Geochronology and correlations in the Central African Fold Belt along the northern edge of the Congo Craton: New insights from U-Pb dating of zircons from Cameroon, Central African Republic, and south-western Chad
Résumé
The Central African Fold Belt (CAFB) is the least well-known of all major Pan African belts. Here, we present new geochronologic work carried out in several critical areas of western Central African Republic, the region standing between northern Cameroon and southwestern Chad, and southern Cameroon. Our results allow us to: (1) clarify the regional extension of the Congo Craton in SE Cameroon and in the SW Central African Republic; (2) demonstrate that the units thrust along the northern edge of the Congo Craton from Cameroon to the Central African Republic are comparable in nature and in age; (3) better constrain the limits and described better the role of the Adamawa-Yadé crustal block during the Pan-African pre-collisional and collisional events in relation to the Congo Craton and the Yaoundé-Yangana nappe units to the South, and to the Poli-Leré magmatic arc to the North and; (4) clarify some of the elements of correlation with NE Brazil. Overall, a model involving two subduction zones is proposed to explain the evolution of the Pan-African belt north of the Congo Craton. The main steps include; (1) break-up and basin development from the early Tonian to at least 620 Ma on the northern edge of the Congo Craton, and on both the southern and the northern edges of the Adamawa-Yadé Block, concomitantly with the development of the Poli-Leré arc in northern Cameroon and Chad; (2) pre-tectonic plutonism in all domains since c. 800 Ma with culmination between 650 and 620 Ma; (3) collisional events starting around 620 Ma with metamorphism reaching the granulite facies at c. 600 Ma in all the domains; (4) nappe tectonics with thrusting of the Yaoundé-Yangana units onto the Congo Craton, accretion of the Poli-Leré arc to Adamawa-Yadé Block, and widespread syntectonic magmatism (600–580 Ma) with emplacement partly controlled by transcurrent regional shear zones, and emplacement of post-tectonic granitoids (c. 550 Ma) in both Adamawa-Yadé block and Poli-Leré magmatic arc. Collisional and post-collisional (620–550 Ma) events were synchronous along the entire belt from Central Africa to Brazil.