Regional geology of West Africa

The West African sub-region is largely covered by the West African craton that has remained stable since about 1.7 Ga. It consists of two major basement domains:

1. The Reguibat shield (in the north around Mauritania)-Archean age

2. The Man shield (in the south between Ghana and Senegal)-Paleoproterozoic age

The two domains are separated by the Taodeni basin of Proterozoic to Paleozoic age. The Man shield covers the southernmost third of the craton. It is divided into two sectors comprising a western portion built up of rocks of Liberian age (3.0 – 2.5 Ga) and an eastern terrain underlain by Birimian rocks of paleoproterozoic age as shown in the map below. The Birimian supra-crustal rocks have been folded, metamorphosed and intruded by granitoids during the Eburnean event (2.1 - 1.95 Ga).

Generally, the West African craton is bounded to the east and southwest by Pan-African mobile belts.

Outcrops of the Birimian terminate against the Liberian cratonic nucleus in western Ivory Coast. In southeast Ghana, the Pan-African orogeny has thrusted the Dahomeyan gneisses over the Birimian terrain.

There are two schools of thoughts on the stratigraphy of the Birimian, based on chronostratigraphy and lithostratigraphy.

The post-Birimian rock formations in the West African subregion are the Dahomeyan System occupying south-eastern corner of Ghana, the Voltaian platform deposits in the eastern part of Ghana, and the supra-crustal rocks covering parts of Mali, Senegal, Togo, Benin and Nigeria.