A Proterozoic-rift origin for the structure and the evolution of the cratonic Congo basin

Abstract

We interpret the cratonic Congo basin, a large circular “Cuvette Centrale” filled with up to 9 km of Proterozoic to Neogene sediments, as the consequence of a Neo-Proterozoic rift. Firstly, the magnitude and the long-term subsidence are consistent with the thermal time-constant of a 200–250 km thick lithosphere inferred from several tomographic studies. Secondly, the surface accumulation of sediments is compensated at depth by crustal thinning, whose magnitude can be estimated from the analysis of the surface gravity: after backstripping the effect of the sediments, a residual NW–SE positive and narrow gravity anomaly is observed across the “Cuvette Centrale” and is interpreted as the remaining crustal thinning associated with this rift. Assuming that isostasy is governed by a necking level and a flexural response to sediment loads, we have estimated the combination of the depth of necking and the equivalent elastic thickness of the lithosphere that provide the best fit with the residual gravity, i.e. 10 km and 100 km respectively. The corresponding uplift of the upper mantle is in the continuity of the Mbuji-Mayi Supergroup to the SE and the Liki-Bembian Group to the NW. These two groups represent older stages of rifting in the Congo craton, which shows that rifting has periodically affected and weakened the “Cuvette Centrale” during a long period of time.