Late Cryogenian arc-related volcaniclastic metasediment successions at Wadi Hammuda, Central Eastern Desert, Egypt: geol
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ORIGINAL PAPER
Late Cryogenian arc-related volcaniclastic metasediment successions at Wadi Hammuda, Central Eastern Desert, Egypt: geology and geochemistry Ahmed E. Khalil 1 & Hatem M. El-Desoky 2 & Taher M. Shahin 2 & Wael Abdelwahab 1 Received: 18 July 2017 / Accepted: 26 December 2017 # Saudi Society for Geosciences 2018
Abstract Wadi Hammuda is dominated by a variety of low grade regionally metamorphosed volcaniclastic metasediments pertaining to two different geotectonic settings and intruded by arc and late collision granitic rocks. Thus, the volcaniclastic metasediments which form extensive outcrops are considered as a member of island arc assemblages. This paper deals with the petrography, geochemistry, and tectonic setting of the island arc volcaniclastic metasediment rock units. The volcaniclastic metasediments consist of interbedded metagreywackes, metasiltstones, metamudstones, and schists as well as metapyroclastics. They are well foliated, crenulated and tightly folded, metamorphosed, and intruded by granitic rocks. Geochemical data support the petrographic classification and reveal that these volcaniclastic metasediments are generally low-K, essentially tholeiitic in character, with the exception of some metasediments and metapyroclastics which exhibits calc-alkaline and tholeiitic affinities and represent the first stage of island arc volcanism. The overthrusted oceanic lithosphere blocks with fragments of the fore arc and/or back-arc marginal basins volcaniclastic metasediments were incorporated among the island arc volcanics which supported by tectonically relationship between the different rock units in the study area. Contemporaneous with this deformation event, Wadi Hammuda was subjected to low grade regional metamorphism and the rocks document an early phase of shearing and/or foliation. Occasionally minor folds were developed particularly in the metasediments and schists. The subsequent emplacement of the syn-tectonic granites (tonalites and granodiorites) resulted in minor local thrusts. During the regional thrusting event which preceded the emplacement of the late-tectonic granites (alkali feldspar granites) and affected the whole region, low grade successions cover the study area similar to the Meatiq volcaniclastic metasediments. Keywords Late Cryogenian . Arc volcaniclastic metasediments . Wadi Hammuda . Eastern Desert . Egypt
Introduction The Arabian-Nubian Shield (ANS) is the largest Neoproterozoic tectono-stratigraphic complex of orogenic terranes and extends over most of NE Africa and the Arabian Peninsula, covering an area of about 3 × 106 km2. The ANS crust extended on both sides of the Red Sea and evolved during East African orogeny (EAO, Stern 1994). Recent isotopic ages (1.12–0.95 Ga, Be'eri-
* Wael Abdelwahab [email protected]; [email protected] 1
Geological Sciences Department, National Research Centre, El-Buhouth St., Dokki, Cairo 12622, Egypt
2
Geology Department, Faculty of Science, Al-Azhar University, PO Box 11884, Nasr City, Cairo, Egypt
Shlevin et al. 2012
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