Petrogenesis of some alkaline
and sub alkaline basalts from Egypt
Hussein Aziz Hegazy
Geology
Department,
Email:
hegazy512000@yahoo.com
Phone.002088
2321015
In an effort to understand the petrogenesis of mid-certiary
basalts in
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.