Lithospheric architecture of the Cameroon Volcanic Line with implications for the asynchronous melt source

Summary To understand the melt source of hotlines with asynchronous volcanoes, we investigate the lithospheric structure of the Cameroon Volcanic Line (CVL), an intraplate hotline without age progression stretching from the Atlantic Ocean into Central Africa. We analyze Bouguer gravity anomalies from the World Gravity Model 2012 using the 2-D power spectrum techniques and 2-D forward modeling to estimate the crustal and lithospheric thickness. We find: (1) thin crust (20–30 km) beneath the oceanic CVL; (2) thick crust (30–43 km) beneath the continental CVL and the Oubanguides Belt, and thicker crust (43–50 km) beneath the Congo Craton; (3) thin lithosphere (90–120 km) beneath the oceanic CVL and thinner lithosphere (75–90 km) beneath the continental CVL; and (4) thicker lithosphere (150–234 km) beneath the Congo Craton. Our seismically constrained forward models reveal a delaminated body beneath the continental CVL and a sharp transition from thick lithosphere beneath the Congo Craton to thin lithosphere beneath the Oubanguides Belt. We interpret that the thin lithosphere beneath the continental CVL is a result of lithospheric delamination. The delaminated body in the uppermost mantle deflects rising mantle plume material, resulting in the Y-shaped distribution of continental volcanoes. Edge-Driven Convection (EDC) resulting from the sharp gradient in lithospheric thickness between the Congo Craton and the Oubanguides Belt focuses the plume material beneath thin lithosphere, producing the continental CVL. The southern volcanoes of the continental CVL are formed from the southward deflection of plume material by the delaminated body, with melt ascent facilitated by the lithospheric-scale Central African Shear Zone. The northward-directed plume material forms the distinct Biu Plateau, and the eastward-deflected plume material forms the Adamawa Plateau. With a continuous influx of plume material beneath the thin continental lithosphere, for mass to be conserved, part of the plume material defiles the gradient of the thicker oceanic lithosphere adjacent to the Congo Craton to flow oceanward. The oceanward flow of plume material is modulated by upwellings from EDC, producing the oceanic CVL, which explains the oceanward decrease in the timing of the onset of volcanism. We therefore conclude that only the continental CVL lacks age progression resulting from the complex interaction of the rising plume with the delaminated body and the lithospheric architecture.