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

ABSTRACT

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