Petrology, geochemistry and age relations of Triassic and Tertiary volcanic rocks from SW Egypt and NW Sudan

Abstract

Petrological, geochemical and K/Ar radiometrical whole rock age data of volcanic rocks from SW Egypt and N Sudan in the area of Gebel Kamil-Lake Nasser-Laqia Arbain-Nile are presented. These rocks are (i) trachytic-phonolitic rocks and (ii) alkali olivine basalts occurring mostly as volcanic plugs. Their petrographic and their major and trace element patterns are typical for continental within-plate volcanism. Two groups of ages were determined: Triassic (240, 233 Ma) with predominantly silicic, differentiated magmas, and Tertiary (60-20 Ma) with predominantly basaltic magmas. Major element abundances of the basalts show a regional trend from west to east from low to high fractionation irrespective of the age of the rock. Their occurrence can be correlated with two W-E uplift zones which are important for the structural development of the large sedimentary basins of the Libyan desert.