Chapter 7 Structural Framework

Publisher Summary In South and Central Africa, five ancient structural provinces constituting the cratonic nuclei are separated by mobile belts in which subsequent tectonothermal events have caused polyphase deformation and high-grade metamorphism. The cratonic areas are composed of granitoid gneisses and greenstone belts constituting a shield overlain in places by Precambrian and Phanerozoic supracrustal rock sequences. The intervening linear mobile belts mark the sites of repeated intense deformation and metamorphism. The limits of the Kaapvaal structural province are not accurately known in the south and east where Mesozoic rocks obscure the Precambrian geology. To the north, the boundaries of the province are not clearly defined because of a gradual increase in metamorphic grade and deformation into the Limpopo mobile belt. A similar radation from the Rhodesian craton into the Limpopo belt is also reported. The Matsap beds overlying the Transvaal rocks are strongly deformed along the western margin of the craton and pass southwestwards with increasing grade of metamorphism into the Kheis Group, which was formerly regarded as a much older rock sequence. The Rhodesian craton consists primarily of a granite-greenstone terrane with younger Precambrian cover sequences preserved along the eastern (Umkondo) and northwestern margins. Recent geologic and geochronologic studies in Zimbabwe have revealed a long history of crustal development extending back to >3.5 Ga. The geology of the small Zambian nucleus also known as the Bangweula Block, is imperfectly understood but appears to be analogous to a craton. It consists of a granitoid and gneissic basement much of which is overlain by the Plateau Series that is older than 1.8 Ga.