The structural geometry and metamorphic evolution of the Umm Gheig shear belt, Central Eastern Desert, Egypt: implications for exhumation of Sibai core complex during oblique transpression

Field and structural studies supported by remote sensing and thermobarometeric data are attempted to decipher the deformation and metamorphic histories of Umm Gheig shear belt which represents the eastern supracrustal rocks of the Sibai core complex in the Central Eastern Desert of Egypt. Umm Gheig shear belt is build up of three major structural domains (Abu Lassaf, Umm Luseifa, and Kab Ahmed) formed by four deformation events (D-1-D-4) during the late Cryogenian-Ediacaran (650-542 Ma). The border between these domains is controlled by major thrusts and sinistral-reverse shear zones. Abu Lassaf shear belt includes NW-oriented major folds, serpentinite klippes, and oppositely dipping bidirectional thrust forming pop-up structures. Umm Luseifa shear belt is marked by a major doubly plunging, curvilinear, asymmetrical anticline, series of fault bounded thrust slices, and bordered by two major NE- and SW-verging thrusts. Kab Ahmed shear belt includes the highly strained rocks and expresses as an imbricate NE-verging thrusts forming a simple piggyback imbricate thrust system with a unidirectional sense of thrust propagation to the NE. Presence of D3-related horsetail splays that grouped into a major of NW-trending sinistral shear zones in the Umm Gheig shear belt gives additional evidence for the formation and exhumation of Sibai core complex in oblique island arc collision zones and includes lateral extrusion in a transpressional collision zone along major strike-slip shear zones. The rocks of the Umm Gheig shear belt are subjected to prograde low-medium-grade regional metamorphism in the range of greenschist to lower amphibolite facies (350-620 degrees C at 2-6 kb). The structures in Umm Gheig shear belt are the products of an E-W shortening phase accompanied by compressional due to oblique shortening of the Arabian-Nubian Sheild between East and West Gondwana.