Sr–Nd isotopes and geochemistry of the infrastructural rocks in the Meatiq and Hafafit core complexes, Eastern Desert, Egypt: Evidence for involvement of pre‐Neoproterozoic crust in the growth of Arabian–Nubian Shield

Abstract

Meatiq and Hafafit core complexes are large swells in the Eastern Desert of Egypt, comprising two major tectono-stratigraphic units or tiers. The lower (infrastructure) unit is composed of variably cataclased gneissose granites and high-grade gneisses and schists. It is structurally overlain by Pan-African ophiolitic mélange nappes (the higher unit). The two units are separated by a low-angle sole thrust, along which mylonites are developed. Major and trace element data indicate formation of the gneissose granites in both volcanic arc and within-plate settings. Nevertheless, all analyzed gneissose granites and other infrastructural rocks, exhibit low initial ratios (Sr i ) (<0.7027), positive e Nd (t) (+4.9 to +10.3) and Neoproterozoic Nd model age (T DM ) (592-831 Ma for the gneissose granite samples). Although these values are compatible with other parts of the Arabian-Nubian Shield considered to be juvenile, the e Nd (t) values and several incompatible element ratios of the gneissose granites are too low to be derived from a mantle source without contribution from an older continental crust. Our geological, Sr-Nd isotopic and chemical data combined with the published zircon ages indicate the existence of a pre-Neoproterozoic continent in the Eastern Desert that started to break up at ca 800 Ma. Rifting and subsequent events caused the formation of oceanic crust and emplacement within-plate alkali basalts in the hinterland domains of the old continent. The emplacement of basaltic magma might have triggered melting of lower crust in the old continent and resulted in emplacement of the within-plate granite masses between 700 Ma and 626 Ma. The granite masses and other rocks in the old continent have been subjected to deformation during the over-thrusting of Pan-African nappes, probably because of the oblique convergence between East and West Gondwanaland. Rb-Sr isotopes of the gneissose granites in both Meatiq and Hafafit core complexes defines an isochron age of 619 Ϯ 25 Ma with Sr i of 0.7009 Ϯ 0.0017 and mean squares of weighted deviates = 2.0. We interpret this age as the date of thrusting of the Pan-African nappes in the Eastern Desert. Continued oblique convergence between East and West Gondwanaland could have resulted in the formation northwest-southeast-trending Meatiq and Hafafit anticlinoriums.

Sr–Nd isotopes and geochemistry of granite-gneiss complexes from the Meatiq and Hafafit domes, Eastern Desert, Egypt: No evidence for pre-Neoproterozoic crust

“…Less compelling inferences that pre-Neoproterozoic crust exist beneath the Eastern Desert continued in a recent and unusual interpretation of Sr-Nd isotopic data for Eastern Desert gneisses (Khudeir et al, 2008). We will show here that Sr-Nd isotopes unequivocally demonstrate that Eastern Desert basement gneisses represent juvenile late Neoproterozoic crust, a conclusion that cannot be challenged by the presence of inherited pre-Neoproterozoic zircons present in some associated supracrustal rocks.…”

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

“…The eugeoclinal thrust complex comprises ophiolitic and volcaniclastic rocks (Shackleton et al 1980;Ries et al 1983) that in the area between Quesir and the Meatiq dome can be subdivided into two: (i) an ophiolite sequence plus a volcaniclastic sequence (''older metavolcanics'') associated with a subduction complex (Khudeir 1983;Hassan and Hashad 1990); and (ii) a sequence dominated by andesitic and rhyodacites flows with a calc-alkaline geochemical affinity (''younger metavolcanics''). The two units are intruded by numerous large and small subduction-related plutonic rocks.…”

“…El-Ramly et al (1984), Greiling et al (1984Greiling et al ( , 1988, and Kröner et al (1987) consider the core complex gneisses to represent variably deformed, calc-alkaline, juvenile igneous rocks associated with the East African Orogen. Others consider them to be an extension of the Mid-Proterozoic gneisses exposed in the Western Desert of Egypt (El-Gaby et al 1984, or to be derived by partial melting of these rocks (Khudeir et al 2007).…”

Microstructural finite strain analysis of the Hafafit granitoids domes South Central Eastern desert of Egypt

“…Several models have been postulated to explain the WHC four tectonic models were proposed to decipher their origin: (1) development of fault-bend fold "antiformal stacks" (e.g.Hafafit domal structure; Greiling et al,1988a), (2) orogen-parallel crustal extension (e.g. HaFafit, Sibai and Meatiq domal structures; Wallbrecher et al, 1993;Fritz et al, 1996Fritz et al, , 2002Bregar et al, 2002;Loizenbauer et al, 2001;Abdel Wahed, 2008;Khudeir et al, 2008), (3) emplacement within regional domal structures (Ibrahim and Cosgrove, 2001) followed by extension parallel to their fold axes (e.g. Sibai dome, Fowler et al, 2007), and (4) interpreted the WHC as a result of fold interference patterns involving multiply deformed sheath folds (Fowler and El Kalioubi, 2002).…”