Effective elastic thickness of Africa and its relationship to other proxies for lithospheric structure and surface tectonics

Detailed information on lateral variations in lithospheric properties can aid in understanding how surface deformation relates to deep Earth processes. The effective elastic thickness, T-e, of the lithosphere is a proxy for lithospheric strength. Here, we present a new T-e map of the African lithosphere estimated from coherence analysis of topography and Bouguer anomaly data. The latter data set derives from the EGM 2008 model, the highest resolution gravity database over Africa, enabling a significant improvement in lateral resolution of T-e. The methodology used for T-e estimation improves upon earlier approaches by optimally combining estimates from several different window sizes and correcting for an estimation bias term. Our analysis finds that T-e is high, similar to 100 km, in the West African, Congo, Kalahari and Tanzania cratons. Of these, the Kalahari exhibits the lowest T-e. Based in part on published seismic and mineral physics constraints, we suggest this may reflect modification of Kalahari lithosphere by anomalously hot asthenospheric mantle. Similarly, the Tanzania craton exhibits relatively lower T-e east of Lake Victoria, where a centre of seismic radial anisotropy beneath the craton has been located and identified with a plume head, thus suggesting that here too, low T-e reflects modification of cratonic lithosphere by an underlying hot mantle. The lowest T-e in Africa occurs in the Afar and Main Ethiopian rifts, where lithospheric extension is maximum. In the western Ethiopian plateau a local T-e minimum coincides with published images of a low P and S seismic velocity anomaly extending to similar to 400 km depth. Finally, the Darfur, Tibesti, Hoggar and Cameroon line volcanic provinces are characterised by low T-e and no deep-seated seismic anomalies in the mantle. Corridors of relatively low T-e connect these volcanic provinces to the local T-e minima within the western Ethiopian plateau. We interpret the low T-e to indicate thinner lithosphere within the corridors than in the surrounding cratons. We speculate that these corridors may provide potential conduits for hot asthenospheric material to flow from the western Ethiopian plateau to the volcanic provinces of central and western Africa. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.