New U-Pb and Sm-Nd data from north-central Cameroon and its bearing on thepre-Pan African history of central Africa

North-central Cameroon is part of the Central African Fold Belt (CAFB) to t he north of the Congo craton. In pre-drift reconstructions of Pangea, the C AFE matches with the Borborema province (BP) of NE Brazil. U-Pb analyses of zircons and Sm-Nd analyses of minerals and whole rock for samples from nor th-central Cameroon show a long and complex crustal evolution beginning in the late Archean and extending to the late Neoproterozoic. This crustal str ucture can be correlated with crustal boundaries in Brazil. The region nort h of the Congo craton in Cameroon was primarily the locus of two successive orogenies, Eburnian at 2100 Ma and Pan African at 600 Ma. The Eburnian eve nt fused the Congo craton with the Sao Francisco craton of Brazil to form a larger, middle Paleoproterozoic Congo-Sao Francisco craton. Archean ages ( 2900-3000 Ma) north of the Congo craton have been obtained primarily as inh eritance (xenocrystic zircons and Nd isotopic signatures) in high-grade met amorphic rocks of the Adamaoua region, although no exposed Archean units ha ve been recognized. The Eburnian event is recorded as metamorphic U-Pb ages in both metasedimentary and metaplutonic rocks. Some of the Paleoproterozo ic rocks were derived from juvenile crustal growth and others show Sm-Nd is otopic signatures indicating derivation from reworking or melting of Archea n crust. Mesoproterozoic Sm-Nd model ages of 1600-1000 Ma occur in northern Cameroon, northwest of the Tchollire-Banyo fault system and correlate with similar terranes in NE Brazil. These model ages are probably the result of mixing of Neoproterozoic material with older crust, as found in Brazil. Ea rly Neoproterozoic Sm-Nd model ages of 1000-700 Ma on metasedimentary and m etavolcanic rocks may correspond to a period of Neoproterozoic crustal rift ing and basin formation dominated by more juvenile sources. The Poll basin is characterized by important development of juvenile rocks while the Yaoun de and Lom basins have substantial amounts of older crustal material. Late Neoproterozoic U-Pb ages (620-580 Ma) correspond to the period of West Gond wana assembly with calc-alkaline magmatism, convergent tectonism, metamorph ism and anatexis. development of regional strike-slip faults, and finally t he uplift of the belt associated with alkaline subcircular massifs. The res ults from north-central Cameroon are dominated by the effects of Eburnian a nd Pan African orogenesis; there is little evidence for the widespread ca. 1000 Ma Cariris Velhos activity found in NE Brazil. Some Sm-Nd data and lim ited zircon data suggest that central Africa may have had a limited middle to early Neoproterozoic tectonic history, similar to that recently document ed for the BP of NE Brazil, but more detailed studies will be needed to exp lore this possibility. (C) 2001 Elsevier Science B.V. All rights reserved.