Geology, Petrography, Geochemistry And Petrogenesis Of The Egyptian Younger Granites

Abstract

One hundred and thirty nine new chemical analyses of major and trace elements for 26 plutons and masses pertaining to the Egyptian Younger Granites are presented together with the chemical analyses of 13 biotites, 32 feldspars, 2 muscovites, 2 garnets and 4 magnetites. The present geological, petrographical and geochemical studies have subdivided the studied Younger Granites in the following four groups: Group (1) less differentiated calc-alkaline to weakly alkaline I-type granodiorite and monsogranite; Group (2) normal alkaline A-type monzogranite to syenogranite and Group (3) strongly alkaline A-type alkali feldspar granite, whereas the fourth group includes the "Apogranite" variety which is characterized by distinct enrichment in Na^O. It is believed that the magmas of the different groups may have been produced by partial fusion and refusion. It is also suggested that Group (1) granites resemble the Caledonian-type granitoids intruded during a phase of post-collsional uplift, relaxation and decompression, whereas Groups (2) and (3) appear to have been emplaced in an extensional tectonic setting.