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

The late Pan-African Fawakhir, Um Had and Um Effein Granite Plutons in the Egyptian Central Eastern Desert are small, elongate to circular bodies of p ink monzogranite and syenogranite, and grey monzodiorite. Structural invest igation of the intrusive contacts of these plutons reveals marginal sub-hor izontal intrusive sheets as magma injection along pre-existing flat-lying s tructures including mineral foliations and thrust faults. Space for emplace ment of granitic plutons was accommodated by uplift of the country rocks al ong steep marginal faults with rotation of the wall rocks whose outer conta cts are in the style of laccoliths. Overall, the Um Had Granite Pluton has a phacolithic shape controlled by a south-plunging domed mylonitic shear zo ne, which separates gneissic rocks (preserved as a pluton core) from low gr ade overthrust units. The structural features of these plutons are consiste nt with upper crustal level emplacements at depths where sigma (3) is verti cal. Emplacement is likely to have occurred after northeast-southwest trans pression, rather than in an extensional tectonic environment. (C) 2001 Else vier Science Limited. All rights reserved.