Repeated magmatic pulses in the East African Orogen in the Eastern Desert, Egypt: An old idea supported by new evidence

This paper presents U–Pb ID-TIMS geochronological data from granitoids in the Hafafit area in the Central and South Eastern Desert, Egypt. It dates several Neoproterozoic magmatic pulses and metamorphic events, and constrains one episode of U, Nb and Ta mineralisation along the Nugrus Shear Zone, part of the Eastern Desert Shear Zone, to 608 ± 1 Ma. The data testify to the localized nature of deformation in the Eastern Desert, illustrating that previous subdivisions of granitoids into “Older” and “Younger” based on field criteria are inadequate. With robust ages from granitoids in the Meatiq, El Sibai and El Shalul areas the new ages indicate 6 pulses of magmatism and/or metamorphism at (1) 705–680, (2) c. 660, (3) 635–630, (4) 610–604, (5) 600–590 and (6) c. 540 Ma. Most pulses are defined by ages from granitoids in both gneiss windows/domes and in the overlying eugeoclinal allochthon; the two tiers represent different crustal levels of related rocks. We propose that pulses 1–3 are syn-orogenic, pulses 4 and 5 reflect exhumation of mid-crustal gneisses along the Eastern Desert Shear Zone, whereas the final pulse post-dates the East African orogeny. Based on available data we propose that the tectono-magmatic evolution above applies to the entire Eastern Desert.