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- 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.
- The limpopo magma-rich transform margin, south Mozambique: 1. Insights from deep-structure seismic imagingPublication . Watremez, L.; LEROY, Sylvie; D'Acremont, Elia; Roche, Vincent; Evain, Mikael; Lepretre, A.; Verrier, F.; Aslanian, Daniel; Dias, Nuno; Afilhado, Alexandra; Schnurle, P.; Castilla, R.; Despinois, F.; Moulin, M.A variety of structures results from the interplay of evolving far-field forces, plate kinematics, and magmatic activity during continental break-up. The east Limpopo transform margin, offshore northern Mozambique, formed as Africa and Antarctica separated during the mid-Jurassic period break-up of the Gondwana supercontinent. The nature of the crust onshore has been discussed for decades in an effort to resolve issues with plate kinematic models. Two seismic refraction profiles with coincident multichannel seismic reflection profiles allow us to interpret the seismic velocity structures across the margin, both onshore and offshore. These seismic profiles allow us to (a) delineate the major regional crustal domains; (b) identify widespread indications of magmatic activity; and (c) map crustal structure and geometry of this magma-rich transform margin. Careful examination of the profiles allows us to make the following observations and interpretations: (a) on land, continental crust is overlain by a >10-km thick volcano-sedimentary wedge related to an early rifting stage, (b) offshore, thick oceanic crust formed due to intense magmatic activity, and between the two (c) a 50-60-km wide transform zone where the crustal structures are affected by intense magmatic activity and faulting. The prominent presence of intrusive and extrusive igneous units may be attributed to the combination of a deep-seated melting anomaly and a trans-tensional fault zone running through thinned lithosphere that allowed melt to reach the surface. A comparison of the crustal thinning along other transform margins shows a probable dependence with the thermal and/or tectonic history of the lithosphere.