The enigmatic continental crust of North-Central Africa: Saharan Metacraton or Central Sahara Shield?

Abstract

The continental crust of North-Central Africa between the Tuareg and Arabian-Nubian shields and south to the Central African Orogenic Belt is enigmatic due to the few bedrock exposures especially within the central region. The current understanding, based on a review of geochronology and isotope geochemistry, is that the central Sahara region is a large, coherent craton that was ‘highly remobilized’ during the Late Neoproterozoic amalgamation of Gondwana and referred to as the Saharan Metacraton. However, new data from the Guéra, Ouaddaï, and Mayo Kebbi massifs and the Lake Fitri inlier of Chad suggest that it may be a composite terrane of older cratonic blocks or microcontinents with intervening Mesoproterozoic to Neoproterozoic domains and referred to as the ‘Central Sahara Shield’. It is postulated that the older crust and juvenile crust were sutured together along a Pan-Gondwana collisional belt (Central Sahara Belt) that bisects the central Sahara region. The ‘Central Sahara Shield’ hypothesis suggests the Chad Lineament, a narrow arcuate gravity anomaly within central Chad, could be a collisional belt suture zone and that it may explain the existence of the relatively juvenile crust that typifies southern and eastern Chad. The new data improves upon the existing knowledge and challenges the lithotectonic paradigm of the Saharan Metacraton. Further investigations are required to fully characterize the crust of the central Sahara region and to test the contrasting hypotheses.