RESEARCH Structural setting of Cretaceous pull-apart basins and Miocene extensional folds in the Quseir–Umm Gheig region, northwestern Red Sea, Egypt Mohamed Abd El-Wahed1,2, Mahmoud Ashmawy1, and Hossam Tawfi k1 1GEOLOGY DEPARTMENT, FACULTY OF SCIENCE, TANTA UNIVERSITY, TANTA 31527, EGYPT 2GEOLOGY DEPARTMENT, FACULTY OF SCIENCE, OMAR AL MOKHTAR UNIVERSITY, AL BEIDA, LIBYA ABSTRACT We examine the evolution of the northwestern Red Sea, Egypt, by study of the Quseir–Umm Gheig subbasin. The subbasin records two main tectonic events. The fi rst event is related to development of Late Cretaceous synclinal basins due to sinistral movement along the reac- tivated Najd fault system. Evidence for this includes: (1) the Cretaceous basins are concentrated mainly in the central Eastern Desert, which represents the main infl uence zone of the Najd fault system, (2) folds are not everywhere parallel to the faults and their axes are curvilinear, (3) the faults dislocated the axial plane of the synclines, (4) the Cretaceous basins occur in an en-echelon arrangement, (5) there is a differ- ence of 20° between the orientation of the sinistral strike-slip shear zones and the associated en-echelon synclinal folds, (6) principal stress σ σ σ directions are delineated by subhorizontal 1 and 3 and subvertical 2, (7) sheared conglomerate is detected in the Nubia Formation, (8) minor overturned folds and minor NE-vergent thrusts occur in the Duwi and Dakhla Formations, and (9) there is a predominance of NE-SW normal faults in Cretaceous–Eocene sequences. The second event is related to the sinistral movement along the NNE-SSW Aqaba–Dead Sea transform and dextral movement along Queih and Hamrawin shear zones. This movement was synchronous with northeast extension of the Red Sea. The structures developed during this movement include: (1) NW-trending extensional faults, (2) extensional fault-related folds in Miocene-Pliocene deposits, and (3) buckle folds in Pliocene and post-Pliocene sequences. Buckle folds were developed during NW compression associated with sinistral movement along NNE-SSW strike-slip faults. Gypsiferous shale-rich beds in Miocene-Pliocene rocks played the main role in development of fault-related folds and buckle folds in the Quseir–Umm Gheig subbasin. LITHOSPHERE; v. 2; no. 1; p. 13–32. doi: 10.1130/L27.1 INTRODUCTION 2006a, 2006b) such as the NW-trending shear magmatic expansion (Bohannon, 1989; Bohan- zone of the Najd fault system (Davies, 1984; non and Eittreim, 1991), (6) asymmetric rifting It is generally accepted that the main Red Stern, 1985). (Dixon et al., 1989), and (7) pull-apart basin(s) Sea extension started 30 m.y. ago during the The Cenozoic Red Sea rift belongs to a rift (e.g., Makris and Rhim, 1991). The major dif- late Oligocene–early Miocene and reactivated system that includes the East African rift in the ferences between the various models center on the steep NW-trending late Pan-African shear south and the Gulf of Aden and the Gulf of Suez the relative timing of updoming, rifting, and zones (McKenzie et al., 1970; Meshref, 1990; in the north (Bosworth et al., 2005; Guiraud et magmatism, and whether the rifting was active Moustafa, 1997; Purser and Bosence, 1998; al., 2005; Kinabo et al., 2007). These rifts were and driven by a mantle plume or passive and due Khalil and McClay, 2002, 2009). The initial rift initiated in the late Oligocene (Rupelian) to to lateral extension of the lithosphere leading to occurred in response to the NE separation of the Miocene in several small, en-echelon, approxi- reactive effects in the mantle (Ghebreab, 1998). Arabian plate from the African plate (Nubia), mately E-W– to ESE-WNW–trending basins in The models that invoke graben-horst formation and basins within the Red Sea rift were gener- the Gulf of Aden province (Fantozzi and Sga- along steep normal faults are supported by the ally asymmetric, 60–80 km wide half grabens vetti, 1998; Watchorn et al., 1998), and they earlier semibrittle stage of extension that corre- (Bosworth et al., 2005). The extension direction fragmented the Arabian-Nubian Shield (Marti- sponds to the predicted low-angle simple shear was N60°E during the late Oligocene to Mio- nez and Cochran, 1988). zone through the lithosphere (Ghebreab, 1998). cene (Bosworth and McClay, 2001). The forma- Several rifting mechanisms have been pro- In order to examine the evolution of Red tion of Cretaceous basins and orientation of rift- posed for the Red Sea (reviewed in detail by Sea continental rifting, Bosworth et al. (2005) related normal faulting were strongly controlled Ghebreab, 1998); they include: (1) prolonged distinguished three phases of rifting: (1) late by the presence of a preexisting Precambrian normal faulting (e.g., Lowell and Genik, 1972), Oligocene–early Miocene rift initiation; (2) early fault zone (Dixon et al., 1987; Bosworth, 1994; (2) lithospheric thinning by faulting and dike Miocene main synrift subsidence; and (3) middle Younes et al., 1998; Ghebreab, 1998; Ghebreab injection (Berhe, 1986), (3) diffuse extension Miocene onset of the Aqaba–Dead Sea trans- and Talbot, 2000; Younes and McClay, 2002; followed by brittle deformation (e.g., Martinez form. The Red Sea rift initially included the pres- El Shemi and Zaky, 2001; Khalil and McClay, and Cochran, 1988), (4) lithospheric simple ent Gulf of Suez, Bitter Lakes, and Nile Delta 2002, 2009; Gawthorpe et al., 2003; Bosworth shear (Voggenreiter et al., 1988), (5) combina- region on the continental margin of North Africa et al., 2005; Guiraud et al., 2005; Jackson et al., tions involving detachment faults and prolonged (Bosworth and McClay, 2001). For permission to copy, contact [email protected] | © 2010 Geological Society of America 13 Downloaded from http://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/2/1/13/3049449/13.pdf by guest on 30 September 2021 ABD EL-WAHED ET AL. A magnetic trend analysis carried out for ° ° ° ° the Gulf of Suez–Red Sea region from both 30 E 40 E 50 E60E 40°N Black Sea Caspian regional and residual magnetic maps (Meshref, Sea Eurasian 1990) indicates the presence of the following 40°N plate regional magnetic trends: (1) Gulf of Suez–Red Turkish Sea, Erithrean, or Clysmic (NW) trend of mid- plate Tertiary age, (2) meridional or East African (N-S) trend of Precambrian age, (3) trans-Afri- Anatolian-Persian plateau can, Qena-Safaga, Idfu-Mersa Alam, or Aualitic (NE-SW) trend, (4) Tethyan, Mediterranean, or Mediterranean Sea 30°N Sheikh Salem (E-W) trend of Paleozoic–Juras- Aqaba-Levant ° sic age, (5) Najd (WNW) trend of Precambrian 30 N Gulf of transform age, (6) Atalla (NNW) trend of Precambrian Suez age, and (7) Gulf of Aqaba, Dead Sea, or Aqaba Najd fault zone Najd fault zone (NNE) trend of mid-Tertiary age. Study The study area occurs in the Eastern Des- Area ert of Egypt between Quseir and Umm Gheig along the Red Sea coast (Fig. 1). The Quseir– Arabian Umm Gheig region contains the southernmost plate 20°N exposures of the pre–Red Sea rift stratigraphic 20°N section of the uplifted Egyptian continental mar- African gin. The well-exposed Cretaceous–Pleistocene plate Gulf of stratigraphic successions (Figs. 1 and 2) are Aden subdivided tectonically into two major catego- ries (Said, 1990): the prerift sequence (Precam- brian to Eocene) and the synrift sequence (Oli- 0 500 km Indian gocene–Pleistocene). These stratigraphic units Ocean Afar 10°N were remarkably affected by the tectonic evolu- 10°N tion of rifting. The prerift structures are variably ° ° ° enhanced and disrupted by the synrift struc- 30 E40E50E tures. The structural architecture and tectonic Figure 1. Location of the Quseir–Umm Gheig subbasin and its relation to the Red Sea rift evolution of the northwestern part of the Red system and the Najd fault zone (modifi ed after Hempton, 1987). Borders of Najd fault zones Sea are still not fully understood. Understand- are adopted after de Wall et al. (2001). ing and reconstruction of the tectonic evolution of the northwestern Red Sea and evaluation of the Quseir–Umm Gheig subbasin, Cretaceous basins, and fault-related folds are the main NNW-vergent thrusts, open folds, imbricate N-S extension in the form of an escaping block objectives of this study. This study was based on structures, and thrust duplexes in the Pan-Afri- (Stern, 1994). detailed fi eld mapping using aerial photographs can nappe (low-grade volcano-sedimentary Many NW-striking strike-slip shear zones (1:40,000) and Landsat images (1:250,000) and rocks), (2) a ENE-WSW compression event cre- (Fig. 2) have been recognized in the Precam- analysis of fi eld and structural data collected ated NE-vergent thrusts, folded the NNW-ver- brian rocks of the central Eastern Desert, e.g., from both the prerift and synrift rocks. gent thrusts, and produced NW-trending major Meatiq, Sibai (Fritz et al., 1996, 2002; Abd El- and minor folds in the Pan-African nappe, and Wahed, 2008, 2009, and references therein), STRATIGRAPHY AND STRUCTURAL (3) sinistral shearing related to the Najd fault Hamrawin, and Queih shear zones (Abdeen et FRAMEWORK system developed along NNW- to NW-striking al., 1992; Moustafa, 1997; Abdeen and Greiling, strike-slip shear zones (660–580 Ma), marking 2005). Both sinistral and dextral movements are Stratigraphy of the Quseir–Umm Gheig the external boundaries of the core complexes. documented along the Hamrawin and Queih region (Fig. 3) and a brief description of the Sinistral shearing produced steeply dipping shear zones (Abdeen et al., 1992). Left-lateral Precambrian, pre-rift sequence and synrift sedi- mylonitic foliation and plunging folds in the slip on these faults was related to movement ments is presented in Table 1. NNW- and NE-vergent thrusts.