Petrogenesis of some alkaline and sub alkaline basalts from Egypt
Hussein Aziz Hegazy
In an effort to understand the petrogenesis of mid-certiary
The content of P2O5 and K2O indicate that the tholeiitic basalt from Abu Roash and Sharm El-Bahari were generated by 21-23% partial melting of pyrolite mantle at pressures less than 15 Kb, whereas the alkali basalt magma of Sharm El-Qibli was formed at greater depth at 15-25 Kb. The crystallization temperature, deduced from the MgO content was 1060ºC for the basalt from Mir, and between 1100ºC to 1200ºC for the basalts from the other localities.
Fe/Mg index, Mg/Mg+Fe and mafic/Felstic ratio indicate an increasing degree of fractionated prior to extrusion in the following order: Sharm El-Bahari, Abu Roash and Mir. The close occurrence of alkali basalt at Sharm El-Qibli and tholeiitic basalts at Sharm El-Bahari, might suggest the presence of deep fractures of varying extension tapping magmas originating at different depths.