Zimbabwe Craton

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... 

Shirey S. B., Harris J. W., Richardson S. H., Fouch M. J., James D. E., Cartigny P., and Viljoen F. (2002) Seismic structure, diamond geology and evolution of the Kaapvaal-Zimbabwe craton. Science 291, 1683-1686. 

Nguuri T. K., Gore J., James D. E., Webb S. J., Wright C., Zengeni T. G., Gwavava O., and Snoke J. A. (2001) Crustal structure beneath southern Africa and its implications for the formation and evolution of the Kaapvaal and Zimbabwe cratons. Geophys. Res. Lett. 28(13), 2501-2504. 

Fig. 1. Map showing station locations, topography and principal geological provinces in the region of study within southern Africa, Fifty-five broadband (REFTEK/STS-2) stations were installed in April 1997 in South Africa, Botswana and Zimbabwe. Stations in light blue were redeployed in April 1998 to sites indicated in yellow. A total of 82 sites were occupied over the two year deployment. In addition, three global seismic network broadband stations (white triangles) are located in the region and their data incorporated in the analysis. The array extends from the Cape Fold Belt in the south, through the Proterozoic Namaqua-Natal Mobile Belt, across the Kaapvaal Craton and Bushveld Province, through the Archaean Limpopo Mobile Belt and into the Zimbabwe Craton. On the west, the array covers part of the Kheis and Okwa Proterozoic Fold and Thrust Belts of Botswana and western South Africa. To the east, the array extends into the Early Archaean Barberton terrane, near the NW border with Swaziland. Published in James et al., GRL28, 2001, fig. 1.

The Archaean Kaapvaal and Zimbabwe Cratons form the nucleus of southern Africa. The Kaapvaal Craton, which is the better studied of the two, is composed of a mosaic of distinct geological terranes covering more than 10 km, with the oldest units generally in the eastern part of the craton and the youngest in the western part (de Wit et al. 1992). These terranes of disparate geological histories were assembled over a 1 Ga period from early Archaean (c. 3.6 Ga) to late Archaean time (c. 2.6 Ga) (de Wit et al. 1992 de Wit Hart 1993 Carlson et al. 2000). 

Stations located within undisturbed Kaapvaal or Zimbabwe Craton typically have sharp, large-amplitude depth images for the Moho. Among the more distinctive results are those from stations located in the Zimbabwe Craton, where Moho depths with one exception cluster tightly... 

Fig. 11. Colour-coded contour map of depth to Moho beneath the southern Africa array based on phasing depth images of Figure 2 (from Nguuri et al. 2001). Crustal thickness colour scale is shown on right. Thin crust is associated with undisturbed areas of craton, particularly in the southern and eastern parts of the Kaapvaal Craton and in the Zimbabwe Craton north of the Limpopo Belt. Greater crustal thickness is associated with the Bushveld region and its westward extension into the Okwa and Magondi Belts and with the Central Zone of the Limpopo Belt and the Proterozoic Namaqua-Natal Mobile Belt.

Gore, J. 2002. Seismological structure of the crust and upper mantle of the Zimbabwe craton and Limpopo belt, southern Africa. PhD thesis. University of Zimbabwe, Harare. 

The Kalahari Craton of southern Africa, consisting of the Kaapvaal and Zimbabwe Cratons and the Limpopo Mobile Belt, has formed a stable unit for the past 2.3 Ga (McElhinny ... 

Great Dyke intrusion, Zimbabwe craton 2574 2 Ma e.g. Wingate 2000... 

Jelsma, H. a. Dirks, P. H. G. M. 2002. Neoarchaean tectonic evolution in the Zimbabwe Craton. In Fowler, C. M. R., Ebinger, C. J. Hawkesworth, C. j. (ed.) The Early Earth Physical, Chemical and Biological Development. Geological Society, London, Special Publications, 199, 183-211. 

Jelsma, H. A., Vinyu, M. L., Valbracht, P. J., Davies, G. R., Wubrans, J. R. Verdurmen, E. A. T. 1996. Constraints on Archaean crustal evolution of the Zimbabwe Craton a U-Pb zircon, Sm-Nd and Pb-Pb whole-rock isotope study. Contributions to Mineralogy and Petrology, 124, 55-70. 

Wilson, J. F., Nesbitt, R. W. Fanning, C. M. 1995. Zircon geochronology of Archaean felsic sequences in the Zimbabwe craton a revision of greenstone stratigraphy and a model for crustal growth. In Coward, M. P. Ries, A. C. (eds) Early Precambrian Processes. Geological Society, London, Special Publications, 95, 109-126. 

The Zimbabwe Craton in southern Africa is composed of 26 greenstone belts that constitute about 20% of the craton, and granite-gneiss complexes that make up the remainder (Fig. la, Blenkinsop et al. 1997). These granite-greenstone terranes... 

Fig. 1. (a) Simplified regional map showing the position of the Zimbabwe Craton, greenstone belts, major shear zones as visible on Landsat TM images (e.g. RGB741), and orogenic belts. The shear zones may represent terrane boundaries and/or late strike-slip fault zones. Numbers refer to greenstone belt names. 

Most of the greenstone successions of the Zimbabwe Craton were formed at c. 2.7 Ga and are referred to as the Upper Greenstones (Wilson 1979), or Upper Bulawayan Group (Wilson et al. 1995). Amongst these, two distinctly different greenstone groupings may be recognized in different parts of the craton, which broadly correspond to Wilson s (1979) eastern and western successions (Fig. 2a). 

---