Influence of Hotspot Magmatism on Breakup Modes and Oceanic Crust Architecture Along a Passive Margin: Insights From Mauritania/Senegal/Guinea Basin

Abstract Passive margins architecture, and thus processes leading to breakup, can vary considerably under the influence of thermal vertical forces/magmatism and mechanical horizontal forces, both being necessary for a rift to succeed. A dense seismic data set, acquired along the Mauritania/Senegal/Guinea (MSG) Basin, provides detailed images of the continent‐ocean transition and oceanic crust architecture, allowing to decipher its architecture. South Central Atlantic breakup occurred around 190 Ma while the Central Atlantic Magmatic Province (CAMP) activity was ending. Five oceanic/magmatic crust facies are described and mapped. In the north, seismic data suggest a typical magma‐poor margin profile with an extremely thinned continental crust and mantle exhumation at the Continent‐Ocean Transition (COT). It is followed by a westward progressive increase in magmatism. In the south, the continental crust thinning is associated with Seaward Dipping Reflectors (SDRs) emplacement, and a thick magmatic crust emplaced in the distal domain, which is typical of magma‐rich margins. A 9–11 km thick magmatic crust is observed directly westward. Locally, a peculiar facies, with intra‐oceanic SDRs, is observed and correlated with the formation of the African Blake Spur Magnetic Anomaly (ABSMA). Therefore, in the south, the breakup was forced through the continental crust due to the remnant activity of a CAMP derived hotspot. In the north, the magmatic input seems directly linked to the plate motion except for the ABSMA during which, despite a brief and sudden acceleration of the plate motion, variations in ambient mantle temperature are needed to explain the change in oceanic crust thickness and facies.