Geology, geochemistry and radioactivity of granitoid rocks of Abu Marw area, South Eastern Desert, Egypt

Abu Marw area is located in the southeastern part of the Eastern Desert, about 150km south east of Aswan. The Abu Marw area is mainly covered by late Proterozoic igneous and metamorphic rocks. These basement rocks are unconformably overlain by late Cretaceous Nubian sandstones in the western and northern parts of the area. Abu Marw granitoid batholiths comprises a co-magmatic calc alkaline I type peraluminous suite of rocks ranging in composition from tonalite, granodiorite, monzogranite, syenogranite to alkali feldspar granite. The variations of some major and trace elements with SiO2 suggest a crystal fractionation model.The tonalite rocks probably had evolved within a continental arc/continental collision environment, while the granodiorite, monzogranite, syenogranite and alkali feldspar granite rocks had evolved in within plat environment. The studied tonalite and granodiorite samples have ΣREE lower than the average REE values (250ppm) of granitic rocks, while the monzogranite, syenogranite and alkali feldspar granite samples have ΣREE above the average REE values of granitic rocks. Chondrite-normalized REE patterns of the considered granites display a gull-wing shape, characterized by large to moderately fractionated patterns and high LREE relative to the MREE and HREE contents. Furthermore, the studied rocks have a steadily decreasing Eu/Eu* values from the tonalite to the alkali feldspar granite with simultaneous increase in the ΣREE contents. The average contents of U and Th in the different granitic rocks resemble the average contents of some international equivalent rocks. The average of U contents increases with differentiation. The uranium and thorium contents in the studied granitic rocks are present in the accessory minerals particularly monazite, zircon, allanite, sphene, apatite and iron oxides, The radioactive minerals in the pegmatite anomalies are mainly zircon, uranothorite and fluorite, while in the sheared granites uranophane as secondary minerals and zircon, allanite, xenotime and uranothorite which are known as U and Th bearing minerals.