Pergamon f ar mal of Afr ican Eanh Sciences. Vol. 21, No. 3. pp. 395.406. 1995 Copyright 0 1995 Elsevier Science L.td Printed in Greal Britain. All rights reserved 0899-536285 $9.50 + 0.M) 0899-5362(95)00095-X The pre-Pan-African deformed granite cycle of the Gabal El-Sibai swell, Eastern Desert, Egypt AL1 A. KHUDEIR,’ SAMIR EL-GABY,’ GAMAL KAMAL EL-DIN,’ ASRAN M. H. ASRAN* and REINHARD 0. GREILING* IGeology Department, Assiut University, Egypt 2Geological Institute, University of Heidelberg, Germany (Received 14 July 1994: revised version received 25 August 1995) A bstract - The Gabal El-Sibai area is a structural high in which variably deformed granites and gneisses are structurally exposed underneath an overthrusted Pan-African ophiolitic melange and intruded by undeformed Pan-African granites. The deformed granites constitute a complete granite cycle starting with autochthotious to parautochthonous, talc-alkaline I-type granites and ending with post-tectonic, within-plate alkaline granites. They indicate that the Sibai infrastructure represents a pre-Pan-African continental crust incorporated in the Pan-African erogenic belt. R&sum6 - La region du Gabal El-Sibai est un relief structural positif compos6 de granites et de gneiss dkfonnks de man&e variable. Ces demiers sont situ& structuralement sous un m&nge ophiolitique pan-africain ch@6 et sont intrudes par des granites pan-africains non d&form&. Les granites deform& constituent un cycle grapitique complet dkbutant avec des granites calco-alcalins de type I autochtones 21 parautochtones et se terminant avec des granites alcalins post-tectoniques k&a-plaques. Ils indiquent que l’infrastructure de Sibai reprksente une crotite continentale pr&pan-africaine incorpo& darts la chaine orogenique pan-africaine. INTRODUCTION Archaean rocks outcrop in the Oweinat area, southwestern Desert (Cahen et aZ., 1984; Richter and Schandelmeier, 1990) fringed by a mid-Proterozoic continental crust (Harris et al., 1984). They constitute part of the East Sahara (or Nile) craton that extends eastward to the Nile valley (Schandelmeier et al., 1988). Further extension into the Eastern Desert is a highly debated issue. Former, pre-plate tectonic lithostratigraphic clas- sifications of the Egyptian basement, based on the geosynclinal concept and associated magmatic activi- ties, accepted the presence of gneisses, granites and high-grade schists older than the low-grade, region- ally metamorphosed, eugeosynclinal volcano-sedi- mentary successions (e.g. El-Ramly and Akaad, 1960; El-Ramly, 1972). Recognition of ophiolite belts and island arc volcanics and volcaniclastics that cover extensive areas in the Arabian-Nubian shield (including the Eastern Desert) popularized the idea that the shield is constituted entirely of accreted en- simatic island arcs with remnants of consumed, for- merly intervening oceanic crust along the suture lines (e.g. Bakor et al., 1976; Greenwood et al., 1976; Gass, 1977; Shackleton, 1977). Akaad and Noweir (1980) 395 and Ries et al. (1983) considered the quartzofeld- spathic gneisses at M eatiq and Hafafit as Neopro- terozoic (or older) shelf sediments metamorphosed during the Pan-African orogeny. However, the quart- zofeldspathic gneisses at Meatiq were found to be mylonites of essentially granitic parentage (El-Gaby, 1976; El-Gaby and El-Nady, 1983; Sturichio et al., 1983) and the quartzofledspathic (or psamniitic) gneisses at Wadi Abu Rusheid-Wadi Sikait area (El-Shazly and Hassan, 1972; Hassan, 1973) are also d&formed granites (see Fig. 8 in Ries et al., 1983; Hegazy, 1984). On the other hand, El-Gaby (1983), El-Gaby et al. (1988) and Hassan and Hashad (1990) ibelieve that the mid-Proterozoic continental crust extends into the Eastern Desert and crops out in gneiss domes under- neath overthrusted Pan-African island arc volcanics and volcaniclastics and associated ophiolites. Krijner et al. (1987) suggest that the Arabian-Nubian shield is a collage of small crustal blocks or microcontinents immersed in more abundant juvenile material. The deformed granites to be dealt with in the pres- ent study cover an area 170 km2 in the central Eastern Desert of Egypt (Fig. 1). They were treated by several workers (Hume, 1934; Sabet, 1961; El-Ramly 1972; El- Anwar, 1983) who claimed that thee granites, to- gether with the undeformed granites, belong to one