STRUCTURE, EVOLUTION AND PALEOGEOGRAPHY OF THE WEST-AFRICAN CRATON AND BORDERING BELTS DURING THE NEOPROTEROZOIC

The West African craton consists of an Archaean or Palaeoproterozoic basement covered by sediments ranging from the Neoproterozoic to the present time. It is entirely surrounded by several Pan-African or Hercynian belts. The old basement is exposed in two shields, and the sedimentary units filled up three main basins: Tindouf, Taoudeni and Volta. The largest one, the Taoudeni basin, is located in the middle part of the West African craton. The Taoudeni basin is made of six different basins or troughs having a non-similar evolution. The structural and sedimentary evolution largely depends on the geodynamic evolution of the neighbouring belts. We have the intention to connect the sedimentary environments and the tectonics events that occurred around the craton. Five main tectonic events have been distinguished: the BI Anti-Atlas event on the northern margin (similar to 685 Ma), the Pan-African I tectonic event on the western side (similar to 660 Ma), the Eastern Pan-African tectonic event (similar to 600 Ma) from Morocco to Brazil, the Pan-African II tectonic event which occurred on the southwestern part at similar to 550 Ma and, finally, the Hercynian tectonic event (similar to 300 ma) on the northwestern margin. Lithostratigraphic correlations between the differents basins take into account this tectonic diachronism. Thus, we distinguished several oceanic, rift, glacial or molassic stages. For example, three glacial events have been recognized from 980 Ma to 500 Ma. Finally, we are proposing here four palaeogeological schemes illustrating four key periods of the Neoproterozoic evolution. This emphasizes the Pan-African structural inheritance.