African cratonic lithosphere carved by mantle convection

How cratons, the ancient cores of continents, evolved since their formation over 2.5 billion years ago is a matter of a long-standing debate. Seismic tomography maps high-velocity anomalies associated with the characteristically cold, thick lithosphere of cratons, but its resolution is only beginning to reach relevant regional tectonic scales, in particular in sparsely sampled continents. Here we use waveform inversion of a very large, newly available dataset and compute a tomographic model of Africa that reveals a much more complex and fragmented cratonic lithosphere than previously observed. Most known diamondiferous kimberlites, indicative of thick lithosphere at the time of eruption, occur where the lithosphere is relatively thin today, implying surprisingly widespread lithospheric erosion since 200 Ma. The timing and location of the erosion rule out subduction and rifting as its sole mechanisms. Emplacement of Large Igneous Provinces (LIPs) near most root-loss locations suggest the impact of thermo-chemical plumes from the deep mantle as a key mechanism. However, LIPs can pre-date the loss of the lithospheric root by tens of million years, which requires a complex erosion mechanism, with weakening of the roots by plumes (and, possibly, rifting) followed by subsequent removal by regional mantle convective processes. Our results indicate that the total volume of cratonic lithosphere has decreased substantially since its Archean formation, with the fate of each craton probably depending on its plate-tectonic movements relative to mantle plumes.