Drainage system organization after mantle plume impingement: The case of the Horn of Africa

Continental areas affected by mantle plume dynamics are characterised by extensive high-elevated regions drained by large radial river networks. Despite successive isostatic adjustments and rifting events, several studies demonstrated that the persistence of these drainage systems for tens of millions of years is possible. In these geodynamic contexts rivers are precious sources of knowledge because, propagating the signals of tectonic and climatic changes across landscape, they shape the topography and allow to recognise the first-order imprint imposed by mantle plume. The Horn of Africa, characterised by the coexistence of a continental rift system, a large igneous province (continental flood basalts), and a wide uplifted plateau, is an ideal test site to investigate the interrelations between surface and deep processes. Studies demonstrated the long-term persistence of some river networks draining the region and the strong influence of dome-like uplift on their evolution. However a regional-scale quantitative river network analysis is missing, as well as, a complete evolutionary scenario of the Horn of Africa drainage system. In this study we quantitatively investigated the topographic configuration of the Horn of Africa and analysed the four principal drainage systems (Blue Nile, Tekeze, Omo, Wabe Shebele basins), extracting the river longitudinal profiles and the main topographic and hydrologic parameters. In order to reconstruct the evolution of the region, we elaborated the pre /syn- and post-flood basalts topographies and calculated the elevation gain and loss with respect to the present configuration. Finally, we delineated a possible future drainage system evolution by analysing the present drainage divides stability. The results allowed to reconstruct the evolutionary scenario of the Horn of Africa river network since Oligocene and to investigate the mutual influence between surface and deep processes in shaping the landscape, providing new constraints to understand the formation and evolution of a drainage system in a context of a topography supported by a mantle plume.