Radiometric ages of laterites and constraints on long-term denudation rates in West Africa

In stable cratonic regions, most tropical weathering mantles evolve over long time scales and record long-term environmental change. They may therefore also reflect tectonism and its denudation-related signals detected through apatite fission-track thermochronology, cosmogenic radionuclide dating, and the age bracketing of laterites by (super 40) Ar/ (super 39) Ar dating of potassium- and manganese-rich oxides. Based on an existing Cenozoic pedimentation model for the West African craton, this study uses the three combined radiometric methods to define rates of Cenozoic denudation. Denudation rates of <2 m/m.y. on the lateritic plateaus, in comparison to rates of 7-13 m/m.y. adjacent to them, fit ages of 45-50 Ma for late stages of bauxite development and 24-25 Ma for one phase of lateritization. Together, they support the theory implicit in the landscape model that depths of denudation in cratonic interiors are equal to, or not significantly greater than, existing elevation differences between lateritic landforms.