The evolution of the Arabian-Nubian Shield and survival of its zircon U-Pb-Hf-O isotopic signature: A tale from the Um Had Conglomerate, central Eastern Desert, Egypt

Abstract In this study, we present in situ U-Pb, Hf and O isotopic analyses of detrital zircon grains from the Um Had Conglomerate from the Wadi Hammamat area in the central Eastern Desert of Egypt. The youngest detrital age population is 625 Ma, which gives an estimate to the maximum depositional age of the Um Had Conglomerate. Based on their Hf isotopic signature and U-Pb ages, detrital zircons fall into two distinct groups: a 625–680 Ma group and a 720–840 Ma group, with minor early Tonian-Stenian and Paleoproterozoic-Archean populations. These groups are consistent with derivation from local sources in the central Eastern Desert of Egypt. The 720–840 Ma group is characterized by exclusively positive e Hf(t) values and it reflects the main juvenile Tonian intra-oceanic island arc stage characterizing the formation of the Arabian-Nubian Shield. On the contrary, e Hf(t) values of the 625–680 Ma zircon group range between −17.5 and +12.8, which indicates involvement of Archean-Paleoproterozoic crust during the Cryogenian-Ediacaran magmatism associated with the accretion and assembly of the arc materials. The transition from juvenile intra-oceanic island arc stage to mixed juvenile magma and older crustal materials during the arc assembly stage in the central Eastern Desert is supported by the increase in δ 18 O values of detrital zircons from dominant mantle-like values in the Tonian to higher values in the Cryogenian-Ediacaran group. A wide variation in the e Hf(t) values (−25.8 to +10) is recorded also in the early Tonian-Stenian population, which results in the double plunge U-Pb-Hf patterns of the detrital zircons. This pattern is similar to the Nile sediments and to the Paleozoic and Mesozoic Nubian sandstone, which may indicate substantial recycling of ANS crustal material by these sediments and survival of its original zircon U-Pb-Hf-O signature despite repeated recycling episodes.