Tectonic Evolution of the Polydeformed Urf Al-Mahib Belt, South-Eastern Desert, Egypt

Abstract

The Urf Al-Mahib area, located to the southern part of the Eastern Desert (SED) of Egypt, is covered mainly by juvenile Neoproterozoic crust and Nubian sandstones. Field investigation and structural analyses give evidence that the area of Urf Al-Mahib developed through four successive phases of deformation (D₁, D₂, D₃ and D₄). D₁ was an attenuated phase represented by tight to isoclinal folds (F₁), tightly appressed fold closures and sheared-out hinges, and axial plane foliation (S₁), as well as mineral and stretching lineations (L₁). Structural fabrics formed during the D₂ phase embrace minor- and map-scale prominent F₂ overturned folds with NW (to NNW)-dipping long upper limbs and short lower overturned limbs and axial planes striking NE (to ENE)‒SW (to WSW) and dipping to the NW at moderate angles. F₂ folds are geometrically- and kinematically-related to thrust propagation, and often have SE (to SSE) vergence. Thrust faults, that striking NE (to ENE)‒SW (to WSW) and dipping NW to NNW, are also common in this stage. D₃ structures contain pervasive vertical to inclined mesoscopic open to very open folds (F₃), whose axes plunge NW (to NNW) and SE (to SSE) at moderate to steep angles. The latest D₄ deformation phase is represented by abundant small- and large-scales WNW‒ESE trending dextral semi-ductile-semi-brittle-shear zones.