Deformation and evolution history of oblique Mozambique margins system

The Gondwana and particularly its south-central part encompassing Africa and Antarctica has recorded a complex rift to drift history during the mid-Jurassic. Large discrepancies between the many kinematic reconstruction models that attempted to reconstruct such an history emphasise the urgent need for a critical reappraisal. Here we combine high-resolution seismic data sets and oil company wells to propose a deformation history and an evolution scenario for the oblique Mozambique margins system from the Davie ridge area to the Agulhas fracture zone through Angoche, Beira High, Limpopo and Natal segments.

Our results indicate large differences in rifting style and magmatism, ranging from wide to narrow rifting associated with restricted and/or widespread magmatic activities (synchronous or post-rift) combined with asymmetric to more symmetrical structures. At first glance, such differences seem to be related to the African mantle plume melting triggering thermal perturbations, but the importance and the influence of inherited lithospheric structures and thick layer of sediments enhancing mantle melt extraction cannot be excluded. We propose a geodynamic model in three main stages for the evolution of the Mozambique margins, from the extension initiation to the seafloor spreading. Stage T₁, representing the first extensional event inducing crustal thinning before the Gondwana’s breakup. It is characterized by an E-W extension trend responsible for the formation of a large fault-controlled basin during the Permo-Trias (e.g. Limpopo). Stage T₂ is marked by the onset of a mantle plume activity responsible for the Karoo Large Igneous Province formation, from about 186 Ma in a cratonic and belt lithosphere. Stage T₂ is defined by NW-SE trending extension leading to mid-Jurassic basins infilling, and to a first onset of oceanic crust from Chron M33 (160 Ma) to Chron M25 (156 Ma), depending on the area. Stage T₃ corresponds to the rift continuation with a stress field rotation ranging from NW-SE to N-S, suggesting that Antarctica moved in a SSE direction with respect to Africa after 156 Ma. This change of kinematics is defined for instance, by flower structures occurrences along the Limpopo margin (i.e. Limpopo transform fault zone), and allowed for the deposition of several seaward dipping reflectors. While the Angoche and Beira High margins recorded a period of quiescence, the Limpopo and Astrid ridge areas experienced an episode of uplift and erosion probably related to mantle dynamics (e.g. mantle plume, small-convection due to the difference of thickness of the lithosphere).