Lesotho, kimberlites

Figure 20 Primitive mantle normalized extended PGE patterns (including rhenium) for cratonic whole-rock garnet peridotite xenoliths from the Letseng kimberlite (Lesotho) (sources Irvine, 2002 and Pearson et al., 2004).

Cratonic peridotite xenoliths from Lesotho, S. Africa, the Jericho kimberlite, Slave craton, and Somerset Island, Churchill Province, northern Canada, along with selected samples from... 

Examination of all data for cratonic peridotites (Figure 19) shows similar features to the Lesotho suite (Irvine, 2002). Highly depleted cratonic peridotites generally have low AI2O3 and very low (Pd/Ir) values. Variation in AI2O3 at very low, constant (Pd/Ir) appears characteristic of cratonic peridotites and may be related to the introduction of late-stage diopside by the host kimberlite (Pearson et ai, 2002a Simon et al,... 

Carswell D. A., Griffin W. L., and Kresten P. (1984) Peridotite nodules from the Ngopetsoeu and Lipelaneng Mmberhtes. Lesotho a crustal or mantle origin. In Kimberlites II The Mantle and Crust-mantle Relationships (ed. J. Komprobst). Elsevier, Amsterdam, pp. 229-243. 

Harte B., Winterbum P. A., and Gurney J. J. (1987) Metasomatic and emichment phenomena in garnet peridotite facies mantle xenoliths from the Matsoku kimberlite pipe, Lesotho. In Mantle Metasomatism (eds. 

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. 

McDade P. and Harris J. W. (1999) Syngenetic inclusion bearing diamonds from Letseng-la-Terai, Lesotho. In Proceedings of the Vllth International Kimberlite Conference (eds. J. Gurney John, L. Gurney James, D. Pascoe Michelle, and H. Richardson Stephen). Red Roof Designs, Cape Town, vol. 2, pp. 557-565. 

Nixon P. H. and Boyd F. R. (1973a) Petrogenesis of the granular and sheared ultrabasic nodule suite in kimberlite. In Lesotho Kimberlites (ed. P. H. Nixon). Cape and Transvaal, Maseru, pp. 48-56. 

Griffin W. L., Carswell D. A., and Nixon P. H. (1979) Lower-cmstal granulites and eclogites from Lesotho, southern Africa. In The Mantle Sample Inclusions in Kimberlites (eds. F. R. Boyd and H. O. A. Meyer). American Geophysical Union, Washington, DC, pp. 59-86. 

Rogers N. W. (1977) Granulite xenoliths from Lesotho kimberlites and the lower continental crust. Nature 270, 681-684. 

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-... 

Boyd, F.R. and Nixon, P.H., 1975. Origins of the ultramafic nodules from some kimberlites of northern Lesotho and the Monastery Mine, South Africa. Phys. Chem. Earth, 9, 431-54. 

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