GABAL ABU HAMR PLUTON: AN EXAMPLE OF A-TYPE ANOROGENIC PERALKALINE GRANITES IN EGYPT

Abstract

Gabal Abu Hamr pluton is an elongated peralkaline granitic mass emplaced along the ENE-WSW Qena-Safaga shear zone as one of the anorogenic peralkaline granites represented in the Eastern Desert of Egypt. The rock is hypersolvus, composed of perthite, quartz and both alkali amphibole (arfvedsonite) and pyroxene (aegerine). It is enriched in Si, Na, K, Ba, Y, Ga and LREE and depleted in Al, Mg, Ca, Mn, Zr and HREE. The rocks exhibit mineralogical and chemical traits typical of within-plate A-type granites, which, due to the ascending of hydrothermal solutions along the ENE-WSW strike-slip fault, dividing the pluton, suffered metasomatic processes causing the leaching of Zr, U and HREE and their escape into the fluids and transported through the structure systems to be concentrated along the tectonic contact between the granite and the adjacent metavolcanics. This pluton may represent the northern extension of both G. Abu Kharif and G. El Dob being emplaced along the same E-NE shear zone trend. The suggested age of emplacement of G. Abu Hamr pluton is from 550 Ma to 450 Ma.