Post-rift influence of small-scale convection on the landscape evolution at divergent continental margins

After decades of geological and geophysical data acquisition along with quantitative modeling of the long-term evolution of the landscape at divergent continental margins, the search for an explanation for the formation and evolution of steep escarpments bordering the coast is still a challenging task. One difficult aspect to explain about the evolution of these escarpments is the expressive variability of denudation rate through the post-rift phase observed in many margins. Here I propose that the interaction of small-scale convection in the asthenosphere with the base of the continental lithosphere can create intermittent vertical displacements of the surface with magnitude of a few hundreds of meters at the continental margin. These topographic perturbations are sufficient to produce an expressive variability in the rate of erosion of the landscape through the post-rift phase similar to the exhumation history observed along old divergent margins. I show that the vertical motion of the surface is amplified when a mobile belt is present at the continental margin, with lithospheric mantle less viscous than the cratonic lithosphere and, consequently, more prone to be partially eroded by the convective asthenosphere. I conclude that the influence of small-scale convection is not the primary explanation for the formation of high topographic features at divergent continental margins, but can be an important component contributing to sustain a preexistent escarpment. The present results are based on numerical simulations that combine thermochemical convection in the mantle, flexure of the lithosphere and surface processes of erosion and sedimentation.