Petrology, geochemistry and tectonic setting of Dyke swarms of Abu Dob area, central eastern desert, Egypt

Abu Dob granitic pluton is traversed by a large number of dyke swarms. The examined dykes are classified into acidic, intermediate, basic and alkaline. Most dyke swarms trend N-s to NNE-SW; some dykes trend NW-SE. The dykes are very steeply inclined at 75-85°. They generally possess a uniform thickness usually ranging from 0.5 to 40 m. The dykes sequence in Abu Dob area starts with the acidic, followed by the intermediate and then the Tertiary basalts and ends by the alkaline dykes. The intermediate and basic dykes are enriched in normative nepheline indicating their alkaline affinity, normative hypersthene is also present in trachydacite, trachyte, trachyandesite and in the alkaline basalt, Normative acmite appears in considerable amounts in the trachyte, phonolite and phonotephrite dykes pointing to a possible alumina deficiency. The mafic and intermediate dykes were possibly derived from alkaline magmas in a within plate environment, while the acidic dykes were derived from the late or orogenic calc-alkaline granitic magma and basalt sample has a tholeiitic nature. The dykes are enriched in HFS elements and depleted in LIL elements

Petrology, geochemistry and tectonic setting of some younger alkaline volcanic rocks, central eastern desert, Egypt

The present paper deals with some alkaline volcanic rocks occurring as small masses and plugs widespread in the Central Eastern Desert of Egypt. They occur in the form of plugs, sheet and dykes at Gebel El-Degheimi, Um Hombos, Um Khors plugs and Wadi El Miyah. The alkaline volcanic rocks are composed essentially of trachyte grading into trachyte, Qz-trachyte or phonolite. The studied volcanics contain acmite, aegirine and aegirine-augite. The alkaline volcanic rocks are enriched in alkalies and characterized by high contents in Nb, Y, Zr, Rb and Zn. Furthermore, the tectonic setting of these late volcanic alkaline rocks suggest that the trachyte masses erupted in a within plate tectonic environment. They were possibly derived from magmatic differentiation of an alkaline basaltic magma that suffered contamination with crustal material

Contribution to the petrogenesis and the temporal varation in arc magmatism yielding the dokhan volcanic rocks in the eastern desert of Egypt

The present paper deals with the overall geochemical characteristics of the Dokhan volcanics in ten selected localities in the Eastern Desert of Egypt and the maturity of the arc magmatism. Dokhan volcanics Comprise mainly basalts, basaltic andesites, andesites, dacites and rhyolites, in addition to their pyroclastic equivalents. The Dokhan volcanics were derived from a Calc-alkaline magma erupted along an active continental margin, the calc-alkaline nature of these rocks is the most pronounced feature of the parent basaltic magma. The resulted volcanic arcs are compared with some modern arcs, e.g. Tonga-South Sandwich, New Zealand and New Guinea. The Dokhan volcanics have active similarity of the mature arcs active continental margin of Chili.,whereas the arc maturity increases towards Esh El-Mellaha range as well as, highly mature volcanic arc similar to that of New Guinea