Pan-African structures, ophiolites and mélange in the Eastem Desert of Egypt: a traverse at 26°N

Abstract

A detailed structural traverse across the basement rocks of the Eastern Desert of Egypt shows that they consist, apart from intrusions, of four broadly recumbent tectonic units. The lowest, of arkosic metasediments of continental shelf facies, is exposed in a dome. This unit is overlain by an allochthonous ophiolitic mélange containing complete and dismembered ophiolitic masses in a matrix of deep-oceanic graphitic pelites and turbidites. A near horizontal, schistose to mylonitic fabric, most intense near and below the base of the mélange, indicates extensive lateral tectonic transport of the ophiolitic mélange over the shelf metasediments, but the mélange originated as an olistostrome before being tectonically transported. The mélange extends over an area of at least 10 000 km 2 . It is locally overlain by calc-alkaline volcanics, in which deformation is less intense but increases, and schistosity flattens downwards, indicating some translation over the mélange. Unconformable on the mélange and calc-alkaline volcanics is a molasse-facies series, itself also locally strongly deformed. Late tectonic granites preceded, and locally post-date, the molasse-facies sediments. Still later, diapiric peralkaline riebeckite granites locally up-domed the recumbent structures. The tectonic evolution is related to a late Proterozoic subduction zone to the SE of the region.