Extended Data Fig. 10: Changing chemistry of kimberlites in the Kaapvaal Craton from 150 to 85 Ma.
From: Rift-induced disruption of cratonic keels drives kimberlite volcanism
a, Interpolated Ti contents of garnet xenocrysts (modified after ref. 40) at 117 and 108 Ma, showing the effects of heating and chemical refertilization of the lower lithosphere by asthenospheric melts, thinning the lithosphere by 30–40 km (vertical grey field). Below this are the chemical compositions of group II kimberlites (orangeites/lamproites) and group I kimberlites, specifically whole-rock (87Sr/86Sr)i (b), whole-rock (143Nd/144Nd)i (c) and whole-rock (206Pb/204Pb)i (d); these data are revised from Smith50. e, (87Sr/86Sr)i of kimberlitic perovskites from Woodhead et al.103. The plot shows the MARID endmember defined from kimberlite xenoliths and thought to derive from a lithospheric mantle source105, and a kimberlite melt endmember105 largely defined from analyses of PIC kimberlite xenoliths. f, Whole-rock ϵNd calculated from the data of Nowell et al.104. The lines on the plots show the statistically defined change points (using CPR; Methods) and two-sigma uncertainty bounds of the two averages (thin red lines) before and after the change point. Step changes occur at 114 Ma (dashed vertical line) for all variables, except (143Nd/144Nd)i, which occurs between 114 and 100 Ma, and ϵNd, which occurs between 118 and 114 Ma. Continent-scale metasomatism occurred before 114 Ma (ref. 109), raising the possibility that migrating chains of convective instabilities (Fig. 2) partially stripped and melted the lithospheric keels, driving infiltration (that is, melt metasomatism) of carbonate melts that caused further destabilization.
