Pan-African volcanism: petrology and geochemistry of the Dokhan Volcanic Suite in the northern Nubian shield

Abstract

The Late Proterozoic Dokhan volcanic suite (620 Ma) of the northern Nubian shield is the product of Late Pan-African volcanism. The suite covers the entire spectrum from basalt to high-silica rhyolite and occurs as two units: a dark-coloured unit containing basalt-andesite-dacite, and a light-coloured unit encompassing dacite-rhyodacite-rhyolite. The latter unit is made up largely of ash flow tuffs and ignimbrites that are locally interstratified with basalt and andesite lava flows. The suite forms a continuum in composition with a wide range of SiO 2 (48-77 wt%), CaO (0.1-8.9 wt%), Sr (81-906 ppm), Zr (85-340 ppm) as well as most other elements, and is moderately enriched in incompatible elements, including rare earth elements (REE). The suite exhibits fractionated, subparallel REE patterns that are similar overall to Andean andesites and ignimbrites. Well-defined major and trace element trends and fractionated REE profiles are consistent with a fractionated basalt to rhyolite calc-alkaline magma series. It is a typical calc-alkaline orogenic complex and exhibits mineralogical-geochemical traits of arc-related volcanism. The suite neither resembles products of extensional nor transitional tectonic regimes as previously thought, but was produced in a subduction-related tectonic environment. The mafic nature of the least-evolved rocks of the suite, along with its relatively low initial ^Sr/^Sr ratio (0.7039) are considered to indicate a mantle source. A mantle-derived basaltic magma fractionated, with amphibole and plagioclase dominating the fractionating assemblage, to produce the more felsic varieties, as suggested by major and trace element fractionation modelling.

Re-Os geochronology of gold mineralization in the Fawakhir area, Eastern Desert, Egypt

“…Subduction and island arc stage (e.g. Abdel-Rahman and Doig 1987;El-Gaby et al 1988;Stern 1994;Abdel-Rahman 1996), orogenic stage (collision of East and West Gondwana) until deposition of molasse sediments (e.g. Stern and Hedge 1985;El-Gaby et al 1988), post-orogenic stage, alkaline granite emplacement and dike swarms development (Stern and Hedge 1985;Stern and Gottfried 1986).…”

Late Neoproterozoic volcanics and associated granitoids at Wadi Ranga, south Eastern Desert, Egypt: A transition from subduction related to intra-arc magmatism

“…During slab-dehydration HFSE and HREE are conservative and such (Pecerillo and Taylor, 1976) and b) (Na 2 O+K 2 O) vs. SiO 2 classification diagram (Middlemost, 1985) for the studied granitoids. Data of compositional fields of the ophiolitic older meta-volcanics (OMV) and island arc younger metavolcanics (YMV) are from Stern (1981), while field of Dokhan volcanics (DV) are from northern Eastern Desert (Stern and Gottfried, 1986;Abdel-Rahman, 1996;Mohamed et al, 2000;Moghazi, 2003;Eliwa et al, 2006).…”

“…Chondrite-normalized REE plots (Taylor and Mc Lennan, 1985) of the studied rocks. The compositional fields labeled (YMV = younger metavolcanics and OMV = older metavolcanics) are from (Ali et al, 2009;Stern, 1981); felsic YMV are from Stern, 1981; mafic DV = Dokhan volcanic and felsic DV are from (Stern and Gottfried, 1986;Abdel-Rahman, 1996;Mohamed et al, 2000;Moghazi, 2003;Eliwa et al, 2006;El-Bialy, 2010;Azer and Farahat, 2011). The studied Basalt/basaltic andesites plotted mainly on the islandarc tholeiitic field with some samples overlap the IAT-BABB fields (Fig. 9b).…”

The significance of gneissic rocks and synmagmatic extensional ductile shear zones of the Barud area for the tectonics of the North Eastern Desert, Egypt

“…Subduction and island arc stage (840-690 Ma) - Stern (1979Stern ( , 1981, Bielski (1982), Bentor (1985), El-Gaby et al (1988), Stern (1994), Abdel-Rahman (1995, 1996, Abdel-Rahman and Doig (1987), Abdelsalam and Stern (1996). Arc suturing and collision of East and West Gondwana (690-620 Ma) - , Stern (1994).…”