This contribution is a detailed structural study concerning the central Egyptian-Nubian Shield (Gabal El Shalul area and environs) utilizing integrated field-structural, remote sensing, petrological and geochemical data. The basement of the area comprises ophiolitic-mélange, arc-related metavolcanics, metasediments, metagabbro-diorites and granitoids. The area experienced two stages of deformation, pre-Najd (~850-630 Ma) and Najd-related (~630-580 Ma). The pre-Najd stage is represented by the assembly/amalgamation of arc-terranes and their N-ward extrusion. The Najd-related stage encompasses three deformation phases (D1, D2 and D3). D1 is a post-collision extensional event, depicting lateral spreading of tectonic terranes and NW-ejection of ophiolitic sequences. The emplacement of El Shalul granite (~ 630 Ma) and the deposition of molasse sediments in E-W and NW-SE extensional basins (Zeidun and Meesar) are D1- related. Following extension is a protracted phase of compression, shearing and transpression that commenced with NW-SE shortening (D2) and deformed the extensional basins by folding and thrusting with mild effects on other basement units. Sinistral shearing (D3a) and transpression (D3b) along the NW-trending faults superseded the D2 compression, while dextral shearing (D3c) on the ENE-WSW and NE-SW faults overprinted the NW-SE penetrative fabrics/structures and controlled the emplacement of post-granitic dykes. The significant conclusions of this study include (1) The El Shalul granite complex is a large alkaline granitic sheet emplaced during a post-collision extensional regime and suffered the subsequent ~630-580 Ma top-to-NW sinistral shearing and SW-directed thrusting (not a gneissic core complex) and (2) The NW-SE and NE-SW structural trends in the Central Eastern Desert are not conjugated. |
