The Pan African of West Africa — the eastern domain

Summary

East of the craton there are many low-grade supracrustal belts mainly occupying a broad elongate NNE-SSWzone in the western half of Nigeria. They are dominated by clastic metasediments, but basic and ultrabasic and banded iron formation lithologies also occur. Most of the belts are probably late Proterozoic in age, deformed and metamorphosed in the Pan African (550 Ma), though some bear the imprint of a Kibaran event (c. 1100 Ma). The extensive basement to the supracrustals has a record of reactivation extending back at least to the Liberian and it contains many scattered older supracrustal relics. Metamorphic grades in the basement are in the amphibolite faciès throughout most of the region, except near the margin of the craton, where granulite faciès rocks are common in Ghana, Togo and Benin. There are abundant large syntectonic to late-tectonic granitic intrusions, most of which give Pan African ages (c. 450–650 Ma). The eastern boundary between the craton and the Pan African terrane is a broad zone of high-angle thrusting towards the west, called the Togo belt. This boundary has been identified as a crustal suture formed by collision with a somewhat poorly defined East. Saharan craton lying to the east of it. The Dahomeyan I terrane east of the thrust zone may have formed by aggregation of smaller continental fragments, island arcs and intervening basins. The case for identifying the Pan African event in the eastern part of West Africa as a collision orogeny is strengthened by well documented evidence from the Hoggar region of Mali and southern Algeria.

The best-known economic mineral deposits in the eastern Pan African domain are of gold in supracrustal belts and of tin-tantalum-niobium minerals in pegmatites. There are many small deposits of other minerals and at least one major occurrence of iron ore.