The crustal configuration of the West and Central African Rift System from gravity and seismic data analysis

Abstract

SUMMARYThe West and Central African Rift System (WCARS) is the only stable continental geological structure on Earth that is formed by large-scale topographic massifs (swells). However, knowledge of the origin and evolution of the WCARS remains limited mainly due to the scarcity of high-resolution geophysical observations. To better understand the crustal structure beneath the entire WCARS, we use the XGM2016 global gravitational model and the ETOPO1 global topographic-bathymetric model to determine a gravimetric Moho (crust-mantle boundary) model constrained by seismic Moho depth estimates at 41 seismological stations distributed irregularly within the study area. The result reveals a regional Moho deepening to ∼40 km beneath the Hoggar, Aïr and Tibesti Massifs. The largest Moho deepening to ∼46 km is detected beneath the Archean Congo Craton, while the Moho depth under the Adamawa Plateau reaches 42 km. The Moho geometry beneath the Chad Basin, the Chad Lineament and the Termit Basin is relatively even with the Moho depth mostly within 24–26 km. A significant Moho deepening as well as large Moho depth variations within 32–45 km beneath the Saharan Metacraton and the Congo Craton (especially under its northern margin) reflect the metacratonization processes that occurred during the Neoproterozoic. The Niger Delta and the Benue Trough are characterized by a very thin continental crust with the Moho depth varying from ∼20 km in the south along the Atlantic coastline to ∼24 km in the northeastern branch of the Cretaceous Benue Trough around the Garoua-Yola Rift.