Structural constraints on the evolution of the Meatiq Gneiss Dome (Egypt), East-African Orogen A. Andresen a, * , L.E. Augland a , G.Y. Boghdady b , A.M. Lundmark a , O.M. Elnady c , M.A. Hassan c , M.A. Abu El-Rus c a Department of Geosciences, University of Oslo, P.O. Box 1047, Blindern 0316 Oslo, Norway b Mining Department, Faculty of Engineering, Assiut University, Assiut 71516, Egypt c Geology Department, Faculty of Science, Assiut University, 71516 Assiut, Egypt article info Article history: Received 15 April 2009 Received in revised form 23 September 2009 Accepted 17 November 2009 Available online 22 November 2009 Keywords: Eastern Desert Egypt Pan-African East-African Orogen Tectonics Crustal extension abstract Amphibolite-grade quartzofeldspathic gneiss domes surrounded by greenschist-grade island arc and ophiolitic assemblages is a characteristic feature of the Arabian–Nubian Shield in the Eastern Desert of Egypt. The mode of formation of these domes, including the Meatiq Gneiss Dome, is controversial, as is the protolith age of these gneisses. Reinvestigation of selected segments of the Eastern Desert Shear Zone (EDSZ), a high-strain zone separating the eugeoclinal units from the underlying quartzofeldspathic gneisses show it to be a top-to-the NW shear zone which was later folded about a NW–SE trending fold axis (long axis of the gneiss dome). Kinematic indicators (shear bands, duplex structures, etc.) along the north-eastern and south-western flanks of the dome therefore show apparent left-lateral and right-lat- eral strike-slip displacement across the EDSZ. These observations are in conflict with most previous tec- tonic models which link formation of the dome to extension in a NW–SE oriented corridor bordered by two sub-parallel left-lateral NW–SE oriented strike-slip faults. Emplacement of upper crustal, low-grade, eugeoclinal rocks tectonically on top of middle crustal amphibolite-grade quartzofeldspathic gneisses indicates that the EDSZ may represents an extensional fault with a possible break-away zone in the southern part of the Eastern Desert. Alternatively it can be explained as the result of two (or more) tec- tonometamorphic events with an intervening episode of erosion and exhumation of high grade rocks prior to emplacement of the eugeoclinal thrust complex. Recent U–Pb TIMS ages on syntectonic orthog- neisses and post-tectonic granites in the area show that shearing and subsequent doming must be youn- ger than 630 Ma, possibly as young as 600 Ma. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction A peculiar feature in the western part of the Arabian–Nubian Shield (ANS) is the presence of medium- to high-grade ortho- and para-gneisses surrounded by low-grade (greenschist grade) metasedimentary and metavolcanic assemblages of island arc affinity with variably well-preserved ophiolite fragments (Fig. 1) (Kröner, 1979; Sturchio et al., 1983; El Gaby et al., 1988, 1990; Fritz et al., 2002; Andresen et al., 2009). These high-grade metamorphic gneiss terrains are particularly well developed in the Eastern Des- ert of Egypt, but also occur in Sinai (Kröner et al., 1994; Blasband et al., 2000). The gneisses appear in most places as dome-like struc- tures, and a high-strain zone, hereafter named the Eastern Desert Shear Zone (EDSZ) separates the high grade rocks from the struc- turally overlying low-grade eugeoclinal rocks. Both the high- and low-grade units are intruded by younger undeformed/post-oro- genic circular granitic plutons. Various tectonic models have been proposed to explain the for- mation of the gneiss domes and the abrupt change in metamorphic grade between the gneiss domes and the overlying eugeoclinal rocks. Sturchio et al. (1983a,b) compared the gneiss domes of the Eastern Desert to metamorphic core complexes associated with crustal scale extension, as in the North American Cordillera (e.g. Lister and Davis, 1989), but Sturchio et al. (1983a,b) concluded that the Meatiq dome was the result of contractional tectonics and thrusting. Others link formation and exhumation of the domes to NW–SE oriented crustal scale strike-slip faulting and formation of pull-apart basins separating the gneiss domes (e.g. Bregar et al., 2002). A third model has been advocated by Fritz et al. (1996, 2002) and Fritz and Messner (1999) who propose that the domes are the result of E–W shortening combined with transcur- rent faulting. The postulated strike-slip faults associated with the gneiss domes in the Eastern Desert are often linked to the NW- striking Najd Fault System on the Arabian Peninsula (Fig. 1; Stern, 1464-343X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.jafrearsci.2009.11.007 * Corresponding author. Fax: +47 22854215. E-mail address: arild.andresen@geo.uio.no (A. Andresen). Journal of African Earth Sciences 57 (2010) 413–422 Contents lists available at ScienceDirect Journal of African Earth Sciences journal homepage: www.elsevier.com/locate/jafrearsci