Kaapvaal craton peridotite xenoliths

Figure 38 Nd-Sr isotope variation of clinopyroxenes and garnet in peridotite xenoliths. (a) Compares cratonic and noncratonic peridotite xenoliths with continental crust. Inset shows restricted field for oceanic mantle. Arrow points to a peridotite from Lashaine, Tanzania, that lies at an Sr/ Sr value of 0.83. (b) Compares cratonic peridotites from the Kaapvaal, Wyoming, and Siberian cratons.

Bedini R. M., Blichert-Toft J., Boyet M., and Albarede F. (2002) Lu-Hf isotope geochemistry of garnet-peridotite xenoliths from the Kaapvaal craton and the thermal regime of the lithosphere. Geochim. Cosmochim. Acta (Spec. Suppl.) 66S1, A61. 

Irvine G. J., Pearson D. G., and Carlson R. W. (2001) Lithospheric mantle evolution in the Kaapvaal craton A Re-Os isotope study of peridotite xenoliths from Lesotho kimberlites. Geophys. Res. Lett. 28, 2505—2508. 

Pearson, D. G., Carlson, R. W., Shirey, S. B., Boyd, F. R. Nixon, P. H. 1995. Stabilisation of Archaean lithospheric mantle a Re-Os isotope study of peridotite xenoliths from the Kaapvaal Craton. Earth and Planetary Science Letters, 134(3-4), 341-357. 

Table 2. Summary of Re Os model age information for peridotite xenolith suites on and around the Kaapvaal Craton...

Fig. 10. Histograms of Trd ages for on- and off-craton peridotites from southern Africa co-plotted with histograms of olivine mg-numbers. Kaapvaal low-L peridotites xenohths, n = 96. Data from Nixon et al. (1983), Walker et al. (1989), Pearson et al. (1995a), Carlson et al. (1999), Menzies et al. (1999) and Irvine et al. (2002). Lrd ages for peridotite xenoliths from kimberlites from East Griqualand, 170 km from the Lesotho on-craton kimberlites (Pearson et al. 1998) and for peridotites from the Farm Louwrencia kimberlite. Southern Namibia (Pearson et al. 1994 Pearson 1999a). It should be noted that no Archaean Trd ages are observed for off-craton peridotites. Olivine compositional data from Boyd Nixon (1979), Nixon (1987) and Boyd (unpubl. data).

Fig. 11. Location map of kimberlites on and around the Kaapvaal Craton from which peridotite xenolith suites have been dated by Re-Os isotopes (after Carlson et al. 2000 Irvine et al. 2001). Data sources Pearson et al. (1994, 1995a, 1998) Pearson (1999) Carlson et al. (1999) Janney et al. (1999) Irvine et al. (2001). Kaapvaal Craton is outlined in dark grey with the Archean Limpopo Metamorphic Belt shaded in light grey.

To date, Re-Os isotope studies of peridotite xenolith suites, taken to be representative of the lithospheric mantle beneath continents, reveal that although some lithospheric mantle began to form beneath continents in Palaeo- to Mesoarch-aean time, major crustal differentiation events continued until Neoarchaean time when, at least in southern Africa, significant volumes of lithospheric mantle formed and stabilized the newly accreted continent. On the Kaapvaal Craton, major magmatic events such as that which formed the Bushveld intrusion, substantially modified or introduced new material into the lithospheric mantle (Carlson et al. 1999) and the lower crust (Schmitz Bowring 2000), but the craton retained its integrity for another 2 Ga. 

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