Mesozoic evolution of NW Africa: implications for the Central Atlantic Ocean dynamics

The Central Atlantic Ocean opened during the Early Jurassic and represents the oldest portion of the Atlantic Ocean. Although the American margin has been well studied, the onshore evolution of its African counterpart is poorly understood. We investigated the evolution of a c. 1300 km transect across the Reguibat Shield (Morocco, Mauritania, Algeria) in the northern West African Craton using low-temperature thermochronology. Fourteen samples were dated using apatite fission-track analysis. Nine of these samples were also dated using (U–Th–Sm)/He analysis. Fission-track ages range from 118 ± 10 to 497 ± 61 Ma, with mean track lengths between 11.2 ± 0.4 and 12.5 ± 0.2 µm. (U–Th–Sm)/He single-grain ages range from 32 ± 3 to 396 ± 32 Ma. Through forward and inverse thermal modelling, we demonstrate that the craton underwent kilometre-scale exhumation between the Early–Middle Jurassic and the Late Cretaceous. Based on our new results, published data on NW Africa and data from the conjugate eastern North American passive margin, we show that this post-rift Early–Middle Jurassic to Early Cretaceous exhumation affected both margins to a similar areal extent and simultaneously. Transient mantle dynamic support is suggested to account for the major erosional phase recorded on both margins.