Lithospheric structure across the Adamawa plateau (Cameroon) from gravity studies

The Adamawa volcanic uplift in central Cameroon forms the eastward termination of the Cameroon Volcanic Line (CVL) in West-Central Africa. This line is unique among intra-plate volcanic provinces in that it straddles a continental margin and has both oceanic and continental volcanic centres. The age of these volcanoes ranges from Tertiary to Recent and there is no apparent age progression along the length of the line. The Adamawa plateau is characterised by altitudes ranging from 800 m in its northern part to 1200 m in its southern part. The uplift is characterised by a long-wavelength negative Bouguer anomaly similar in shape and amplitude to those of other African basement uplifts. A gravity profile derived from the Bouguer gravity map of Cameroon, perpendicular to the anomaly associated with the uplift shows a broad negative and an axial positive Bouguer anomaly. This profile is used as a basis for a 2D gravity modelling. The broad negative and central positive anomalies beneath the Adamawa uplift are interpreted as a consequence of lithospheric thinning (40 km) and crustal thinning (10 km), respectively. Compared to the Kenya dome, the Adamawa uplift may be in an early stage of continental rifting, along the site of a pre-existing basement weakness, the Central African Shear Zone (CASZ). This shear zone has acted as a major pathway for magmas to reach the surface.