Kaapvaal Craton stabilization

The results of intensive study of Kaapvaal Craton peridotites have implications for different craton generation models and hence for the stabilization of the earliest continents. It has been suggested that the opx-rich Kaapvaal lithospheric mantle could have formed from primitive. Si-enriched material in Hadean time (Herzberg 1993). There are no clear indications of Hadean... 

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. 

The relatively small number of late Archaean basins may reflect a low preservation potential, but may also indicate that relatively few cratonic nuclei had stabilized before the end of the Archaean. Examples of late Archaean basins include the (3.1-2.7 Ga) Witwatersrand basin in South Africa (Robb Meyer, 1995), and its correlative the 3.0-2.67 Ga Pongola Supergroup in Swaziland (Walraven. Pape, 1994 Gold von Veh, 1995), both unconformable upon the Kaapvaal Craton. In western Australia the 2.77-2.71 Ga Fortescue Group is unconformable upon older Archaean rocks of the Pilbara Craton (Blake et al., 2004). 

Relatively little well preserved sedimentary rock and associated C can be found in lithosphere older than 3.0 Ga. The tectonically active Archean marine basins favored rapid destruction of crust by continental collisions, partial melting and mantle/crust exchange (Windley 1984). Most of Archean continental crust had not yet become stabilized by cratonization (Rogers 1996), therefore a greater fraction of continental sediments experienced greater instability and thermal alteration. The freshest sediments occur in the 3.5 to 3.2 billion-year-old Kaapvaal Craton of South Africa and the Pilbara Block of Western Australia (Lowe 1992). These deposits are associated with episodes of greenstone activity and intrusive events that created stable microcontinents or cratons. These cratons became the nuclei of full-sized modern continents. 

The Kaapvaal Project was vmdertaken to study the formation, stabilization and evolution of cratons, and to image the deep structure of the tectosphere (Carlson et al. 1996) (see also http // www.ciw.edu/kaapvaal for participants and a description of the project). A cornerstone of the Kaapvaal Project was a large-scale broadband seismic experiment designed specifically for geo-logical-scale imaging of the crust and upper mantle beneath the cratons and adjacent Proterozoic provinces of southern Africa (Fig. 1). The... 

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