DATING OF LATE PROTEROZOIC OPHIOLITES IN EGYPT AND THE SUDAN USING THE SINGLE GRAIN ZIRCON EVAPORATION TECHNIQUE

Zircons from gabbro and plagiogranite in late Proterozoic ophiolites of the Arabian-Nubian Shield (ANS) in Egypt and the Sudan, as well as post-ophiolite granites have been dated using the stepwise evaporation method. Zircons from a plagiogranite in the Wadi Ghadir ophiolite, Eastern Desert of Egypt, yielded a mean Pb-207/Pb-206 age of 746 +/- 19 Ma, while a gabbro and diorite associated with the Abu Swayel ophiolite nappe approximately 250 km southwest of Wadi Ghadir provided zircon Pb-207/Pb-206 ages of 729 +/- 17 and 736 +/- 11 Ma, respectively. Zircons from layered gabbro along the western margin of the Jabal Gerf ophiolite just north of 22-degrees-N were dated at 741 +/- 21 Ma, indistinguishable from the Wadi Ghadir and Abu Swayel results. A plagiogranite sample from the Onib ophiolite in the northern Red Sea Hills, Sudan, contains zircons with a Pb-207/Pb-206 age of 808 +/- 14 Ma, while granites which cross cut layered gabbro in this complex have zircon ages of 713 +/- 12 and 714 +/- 5 Ma respectively. The youngest granite at Onib was dated at 646 +/- 10 Ma and may reflect a phase of post-accretionary intraplate magmatism. Our zircon data document ocean crust generation between approximately 810 and approximately 730 Ma ago in the Nubian segment of the ANS, and the age data compare well with ophiolite generation in Saudi Arabia. However, some of our data cast doubt on large-scale correlations of suture belts between the Arabian and Nubian segments of the shield.