Oppositely dipping thrusts and transpressional imbricate zone in the Central Eastern Desert of Egypt

Journal of African Earth Sciences 100 (2014) 42–59

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Oppositely dipping thrusts and transpressional imbricate zone in the Central Eastern Desert of Egypt Mohamed A. Abd El-Wahed ⇑ Geology Department, Faculty of Science, Tanta University, Tanta 31527, Egypt

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Article history: Received 11 November 2013 Received in revised form 15 June 2014 Accepted 17 June 2014 Available online 27 June 2014 Keywords: Mubarak–Barramiya shear belt Central Eastern Desert Oppositely dipping thrusts Dungash Um Khariga Dextral transpression

a b s t r a c t This paper documents the 40–60 km wide ENE–WSW trending Mubarak–Barramiya shear belt (MBSB) in the Central Eastern Desert of Egypt by examining its structural styles, kinematics and geometry. Our study revealed the existence of prevalent dextral and minor sinistral conjugate shear zones. The MBSB is metamorphic belt (greenschist–amphibolite) characterized by at least three post-collisional (740– 540 Ma) ductile Neoproterozoic deformation events (D1, D2 and D3) followed by a brittle neotectonic deformation (D4). D1 event produced early top-to-the-northwest thrust displacements due to NW–SE shortening. D2 produced discrete zones of NNW-trending upright folds and culminated in initiation of major NW-trending sinistral shear zones of the Najd Fault System (NFS, at c. 640–540 Ma ago) as well as steeply dipping S2 foliation, and shallowly plunging L2 lineation. NW-to NNW-trending F2 folds are open to steep and vary in plunge from horizontal to vertical. D2 deformational fabrics are strongly overprinted by D3 penetrative structures. D3 is characterized by a penetrative S3 foliation, steeply SE- to NW-plunging and shallowly NE-plunging stretching lineations (L3), asymmetric and sheath folds (F3) consistent with dextral sense of movement exhibited by delta- and sigma-type porphyroclast systems and asymmetric boudinage fabrics. D2–D3 represent a non-coaxial progressive event formed in a dextral NE- over NW-sinistral shear zone during a partitioned transpression in response to E–W-directed compression during oblique convergence between East and West Gondwana developed due to closure of the Mozambique Ocean and amalgamation of the Arabian–Nubian Shield in Cryogenian-early Ediacaran time. Ó 2014 Elsevier Ltd. All rights reserved.

1. Introduction The East African Orogen (EAO) is an accretionary orogen that extends from Arabia to East Africa and into Antarctica and related to closure of the Mozambique Ocean, which formed in association with the breakup of Rodinia 800–900 Ma (Stern, 1994). The Mozambique Belt is the southern part of the EAO and comprises mostly pre-Neoproterozoic crust with a Neoproterozoic–early Cambrian tectonothermal overprint (Bingen et al., 2009). The Mozambique Ocean closed during a protracted period of island-arc and microcontinent accretion between 850 and 620 Ma (Fritz et al., 2013). The Arabian–Nubian Shield (ANS) is the northern part of the EAO and composed mainly of juvenile Neoproterozoic crust (e.g. Stern, 1994, 2002; Johnson and Woldehaimanot, 2003; Johnson et al., 2011). This crust was generated when arc and back arc crust developed within and around the margins of the Mozambique Ocean. ⇑ Tel.: +20 1273960983. E-mail addresses: [email protected], mohamed.abdelwahad@science. tanta.edu.eg http://dx.doi.org/10.1016/j.jafrearsci.2014.06.010 1464-343X/Ó 2014 Elsevier Ltd. All rights reserved.

The late Proterozoic (Pan-African, 900–550 Ma) Arabian– Nubian Shield (ANS) forms the suture between East and West Gondwana at the northern end of the East African Orogen (EAO). The Arabian–Nubian Shield was caught between fragments of East and West Gondwanaland as these collided at about 600 Ma (Meert, 2003). The ANS includes Middle Cryogenian–Ediacaran (790–560 Ma) sedimentary and volcanic terrestrial and shallowmarine successions unconformable on juvenile Cryogenian crust (Johnson et al., 2013). The ANS extends from Jordan and southern Israel in the north to Eritrea and Ethiopia in the south and from Egypt in the west to Saudi Arabia and Oman in the east. The Nubian Shield is separated by the Red Sea from its counterpart, the Arabian Shield. The ANS consists of gneisses, granitoids, and various metavolcanic and metasedimentary rocks. The Precambrian basement of the Eastern Desert of Egypt is the northwestern extension of the Arabian–Nubian Shield (ANS). The Central Eastern Desert (CED) is characterized by two distinctive tectonostratigraphic units. The lower unit comprises high-grade metamorphic gneisses, migmatites, schists and amphibolites and is commonly referred to as the structural basement (El-Gaby

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et al.,1990; Loizenbauer et al., 2001). The upper unit includes lowgrade metamorphosed ophiolite slices (serpentinites, pillow lavas, metagabbros), arc metavolcanics, arc metasediments and is commonly referred to as structural cover or the Pan-African nappes (e.g. El-Gaby et al.,1990; Fritz et al., 1996; Abd El-Rahmana et al., 2012). Both the two units were intruded by syn-tectonic calc-alkaline granites and metagabbros–diorite complex. The later stage of the crustal evolution of the CED is characterized by the eruption of the Dokhan volcanic suite which is associated with the formation of molasse-type Hammamat sedimentary rocks that were deposited in non-marine, alluvial fan/river environments (Grothaus et al., 1979; Abd El-Wahed, 2010; Bezenjania et al., 2014). These crustal rocks were intruded by a series of late to post-tectonic granites. The syn-tectonic granite in the CED has a magmatic emplacement age of 606–614 Ma (Loizenbauer et al., 2001; Andresen et al., 2010) whereas, the late to post-tectonic granites were emplaced at ca. 590–550 Ma (Hassan and Hashad, 1990; Rice et al., 1993). The presence of a series of gneiss domes or core complexes (e.g. Meatiq, Sibai, El- Shalul, Hafafit) in the CED is a subject of controversy over whether gneiss domes and migmatites represent a preNeoproterozoic crust or exhumed Neoproterozoic rocks. The process forming the gneiss domes and the surrounding shear zones is still a matter of debate. Gneiss domes have either been interpreted as: (1) antiformal stacks formed during thrusting (e.g., Greiling et al., 1994), (2) core complexes during orogen-parallel crustal extension (e.g., Fritz et al., 1996; Bregar et al., 2002; Abd El-Wahed, 2008), and (3) interference patterns of sheath folds (Fowler and El Kalioubi, 2002). Geochronology suggests that extension and exhumation of gneiss domes commenced around 620–606 Ma (Fritz et al., 2002; Andresen et al., 2009). Another controversy is about the role of sinistral shearing and transpression related to the Najd Fault System (NFS) in the exhumation of these gneiss domes and in deformation styles of the CED. The Najd Fault System (NFS) consists of brittle–ductile shears in a zone as much as 300 km wide and more than 1100 km long, extending across the northern part of the Arabian Shield. Nowadays, sinistral shearing along the NW-trending shear zones of the NFS has been used to explain the tectonic history of the Central Eastern Desert of Egypt (e.g. Fritz et al., 1996, 2002, 2013; Bregar et al., 2002; Shalaby et al.,2005; Abd El-Wahed, 2008, 2010; Abd El-Wahed and Kamh, 2010). Also, deformation along the NFS is genetically linked with deposition and deformation of Hammamat sediments (Abd El-Wahed, 2010) and emplacement of syntectonic granitoids (Fritz et al., 2013). The CED is characterized mainly by the prevalence of a NWtrending tectonic fabric marking the NW–SE sinistral shear zone of the NFS (Abd El-Wahed and Kamh, 2010). The directions of nappe transport reported from the CED vary from top to the NE (e.g. Elbayoumi and Greiling, 1984), top to the NW (e.g. Ries et al., 1983; Greiling, 1987), top to the SE (e.g. Kamal El Din et al., 1992), and top to the SW (e.g. Abdeen et al., 2002; Abdelsalam et al., 2003). Currently, sinistral and dextral transpression involving oblique convergence has been utilized to explain the deformation styles in the Central Eastern Desert of Egypt (Fritz et al., 1996, 2002, 2013; Loizenbauer et al., 2001; Makroum, 2001; Bregar et al., 2002; Helmy et al., 2004; Shalaby et al., 2005; Abd El-Wahed, 2008, 2010; Abd El-Wahed and Abu Anbar, 2009; Shalaby, 2010; Abd El-Wahed and Kamh, 2010; Zoheir and Lehmann, 2011; Zoheir and Weihed, 2013). Abd El-Wahed And Kamh (2010) arranged the deformation events in the CED of Egypt as follows: (1) D1 linked to NNW-directed thrusts; (2) D2 related to NE- and SW-directed thrusts; (3) D3 attributed to sinistral movement along the NW-trending shear zones of the NFS; (4) D4 associated with dextral movement along NE-trending shear zones; and (e) D5 later events.

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The central part of the CED is marked by a huge NE-trending shear belt (up to 110 km in length) that occupies the area between Wadi Barramiya and Wadi Sha’it to the west (up to 60 km in width) and extends through the whole width of the Central Eastern Desert to include the area between Wadi Mubarak and Wadi Ghadir on the Red Sea coast (up to 120 km in width) (Fig. 1). There is a great controversy about the origin and the deformation styles in the Mubarak–Barramiya shear belt due to its discordant to the NWtrending tectonic fabric marking the CED. The transpressionrelated NW-trending sinistral shear along the NFS is superimposed by the dominant dextral transpression along NE–SW trending shear zones (Shalaby et al., 2005; Abd El-Wahed and Kamh, 2010). This dextral shearing is characterized by the development of NNE- to NE-trending cleavage, strike–slip duplex, NNE- and NE-trending folds, and NNW-directed thrusts (Abd El-Wahed and Kamh, 2010). This study examines the structural and tectonic evolution of the post-accretionary deformational belts in the Arabian–Nubian Shield using new structural data from the Mubarak–Barramiya shear belt (MBSB) and published data for other belts. The main aims of this contribution were to:(i) establish the geometrical features and the detailed structural analysis of the entire MBSB, (ii) examine the role of sinistral and dextral transpression during the dominant deformation events in the shear belt and (iii) establish architecture of the transpressional belt and the kinematics of deformation. We focused on four areas from the Mubarak-Barramiya shear belt (Fig. 1), where kinematic criteria for dextral sense of shear have been recognized, in contrast to sinistral sense of shear to the north and the south of the MBSB. The result suggests that three ductile Late Neoproterozoic deformational events have been involved in the structural history of the MBSB, a coaxial/flattening D1 and a transpressional sinistral (D2) and dextral (D3) over NNWdirected thrusting D1. These three ductile deformational events are later followed by a younger D4 brittle deformation.

2. Geology of the Mubarak–Barramiya shear belt The Mubarak–Barramiya shear belt (MBSB) runs NE–SW to ENE–WSW in the CED (Fig. 1) and deforms supra-crustal successions and structures associated with the NW-trending shear fabric. It constitutes well-defined ophiolite-decorated linear belt where serpentinites represent the most characteristic lithological unit. The geology of the MBSB is commonly described in terms of three major lithotectonic units, namely (i) ophiolite slices and ophiolitic mélange, (ii) island arc metavolcanic and metasedimentary successions and (iii) syn- to post-orogenic gabbroic to granitic intrusions. The ophiolites display imbricate thrust sheets and slices of dismembered ophiolite suites distributed along several localities within the MBSB (Fig. 1). The ophiolitic rocks cropping in MBSB include serpentinized peridotites and dunites, metagabbro, diabase and pillow lavas. They occur as fragments in a metasedimentary matrix that encompasses conglomerates, greywackes, mudstones, volcanoclastics and schists (Takla et al., 1982; Abu El-Ela, 1985; Khalil and Azer, 2007; Ali-Bik et al., 2012). The ophiolitic rocks were dated at approximately 870–740 Ma (Stern et al., 2004; Johnson et al., 2004) and have been formed in the Mozambique Ocean that was formed upon rifting of Rodinia (Abdelsalam and Stern, 1996; Stern, 1994). Farahat et al. (2004) suggested continental (ensialic) back-arc basin origin for Mubarak and Ghadir ophiolites. Serpentinite exposures are thrust-bounded and usually aligned along major suture zones or thrust faults separating the structural basement from the Pan-African nappes. The structural trend and the elongation of serpentinite masses are controlled by major folds which trend mainly NE–SW and NW–SE respectively (Ries et al.,

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Fig. 1. Geological map of the southern part of the Central Eastern Desert of Egypt (modified after KlitzKlitzch et al., 1987). 1; Core complexes 2; serpenitintes, 3; ophiolitic metagabbros, 4; metavolcanics and metasediments, 5; syn-tetonic intrusive metagabbros, 6; syn-tectonic granite, 7; Dokhan volcanics, 8; molasse sediments, 9; felsites, 10; gabbros, 11; post to late tectonic granites; 12; ring complex, 13; Natash volcanics and 14; trachyte plugs. GAK; Gebel Abu Khruq, HCC; Hafafit core complex, GOM; Wadi Ghadir ophiolitic mèlange, HM; Hamash gold mine, NSZ; Wadi Nugrus shear zone, WDSZ; Wadi Abu Dabbab shear zone, WUSZ; Wadi El Umra shear zone, GS; Gebel Sukkari and Sukkari Gold mine, GUK; Gebel Um Khariga, IG; Igla molasse basin, DMD; Dubr metagabbro–diorite complex, GIA; Gebel Igl Al-Ahmar, HW, Gebel Homrat Waggad, GY, Gebel El-Yatima, GUS; Gebel Umm Salim, US, Gebel Umm Saltit, GK; Gebel Abu Karanish, GM, Gebel Al Miyyat, USZ; Um Nar shear zone, GUM; Gebel El-Umra, GK; Gebel Kadabora, GA; GH; Gebel El-Hidilawi, GU; Gebel Umm Atawi, GSH; Gebel El Shalul, GR; Gebel El Rukham; SCC; Sibai core complex, GS; Gebel Sibai, WZ; Wadi Zeidon, WSSZ; Wadi Sitra shear zone, WKSZ; Wadi Kab Ahmed shear zone, K; Kareim molasse basin. The major structures are after Akaad et al. (1994), Fritz et al. (1996), Helmy et al. (2004), Shalaby et al. (2005), Abd El-Wahed (2008) and Abd El-Wahed and Kamh (2010), Area labeled (a) is studied in detail by Abd El-Wahed and Kamh (2010).

1983; El Ramly et al., 1984). Metamorphosed ultramafic blocks in the mélange display both mid-ocean ridge (MOR) and supra-subduction zone (SSZ) affinities (El Bahariya, 2012). The ophiolitic mélange components in the CED are mainly confined to the zones of major thrust faults (El-Gaby et al., 1990) marking the regional shear zones. Ophiolitic mélanges (e.g. Mubarak, and Garf mélanges) comprise a highly sheared and schistose matrix of volcaniclastic metasedimentary and metapyroclastic rocks and both native and exotic clasts and blocks of variable sizes, shapes and types (El Bahariya, 2012). The ophiolitic metagabbros

(massive isotropic and layered) and metabasalts (pillowed and massive nonpillowed metabasalts) occur as allochthonous, elongate blocks, set in a volcaniclastic foliated matrix. The occurrence of volcaniclastic metasedimentary and metapyroclastic rocks with the ophiolitic rocks suggests that the ophiolites formed in an intraoceanic back-arc basin, where the volcaniclastic metasedimets were derived mainly from a coeval volcanic arc (El Bahariya, 2012). On the western parts of the MBSB exists the Barramiya ophiolitic mélange (Fig. 1) that constitutes the largest ophiolitic belt in the CED and hosts several gold occurrences with gold bearing quartz

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veins mostly situated along the ENE-trending shear zones (Zoheir and Lehmann, 2011; Harraz et al., 2012). The tectonically admixed volcanoclastic metasediments and ophiolitic rocks form the Barramiya ophiolitic mélange matrix in the area. The ophiolitic mélange forms an arcuate belt trending WNW–ESE and ENE–WSW, covering an area of about 483 km2. It consists principally of imbricated slices of weakly metamorphosed flyschoid metasediments (distal turbidites and olistostromal deposits), and dismembered ophiolitic sequences, which is formed of serpentinites and talc–carbonate rocks, metagabbros, sheeted metadiabasite dykes, and pillow metabasalts (Abu El-Ela and Farahat, 2010). On the eastern parts of the MBSB exists the Mubarak ophiolitic mélange. It comprises a wide zone of highly sheared ophiolite slices, volcano-sedimentary rocks, arc metavolcanics and volcaniclastics, and intrusive magmatic rocks (Abd El-Wahed and Kamh, 2010). The volcaniclastic metasediments consist of an interbedded sequence of metagreywackes, metasiltstone, metamudstone, lithic metaarenites, metaconglomerates and pelitic schists. The MBSB was intruded by a number of weakly deformed, syntectonic calcalkaline gabbros and granodiorites (670–630 Ma, Farahat and Azer, 2011). The Mubarak–Dubr metagabbro–diorite complex is the largest of such complexes in the CED. This complex is of an island arc, calc-alkaline to minor tholeiitic affinity (Abu ElEla, 1985, 1997; Akaad et al., 1996). Also, the MBSB was intruded by a number of undeformed calc-alkaline granitoids and alkaline/ peralkaline granitoids that formed during late- to post-collisional stage (630–580 Ma) of the ANS crust evolution (Farahat et al., 2007, 2011; Farahat and Azer, 2011). Wadi Igla molasse-type sedimentary basin occurs in the eastern part of Mubarak–Barramiya shear belt. Wadi Igla detrital zircons define a maximum depositional age of 628 ± 6 Ma (Bezenjania et al., 2014), Cryogenian to early Ediacaran in age. Abd El-Wahed (2010) records three deformational eventsin Igla molasse basin; D1 reflects imbricate thrusting in basement rocks in the southeastern part of the basin, with the predominance of NE-trending symmetric folds in the molasse sediments. D2 is related to sinistral movement along NW–SE strike–slip faults of the Najd Fault System and development of ESE plunging folds. D3 is associated with Red Sea rifting and formation of NE–SW dextral strike–slip faulting. The MBSB has been interpreted as a dextral transpressive shear zone and modeled in terms of a regional ‘flower structure’ (Abd ElWahed and Kamh, 2010). The main characteristic features of the MBSB include the following: (i) dominance of NE-, ENE- and E–W structural trends (Makroum, 2001; Shalaby et al., 2005; Abd ElWahed and Kamh, 2010), (ii) existence of highly sheared ophiolite slices and ophiolitic mélange (Abu El-Ela, 1985; Akaad et al., 1994; Farahat et al., 2004; El Bahariya, 2012), (iii) the northern border of the MBSB is marked by SE-dipping thrusts, whereas the southern parts are characterized by NW-, NNW-dipping thrusts (Fig. 1), (iv) the presence of local NW-trending sinistral shear zones (eg. Abu Dabbab and Dungash), (v) existence of thrust fans related to both sinistral and dextral transpression along NW-trending and NE-trending shear zones (Abd El-Wahed and Kamh, 2010), and (vi) the southern parts of the MBSB is separated from the Hafafit gneissic complex by the northwesterly dipping Sha’it normal faults (Shalaby, 2010).

3. Structural setting The MBSB extends northeast–southwest for about 120 km with a width of 60–120 km (Fig. 1). Regionally, the eastern part of the MBSB consists of three major shear zones which include the following: (i) an NE–SW trending 2–10 km wide zone with steep foliations dipping SE along a valley described as Wadi El-Umra shear zone (WUSZ, Fig. 1), (ii) NW–SE trending (3-km-wide, 15-km-long)

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Wadi Abu Dabbab shear zone (WDSZ, Fig. 1) and (iii) NNE–SSW trending Um Khariga shear zone (up to 10 km wide). WUSZ and WDSZ are structurally investigated in detail by Abd El-Wahed and Kamh (2010). Southerly dipping Barramiya (9 km wide) and Dungash (4 km wide) shear zones marks the western part, whereas, the northerly dipping Sha’it shear zone represents the southern boundary of the MBSB. Wadi El-Umra and Barramiya shear zones marks the northern boundary of the MBSB. The eastern and the western shear zones are connected by a set of small-scale shear belts with an average width of 3 km and subvertical high strain foliation traversing the central part the MBSB such as Wadi Garf and Wadi Muweilah shear zones. The shear zones within the MBSB have both low and high strain zones. The low strain zones are fold dominated and show multiple phases of folding whereas, the high strain zones are marked by the presence of well-developed stretching lineation, mylonites, phyllonites and asymmetric fold structures. This study investigates the structural and geometrical features of Barramiya, Dungash, Um Khariga and Wadi Garf shear zones. 3.1. Barramiya shear zone (BSZ) The Barramiya shear zone (BSZ) comprises an association of highly tectonized serpentinites, talc–carbonate together with basic metavolcanic rocks and ophiolitic metagabbros embedded in a matrix volcanoclastic metasediments and schists (Fig. 2). The volcano-sedimentary sequence composed dominantly of different varieties of schists, quartzites and marbles. The schist varieties include chlorite-, graphite-, actinolite-, actinolite–tremolite, tremolite–talc, hematite-, and quartzo-feldspathic schists. Shists are locally intercalated with metagreywackes, metasiltstone and metamudstone. The Barramiya serpentinites represent a fragments of the oceanic lithosphere formed in a back arc basin and belong to the ultramafic cumulate ophiolite rocks (Gad and Kusky, 2006; Zoheir and Lehmann, 2011; Harraz et al., 2012; Ali-Bik et al., 2012; Salem et al., 2012). The serpentinites occur in the form of steeply dipping masses, sheets and lenses emplaced along thrust planes and elongated in ENE–WSW direction parallel to the penetrative foliation of the ophiolitic mélange matrix. Schists, talc–magnesite rocks, listvenite and chromite veinlets mark the thrust contacts between tectonized serpentinites and other mélange components. The northern part of the Barramiya ophiolitic mélange is distinctly intruded by deformed syn-orogenic quartz–diorite/granodiorite and post-orogenic biotite granite. Also, the deformed and folded metagabbro–diorite cuts the schistose metasediments and the metavolcanics in the eastern part of the study area. The southern parts of the map area (Fig. 2) are occupied mainly by island arc metavolcanics of andesitic and basaltic–andesitic compositions. The dominant tectonic fabric comprises the metamorphic shear foliation, which is parallel to lithological contacts. This is well reflected in satellite data and is helpful in the definition of major shear zones, large-scale fold and the disposition of intrusive bodies. The shear zones are defined by deflection and intensification of this prevailing foliation. They are narrow and discrete bands, with a maximum width of a few centimeters, which define an anastomosed pattern. S1 foliation in the MBSB striking ENE–WSW and is related to earlier nappe translation associated with NNW-directed low angle thrusts. Based on the foliation deflection patterns, two main sets of shear zones, NW–SE-trending sinistral and NE– SW-trending dextral, can be distinguished in the BSZ. 3.1.1. NW–SE-trending shear zones Metagabbros and metavolcanics were ductilely deformed into protomylonites along the NW–SE shear zone (Fig. 2a). Mylonitic foliations dip steeply NNE to NE, and a stretching lineation in the

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Fig. 2. (a) Geological map of Wadi Barramiya (lithology modified from Botros, 2004; EGSMA, 1992; Zoheir and Lehmann, 2011) showing major structural elements. (b) and (c) Interpreted structural cross-section across Barramiya shear zone.

direction of strike is generally penetrative. The more competent metagabbro–diorite accommodates strain in relatively narrow, widely separated shear zones, whereas strain is highly localized into a 200 m-wide zone within the less competent metavolcanics. The NW–SE shear foliation around Wadi Beizah is folded into a series of major NNW-trending asymmetric moderately plunging anticlines and synclines (Fig. 2b) in deformed metagabbros and metavolcanics. These folds are clearly seen through the satellite images. These folds gradually open up to the west and the fold hinges (L2) plunge 20° to the NNW. The anticline exists in southeastern corner of the map shows folding of pre-existing NNWdirected thrusts of D1 structures (Fig. 2a). The penetrative foliation (S2) is a product of ductile shearing along NW–SE shear zones and has developed at high angle to the pre-existing S1 foliation. Poles to S2 from the main outcrops show a girdle distribution (Fig. 3a), which is interpreted to indicate folding about an axis plunging 15° to the N52°W. Close to the contact between the deformed metagabbros and the metavolcanics, folds are tight and the steep shear zones are

common, defining a qualitative increase in strain close to the rock boundaries. In higher strain zones, fold axial planes are nearly vertical and are subparallel to shear foliation. Small asymmetrically folded and boudinaged quartz veins (Fig. 4a) with a thickness of 3–5 cm embedded in fine-grained, schistose metasediments. The folds are almost vertical and show ESE-vergence. Ductile shear bands, asymmetric porphyroclast systems, foliation deflections at the shear zone margins and pressure shadows indicate sinistral shear. In the higher schistose parts of the metavolcanics there are many of quartz veinlets concordant with S2 in the shear zones. Kinematic indicators in these sheared and folded quartz show top-to-NW sinistral shear sense (Fig. 4a). 3.1.2. NE–SW-trending shear zones These shear zones are concentrated around the main course of Wadi Barramiya. They are characterized by well-developed linear structures, with well-developed mylonitic planar fabric (S3). The morphology of S3 foliation varies according to the rock type. In the volcanoclastic metasediments and schists a strongly anastomosing foliation develops. Porphyroclastic textures and S–C fabrics

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Fig. 3. Lower-hemisphere equal-area stereographic projection of NW–SE (a) and NE–SW (b) striking foliations from Barramiya shear zone, contoured at 0%, 5%, 10%, 15% and 20%; (c) NW- and SE-dipping thrusts as well as dip slip lineation.

are common. Highly deformed bands and the stretching lineation are well-developed. Petrographic and microtectonic descriptions suggest that deformation began to occur in amphibolite facies conditions and progressed to greenschist facies, preserving a welldeveloped mylonitic fabric. In schists, lineation can be clearly

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marked by aligned actinolite, chlorite crystals and recrystallized quartz. Deformation within the BSZ produced a penetrative regionalscale foliation (S3) which developed in the chlorite-, graphite-, actinolite-, actinolite–tremolite, tremolite–talc schist, hematite-schists and quartz–feldspar mylonite. The earlier foliation (S1) has a mean orientation of N85°E, 35°SSE (Fig. 3a) and is subparallel to parallel to (S3) and the thrust sheets in the study area. S3 mylonitic foliation varies in direction from ENE–WSW to NE–SW and dipping steeply to SE and NW. A stereographic plot of mylonitic foliation (Fig. 3b) indicates folding about an axis shallowly plunging to the NE and SW. Locally, the S3 mylonitic foliation can be parallel to constrictional crenulation foliation. The crenulation foliation is commonly developed in mylonite schist as a conjugate set which is commonly associated with S-shaped asymmetric crenulations. Lineations formed in the BSZ are stretching lineation in the mylonites and defined by the long axes of the quartz ribbons, mesoscopic and hinges of minor folds. Throughout the area, the mean plunge and trend of the L3 lineations are 20–50° to NE and SW (Fig. 3c). Schists and schistose metasediments around Gebel Um Salatit and Gebel Um Salim serpentinite masses represent the high-strain rocks in the NE–SW shear zones. These rock show well-developed steeply dipping mylonitic foliation (S3) that defined by preferred alignment of actinolite, chlorite, quartz ribbons and feldspar augens. The stretching lineation (L3) has a moderate to steep south-easterly plunge and defined by preferred mineral orientation. Slip lineation plunge southeast and south-southeast, down the dip of foliation, and recognized by stretched talc carbonate pods, stretched amphiboles and quartz fibers. A rare example of the presence of both steep as well as shallow plunging lineations in the same outcrop (Fig. 4b) has been described from the BSZ. Oppositely dipping thrusts to SE in the northern bank of Wadi Barramiya, and to NW in the southern bank displays a typical fan-like structure (Fig. 2c) in BSZ. The thrusts in the BSZ show an ‘‘in-sequence’’ style of propagation. Every new thrust develops in footwall of the previous thrust in piggyback thrust manner. Popup structures (Fig. 4c and e), flower-like cleavage (Fig. 4d and e) and opposite thrusts are clearly observed. Continuity of dip–slip movement in a sense of reverse induced stacking of the rock masses in the hanging wall above sole thrust in the meantime antithetic movement is activated, forming a back thrusting and pop-up structures. The uplifted hanging wall block between the fore (main) thrust and back thrust is the pop up. Propagation of thrust slices bounded by sole thrusts at the base and by roof thrusts at the top is encountered, forming occasional thrust duplex structures and F3 thrust-related folds. In the northeastern part of the map area, NE- to NNE-trending shear foliation, imbricated ophiolite slices (Fig. 4f and g) and stacking form duplexes range from centimeters to meters in scale. A mesoscopic thrust duplexes comprise the ramps that formed the summit of Gebel Um Salatit (serpentinites, 520 m) and Gebel Um Salim (serpentinites, 500 m) (Fig. 2a). The NE–SW-striking S3 shear foliation is moderately to strongly folded about gently NE or SW-plunging axes. Decimeter- to mapscale steeply plunging folds (F3) are observed especially in schistose metasediments around Wadi Barramiya. These folds are open to tight, asymmetrical overturned and recumbent (Fig. 4h and i). Locally, such folds are non-cylindrical, presenting curved axes and form sheath folds. F3 folds have amplitudes of 2 km and wavelengths of 1 km, and fold hinges trend mainly parallel to the stretching lineation. Asymmetric folding is an important structural feature within the BSZ (Fig. 2a). These folds are observed on a cm- to m-scale and consist of long, SE-dipping and NW-dipping fold limbs. Parasitic, cm-scale M- and S-folds are also observed in the hinge zones of larger-scale structures. The vergence of these

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Fig. 4. (a) Asymmetrically folded and boundinaged quartz veins show top-to-NW sinistral shear sense; (b) shallow and steep plunging lineations in the same outcrop close to Barramiya gold mine; (c) uplifted hanging wall block between the fore (main) thrust and back thrust is the pop up, Wadi Barramiya, looking SW; (d) flower-like cleavage in serpentinites, Wadi Barramiya, looking SW; (e) flower-like and pop-up structures in serpentinites, Wadi Barramiya, looking SW; (f) and (g) imbricate thrusts between serpentinites and talc–carbonate pods, Wadi Barramiya, looking NE and NW respectively; (h) overturned steeply plunging F3 fold in schistose metasediments, looking NE, and (i) moderately plunging asymmetrical F3 fold in schistose metagreywacke, Wadi Barramiya, looking NW.

major asymmetric folds is consistent with a top-to-the-NW sense of movement. Well-developed kinematic indicators are recognized throughout the NE–SW shear zone at both outcrop and thin-section scale. These include shear bands (S-shaped asymmetric crenulations), the asymmetric r and d shaped quartz and feldspar porphyroclasts with symmetrical and asymmetrical augen tails and sigmoidal rock clasts and large augen-shaped structures. Gebel Um Salim and Gebel UM Saltit present a clear example of sigmoidal serpentinite clasts with dextral sense of shear (Fig. 5). The larger quartz grains and porphyroclasts contain sub-grains and fine-grained quartz and show deformational bands and undulatory extinction. Kinematic indicators show a consistent top-to NE-dextral shear sense and reverse dip–slip component with top-to-NW sense of strain components. 3.2. Dungash shear zone (DSZ) Wadi Dungash area is part of Muweilah–Dungash mélange sequence which represents remnants of imbricate ophiolitic slices tectonically intermixed with island arc metavolcanic/volcaniclastics and metasedimentary rocks metamorphosed to greenschist

Fig. 5. ETM-Landsat 7 image showing the less deformed augen-shaped serpentinite masses of Gabal Um Salim and Gabal UM Salatit within the high-strain zone of Barramiya shear zone (BSZ) indicating dextral sense of shear.

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facies (Helba et al., 2001; Zoheir et al., 2008; Khalil et al., 2003; Abu El-Ela and Farahat, 2010; Zoheir and Weihed, 2013). Ophiolites include serpentinites, metagabbro and pillow basalt, embedded in schistose metasediments matrix. Serpentinites are usually associated with talc-magnesite rocks and form masses and slices overthrusted the island arc assemblage (Fig. 6a). The later ranging in composition from basic to intermediate metavolcanics (andesite to basaltic andesite and subordinate dacite) together with pyroclastic tuffs. Metagabbros and metavolcanics are variably deformed and show major and minor NE- to E–W-trending folds. Schistose metasediments are strongly folded and comprises a succession of metasiltstone, metagreywacke, phyllite and schist, and show gradational contacts with volcaniclastic rocks. These rocks are intruded by calc-alkalic and alkalic granitic rocks. DSZ is an east–west–trending shear zone that dips steeply to the north and rarely to south. The DSZ is defined by deflection and intensification of the prevailing foliation (F3). It comprises narrow and discrete bands, with centimeter to meter-scale shear zones showing an anastomozing and undulating geometry (Fig. 7a). It is dissected by dense networks of quartz veinlets along strike. The morphology of foliation (F3) in DSZ varies according to the rock type and generally shows NNE- to SSW-dipping foliation (Fig. 6b) and WSW–SW-and NW-plunging stretching lineation (L3) (Fig. 6c). In the schistose metasediments, sheard metavolcanics and schists, anastomosing foliation develops. Porphyroclastic textures and S–C mylonites are common. The deformed metavolcanics are moderately to strongly folded about gently WNW or EW-plunging axes. Decimeter- to meterscale folds are observed along Wadi Dungash. These folds are open to asymmetrical overturned (Fig. 7b and c). The Folds are restricted to some outcrops and occasionally rootless. The axial surfaces of these folds run parallel to the mylonitic foliation, and their curved axes lie at an angle to the stretching lineation. Asymmetric fold

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traces on horizontal sections are everywhere dextral and compatible with the sense of shearing along DSZ. The transpressive character of deformation in the DSZ is shown by the coexistence of strike–slip and compressive structures. The orientation of the stretching lineation shows different geometrical relations with respect to the transport direction. In DSZ, the stretching lineation is parallel to the direction of tectonic transport. Moderately NW-plunging stretching lineations are associated with EW-oriented thrusts (Fig. 6c, Fig. 7d and e) whereas sub-vertical foliation and subhorizontal stretching lineations (Fig. 6d, Fig. 7f and g) characterize the EW- to ENE-directed shear zones. Kinematic indicators throughout the DSZ include the S-shaped geometry of the central part of Wadi Dungash, r and d shaped quartz and feldspar porphyroclasts and shear bands and sigmoidal geometry of undeformed clasts (Fig. 7a). The main ductile deformation was partitioned into a horizontal dextral strike–slip and a top-to-theNNW sense of strain components, depending on whether or not a mineral lineation is developed on the foliation. The gold deposits at Dungash mine area (24°560 2000 N and 33°510 3000 E) occur in an EW-trending quartz vein along post-metamorphic brittle-ductile shear zones in metavolcanic and metasedimentary host rocks. Zoheir and Weihed (2013) investigated the Dungash mine area and stated that the auriferous structures define E–W dextral shear system between foliated metavolcanic/volcaniclastic rocks and metasediments based on the sigmoidal geometry of quartz pods zone. 3.3. Um Khariga imbricate thrusts Um Khariga area consists of metavolcanics, volcaniclastic metasediments and serpentinites (Fig. 8a). The metavolcanics around Wadi Um Khariga are mainly basaltic and dacitic–rhyodacitic flows and volcaniclastics. Around Wadi El Sukari, there is

Fig. 6. (a) Geological map of Dungash area (lithology modified from Helba et al., 2001) showing different structures; (b) lower-hemisphere equal-area stereographic projection of foliation from Dungash area, poles (65) are contoured at 0%, 5%, 10%, 15% and 20%; (c) NW- and SE-dipping thrusts as well as dip slip lineation; and (d) dextral shear zones and sub-horizontal lineation.

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Fig. 7. (a) East–west–trending shear zone comprises narrow and discrete bands and showing an anastomozing and undulating geometry; (b) and (c) open to asymmetrical overturned folds (F3) in deformed metavolcanics and serpentinites respectively; (d) and (e) EW-oriented imbricate thrusts; (f) and (g) sub-vertical foliation and subhorizontal stretching lineations in metaandesite and banded metatuffs respectively.

succession of coarse metatuffs interbedded with lapilli metatuffs and metabasalt agglomerates (Abu El-Ela, 1992; Akaad et al., 1994). Um Khariga metapyroclastics comprise fine and coarse metatuffs, lapilli metatuffs and agglomerates together with subordinate flows of metadacite and metarhyodacite. The Um Khariga serpentinites form dissected elongated massive masses with sheared and foliated peripheries. The serpentinite bodies are altered to talc– carbonate rocks along the shear zones. Geochemical compositions of serpentinites indicate that they formed at spreading centers associated with subduction zones (Khalil and Azer, 2007). Um Khariga metavolcanics are intruded by metagabbro–diorite, dolerites and alkali feldspar granite of Gebel El Sukari. The metavolcanics are overlain unconformably by molasse-type sediments of Wadi Igla. Schistosity (S3) is well developed and has 25–65° dip to the WNW throughout the Um Khariga study area (Figs. 8c and 9a). Um Khariga metavolcanics/volcaniclastic metasediments are tectonically emplaced over the metapyroclastic along NW-dipping major thrust (Fig. 8b and d). Also, tabular and lenticular masses of serpentinite are tectonically emplaced over El Sukari

metavolcanics along another major NW-dipping thrust (Figs. 8d and 9b). These major thrusts together with many of minor thrusts within metapyroclastics and volcaniclastic metasediments constitute an imbricate thrust in the eastern part of the MBSB. These NW-dipping thrusts were previously mapped as SE-dipping thrusts to represent the northern extension of the NW-trending thrusts east of the Hafafit dome with top-to-the-WNW senses of movement forming a single thrust duplex as proposed by Fritz et al. (1996) and Helmy et al. (2004) and associated with Nugurs left-lateral strike–slip shear zone to the east of Hafafit dome (Fig. 1). Folds with high amplitudes and short wavelengths occur in schistose metasediments and volcaniclastics whereas, low amplitude folds with parallel geometry occur in sheared metavolcanics (Fig. 9c). Axial planes of these folds are moderately to steeply dipping to the east with axes plunging moderately to the north. Kinked shear foliation (Fig. 9d), boudinage and pinch-and-swell structures (Fig. 9e), augen-shaped clasts (Fig. 9d), and WNWplunging stretched lineations indicate top-to-the-ESE senses of movement along the Um Khariga imbricate thrusts.

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Fig. 8. (a) Geological map of Um Khariga (lithology modified from Akaad et al., 1994) showing major structures; (b) Interpreted structural cross-section across Um Khariga imbricate thrust system. Lower hemisphere, equal area projections of the structural elements developed at Um Khariga area, (c) poles to S3 foliation, contoured at 0%, 5%, 10%, 15% and 20% per 1% area, and orientations of L3 fold axes; (d) NW-dipping thrusts and dip slip lineation.

The Sukari gold mine is the largest such mine in the CED of Egypt. The Sukari granitoid is elongated in a NNE direction, bounded from west and east by two steep shear zones and dissected by numerous quartz vein some of which have gold mineralization and trend (N–S, NNE–SSW). At Sukari, bulk NE–SW strike–slip deformation was accommodated by a local flower structure and extensional faults (Helmy et al., 2004). 3.4. Wadi Garf imbricate thrusts Wadi Garf area occurs to the north of Migif–Hafafit gneiss dome and comprises volcaniclastic metasediments, metavolcanics and serpentinite and related rocks (Fig. 10a) forming a typical tectonic mélange (Masoud, 2009; El Bahariya, 2012; Abu El-Ela et al., 2013). The volcaniclastic metasediments consist mainly of interbedded metamudstones, metagreywackes, metaconglomerates, and schists. The serpentinite and related rocks form conspicuous slices and elongated masses running parallel to the main trend of foliation. The tectonic mélange contain a number of rigid masses,

blocks and lenticels of serpentinites and ophiolitic metabasalts enclosed within a penetratively-deformed mélange matrix forming an anastomosing structural slice shear system. Slabs and dike-like bodies of quartz–carbonate rocks are widely scattered throughout the Garf tectonic mélange. The metavolcanics, ophiolitic metabasalts and all the serpentinites are thrusted over the volcaniclastic metasediments forming series of SW-verging imbrication thrust fan (Fig. 10b and d). Metamorphism is dominantly greenschist facies and synchronous with deformation and development of regional foliation. Foliation in the deformed mélange matrix strike NNE–SSW in the eastern part of Garf area, then turn to NW–SE close to the central parts and show E–W attitude in the western parts (Fig. 10c). The orientation of the stretching lineation change from NNE-plunging in the eastern parts to NW-plunging in the western parts depending on the transport direction. There is a series of major anticlines and synclines with WNW-plunging axes associated with imbricate thrusts in the volcaniclastic metasediments (Fig. 10d and e). The fold hinges are at an angle to the mineral lineation and the folds

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Fig. 9. (a) Well-developed NNE–SSW striking foliation in Um Khariga metapyroclastics; (b) serpentinite are tectonically emplaced over El Sukari metavolcanics along NWdipping thrust; (c) low amplitude F3 folds in sheared metavolcanics; (d) Kinked shear foliation in metapyroclastics; boundinaged serpentinites and pinch-and-swell structure in metapyroclastics and (e) augen-shaped clast in metpyroclastics.

are typically non-cylindrical with moderate to steep plunge angles (Fig. 10f). Scarce dextral shear zones composed of narrow and discrete bands and defined by deflection and strengthening of foliation (Fig. 10g). Kinematic indicators such as slip lineations and steps on the fault surfaces as well as the vergence of the mesoscopic folds indicate thrust transport toward the SSW. 4. Shear kinematics In high strain zone accompanied by steep foliation and sub-horizontal stretching lineation, dextral shear sense is clear from asymmetric fabric geometries and centimeter-scale folds of the foliation exposed in outcrops. These asymmetric shear microstructures indicate that the MBSB is a dextral strike–slip ductile shear zone. The outcrop-scale kinematic criteria, obtained from rocks in the field and thin-sections cut parallel to the lineation and perpendicular to foliation, include asymmetric quartz and feldspar porphyroclasts with recrystallized tails (Fig 11a–d), r-type serpentinite porphyroclasts and S–C composite fabrics in talc–carbonate serpentinites (Fig 11e), asymmetric plagioclase augensand en echelon boudinages (Passchier and Simpson, 1986) indicate a dextral sense of shear in an northeast–southwest direction along the MBSB. On the other hand, kinematic analysis indicates that dip–slip movements predominate with a consistent top-to-the-NW and top-tothe-SE sense of movement across the entire thrust fan-like structure. The MBSB combines strike- and reverse slip sense of movements therefore, it accommodates a characteristic compressional strike–slip duplex in the CED. This strike–slip duplex, which include a collection of dextral strike–slip and thrust faults have a flower structure in cross section. According to the Riedel shear structure, first reported by Cloos (1928) and Riedel (1929), The NW-trending major sinistral shear zones and NE-trending dextral shear zones in the CED represent conjugate shear zones and denoted synthetic Riedel shear faults (R), antithetic Riedel shear faults (R0 ) respectively. The R0 -bands are antithetic to the sense of slip across the shear-zone, forming arrays dextral along sinistral shear-zones (Figs. 12 and 13).

5. Deformation history The MBSB evolved through three phases of deformation (Dl, D2 and D3) related to collision between East and West Gondwana (Stern, 1994) at c. 740–540 Ma ago. D1 phase involves NNW–SSE shortening and is documented in the BSZ (Fig. 2). This phase is represented by a set of ENE–WSW trending imbricate thrust sheets dipping toward the NNW (Fig. 12a), shear foliations (S1) along thrust planes, and NNW plunging stretching lineation. These imbricate thrusts were folded by D2 structures to produce NNW-trending major upright folds in metavolcanics and serpentinites. The early NNW–SSE shortening event is related to oblique island arc accretion (740–680 Ma) and characterized by stacking and imbrications of Pan-African nappe (Fig. 12a) from SSW to NNW. NNW–SSE shortening is documented by large-scale thrusting (toward the NNW) and folding, distributed over the Eastern Desert of Egypt (Greiling et al., 1994). A regional nappe transport toward the NW is documented in the CED from Meatiq (MCC), Sibai (SCC), Hafafit (HCC, Fig. 1) core complexes (Greiling, 1997; Fritz et al., 1996; Loizenbauer et al., 2001; Abd El-Wahed, 2008) and from Wadi Mubarak belt (Shalaby et al., 2005). Similar NNW or SSW direction of thrust transport has been reported in the Allaqi–Heiani suture, southeastern Egypt (Abdelsalam et al., 2003; Abdeen and Abdelghaffar, 2011) and from Oko shear zone, northern Sudan (Abdelsalam, 1994). D2 is associated with NW-trending sinistral strike–slip faults of the Najd Fault System (NFS), which developed at c. 640–560 Ma ago. The preserved D2 structures in the MBSB include NW- to NNW-trending (Fig. 12b), and steeply dipping strike–slip shear zones with dominant sub-vertical foliation and sub-horizontal Lineation. S2 varies in direction from NNW- to NW–SW and dipping steeply to NE and SW. F2 folds are of NW- to NNW-trending axial plans (Fig. 12b), open to steep and vary in plunge from horizontal to vertical. These folds are identified as representing the oldest folds within the MBSB phase since they folded the pre-existing ENE–WSW trending imbricate thrusts and overprinted and truncated by D3 shear fabric. The folded quartz veins were involved in NNW-directed thrusting (D1) and folded during D2.

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Fig. 10. (a) Geological map of Wadi Garf area (lithology modified from Masoud, 2009; and Abu El-Ela et al., 2013) showing major structures; (b) interpreted structural crosssection across Wadi Garf imbricate thrust system. (c) Lower hemisphere, equal area projections of poles to S3 foliation, contoured at 0%, 5%, 10%, 15% and 20% per 1% area, and orientations of L3 fold axes; (d) NNE-dipping thrusts and dip slip lineation; (e) metagreywacke trusted over schistose metamudstone along NW-dipping thrust; (f) asymmetrical fold in volcaniclastic metasediments and (g) dextral shear zones composed of narrow and discrete bands and defined by deflected foliation.

D2 structures of the NW-trending sinistral shear zones are truncated and overprinted by the D3 shear structures related to the NEtrending dextral shearing along MBSB (Fig. 12c). The thrust fans related to the sinistral shearing (e.g. Nugrus and Abu Dabbab thrust fans) are markedly overprinted and dislocated by another imbricate fan formed during oblique dextral movement along the MBSB. The plunges of some D2 fold axes changed from sub-horizontal to sub-vertical D3 folds due to dextral shearing along MBSB. The geometrical relationship between D2 folds and D3 dextral shearing indicates that the two events represent a progressive deformation phase as indicated by the break of D3 NE-trending dextral strike–slip shearing along the inflection planes of D2

NNW-trending folds (Fig. 12c). The D3 dextral strike–slip shear zones were initiated as conjugate ductile shear zones along NWsinistral and NE-dextral complementary orientations. The initiation of a major sinistral transpression (660–645 Ma) along the NW-trending shear zone in the CED was accompanied and followed by a dextral transpression (645–540 Ma) along the NEtrending planes especially along MBSB. Deformation associated with both NW- sinistral and NE-dextral strike slip shear zones in the CED occurred under low greenschist facies metamorphism. This is principally marked from the mineral assemblages of the metavolcanics and volcaniclastic metasediments where typical low greenschist facies metamorphic minerals such as chlorites and green amphiboles are observed.

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Fig. 11. Shear indicator with dextral sense of shear from Mubarak–Barramiya shear belt (MBSB), (a) recrystallized quartz porphyroclasts in mylonite, (b–d) slightly altered plagioclase porphyroclasts in mylonite and (e) r-type serpentinite porphyroclast and S–C composite fabric in talc–carbonate serpentinites from Umm Khariga shear zone to the southwest of Sukari gold mine.

6. Discussion 6.1. Transpressional deformation in the MBSB In the Eastern Desert, both extensional, compressional and transpressional deformation, as they are recognized in the Arabian Nubian Shield (ANS), represent post-collisional structures (Greiling et al., 1994; Fritz et al., 1996; Abd El-Wahed and Kamh, 2010; Abdeen and Abdelghaffar, 2011). The early compressional structures (NNW-directed thrusts and early F1 folds, Fig. 12a) were overprinted by transpression, which is localized to particular zones (Greiling et al., 1994; Fritz et al., 1996, 2013; Abd El-Wahed, 2008, 2010; Abd El-Wahed and Kamh, 2010), for example the Allaqi–Heiani shear zone, the NW–SW oriented Wadi Kharit–Wadi Hodein (Fig. 13), and the N–S-oriented Hamisana and the Oko shear zones in southern Eastern Desert (Fig. 9 and 10 in Greiling et al., 1994) and the Najd fault zones in the CED. The most important of such faults in the northwestern ANS are the NW–SE-oriented Najd Fault System (NFS) and represent the youngest major structural element in the Eastern Desert (Stern, 1985). The structures in the Najd Fault zone were developed in response to a sinistral transpressive tectonic regime, with the axis of maximum compressional stress oriented at oblique angles to the NW-trending orogenic front (Fig. 13). The sinistral strike–slip shearing along the NFS was accompanied by transpressional and transtensional tectonic regimes (Fritz et al., 1996). Transpression resulted in formation

of ESE- to ENE-shortening that produced NNW- to NW trending folds throughout the CED. These are superimposed on early NNW-directed thrusts and related structures (Fig. 12B). In the MBSB, mylonitization and phyllonitization affected a variety of protoliths, including serpentinites, volcano-sedimentary succession and quartz–diorite/granodiorite. S3 varies in intensity from very weak at the margin of undeformed areas to mylonitic within high-strain zones. Two main types of S3 planar structure related to ductile deformation are present in the MBSB: (1) A main foliation (S3) is developed in all rock types. It is defined by the preferred orientation of amphiboles, flattened quartz and relic feldspar phenocrysts in the volcaniclastic metasediments, schists, sheard metavolcanics, and peripheries of elongated serpentinites masses. S3 is penetrative in character, except for the areas containing metavolcanics and huge masses of metagabbro-diorites (e.g. Um Khariga, Dungash and Wadi Dubr). (2) A mylonitic foliation (S3m) occurs in the eastern and western parts of the MBSB and within the high-strain zones. The mylonitic foliation consists of bands (cm to several m wide) of fine-grained mylonite and protomylonite. A stretching lineation (L3) is well developed in the highstrain zones and decreases in intensity toward the undeformed areas. It is defined by a linear preferred orientation of actinolite streaks on S, C and Sm surfaces, and as a shape elongation of feldspar porphyroclasts and quartz grains. The fold axes lying parallel and close to the stretching lineation. This parallelism suggests that simple shear caused the folding can

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Fig. 12. Cartoon showing tectonic evolution of the Central Eastern Desert (CED) and Mubarak–Barramiya shear belt (MBSB).

be interpreted as indicators of high finite shear strain (e.g. Dehler et al., 2007). The geometrical relationship between mylonitic foliation and the stretching lineation suggests the predominance of oblique movements over strike–slip and dip–slip movements. Planar and linear data relationships are coherent with highly oblique dextral displacements. The sub-horizontal mineral stretching lineations and sub-vertical mylonitic foliations, concentrated on foliation planes and typical shear indicator (Simpson and Schmid, 1983), define the MBSB as a dextral strike–slip ductile shear zone. Two major oppositely dipping ductile thrust systems with contrasting senses of displacement (Fig. 12c) associated with gently plunging folds occur on both sides of the strike–slip axial zone of the MBSB. The geometry of the composite shear zone is considered to reflects a crustal-scale flower structure (Abd El-Wahed and Kamh, 2010) or fan-like structure related to regional transpression causing locally horizontal shortening and vertical extruding. The geometric relations between SE-dipping and NW-dipping of thrusts and the consistent down dip orientation of the mineral stretching lineation, in combination with the kinematic data,

indicate reverse dip–slip displacement along the thrusts. These thrusts may represent fore-arc and back-arc thrust systems obliterated the earlier dextral strike–slip translational components. The MBSB consists of oppositely dipping foliations to SE in its northern parts, passes through the vertical and flips over to NW in the southern parts forming a fan-like structure in the CED. This geometry is considered as a late synclinal folding due to northwestward thrusting (Fowler and osman, 2009) or as a mega flower structure related to dextral transpressive deformation (Abd ElWahed and Kamh, 2010) on the basis of variations in fabrics and the presence of thrust faults. Similar structures have also been recognized in other transpressional zones in the southern parts of the ANS like Oko shear zone, Sudna (Abdelsalam, 1994), Kaoko Belt, Namibia (Goscombe and Gray, 2008) and Madagascar (Tucker et al., 2007; Raharimahefa and Kusky, 2008). Transpression is a combination of simple shearing and an orthogonal pure shearing (Harland, 1971; Woodcock and Rickards, 2003; Dehler et al., 2007; Goscombe and Gray, 2008; Kumar and Prasannakumar, 2009; Abd El-Wahed and Kamh, 2010, 2013). Tikoff and Greene (1997) have shown that in

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Fig. 13. Major structure in the Central Eastern Desert (CED) where the NW-trending major sinistral shear zones and NE-trending dextral shear zones represent conjugate shear zones and denoted synthetic Riedel shear faults (R), antithetic Riedel shear faults (R0 ). The Najd Fault Zone in the Eastern Desert is enclosed between Kharit–Hodein shear zone in the south and Duwi Shear Zone to the north. SED; South Eastern Desert, CED; Central Eastern Desert, NED; Northern Eastern Desert, NSZ, Nugrus shear zone, UNSZ, Um Nar shear zone, HCC; Hafafit Core Complex, SCC; Sibai Core Complex; MCC; Meatiq Core Complex. This map is compiled from Greiling et al. (1994), Fritz et al. (1996), DeWaele et al. (2011) and the present study.

wrench-dominated transpression, stretching lineations are either horizontal (low strain) or vertical (high-strain) whereas, they are always vertical in a pure shear dominated transpression. Vertical stretching lineations within a vertically oriented shear zone, perpendicular to the simple shear component of deformation and the direction of tectonic movement, were first interpreted to be the result of transpressional deformation by Hudleston et al. (1988). Theoretical models of heterogeneous transpression (Robin and Cruden, 1994; Jiang and Williams, 1998) interpret that lineations could range from horizontal to vertical continuously, depending upon the value of finite strain. The present MBSB shows both sub-horizontal and sub-vertical stretching lineations at low and high strain zones. The behavior and the attitude of stretching lineations along the MBSB is complex. The imbricate thrusts are dominated by steeply plunging lineations, whereas steeply dipping foliation is associated with shallow to gently plunging lineations. The dextral strike–slip shear movements within the MBSB are associated with Riedel shears and the kinematic indicators are consistent with predominance of dextral movements along the MBSB (Fig. 13).

6.2. Regional significance of transpression The style of NE-dextral deformation in the MBSB is exceptional and this invites comparison with other major shear zones within the CED. The core complexes in the CED (e.g. Meatiq, Sibai, Shalul and Hafafit) are distributed along a NW-trending major zone that extends for more than 400 km between Wadi Hodien in the south to Wadi Quieh in the north (Fig. 12). There are two main tectonic models explain the formation and exhumation of these core complexes in the CED; (i) orogen-parallel extension model of Fritz et al. (1996) assigned the evolution of the core complexes to sinistral shearing along the NW-trending shear zones of the NFS (e.g. Greiling et al., 1994; Fritz et al., 1996, 2002, 2013; Bregar et al., 2002; Shalaby et al.,2005; Abd El-Wahed, 2008; Abd El-Wahed and Kamh, 2010; Zoheir and Weihed, 2013), (ii) the second model attributed the formation of gneiss-cored domes to extensional tectonics by an overlap between NW–SE complex folding and NW–SE extension (e.g., Greiling et al., 1988; Fowler and Osman, 2001, 2009; Fowler et al., 2006, 2007; Andresen et al., 2010).

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The structural fabric in CED is related to three major tectonic event; D1 structures related to NNW-directed thrusts, D2 structures produced by NW-trending sinistral shear zones and D3 is associated with NE-trending dextral shear zones. The NNW-directed thrusts were produced as a consequence of compressional oblique island arc-accretion between 690 and 650 Ma in Sibai dome (Bregar et al., 2002; Fowler et al., 2007; Augland et al., 2012) and 630 and 609 Ma in Meatiq and Hafafit domes (Andresen et al., 2009). The tectonic regime changed from the compressional arcaccretion setting to the sinistral transpressional regime between 650 and 540 Ma. The Najd Fault System (NFS) is a complex set of left-lateral strike–slip faults and ductile shear zones that strike NW–SE across the Arabian–Nubian Shield (Stern, 1985). The NW-striking shear zones and faults of the Najd Fault System are the dominant structural elements within the CED (Fig. 13). They are preserved to the north (Sibai and Meatiq core complexes) and south (Hafafit core complex) of the Mubarak–Barramiya shear belt (MBSB) (Figs. 1 and 13). The core complexes (Fig. 13) are bounded in the northeast and southwest by NW-trending sinistral strike–slip shear zones related to the NFS such as Nugrus shear zone to the east of Hafafit core complex and Um Nar shear zone to the north of MBSB. These two major shear zones are dominated by strike–slip duplexes and linked with imbricate ramps and thrusts (Makroum, 2003; Shalaby et al., 2005). Fritz et al. (1996) interpreted the Wadi Ghadir SE-dipping thrusts as an example of a flower structure associated with sinistral transpressional along Nugrus shear zone. Shalaby et al. (2005) considered that the Um Nar and Wadi Nugrus shear zones (Fig. 1) to represents a continuous regional sinistral structure in the CED. Our study argues against the presence of the Um Nar– Nugrus sinistral shear zone within the MBSB where the D3 dextral structures superimposed on D2 sinistral shearing. Also, the area between the Um Nar and Wadi Nugrus shear zones is intruded by late to post-tectonic granite and exhibits NE-trending structural fabric. On the other hand, the northern part of Wadi Hafafit culmination is separated from MBSB by northwestward dipping and NE– SW striking Sha’it normal fault (Fig. 9, Fowler and Osman, 2009). This fault ends eastward on the Nugrus sinistral strike–slip shear zone and considered by Shalaby (2010) to represent subsidiary R- and P-shears to the Nugrus master shear zone and developed either older than or synchronous to this shear zone. Accordingly, Nugrus sinistral shear zone and their secondary normal shear zone to the east and the north of Wadi Hafafit culmination respectively, are older than D3 dextral structures within the MBSB. The NW-trending transpressional shear zones that bound the core complexes were developed in response to a sinistral transpressive tectonic regime (Fritz et al., 1996, 2013; Bregar et al., 2002; Abd El-Wahed, 2008) and display a well-developed vertical foliation and sub-horizontal lineation. The sinistral shear zones that bound Hafafit core complex may represent a continuous regional sinistral structure with those bounding Sibai and Meatiq core complexes and then dislocated by NE-dextral transpressional shearing of the MBSB. This assumption is evidenced by: (i) There is no evidence in the field for the continuation of any NW-trending sinistral shear zone within the MBSB (e.g. discontinuity of Um NarNugrus shear zone within the MBSB), (ii) the thrust fan to the east of Hafafit dome is dragged from NW to NE and consists of SE-dipping thrusts compared with NW-dipping thrusts of Um Khariga imbricate thrusts to the west of Maras Alam (Fig 13), and (iii) the dragging and curving of foliation trajectories to NE- and WNWtrending to the north and northeast of Hafafit dome. We interpret the MBSB as a NE-dextral transpressional structure dividing and dextrally dislocating the central part of the Cental Eastern Desert (CED) of Egypt into two subregions, the northern one includes the Sibai and Meatiq core complexes while the southern one includes the Hafafit core complex.

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7. Conclusions The MBSB is post-accretionary deformational belts in the Arabian–Nubian Shield and characterize by the following evolutionary sequence: (1) Early NW–SE shortening (D1) associated with accretion of island arcs and obduction of ophiolites over old continent. D1 produced NNW-directed thrusts and ENE–WSW oriented folds in the CED. (2) an E–W-directed shortening deformation was superimposed due to oblique collision between the Arabian– Nubian Shield and the Nile Craton (D2) this produced NW-trending upright folds, NE-dipping and SW-dipping thrusts and discreet NW–SE tending shear zones in the CED. NNW-directed thrusts belonging to D1 were folded around NNW–SSE trending fold axes. Continuing E–W shortening rotated the folded thrust to steeply dipping orientations and initiation of major NW-trending sinistral shear zones and culminated in the initiation of major dextral strike–slip shear zones (D3) as conjugate sets with the NW-trending sinistral shear zones at c. 640–540 Ma ago. The structures associated with the NW-sinistral shear zones are strongly superimposed by the NE-trending transpressional deformation of the MBSB. S3 varies in intensity from very weak at the margin of undeformed rocks to mylonitic within high-strain zones. The MBSB consists of oppositely dipping imbricate thrusts to SE in its northern parts, passes through the vertical foliation and flips over to NW in the southern parts forming a fan-like structure in the central part of the CED. Almost, the same E–W collision deformed the Arabian Nubian Shield along NNW–SSE shortening regime (Stern et al., 1990; Abdelsalam, 1994; Abdeen and Abdelghaffar, 2011) and major NW-trending, sinistral strike–slip shear zones (e.g. Moore, 1979; Davies, 1984; Stern, 1985; Agar, 1987; Berhe, 1990; Sultan et al., 1986; Stoeser and Stacey, 1988; Abdelsalam, 1994; DeWaele et al., 2011) and slight northeast trending, dextral strike–slip faults (Berhe, 1990; Abdelsalam, 1994; Shalaby et al., 2005; Abd ElWahed, 2008, 2010; Shalaby, 2010; Abd El-Wahed and Kamh, 2010; Zoheir and Lehmann, 2011; Zoheir and Weihed, 2013; Fritz et al., 2013). We interpret the MBSB as a NE-dextral shear zone characterized by wrench-dominated transpressional structures such as oppositely dipping thrusts, pop-up structures and flower-like cleavage. The MBSB is composed of a network of anastomosed shear zones arising from conjugate shears with a prevalent dextral sense. The sinistral and dextral shears were active together producing a complex deformation history in the CED. Acknowledgements The author would like to thank Samir Kamh and Esmaeel Abdel Rasoul, Geology Department, Tanta University and Mohamed El Behiry, Sukari gold mine for their field work assistance. The manuscript was substantially improved by the helpful comments of two anonymous referees. References Abd El-Rahmana, Y., Polatc, A., Dilekd, Y., Kuskye, T., El-Sharkawia, M., Saida, A., 2012. Cryogenian ophiolite tectonics and metallogeny of the Central Eastern Desert of Egypt. Int. Geol. Rev. 54 (16), 1870–1884. Abd El-Wahed, M.A., 2008. Thrusting and transpressional shearing in the PanAfrican nappe southwest El-Sibai core complex, Central Eastern Desert, Egypt. J. Afr. Earth Sci. 50, 16–36. Abd El-Wahed, M.A., 2010. The role of the Najd Fault System in the tectonic evolution of the Hammamat molasse sediments, Eastern Desert, Egypt. Arab. J. Geosci. 3, 1–26. Abd El-Wahed, M.A., Abu Anbar, M.M., 2009. Syn-oblique convergent and extensional deformation and metamorphism in the Neoproterozoic rocks along Wadi Fatira shear zone, Northern Eastern Desert, Egypt. Arab. J. Geosci. 2, 29–52.

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