Thrusting and transpressional shearing in the Pan-African nappe southwest El-Sibai core complex,Central Eastern Desert,Egypt |
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| Institution: | 1. Department of Mineral Resources and Rocks, Faculty of Earth Sciences, King Abdulaziz University, P.O. Box 80206, Jeddah 21589, Kingdom of Saudi Arabia;2. Beijing SHRIMP Centre, Department of Geology, Chinese Academy of Geological Sciences, Beijing, China;3. Deptartment of Geosciences, University of Mainz, D-55099 Mainz, Germany;4. Department of Geo- and Environmental Sciences, University of Munich, D-80333 München, Germany;5. Department of Earth Sciences, The University of Hong Kong, Pukfalam Road, Hong Kong, China;6. University of Science and Technology of China, School of Earth and Space Sciences, Hefei 230026, China;7. Geology and Geophysics Department, College of Sciences, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia;8. Geology Department, Faculty of Science, Assiut University, Assiut 71516, Egypt;1. Department of Mineral Resources and Rocks, Faculty of Earth Sciences, King Abdulaziz University, P.O. Box 80206, Jeddah 21589, Kingdom of Saudi Arabia;2. Department of Geology, Faculty of Science, Benha University, 13518 Benha, Egypt;3. Geosciences Department, University of Texas at Dallas, 800 W Campbell Rd., Richardson, TX 75080, USA;4. Department of Geosciences, P.O. Box 1047, University of Oslo, Blindern, 0316 Oslo, Norway;5. Department of Geosciences, Swedish Museum of Natural History, P.O. Box 50007, SE-104 05 Stockholm, Sweden;6. Geology Department, Faculty of Science, Assiut University, Assiut 71516, Egypt |
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| Abstract: | The Wadi El-Shush area in the Central Eastern Desert (CED) of Egypt is occupied by the Sibai core complex and its surrounding Pan-African nappe complex. The sequence of metamorphic and structural events in the Sibai core complex and the enveloping Pan-African nappe can be summarized as follows: (1) high temperature metamorphism associated with partial melting of amphibolites and development of gneissic and migmatitic rocks, (2) between 740 and 660 Ma, oblique island arc accretion resulted in Pan-African nappe emplacement and the intrusion of syn-tectonic gneissic tonalite at about 680 ± 10 Ma. The NNW–SSE shortening associated with oblique island arc accretion produced low angle NNW-directed thrusts and open folds in volcaniclastic metasediments, schists and isolated serpentinite masses (Pan-African nappe) and created NNE-trending recumbent folds in syn-tectonic granites. The NNW–SSE shortening has produced imbricate structures and thrust duplexes in the Pan-African nappe, (3) NE-ward thrusting which deformed the Pan-African nappe into SW-dipping imbricate slices. The ENE–WSW compression event has created NE-directed thrusts, folded the NNW-directed thrusts and produced NW-trending major and minor folds in the Pan-African nappe. Prograde metamorphism (480–525 °C at 2–4.5 kbar) was synchronous with thrusting events, (4) retrograde metamorphism during sinistral shearing along NNW- to NW-striking strike-slip shear zones (660–580 Ma), marking the external boundaries of the Sibai core complex and related to the Najd Fault System. Sinistral shearing has produced steeply dipping mylonitic foliation and open plunging folds in the NNW- and NE-ward thrust planes. Presence of retrograde metamorphism supports the slow exhumation of Sibai core complex under brittle–ductile low temperature conditions. Arc-accretion caused thrusting, imbrication and crustal thickening, whereas gravitational collapse of a compressed and thickened lithosphere initiated the sinistral movement along transcurrent shear zones and low angle normal ductile shear zones and consequently, development and exhumation of Sibai core complex. |
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