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Vol.3 , No. 3, Publication Date: May 25, 2016, Page: 25-27
 is a member of an alkaline province including complexes of similar size, structure and composition which crop out along the western margin of the Red Sea in Egypt. ERC (5x6 km) occurs as oval intrusion, rising up to 1018 m.a.s.l. at the intersection of latitude 24° 08' 18″and longitude 34° 38' 55″, belongs to the youngest group of Phanerozoic ring complexes having an emplacement age of 92±5Ma (Lutz et al., 1988; Serencsits et al., 1981). It is related to structural lineament trending N 30º W parallel to the Red Sea and was controlled by pre-existing deep crustal lines of weakness in the basement complex. Field investigation revealed that ERC is composed of two intrusive phases, i.e. oldest one represents by essexite gabbros, and the later phase of syenitic rocks. The syenites formed the inner zone are highly sheared undersaturated syenites (i.e. Litchfieldite and cancrinite syenites) grading into quartz syenites, while the outer ring massif is composed of massive alkaline syenites with less of quartz syenites. The extrusive rocks of trachyte, basalt and rhyolite present as plugs, sheets and ring dykes. The mineralogical and chemical features show that these rocks belong to anorogenic interplate A-type alkaline suite (i.e. enriched in alkalis and HFS elements, Nb, Ta, Zr, Hf, Y, HREE) and peralumineous in nature. The Y/Nb and Ce/Nb ratios suggest fractional crystallization of primary source of picritic basalt magma in the asthenospheric mantle. The calculated agpaitic coefficient values show that the alkaline rock samples of El Kahfa area are of miaskitic type with some tendencies to possess an intermediate alkaline affinity. Open-system processes by which nepheline syenitic magma undergo assimilation of silica- rich crustal material (crustal contamination) and fractional crystallization have been suggested. It is believed that under these conditions undersaturated magma evolves across the feldspar join and become oversaturated.&picture=http://www.aascit.org/aascit/decorators/img/journal/899.jpg)
| [1] | Hussein A. Hegazy, Geology Department, Faculty of Science, Assiut University, Assiut, Egypt. |
| [2] | Andrei A. Arzamastsev, Institute of Precambrian Geology and Geochronology, Russian Academy of Sciences, Moscow, Russia. |
| [3] | Eman Saad, Geology Department, Faculty of Science, Assiut University, Assiut, Egypt. |
El kahfa Ring Complex (ERC) is a member of an alkaline province including complexes of similar size, structure and composition which crop out along the western margin of the Red Sea in Egypt. ERC (5x6 km) occurs as oval intrusion, rising up to 1018 m.a.s.l. at the intersection of latitude 24° 08' 18″and longitude 34° 38' 55″, belongs to the youngest group of Phanerozoic ring complexes having an emplacement age of 92±5Ma (Lutz et al., 1988; Serencsits et al., 1981). It is related to structural lineament trending N 30º W parallel to the Red Sea and was controlled by pre-existing deep crustal lines of weakness in the basement complex. Field investigation revealed that ERC is composed of two intrusive phases, i.e. oldest one represents by essexite gabbros, and the later phase of syenitic rocks. The syenites formed the inner zone are highly sheared undersaturated syenites (i.e. Litchfieldite and cancrinite syenites) grading into quartz syenites, while the outer ring massif is composed of massive alkaline syenites with less of quartz syenites. The extrusive rocks of trachyte, basalt and rhyolite present as plugs, sheets and ring dykes. The mineralogical and chemical features show that these rocks belong to anorogenic interplate A-type alkaline suite (i.e. enriched in alkalis and HFS elements, Nb, Ta, Zr, Hf, Y, HREE) and peralumineous in nature. The Y/Nb and Ce/Nb ratios suggest fractional crystallization of primary source of picritic basalt magma in the asthenospheric mantle. The calculated agpaitic coefficient values show that the alkaline rock samples of El Kahfa area are of miaskitic type with some tendencies to possess an intermediate alkaline affinity. Open-system processes by which nepheline syenitic magma undergo assimilation of silica- rich crustal material (crustal contamination) and fractional crystallization have been suggested. It is believed that under these conditions undersaturated magma evolves across the feldspar join and become oversaturated.
Keywords
ERC, Red Sea, Essexite Gabbros, Miaskitic
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