Crustal structure of the East-African Limpopo Margin, a strike-slip
rifted corridor along the continental Mozambique Coastal Plain and
North-Natal Valley
Authors: Evain Mikael , Schnürle Philippe , Leprêtre Angélique , Verrier Fanny , Watremez Louise , Thompson Joseph Offei , de Clarens Philippe , Aslanian Daniel , Moulin Maryline 
Published: February 2021

Abstract. Deep seismic acquisitions and a new kinematic study recently highlighted the presence of continental crust in both the southern Mozambique's Coastal Plain (MCP) and further offshore in the North Natal Valley (NNV). Such findings falsify previous geodynamic scenarios based on the kinematic overlap between Antarctica and Africa plates, thus profoundly impacting our understanding East-Gondwana break-up. Using an updated position of Antarctica with respect to Africa this study reconsider the formation mechanism of East-African margins and most specifically of the Limpopo margin (LM). Coincident wide-angle and multi-channel seismic data acquired within the PAMELA project are processed to image the sedimentary and deep crustal structure along a profile that runs from the northeastern NNV to the Mozambique basin (MB) striking through the LM. This dataset is combined with companion deep seismic profiles and industrial onshore-offshore seismic lines to provide a robust scenario for the formation and evolution of the LM. Our P-wave velocity model consists of an upper sedimentary sequence of weakly compacted sediments including intrusions and lava flows in the NNV while contourites and mass transport deposits dominates the eastern edge of the LM. This sequence covers a thick acoustic basement that terminates as a prominent basement high just west of the contourites and mass transport deposits domain. The acoustic basement has a seismic facies and velocity signature typical of a volcano-sedimentary basin and appears widespread over our study area extending toward the eastern MCP and NNV. Based on industrial well logs that calibrate our tectono-stratigraphic analysis we constrain its age to be pre-Neocomian. We further infer that either strike-slip or trans-tensional deformation occurred at the basement high which sustained uplift up to the Neocomian. At depth, the crystalline basement and uppermost mantle velocity structures show a progressive eastward crustal thinning of continental crust along the edge of the MCP/NNV and up to the location of the basement high. On its eastern side, however, a corridor of anomalous crust depicts the velocity signature of a volcanic basement overlying lower continental crust. We infer that strike-slip rifting along the LM was accommodated at depth by ductile shearing responsible for the thinning of the continental crust and an oceanward flow of lower crustal material. This process was accompanied by intense magmatism that extruded to form the volcanic basement and gave to the corridor its peculiar structure and mixed nature. The whole region remained at a relative high level and a shallow marine environment dominated during this period. Only after break-up in the MB decoupling occurred between the MCP/NNV and the corridor allowing for the latter to subside and being covered by deep marine sediments. We provide new insights into the early evolution and formation of the LM that takes into account both kinematic and geological constraints. This scenario favors strike-slip rifting along the LM meaning that no changes in extensional direction occurred between the rifting and the opening of the MB.