Terra Nova, 24, 27–33, 2012


The Moroccan lithosphere is characterized by an anomalously thinned area, located beneath the Atlas domains, which forms a singular narrow NE–SW directed strip overlain by Cenozoic alkaline volcanism. The origin of this thinning and volcanism is still a matter of debate. The proposed models invoke processes either related to the Mediterranean slab or mantle plumes. Herein, we propose an alternative Edge-Driven Convection (EDC) model involving small-scale convection at the boundary between the West-African craton and the Atlas lithosphere. Our comparison of the Atlas lithosphere velocity and volcanism episodes during the last 80 Ma points out that volcanism occurs when plate moves at velocities c.<1 cm a−1, a velocity sufficiently low to trigger EDC. This is the first process that could explain the c. 20 Ma volcanism shutdown separating the two volcanic episodes of the Atlas. In addition, it may successfully account for the lithosphere thinning location and geometry and volcanism geochemistry.