A STRUCTURAL SYNTHESIS OF THE PROTEROZOIC ARABIAN-NUBIAN SHIELD IN EGYPT

Detailed structural geological and related studies were carried out in a number of critical areas in the Proterozoic basement of eastern Egy pt to resolve the structural pattern at a regional scale and to assess the general characteristics of tectonic evolution, orogeny and terran e boundaries. Following a brief account of the tectonostratigraphy and timing of the orogenic evolution, the major structural characteristic s of the critical areas are presented. Collisional deformation of the terranes ended about 615 - 600 Ma ago. Subsequent extensional collapse probably occurred within a relatively narrow time span of about 20 Ma (575 - 595 Ma ago) over the Eastern Desert and was followed by a furt her period of about 50 Ma of late to post-tectonic activity. The regio nal structures originated mainly during post-collisional events, start ing with those related to extensional collapse (molasse basin formatio n, normal faulting, generation of metamorphic core complexes). Subsequ ent NNW - SSE shortening is documented by large-scale thrusting (towar ds the NNW) and folding, distributed over the Eastern Desert, although with variable intensity. Thrusts are overprinted by transpression, wh ich was localized to particular shear zones. Early transpression produ ced, for example, the Allaqi shear zone and final transpression is doc umented in the Najd and Wadi Kharit-Wadi Hodein zones. Two terrane bou ndaries can be defined, the Allaqi and South Hafafit Sutures, which ar e apparently linked by the high angle sinistral strike-slip Wadi Khari t-Wadi Hodein shear zone with a tectonic transport of about 300 km tow ards the W/NW. In general, the tectonic evolution shows that extension al collapse is not necessarily the final stage of orogeny, but may be followed by further compressional and transpressional tectonism. The l ate Pan-African high angle faults were reactivated during Red Sea tect onics both as Riedel shears and normal faults, where they were oriente d favourably with respect to the actual stress regime.