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FIGURE 4 Overlay of P-wave seismic velocity variations at a depth of 150 km and average Re-Os model ages for mantle samples from kimberlites distributed across southern Africa. The points show kimberlites containing mantle samples from depths of up to 200 km. The points are color coded according to the average Re-Os age for all the mantle samples studied from each individual kimberlite. The red line outlines areas of Archean crust. Within the Archean crustal section, most mantle samples give Archean ages and most diamond-bearing kimberlites are confined to the blue areas of fastest seismic velocities. The fields outlined in black show the surface outcrop of the 2.05 Ga Bushveld and Molopo Farms igneous intrusions. The one kimberlite erupted near this area (Premier kimberlite, black dot) contains mantle samples that predominantly give Re-Os ages near 2 Ga. The correlation of younger mantle ages at Premier with slower seismic velocities suggests that the Bushveld event substantially modified the mantle under this part of the ancient southern African crust. Off the Archean craton, mantle samples give only Proterozoic ages, consistent with the age of the overlying crust. The light grey lines show boundaries between crustal terranes of different ages. Tomography is from Fouch et al. (2004), and Re-Os data are summarized in Carlson et al. (2005).

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