PRESENT STATUS OF GEOCHRONOLOGICAL DATA ON THE EGYPTIAN BASEMENT COMPLEX

Abstract

Compilation of 168 isotopic ages for the rocks of the Egyptian basement complex indicates an upper age limit of 1200 Ma for the geosynclinal metasediments and metavolcanics which are stratigraphically the oldest rocks in the basement. The geochemistry of the metasediments and their initial Sr isotopic ratios suggest derivation from relatively homogeneous Rb-poor source rocks, possibly intermediate to basic volcanics. Gneisses which usually give much younger ages are most probably gneissified older metasediments and metavolcanics but influenced by the age of younger intrusions responsible for the gneissification processes.