The Cameroon Volcanic Line Triggered by Spontaneous Gravitational Instability of the Lithosphere at the Margin of the Congo Craton

Over geological timeframes, cratons generally exhibit low rates of surface erosion, a feature attributed to their neutral buoyancy. Nevertheless, certain continental regions—most prominently Africa—feature exceptionally elevated topographic features along numerous craton margins. Associated magmatic activity in such areas can endure for more than 66 million years (Ma), as exemplified by the Cameroon Volcanic Line (CVL) bordering the Congo Craton, though its genetic mechanism remains a subject of intense debate. In this study, we demonstrate that sustained uplift of the CVL at the cratonic margin is driven by Rayleigh-Taylor instability, triggered by a sharp lithospheric boundary generated during the Cretaceous rifting of the Benue Trough—a rift basin situated northwest of the CVL. Seismic observations and geodynamic analyses focused on the CVL have uncovered processes of lithospheric dripping and asthenospheric upwelling, which align with this instability-driven mechanism. Finite element simulations further reveal that the lithosphere in this region possesses a density excess of approximately 25–30 kg/m³ relative to the asthenosphere. This density difference enables convective removal of the lithosphere following rifting, thereby inducing localized magmatism and surface uplift. Critically, the inferred lithospheric viscosity (7.0×10²¹ Pa∙s) allows this instability to persist for at least 66 Ma—six times longer than the duration of typical subduction-associated instability events. These findings challenge conventional paradigms by showing that cratons along passive margins are capable of undergoing long-lived, plume-independent deformation. This points to a robust coupling between the Earth’s upper mantle and its surface, which regulates volcanic and tectonic processes over surprisingly extended timescales.