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

ABSTRACT

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: