THE ASSEMBLY OF NORTH-CENTRAL AFRICA THROUGH MULTIPLE ACCRETIONARY-COLLISIONAL EVENTS DURING THE LATE NEOPROTEROZOIC

The continental crust of North-Central Africa between the Tuareg and Arabian-Nubian shields and south to the Central African Orogenic Belt is poorly exposed and its geological evolution is not well understood. The current view is that the central Sahara crust represents a large, coherent craton that was ‘highly remobilized’ during the Late Neoproterozoic amalgamation of Gondwana and is referred to as the Saharan Metacraton. However, recent studies on the Guéra, Ouaddaï, and Mayo Kebbi massifs and the Lake Fitri Inlier of Chad suggest that the Saharan Metacraton may be a composite terrane of older cratonic nuclei with intervening Mesoproterozoic to Neoproterozoic domains. It is postulated that older crust and juvenile crust were sutured along a Pan-Gondwana collisional belt (Central Sahara Belt) that bisects the central Sahara region and should be considered as shield terrane rather than a single craton. Basement rocks collected from oil exploration drill wells of the Doba Basin, southern Chad, are compositionally similar to volcanic-arc granite and yielded Ediacaran zircon U-Pb ages of 594 ± 4.4 Ma, 594 ± 4.2 Ma, and 594 ± 5.4 Ma. The Doba granites temporally correlate with volcanic-arc granites ~400 km to the NE in the Guéra Massif and it is possible that these volcanic-arc granites are part of the same NE-SW trending Late Neoproterozoic active margin. The proposed Doba-Guéra arc is parallel to the Chad Lineament, a narrow arcuate gravity anomaly within central Chad considered to be the suture zone of a major Pan-Gondwana collisional belt. The implication of the new findings is that the crust of North-Central Africa amalgamated through multiple accretionary-collisional events and was not a coherent craton.