhonha basin is a made of exhumed lower continental crust.
- Deep structure of the North Natal Valley (Mozambique) using combined wide-angle and reflection seismic dataPublication . Lepretre, A.; Schnurle, P.; Evain, Mikael; Verrier, F.; Moorcroft, D.; Clarens, P. de; Corela, C.; Afilhado, Alexandra; Loureiro, Afonso; LEROY, Sylvie; D'Acremont, Elia; Thompson, J.; Aslanian, D.; Moulin, MarylineThe North Natal Valley (NNV) and the Mozambique Coastal Plain (MCP) are key areas for the understanding of the SW Indian Ocean history since the Gondwana break-up. Nevertheless, the deep structures and the nature of the NNV and MCP remain discussed in the absence of deep geophysical data. In 2016, the NNV, MCP and Limpopo margin (LM) have been investigated along seven wide-angle and MCS profiles. The combined wide-angle and reflection seismic interpretation along the N-S MZ7 profile reveals an upper sedimentary sequence characterized by low velocities generally not exceeding 3 km/s, with thicknesses varying from 0.150 km in the central part to similar to 2.8 km in the south. The underlying sequence is formed of a 2.53.0 km thick volcano-sedimentary sequence which presents important lateral and with depth changes and presence of high velocity lenses, indicating inter-bedded volcanic sills and recurrent magmatic episodes. The south of the NNV including the Naude Ridge (NR) presents a disturbed sedimentary cover with structural highs and southward-dipping reflectors and sub-basins. The crust, reaching 35-40 km onshore below the MCP, gently thins below the continental shelf to a regular thickness of similar to 29 km below the NNV. Crustal velocities reveal low velocity gradients, with atypical high velocities. South the ND, the crust thins to 15 km. We interpret the velocity architecture combined with the evidences of volcanism at shallower depths as indicating an intensively intruded continental crust. Contrary to what is proposed in most geodynamic models, the Mozambique Coastal plain and the Natal Valley are both of continental nature, with an abrupt necking zone located south of NR. The Antarctica plate was therefore situated at the eastern limit of these two domains before the Gondwana breakup.