PAN-AFRICAN MAGMATISM IN THE WADI-EL-IMRA DISTRICT, CENTRAL EASTERN DESERT, EGYPT - GEOCHEMISTRY AND TECTONIC ENVIRONMENT

The Late Proterozoic rocks of the Wadi El-Imra district of the Central Eastern Desert, Egypt, comprise a metagabbro-diorite complex (oldest) and Older and Younger Granitoid complexes. Trace element characterist ics show that the basic and granitoid rocks are of calc-alkaline affin ity, but some of the Younger Granitoids grade into alkaline granites. The epsilon(Nd) values of the the basic and granitoid rocks range from +8.3 to +4.9, and Nd model ages are younger or rather similar to crys tallization ages. These data suggest a predominant depleted mantle der ivation, indicating formation by subduction in an oceanic setting. REE patterns of the granitoid rocks suggest different modes of petrogenes is. This, coupled with the occurrence of amphibolite xenoliths in the Older Granitoids, may indicate that some of these rocks represent part ial melts from basic rocks that have been amphibolitized at deep crust al levels of the oceanic are.