The northern dome of Wadi Hafafit culmination, Eastern Desert, Egypt: Structural setting in tectonic framework of a scissor-like wrench corridor

Although the gneissic domes in Eastern Desert of Egypt have been studied recently in a considerable detail; their origin remains controversial. Basically four schools of thought exist: one argues for an origin parallel crustal extension, a second suggests emplacement within antiformal stacks, a third envisages young emplacement within a core of a sheath fold and finally some authors believe that the emplacement is due to overlap of regional folds and extension parallel to the fold axes. The Wadi Hafafit Culmination is one of these domes and occupies the southern part of the Central Eastern Desert of Egypt. The culmination is cored with five separated gneissic domes ranging in composition from orthogneiss to paragneiss. They are overthrust by a low-grade, volcano-sedimentary association constituting the Pan-African cover nappes. Detailed structural mapping of the northern dome reveals that, the gneisses are vertically emplaced through the cover rock units. This is based on field evidence which shows that the gneisses experienced vertical flattening associated with exhumation corresponding to coaxial deformation. It is suggested that the emplacement of gneissic core occurred during accretion of the Pan-African nappes. Later, strike-slip shear zones of Najd Fault System and the associated subsidiary shear arrays postdate emplacement of the dome. The gneisses contiguously underlie the Pan-African nappe assemblages through discrete low-angle left-lateral thrust-dominated shear zones from the east. Ongoing accretion of nappe assemblages on the gneisses increases the density contrast between the overlying denser nappe and the underlying lighter quartz-rich gneisses, leading to squeezing the gneissic materials in oblique convergence regime. As a consequence, the gneisses are suggested to have up-domed vertically through the nappe rock units.