Petrogenesis and Tectonic Evolution of Neoproterozoic Volcanic Rocks from Um Khariga, Egyptian Nubian Shield: Implications for Early Crustal Growth Stage

Abstract The Neoproterozoic Arabian-Nubian Shield (ANS) contains one of the most extensive exposures of juvenile continental crust on Earth, with the Egyptian segment, the Nubian Shield (ENS), representing a critical component of this shield. Within the ENS, the Um Khariga volcanic province represents one of the largest and most prominent volcanic complexes. This study examines the geochemical, isotopic, and petrogenetic characteristics of the Um Khariga volcanic rocks to assess their contribution to the early stage of crustal evolution of the ENS. Formed between ~800 and ~750 Ma, these volcanic rocks are interbedded with arc-related serpentinites and intruded by I-type granitoids, indicating an island arc tectonic environment. Whole-rock geochemical data reveal low- to medium-K tholeiitic to calc-alkaline affinities, with enrichment in large-ion lithophile elements (LILEs) such as Ba, Sr, and Pb pointing to a subduction-modified mantle source, with εNd(t) values ranging from +4.8 to +6.8 and low initial 87Sr/86Sr(t) ratios (~0.702), both consistent with a juvenile mantle origin. Geochemical modeling suggests that the Um Khariga volcanics were generated by 15%–20% partial melting of a mantle source metasomatized by approximately 1%–15% subduction-derived fluids. These results highlight the significance of arc magmatism in the precollisional magmatic history of the ENS, contributing substantially to the early formation stage of the ENS Neoproterozoic continental crust. Ultimately, this study sheds light on early crustal growth processes in the ANS and the geodynamic evolution associated with the Rodinia–Gondwana transition.