What does it link the surface to the deep Earth’s processes? The tectonic evolution of the Congo basin: an example of intracratonic basin

Abstract

The origin of the intracratonic basins (ICBs) is still highly debated and several hypotheses have put forward to explain their long-lasting subsidence, characterized by prolonged intervals of low rate subsidence alternating with episodic accelerations in subsidence rate (e.g., Hartley & Allen, 1994). The Congo basin (CB) is a natural laboratory for investigating the processes that govern the long–term evolution of the ICBs, due to its long tectonic history, during which a large thickness of sediments deposited (up to about 9 km). Its subsidence initiated very probably as a failed rift in late Mesoproterozoic and evolved during the Neoproterozoic and Phanerozoic under the influence of far-field compressional tectonic events, global climate fluctuation between icehouse and greenhouse conditions and drifting of Central Africa through the South Pole then towards its present-day equatorial position (Delvaux et al., 2021). We reconstructed the depth of the basement and of main sedimentary layers of the CB, by integrating the interpretations of almost 3000 km of seismic reflection profiles with the analysis of the gravity field. The obtained results show a very heterogeneous basement depth, characterized by a series of topographic highs and lows NW-SE oriented (Delvaux et al., 2021; Maddaloni et al., 2021). We further observed the migration of the sedimentary depocenters from the Proterozoic to Jurassic times and lateral thickness variations of the sedimentary layers. Both types of observations reflect a different behavior of the CB during the stages of its evolution, with a progressive decrease in the influence of the initial rift structure. The rift phase that gave origin to the CB has been simulated applying multidirectional slow divergent velocities to a cratonic block having a central weak zone, representing the suture area between the cratonic pieces composing the Congo craton. The numerical models, after a time lapse of 200 Myr, show the formation of a central circular subsided area, as effect of the radial extension, induced by the asthenosphere upwelling. The main structures, formed within the depressed topographic area, resemble the present-day basement depth of the CB, supporting the hypothesis that the origin of some ICBs can be due to the effect of multi-extensional stress applied on a cratonic area.