Petrochemistry and Tectonic Evolutions of the Tertiary basalt along Red Sea Coast, Central Eastern Desert, Egypt..

To investigate the petrochemistry and genesis of Tertiary basalts in Egypt, which are among the most extensively distributed Tertiary basaltic flows in the region, nineteen basaltic samples were collected from basaltic rocks situated south of Qusier city, specifically in Wadi Sharm El Bahari, Wadi Sharm El Qiblli and Wadi Wizr along the Red Sea Coast. The samples were analyzed mineralogically and geochemically. The field investigation indicates that the basaltic rocks are oriented in a NW-SW direction, parallel to the Red Sea Rift. Petrographic analyses elucidate the existence of olivine basalts, porphyritic basalts, amygdaloidal olivine basalts and porphyritic olivine basalts. Some basalt flows exhibit slight alteration, showing the development of chlorite, serpentine, clay minerals and actinolite, along with the release of iron oxide. Geochemical data, encompassing major and trace elements, were evaluated. Variation diagrams validated that the basalts originated from partial melting and fractional crystallization. The significance of fractional crystallization processes, as opposed to crustal contamination processes, is accentuated by plotting Nb/Y versus Rb/Y. The Rb/Nb ratios (>2) signify the crustal compositions and melts, with the magma source originating from the OIB-source mantle. As indicated by discrimination diagrams, the basalts exhibit an alkaline to tholeiitic magma type and an orogenic, within-plate tectonic context. Their estimated crystallization temperatures range between 1180-1200°C. The oceanic characteristics of some basalt samples on the TiO2-K2O-P2O5 diagram indicate their association with the earliest rifting phase of the Red Sea.