PETROLOGY, RADIOACTIVITY AND 1 / TECTONIC EVOLUTION OF SOME SELECTED A-TYPE GRANITOID MASSES, EASTERN I DESERT, EGYPT.

Abstract

The present study essentially investigated the geological, petrographicaL geochemical and radiometric characteristics of five selected A-type granite plutons pertaining to the Younger Granites of Egypt. These pi utons include Gabals Gharib, El Himeiyir, H01met Ghannam, Umm Naggat and El Atawi. Ghal'ib granite pluton is situated in the northern part of the Estern Desert of Egypt. It covers on area of about 45Km2 and possesses a roughly oval shaped outcrop extending in a N - S direction. The eastern and northeastern peripheral parts of the pluton are highly deformed and strongly sheared. The pluton is cut by some milky and white quartz veins and a few pegmatite veins of high radioactivity.

The studied granite pluton consists predominantly of alkaline granite, together with only subordinate alkali-feldspar granite. The alkaline granite contains noticeable amounts of alkali pyroxenes (aegirine, aegirine-augite and acmite) and alkali amphiboles (riebeckite and arfvedsonite) in addition to the main constituents of K­ feldspar and quartz. On the other hand, the alkali feldspar granite, nearly lacks alkaline minerals and consists mainly of K-feldspar, quartz, plagioclase in minor amounts together with subordinate amounts of biotite and hornblende. Zircon. tourmaline, fluorite, allanite, sphene, apatite and iron oxides are the main accessory minerals in both rock varieties. K-feldspar in the two rock varieties is essentially perthite which represented by string and vein types.