A structural synthesis of the Proterozoic Arabian-Nubian Shield in Egypt

Abstract

Detailed structural geological and related studies were carried out in a number of critical areas in the Proterozoic basement of eastern Egypt to resolve the structural pattern at a regional scale and to assess the general characteristics of tectonic evolution, orogeny and terrane boundaries. Following a brief account of the tectonostratigraphy and timing of the orogenic evolution, the major structural characteristics of the critical areas are presented. Collisional deformation of the terranes ended about 6 1 5 -6 0 0 Ma ago. Subsequent extensional collapse probably occurred within a relatively narrow time span of about 20 Ma ( 5 7 5 -595 Ma ago) over the Eastern Desert and was followed by a further period of about 50 Ma of late to post-tectonic activity. The regional structures originated mainly during post-collisional events, starting with those related to extensional collapse (molasse basin formation, normal faulting, generation of metamorphic core complexes). Subsequent N N W -S S E shortening is documented by large-scale thrusting (towards the NNW) and folding, distributed over the Eastern Desert, although with variable intensity. Thrusts are overprinted by transpression, which was localized to particular shear zones. Early transpression produced, for example, the Allaqi shear zone and final transpression is documented in the Najd and Wadi Kharit-Wadi Hodein

U–Pb TIMS age constraints on the evolution of the Neoproterozoic Meatiq Gneiss Dome, Eastern Desert, Egypt

“…Meatiq-, Hafafit-, and Sibai Gneiss Domes; Fig. 1) (Sturchio et al 1983;Fowler and Osman 2001;Greiling et al 1994). The appearance and formation of the gneiss domes are interpreted to be closely linked to tectonic activity along the northward continuation of the Najd Faults System (e.g.…”

“…2 (frame) ortho-and paragneisses, formed as a result of NW translation of the eugeoclinal thrust sheet during the East African orogeny (e.g. Greiling et al 1994). Loizenbauer et al (2001) interpreted the Meatiq Gneiss Dome to be a metamorphic core complex formed by orogen-parallel crustal extension following thrusting.…”

“…Based on the nature and structural position of ophiolites and associated island arc sequences we prefer to group them together and use the term the eugeoclinal thrust sheet/complex. Various tectonic models, including crustal extension, crustal shortening, transcurrent faulting, or a combination of these processes, have been proposed to explain the age and origin of the gneiss domes (Greiling et al 1994;Fritz et al 1996Fritz et al , 2002Fowler and Osman 2001;Loizenbauer et al 2001;Bregar et al 2002). Contributing to this lack of understanding is that the age, origin and plate tectonic setting of the orthogneisses exposed in the core of the domes remain unclear and the subject of debate.…”

Nd–Sr–Hf–O isotope provinciality in the northernmost Arabian–Nubian Shield: implications for crustal evolution

“…Regarding the timing of deformation we note the important difference between the northernmost ANS and more southern ANS segments. In the Central Eastern Desert of Egypt as well as in NW Arabia deformation younger than 620 Ma generally associated with the Najd Fault System is common (Greiling et al 1994).…”

Recent uranium mobilization and radioactivity of metamorphosed sandstones at Sikait area, South Eastern desert of Egypt

“…The region is composed of metapelitic schists, gneisses and granites and is cut by a number of dykes of different compositions, together with various types of aplitic and pegmatitic veins. Greiling et al (1994) concluded that post collisional evolution in Eastern Desert of Egypt started with extensional collapse, which was followed by NNW-SSE shortening and related large -scale thrusting (toward the NNW) and folding, distributed all over the Eastern Desert, followed by further period of Late to Postactivity. Assaf et al (2000) studied the polyphase folding in Nugrus-Sikait area and reported that the lithological constitution of the area comprise a sequence of dismembered ophiolites, ophiolitic mélange association and arc assemblage.…”