New evidence for the asthenospheric origin of the Cameroon Volcanic Line from 1D shear wave velocities

Abstract

The composition of the lithosphere beneath Cameroon and the origin of the Cameroon Volcanic Line (CVL) are still debated by the Science Community. Although many studies based on regional or global observations provide good arguments for the setting of the CVL, none of them are strong enough to be considered as unique. In this work we used the joint inversion of Rayleigh wave group velocities and Rayleigh wave group velocities to provide shear wave velocity profiles of the lithosphere beneath Cameroon. Preliminary results show that lithosphere is, on average, faster beneath the Congo Craton than the Pan-African lithosphere beneath Cameroon. Due to the limited resolution of the dispersion curves, the maximum investigation depth was taken to be 200 km. The calculated velocity-depth profiles do not show any sharp discontinuity that could be interpreted as the lithosphere-asthenosphere transition. In addition there is no clear evidence of the existence of a low velocity zone beneath any geologic province within Cameroon. The smooth velocity contrasts observed on the velocity models are believed to be influenced by lateral mantle heterogeneities rather than vertical ones. The shear wave velocities for the uppermost mantle are in general greater than 4.3 km/s at all stations. This is higher than the values obtained in the Main Ethiopian Rift, and suggest that the lithosphere is not globally perturbed by thermal anomalies. This suggests that the source of volcanism along the CVL is from small scale convection in the asthenosphere and occucontrolled by lithospheric fractures that are probably driven by the cold (and fast) edge of the Congo Craton.