Pan-African granite emplacement mechanisms in the Eastern Desert, Egypt

The late Pan-Africa Fawakhir, Um Had and Um Effein Granite Plutons in the Egyptian Central Eastern Desert are small, elongate to circular bodies of pink monzogranite and syenogranite,and grey monzodiorite. Structural investigation of the intrusive contacts of these plutons reveals marginal sub-horizontal intrusive sheets as magma injection along preexisting flat-lying structures including mineral foliations and thrust faults. Space for emplacement of granitic plutons was accommodated by uplift of the country rocks along steep marginal faults with rotation of the wall rocks whose outer contacts are in the style of laccoliths. Overall, the Um Had Granite Pluton has a phacolithic shape controlled by a south-plunging domed mylonitic shear zone, which separates gneissic rocks (preserved as a pluton core) from low grade overthrust units. The structural features of these plutons are consisted with upper crustal level emplacements at depths where σ₃ is vertical. Emplacement is likely to have occurred after northeast-southwest transpression, rather than in an extensional tectonic environment.