Peridotites Kaapvaal

Figure 6 P-T arrays compiled for garnet peridotite xenoliths from several suites using two-pyroxene thermometry and Al-in-orthopyroxene barometry (Tbkn and Rbkn methods, Table 5). Data sources given in Rudnick and Nyblade with additional data here for Vitim (Ionov et al., 1993a) and Canada (MacKenzie and Canil, 1999 Schmidberger and Francis, 1999). The best-fit line for the Kaapvaal data is plotted in each figure for reference. Intersection of P-T array with mantle adiabats (shaded field) represents an estimate of the thickness of lithosphere at the time of sampling.

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.

Figure 43 CHf versus cnj isotope diagrams for lithospheric mantle peridotite minerals. Kaapvaal peridotite data are ah garnets and clinopyroxenes (Simon et al, 2002). Slave peridotite data are garnets and whole rocks from Schmidberger et al (2002). Salt Lake Crater peridotites (Hawaii), Kilboume Hole and Abyssal peridotites, are from Salters and Zindler (1995). Siberian and Mongohan peridotite Held are chnopyroxene data from cratonic and off-craton peridotites (field taken from Ionov and Weis, 2002). Fields for MORE (N-MORB) and OIB are from Nowell et al (1998). Field for Beni Bousera peridotites from Pearson and Noweh (2003).

Figure 47 Garnet compositions for eclogites from Siberia, South Africa, and Koidu (Sierra Leone) compared to low-L Kaapvaal peridotites, in terms of their pyrope, grossular, and almandine calculated end-members (sources Sobolev, 1974 Hatton and Gurney, 1987 Mazonne and Haggerty, 1989 Taylor and Neal, 1989 Jacob et al, 1994 Hills and Haggerty, 1989 Viljoen et al., 1996 Pyle and Haggerty, 1998 and Barth et al, 2001).

Until the application of the Re-Os isotopic system to whole-rock peridotites (Section 2.05.2.7.4) the Archean and Proterozoic Pb-Pb and Sm-Nd model ages and isochrons obtained on diamonds were the chief constraints on the antiquity of the continental hthospheric mantle (Kramers, 1979 Richardson et al, 1984). Early work, most of which was on diamonds from the Kaapvaal-Zimbabwe craton because of sample availability, suggested a simple difference from Meso-Archean P-type (harzburgitic) diamonds and Proterozoic E-type diamonds (Richardson, 1986 Richardson et al, 1984, 1993). More recent Re-Os work on single sulfide inclusions from the Kaapvaal-Zimbabwe craton has underscored the importance of a Neo-Archean E-type diamond... 

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. 

Boyd F. R., Pearson D. G., and Mertzman S. A. (1999) Spinel-facies peridotites from the Kaapvaal root. In Proc. 7th Int. Kimb. Conf. (eds. J. J. Gurney, J. L. Gurney, M. D. Pascoe, and S. H. Richardson). National Book Printers, Red Roof Design, Cape Town, vol. 1, pp. 40-48. 

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. 

Rudnick R. L., McDonough W. F., and Orpin A. (1994) Northern Tanzanian peridotite xenohths a comparison with Kaapvaal peridotites and inferences on metasomatic interactions. In Proc. 5th Int. Kimberlite Conf. (eds. H. O. A. Meyer and O. H. Leonardos). CRPM, vol. 1, pp. 336-353. 

Saltzer R. L., Chatterjee N., and Grove T. L. (2001) The spatial distribution of garnets and pyroxenes in mantle peridotites pressure-temperature history of peridotites from the Kaapvaal craton. J. Petrol. 42, 2215-2229. 

Herzberg C. T. (1993) Lithosphere peridotites of the Kaapvaal craton. Earth Planet. Set Lett 120, 13-29. 

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. 

Kaapvaal peridotites that have low equilibration temperatures, coarse grain size and relatively un-... 

The effects of post melt-depletion interaction with fluid or melt components in the lithospheric mantle has been extensively documented (e.g. Menzies Hawkesworth 1987, and references therein Harte et al. 1993 Pearson 1999 ) and it is widely accepted that these phenomena dominate the minor element geochemistry of cratonic peridotites. Extensive studies of the effect of metasomatism on the major element chemistry of lithospheric peridotites have also been made (Boyd Mertzman 1987 Keleman et al. 1992, 1998 Walter 1999). To date, most of the discussion has centred around the apparent excess of orthopyroxene, especially in Kaapvaal peridotites. However, major and trace element studies show that it is likely that the abundances of garnet and clinopyroxene are also grossly affected (Burgess Harte 1999 Shimizu 1999). 

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). 

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