Geochronology,geochemistry and tectonics of the NE Bayuda Desert,N Sudan: Implications for the western margin of the late Proterozoic fold belt of NE Africa

Five suites of rocks collected from the Precambrian basement in the NE Bayuda Desert of central northern Sudan give late Proterozoic whole-rock $\text{Rb}\text{Sr}$ isochron ages. The Abu Harik Complex, thought by some previous workers to be an older basement, gives an age of 898 ± 51 Ma. Upper amphibolite-facies metasediments give a metamorphic age of 761 ± 22 Ma. The supposedly younger greenschist-facies El Koro Volcanic Series were erupted 800 ± 83 Ma ago. These are chemically similar to the volcanics which unconformably overlie the Sol Hamed ophiolite in the Red Sea Hills of NE Sudan and to some modern island are volcanics. The metasediments were intruded 678 ± 43 Ma ago by the Diefallab Granite, which is itself deformed. The younger, weakly-deformed Amaki Series, with a basal conglomerate containing basement clasts overlain by purple grits, is probably equivalent to the molasse-type Hammamat Group of the Eastern Desert of Egypt which was deposited between 616 and 596 Ma ago. Finally, the post-tectonic Shallal Granite, with within-plate geochemistry, was intruded 549 ± 12 Ma ago. Geochemical data suggest that the Abu Harik Complex, the El Koro Volcanic Series and the Diefallab Granite are arc-related magmatic rocks. They were intruded into, or thrust onto, shallow-water, shelf sediments during subduction and then collision, between c. 900 and 550 Ma. The data presented here give no support to previous views that the high-grade metasediments were metamorphosed prior to the late Proterozoic events, that they unconformably overlie a still older, perhaps Archaean, basement or that they are unconformably overlain by younger late Proterozoic low-grade volcanics. The Precambrian rocks along the E side of the Bayuda Desert must now all be assigned to the late Proterozoic and the boundary between this late Proterozoic fold belt and an older craton, known to crop out at Jebel Uweinat, must lie farther to the W.