Provenance of conglomerate clasts from the volcano-sedimentary sequence at Wadi Rutig in southern Sinai, Egypt as revealed by SIMS U–Pb dating of zircon

Abstract

The volcano-sedimentary succession at Wadi Rutig, Sinai, at the northernmost segment of the Arabian Nubian Shield comprises early Ediacaran volcanic rocks interbedded with immature sediments including variable sized conglomerates, sandstones and siltstones. We report new SIMS U–Pb ages of zircons separated from conglomerates of various levels in the succession and from single cobbles of these conglomerates. The age probability patterns of two conglomerate samples reveal major contribution from 600 to 860 Ma components with a prominent gap at 640–710 Ma and some contribution from ca. 900 to 1100 Ma components. Single cobbles of granitic and dacitic compositions yield ages of ca. 615 Ma and 629 Ma respectively. The provenance patterns are compatible with major derivation from known ANS age material in Sinai (600–850 Ma), but also indicate that pre-870 Ma components of dominantly latest Mesoproterozoic to earliest Neoproterozoic were more widespread in the northernmost ANS than previously appreciated. The 640–710 Ma age gap supports a lull in magmatic activity at this time in the northernmost ANS especially in Sinai, which is in marked contrast with the evolution of more southerly ANS segments. The ca. 710–740 Ma age detrital zircons in the Rutig conglomerates are interpreted to reflect magmatic source of this age range, hitherto not identified in the northernmost ANS. U–Pb ages of youngest detrital zircons combined with other evidence indicate that deposition of conglomerates can be confined to ca. 620–610 Ma and 600–590 Ma. The recognition of two erosion–deposition phases is discussed within the context of a changing geodynamic setting during post-collisional collapse of the ANS orogen after ca. 630 Ma. Both provenance patterns and basin evolution are compared to other late Neoproterozoic volcano-sedimentary successions of the northernmost ANS.