Quantifying passive margin denudation and landscape development using a combined fission-track thermochronology and cosmogenic isotope analysis approach

A new approach to empirically constraining numerical models of denudation and landscape development across passive continental margins is presented involving a combination of apatite fission-track thermochronology and cosmogenic isotope analysis. This integrated strategy is applied to the Namibian sector of the south-west African margin where the conventional landscape evolution model of inland retreat of an escarpment initiated at the coast at break-up implies a mean rate of retreat of ∼1 km Ma−1. The thermochronological and cosmogenic isotope data are incompatible with a simple escarpment retreat model since they show that denudation rates oceanward of the present escarpment position have been low (<20 m Ma−1) since the end of the Eocene, and the estimated rate of escarpment retreat has been only ∼10 m Ma−1. This low rate of retreat is, however, consistent with numerical landscape evolution models where the escarpment is pinned at an inland drainage divide.