Petrological, geochemical and geodynamic evolution of the Wadi Al-Baroud granitoids, north Arabian-Nubian shield, Egypt

The Wadi Al-Baroud area, in Egypt's Eastern Desert, exposes Neoproterozoic rocks of the Arabian-Nubian Shield (ANS), including both syntectonic granitoids (granodiorite and tonalite) and post-collisional granites. We present field work, petrographic study, mineral compositions, and whole-rock geochemistry results from these granitoids and discuss their petrogenesis, magmatic sources, evolution, and tectonic significance. The syntectonic granitoids show subduction affinity and an anomalous steep trend of K-enrichment that suggests assimilation of a granitic component during their evolution. The post-collisional granites form two plutons, on opposite sides of Wadi AlBaroud, named here the Ras Baroud pluton (RBP) and the Abu Hawis pluton (AHP). They intruded the syntectonic granitoids with sharp intrusive contacts. The post-collisional plutons are devoid of mafic enclaves and are cut by very few dikes. They dominantly consist of biotite monzogranite that grades into muscovite monzogranite. The latter lithology hosts Nb-Ta oxide minerals (columbite, tantalite, and wodginite) displaying a variety of textural and compositional features. The cores are primary columbite-(Mn), whereas rims are overgrown or partly replaced by tantalite-(Fe) and wodginite due to late interactions with highly fractionated residual melt. The highly-evolved AHP and RBP granites are typical of the post-collisional granitoids of the ANS, including high concentrations of rare earth elements (REE), Ta, Hf, Nb, Zr, Y, and Rb; elevated ratios of Ga/Al; and low contents of Sr, CaO, and MgO. Their geochemistry suggests that the parental magma of both plutons formed from an I-type tonalitic source rock that underwent partial melting during the thermal disturbance that followed a lithospheric delamination event during the post-collisional stage of the East African Orogeny. The variations in major oxide and trace element contents among individual samples of the AHP and the RBP cannot be explained as a liquid line of descent due to fractional crystallization; rather we interpret them as sampling variable proportions of an evolved liquid and the solid crystals in equilibrium with that liquid.