Interior cratonic basins of Africa: relation to continental break-up and role of mantle convection

The history of the African continent since the beginning of fragmentation of Pangaea is one of widespread rifting in the Late Jurassic to Early Cretaceous, extensive inundation under elevated Cretaceous sea-levels, widespread epeirogenic uplift beginning in the Early Tertiary and off-rift domal uplift associated with alkaline igneous activity in the Tertiary and especially in the Neogene. The cratonic basins have developed against this post break-up background, The cratonic basins of Africa are located between a relatively dense array of highspots and hotspots. Although there is a clear underlying structural fabric in the form of the Central African and West African rift systems, the present location of these basins cannot always be unequivocally linked to the presence of underlying rifts. The Congo Basin stands out as overlying a rigid rather than stretched lithosphere, and no reasonable density contrasts in the crust can explain the isostatic anomalies over the basin. Either there is a cold, dense region situated at depths typical of the upper mantle beneath the basin, or a downward-acting dynamic force on the base of the lithosphere is necessary to explain the gravity field. Together, this points to the likelihood of a convective downwelling beneath the African plate under the Congo region. The African cold-spot model may be applicable to the Early Palaeozoic cratonic basins of North America. Their location and timing of development with respect to the adjacent plate margin, size and shape may be analogous to the African examples.