Extended Data Fig. 6: Structure of the lithospheric keels beneath South Africa.

a, The Limpopo Belt area⁵. The section shows an ultradepleted layer from 140–180 km depth, overlain by a more fertile layer with high X_Mg^Oliv (refs. ^5,29,30). The deeper part is moderately melt-metasomatized with the introduction of Al and Fe, corresponding to sheared lherzolites, but chromite is most abundant at 170–190 km depth, and the depleted root may originally have extended to depth of about 210 km. Van der Meer et al.⁸³ have verified the structure with xenolith studies and suggest that the two layers have distinct provenances. b, The northern Lesotho area. Harzburgites are mostly confined to the more fertile layer (high Al₂O₃) above 120 km, but the section is dominated by depleted lherzolites from 140–180 km depth, and the base is marked by a dominance of lherzolites produced by intense melt-related metasomatism. c, The northern Botswana area. A relatively depleted (but mainly lherzolitic) section from 120–190 km depth is overlain by more fertile (higher-Al₂O₃) rocks, but with similarly high X_Mg^Oliv more characteristic of depleted rocks. This suggests that the upper layer in this case represents the refertilization of a depleted section, rather than a separate unit.