Crustal evolution in north-east and east Africa from model Nd ages

Abstract

The relationships between the various crustal provinces that comprise north-east and east Africa are far from clear and reflect diverse tectonic and magmatic processes which took place during the Proterozoic. Here we present the results of an Nd isotope study on the major rock units of the Pan-African (1,100–500 Myr BP) terrane. Charnockites from Jabel Uweinat, a basement inlier at the junction of Egypt, Libya and the Sudan, yield middle Archaean model Nd ages, whilst model ages of <1,200 Myr have been obtained in a belt from the Eastern Desert of Egypt to north-west Kenya. This, therefore, represents a westward extension of the juvenile Pan-African crust of the Arabian Shield (Fig. 1). The shield itself is characterized by comparatively rapid crustal growth1, probably in an accreting island arc environment2. Between the two areas, there is a marginal zone of Pan-African rocks with relatively low ɛNd(T) values (see Table 1) due to increased contributions from the pre-Pan African crust. Overall, the Pan-African rocks from north-east and east Africa and those from the Damara of Namibia3 exhibit a wide range of ɛNd(T) from +7.5 to −18.0 which reflects regional changes in tectonic style and is not readily reconciled with simple models for the evolution of average continental crust.