GEOLOGICAL, STRUCTURAL AND RADIOACTIVITY STUDIES OF WADI SUTRAH-UMM GHEIGAREA, CENTRAL EASTERN DESERT, EGYPT

ABSTRACT Wadi Sutrah-Umm Gheig area is located in the Central Eastern Desert, 20 km west of Marsa Alam international airport and 50 km south of the Quseir city. The area represents a part of the Arabian-Nubian Shield. It is also pertaining to the pan-African complex which consists of a folded belt of metasediments and metavolcanics subjected to greenschist-amphibolite facies metamorphism associated with partial melting of amphibolites and development of gneissic and migmatitic rocks. The rocks of the metasediments are tectonically enclosed sheets and lenses of serpentinites, forming an ophiolitic mélange. These rock units intruded by four granitoid groups related to different magmatic and tectonic events. The area was affected by three distinct deformational events (D1–D3). D1 interpreted to have resulted from the closure of inter-arc basins, ophiolite obduction, and collision of East and West Gondwana, representing the earliest phase of deformation in the area. In the area of Umm Ghamis, D1 represented by a series of tight overturned folds which have a NW-SE strike with NE and SW dip directions. During D2 transpression, which marked the terminal stages of the Pan-African Orogeny, along Wadi Sutrah a series of open folds with NW–SE trending axes that plunge mostly to the SE. D3 deformation is thought to be belongs to the regional Najd system, represented by several prominent shear zones and strike-slip faults. The F3 phase folds are trending nearly E-W discordant to the other older two phases F1 and F2.