Mantle seismic structure beneath the Kaapvaal and Zimbabwe Cratons

We present results of seismic tomography for a broad region of southern Africa using data from the seismic component of the Kaapvaal Project, a multinational, multidisciplinary experiment conducted in the late 1990s. Seismic images provide clear evidence of mantle structures that mimic the surface geology across the region and provide important constraints on subcrustal structure associated with Archean cratons. Specifically, a thick (~250 to 300km) mantle keel exists beneath the Kaapvaal craton; a slightly thinner (~225 to 250km) keel exists beneath the Zimbabwe craton and parts of the Archean Limpopo mobile belt. Mantle velocities lower than surrounding regions are evident across a broad swath beneath the surface expression of the Bushveld Complex, a ~2.05 Ga layered mafic intrusion. These reduced velocities may be due to mantle refertilization during intrusion of Bushveld magmas, or they may be caused by a thermal perturbation of more recent origin, perhaps related to the ~183 Ma Karoo magmatic event.