Fig. 3. Seismic velocity in the lithosphere beneath kimberlites and lamproites.

The emplacement age ranges from⁶⁵ are indicated on the map for the different areas (dashed lines). Values of the average $\delta V_S$ over the 110–150 km depth range and within a 200-km-radius circle around each Kimberlite sample are plotted on the map (a) and as a histogram (b). $\delta V_S$ colour scale is as in Fig. 1c. The circle sizes show the lateral averaging area. Average $\delta V_S$ across all diamondiferous and unknown-diamond-content kimberlites and lamproites is shown with a red line and dot (b), with the standard deviation also shown. Average $\delta V_S$ for diamondiferous samples only is shown with a grey line and dot. Both groups present the same pattern: most are not on thick cratonic lithosphere at present. Elevation and bathymetry are plotted on panel a; plate boundaries are plotted in green.