Differential denudation and flexural isostasy in formation of rifted-margin upwarps

MARGINAL upwarps are common features of rifted continental margins^1,2, but tectonic models of the evolution of rifted margins have not adequately explained their form, or their persistence along some margins more than 100 Myr after continental rupture. Marginal upwarps not only significantly influence the geomorphological evolution of rifted margins and their adjacent continental interiors, but are also important in determining patterns of offshore sedimentation. Here we show that the contrast in denudation rates between the evolving coastal flanks of rifted margins and their interior hinterlands can promote significant marginal upwarps if the lithosphere responds flexurally to the resulting differential unloading^2,3. Using data for the western margin of southern Africa, we demonstrate that upwarps of 600 m with respect to the adjacent continental interior can be generated by this process independently of the mechanics of rifting.