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

The late Pan-African Fawakhir, Urn Had and Urn 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 Urn 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 consistent with upper crustal level emplacements at depths where o3 is vertical. Emplacement is likely to have occurred after northeast-southwest transpression, rather than in an extensional tectonic environment. @ 2001 Elsevier Science Limited. All rights reserved. RESUME-Les plutons granitiques pan-africains tardifs de Fawakhir, Urn Had et Urn Effein dans le centre du Desert Oriental Bgyptien sont des petits corps allonges a circulaires form&s de syenoet monzogranites roses et de monzodiorites grises. Les observations structurales aux contacts intrusifs de ces plutons indiquent qu’il s’agit de lames intrusives marginales subhorizontales, correspondant a des injections de magmas le long de structures planes preexistantes incluant foliations minerales et failles de charriage. L’espace necessaire a la mise en place de ces plutons granitiques a 6te accommode par le bombement des roches environnantes encaissantes dont les contacts exterieurs sont dans le style des laccolites. D’une man&e g&Wale, le pluton granitique d’Um Had possede une forme phacolitique contr6lee par un couloir cisaillant mylonitique bombe et a pente sud, qui separe les roches gneissiques (preservees comme coeur du pluton) des unites charriees peu metamorphiques. Les caracteristiques structurales de ces plutons sont en accord avec une mise en place dans la croute la plus superieure, a une profondeur ou o3 est vertical. Cette mise en place s’est probablement produite apres une transpression NE-SO plutot que dans un environnement. Q 2001 Elsevier Science Limited. All rights reserved. (Received 12/l l/98: accepted 6/4/00) INTRODUCTION The Egyptian Eastern Desert has been described as African alkali feldspar granite to monzogranite plutons one of the most intensively dyke-intruded and granitoid of the Eastern Desert range in Rb-Sr age from 620 to pluton-pierced segments of the continental crust (Vail, 570 Ma (Hassan and Hashad, 1990). These plutons 1968; Bentor, 1985). The small epizonal late Panare typically round to elliptical or teardrop-shaped. Journal of African Earth Sciences 6 1