The Precambrian geotectonic evolution of Africa: plate accretion versus plate destruction

The classical model of continental accretion and progressive cratonization, starting with an ancient nucleus onto which younger orogenic belts are welded (onion skin tectonics), has dominated geotectonic research for many years and has received new impetus with the general acceptance of the theory of plate tectonics. It has also been applied to the geotectonic evolution of large Precambrian crustal segments such as Africa.It is demonstrated, however, that new structural, geochronological and paleomagnetic data from Africa provide strong evidence for the existence of large cratonic continental plates since at least the Early Proterozoic which were later transected by linear mobile belts and thus partly destroyed. Crustal reworking and rejuvenation in these belts now gives the impression of younger orogens surrounding ancient “nuclei”.The geotectonic evolution of Africa is therefore characterized by plate destruction rather than by plate accretion with progressive cratonization, and only the “nuclei” have escaped this process.Many phenomena in the African mobile belts seem to indicate processes involving little or no relative motion of crustal plates or crustal shortening between them, and there is as yet no evidence of former oceanic plates to have been generated or consumed. It is therefore suggested that large-scale dispersive movements of major continental fragments were uncommon or absent in the Early and Middle Precambrian.Widespread drift may only have begun during the Late Precambrian/Early Paleozoic Pan African Tectogenesis, eventually leading to a crustal evolution as envisaged by the modern theory of global tectonics.