Abstract
Three post-orogenic granitic plutons exposed in the Egyptian basement complex, namely Homr Akarem, Homrit Mukbid and Nuweibi were selected for geochemical and NdSr isotopic studies. Based on petrographic and geochemical considerations, the granitic rocks are divided into medium-grained pink granites and albite-rich granites. Both types exhibit peraluminous character with many chemical similarities to the high Y/Nb A-subtype granites. Owing to the extreme fractionated nature and complex magma source of these granitic rocks in addition to the high volatile activity, their compositions resemble within-plate magma originated in attenuated crustal lithosphere. Whole-rock RbSr isochron ages of the medium-grained pink granites from Homr Akarem and Homrit Mukbid plutons are 541 ± 4 Ma and 527 ± 26 Ma, respectively. The Nuweibi albite granite (NAG) represents the youngest granite phase and yields a RbSr age of 490 ± 27 Ma. The medium-grained pink granites show a moderate and narrow range of initial 87Sr/ 86Sr ratio (0.7064−0.7081) and negative ϵ t Nd values (−1.31 to −6.68). The NAG has an initial 87Sr/ 86Sr (0.7071) and ϵ t Nd (−3.26 to −4.72), comparable to those of the medium-grained pink granites. The SmNd data yield model ages (T DM) of 0.96 to 1.70 Ga. Similar Nd model ages (1.2−1.8 Ga) have been reported for other post-orogenic granites from southwest Egypt and northern Sudan. The Nd and Sr isotopic compositions of the studied mineralized granites suggest the involvement of old, LREE-enriched continental crust of Pre-Pan-African age and lower crust- or mantle-derived magmas. The Nd and Sr isotopic variations can be explained by a mixing hypothesis.
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