Crustal structure of the Central African Plateau from receiver function analysis

SUMMARY The Central African Plateau records multiple stages of continental extension and assembly between the Congo and Kalahari cratons in south-central Africa. Of significant interest is the formation of the Neoproterozoic Katangan Basin which was subsequently closed during the Pan-African assembly of Gondwana—a region that contains some of the world’s largest sediment-hosted copper and cobalt deposits. Whether Katangan Basin development only involved continental extension or progressed to incipient sea-floor spreading is uncertain; so too the extent to which mafic magmatism has modified bulk-crustal structure. Also debated is whether crustal re-working during overprinting by the Pan-African Orogeny to form the Lufilian Arc, was localized or broadly distributed across the entire Katangan Basin. To address these questions, we calculate crustal thickness (H) and bulk-crustal $V_{P}/V_{S}$ ratio ($\kappa$) using H-$\kappa$ stacking of teleseismic receiver functions recorded by seismograph networks situated across the Central African Plateau, including the new Copper Basin Exploration Science (CuBES) network. Crustal thickness is 45–48 km below the Congo Craton margin, Mesoproterozoic Irumide belt and Domes region of the Lufilian Arc, 38–42 km below the Bangweulu Craton and 35–40 km below the Pan-African Zambezi Belt in southeastern Zambia. Bulk-crustal $V_{P}/V_{S}$ is generally low ($<$1.76) across the majority of the Plateau, indicating a dominantly felsic bulk-crustal composition. The formation of the Katangan Basin in the Neoproterozoic is thus unlikely to have been accompanied by voluminous mafic magmatism, significant lower crustal intrusions and/or the formation of oceanic crust. The early-Paleozoic overprinting of the basin by the Pan-African Orogeny, forming the Lufilian Arc, appears to have been most intense in the Domes region, where a deep and highly variable (38–48 km) Moho topography at short length scales ($<$100 km), is evident in our H-$\kappa$ stacking results. In contrast, shallow and flat Moho architecture with consistently low bulk crustal $V_{P}/V_{S}$ ratios are observed further south. This flat region includes the Mwembeshi Shear Zone, which is also not associated with a $V_{P}/V_{S}$ ratio contrast, suggesting the fault likely separates two very similar crustal domains.