Petrogenesis,Geodynamics and Radioactivity of the Granitic Rocks of the Nugrus Weakness Zone,South Eastern Desert,Egypt

摘要

The studied granitic bodies belong to the south Eastern Desert of Egypt.They extend in a NNW–SSE trend along the same strike of the Nugrus weakness zone by which they are structurally controlled.These rocks are composed of biotite and biotite-muscovite monzogranites to syenogranites.Geochemically,a higher abundance of Ba and Rb in biotite granites with a relatively low abundance in biotite-muscovite granites as well as the diversity of Th,U,Nb,Ta,Zr,and REE reflects their origin from different sources and geodynamic settings.The biotite granites are predominantly metaluminous to low peraluminous whereas the biotite-muscovite granites have a peraluminous nature.Potassium enrichment at the expense of calcium in these rocks reflects a derivation from crustal sources by partial melting in the presence of a volatile system.Radiometric investigation showed high abundances of U(up to 38 ppm)and Th(up to 26 ppm)in biotite-muscovite granites relative to biotite granites(up to 5 ppm U and 18 ppm Th).Radioactive anomalies furthermore have been recorded in parts of biotite-muscovite granites that were affected by the faults(up to 116 ppm eU and 97 ppm eTh).Consequently,biotite-muscovite granites form a potentially fertile source for uranium mineralization.