A geochronological study of the basement complex of Uganda

Abstract

Geochronological reconnaissance of the Uganda basement suggests that the Watian Granulites of the West Nile are the oldest rocks. These rocks have been closed chemical systems for at least 2880 m.y. although throughout the basement they have also been reactivated at about 2550 m.y. This reactivation is seen as a widespread migmatization event involving a calc-alkaline granitic host magma. Towards the Mozambique Fold Belt in E. Uganda the basement gneisses are involved in a much younger granitic injection phase that dates close to 650 m.y. and is therefore considered to be related to the Mozambique event. The Mirian gneisses of the West Nile, which are unconformable on the older granitic gneisses, contain 950 m.y. zircons. This evidence favours the Mirian event as being the metamorphic equivalent of the 1200 m.y. Karagwe-Ankolean sediments found to the south. A summary of the available ages on the Uganda basement is presented.