5 A Geological and Isotopic Framework of Precambrian Terrains in Western Central Africa: An Introduction Denis Thiéblemont, Yannick Callec, Max Fernandez-Alonso, and Frédéric Chène Abstract This chapter presents an up-to-date geological map of Western Central Africa, the region of equatorial Africa extending from the East-African rift to the Atlantic Ocean. Some 18 geological domains of Precambrian age are distinguished in this region, covering all the geolog- ical periods from the Paleoarchean to the Neoproterozoic. An overview of the lithostratigraphy of each domain is presented, based on the most recent geochronological data. A compilation of Sm–Nd isotopic data enables these domains to be discriminated by their isotopic signatures and integrated into a crustal growth model. Keywords Western Central Africa Á Geological Map Archean Á Proterozoic Á Geochronology Á Nd-isotopes Crustal growth 5.1 Introduction Since the pioneer works of Cahen et al. (1984), followed at the end of the 1980s by the first edition of the Geological Map of Africa at 1:5,000,000 scale (Choubert and Faure-Muret 1985–1990), the degree of knowledge of the geology of Africa has greatly increased, especially owing to the more and more intensive use of precise geochronological methods. Integration of these works into a geological map covering the whole of Africa was achieved in 2004, with the presentation, of the second edition of the Geological and Major Mineral Deposits Map of Africa at 1:10,000,000 scale (Milesi et al. 2004) in the frame of the 21 Congress on African Geology. Starting from the same cartographical framework, the Tectonic Map of Africa was published in 2010 (Milesi et al. 2010). This expressed, in a finished cartographical form on a continental scale, the project of Cahen et al. (1984) to draw a temporal scenario of the geological evolution of Africa. As far as Western Central Africa is concerned (i.e., the region comprised between latitudes 10°N and 10°S, west of the East-African rift), two recent syntheses have been pub- lished, thus making useless any attempt to re-expose in a concise way the geology of this region: the Geological and Mineral Deposits map at 1:4,000,000 scale presented by Milesi et al. (2006) and the SIG-based synthesis of the basement of the Congo Basin exposed by De Wit and Linol (2015). Nevertheless, important geological mapping projects have been conducted since 2004 (Delor et al. 2007; Fernandez-Alonso et al. 2015a, b; Callec and Fullgraf 2015; Thiéblemont 2009; Thiéblemont et al. 2009; Pinna et al. 2008; Fernandez-Alonso 2007), which have resulted in significant improvements in the cartographical framework and geological understanding of large regions of Central Africa, including its basement region of Archean to Paleo- proterozoic age. This region is sometimes referred to as the Congo Craton. However, the extension of what can be called the Congo Craton—that is, the extent to which individual ‘blocks’ of Archean rocks may be correlated to others across Central Africa and even South America—is still a matter of debate (e.g., Fernandez-Alonso et al. 2011; De Wit and Linol 2015). Thus we avoid using the term Congo Craton and do not enter this debate, which is beyond the scope of this chapter. The recent large-scale mapping projects conducted in Central Africa and other regions of this continent have motivated the preparation of the third edition of the Geo- logical Map of Africa at 1:10,000,000 by a team of European and African geologists under the supervision of the Com- mission for the Geological Map of the World and Geological Society of Africa. This map was first presented at the 35th D. Thiéblemont (&) Á Y. Callec Á F. Chène BRGM, DGR, B.P. 6009 45060 Orléans Cedex, France e-mail: d.thieblemont@brgm.fr M. Fernandez-Alonso Department of Geology, Royal Museum for Central Africa, Steenweg op Leuven 13, 3080 Tervuren, Belgium © Springer International Publishing AG, part of Springer Nature 2018 S. Siegesmund et al. (eds.), Geology of Southwest Gondwana, Regional Geology Reviews, https://doi.org/10.1007/978-3-319-68920-3_5 107