Precambrian basement of the Congo Basin and its flanking terrains

Abstract

Africa’s four major Proterozoic shields were tectonically separated from one-another within the late Meso-to early Neo-Proterozoic Rodinia supercontinent along Rodinian mobile belts (‘Grenvillian’ in North America; ‘Kibaran’ in Africa; although, ironically, the type Kibaran rocks of Africa, now Karagwe-Ankole Belt in Rwanda and Burundi, have been found to be older and no longer define a Rodinian-age mobile belt. Following subsequent break-up of Rodinia, the four disparate African Shields welded together during the late Neoproterozoic to Early Cambrian amalgamation of Gondwana (ca. 500-800 Ma). The geology, geochronology and evolution of one of these Shields, the Central African Shield (CAS) is described here in some detail because it forms the basement to the Congo Basin (CB) that is the focus of this book. The CAS hosts both the world’s oldest (2.8 Ga) and youngest diamondiferous kimberlites and a number of complex Archean Cratons that outcrop along the flanks of the CB. The CB of central Africa is underlain and completely surrounded by peneplained Precambrian basement that spans a history more than 3.6 Ga, including rocks along its northeastern edge possibly as old as 4.0 Ga, separated and surrounded by numerous Paleo-to Neo-Proterozoic mobile belts. This Precambrian complex assemblage includes the peripheral (outcropping) Kasai, Cuango, Ntem, Bouca and Mboumou-Uganda cratonic blocks that can be assembled into three larger Congolese Cratons unexposed beneath the CB: The SouthWest-, the Cuvette-(or Central-), and the NorthEast-Congo Cratons (SW-, C-and NE-CC) and that in turn, together, constitute the Congo Shield (CS). Subsequently these three aggregated along the Central Angola Mobile Belt (CAMB; ca. 2.0-2.3 Ga) and the West Central African Mobile Belt [WCAMB; ca. 2.0-2.5 Ga to form the SouthWest Congo Shield (SWCS). In the east, the CS enlarged farther to form the CAS during the Proterozoic along Eburnian, Kibaran and Pan-African orogenic belts, but the details of the accretion processes of these continental domains remain uncertain.