Kimberlites Kaapvaal Craton

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. 

Kaapvaal Craton, South Africa Newlands Kimberlite, K PG U-Pb 114Ma... 

Schmitz, M. D., Bowring, S. A. Robey, J. v. A. 1998. Constraining the thermal history of an Archean craton U-Pb thermochronology of lower crustal xenoliths from the Kaapvaal craton, southhem Africa. In 7th International Kimberlite Conference, Extended Abstracts. University of Cape Town, Cape Town, 766-768. 

To illustrate the appUcation of these methods we have analysed selected samples from different suites of cratonic peridotites for PGE abundances and Re-Os isotopic composition that had been previously analysed for major elements (Table 1). The sample set comprises three peridotites from the Jericho kimberlite, Northern Slave Craton (Irvine et al. 1999 Kopylova Russell 2000) two peridotites from the Kaapvaal Craton (Pearson et al. 1995a Carlson et al. 1999) three peridotites from the Farm Louwrencia kimberlite, Southern Namibia, on the periphery of the Kaapvaal Craton (Pearson et al. 1994, 1998a Hoal et al. 1995 Frantz et al. 1996) three peridotites from the Vitim alkali basalt field, on the southern margin of the Siberian Craton (Ionov et al. 1993 Pearson et al. 19986). 

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).

Peridotites from the Newlands kimberlite, in the southern part of the Kaapvaal Craton, have a similar, but less tightly clustered mean Tru age of 2.6 0.4Ga, median 2.6 Ga (Table 2) compared with the Northern Lesotho peridotites. Those from the Kimberley area, in the SW of the craton, show a tightly clustered distribution of Tro and Tma ages with a mean Trd age of 2.6 0.2 Ga, median 2.7 Ga, and a mean Tma age of 2.9 0.1 Ga (Table 2). Peridotites forming lithosphere in the north of the craton (Letlhakane, Bots-... 

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.

Fig. 6. Chondrite-normalized PGE patterns of whole-rock peridotites from the Jericho kimberlite. Northern Slave Craton and for Kaapvaal peridotites. Data from Table 1. Normalizing values taken from McDonald et al. (1995).

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