Cryogenian accretion of the Northern Arabian-Nubian shield: Integrated evidence from central Eastern Desert Egypt

Abstract

Accretionary geology of the Arabian-Nubian shield (ANS) is critical in deciphering the Neoproterozoic global tectonics. Multidiscipline investigation of ophiolites, sediments, and igneous units of central Eastern Desert Egypt results in a revisited tectono-magmatic scenario. The first baddeleyite U-Pb age (ca. 687 Ma) of the ANS ophiolites is obtained from the layered gabbro of the Wadi Ghadir ophiolite, which limits the back-arc spreading age. Significant Archean-Paleoproterozoic detrital zircon age spectrum, similar to those of the Saharan-Congo craton, is identified from a conglomerate of the Atud turbidites, indicating the existence of craton basement in the shield. Significant ca. 840 Ma and ca. 750 Ma detrital zircon ages with a mixing of juvenile and ancient Hf isotope features approve the provenances to be arc(s) with craton basement. Two episodes of calc-alkaline units represented by the Umm Rus complex (URC) and the El Sibai complex (ESC) are dated at ca. 680 Ma and ca. 660 Ma, respectively. They were both originated from juvenile sources (in situ zircon ɛHft = +6.1 ∼ +12.2) with depleted high-strengthen field elements (e.g., Nb, Ta, Zr, Hf) but enriched large ion lithophile (e.g., Ba, Sr) and radiogenic elements (e.g., Th, U). The Ti-in-zircon temperature of the ESC granitoids (696 ± 16 °C) is lower than that of the older URC (749 ± 21 °C), as well as the inferred ca. 840 Ma and ca. 750 Ma arcs; and this reconciles an increased hydrous melting during the final Gondwana assembly. The older plutons represented by the URC show an E-W elongated distribution consistent with the alignment of the regional imbricated thrusting; whereas the elongation of the younger generation represented by the ESC is N-NE to S-SW and is coherent with the axis of the core complexes and the major strike-slip faults of the region. This possibly coincides a direction-change of paleo-subduction. In summary, the Northern ANS likely represents a superimposed arc accreted at 680–660 Ma during the closure of the Mozambique ocean.