The detrital zircon U–Pb–Hf fingerprint of the northern Arabian–Nubian Shield as reflected by a Late Ediacaran arkosic wedge (Zenifim Formation; subsurface Israel)

Abstract

The Neoproterozoic Arabian–Nubian Shield (ANS), which comprises the northern sector of the East African Orogen (EAO), has been deeply denuded in Ediacaran times and its erosional products were deposited across NE Africa and Arabia; they are also found in a number of peri-Gondwana terranes. A vast Late Neoproterozoic clastic wedge, locally interbedded with volcanics, developed on the northern outskirts of the ANS and spread into areas currently at the foothills of the Taurus and Zagros belts to coalesce into a wide peri-Arabian-Mesopotamian basin. The southern limit of this basin is manifested in the subsurface of Israel and Jordan by a few km thick arkose sequence, the Zenifim Formation, which underlies the Cambro–Ordovician quartz-rich sandstones. The detritus stored in this formation was mostly eroded from the adjacent ANS at the cessation of Neoproterozoic orogeny.Along a ∼150km long transect in the subsurface of Israel, the arkosic facies of the Zenifim Formation changes from a proximal alluvial fan in the south, to a sea marginal facies in the north reflecting the transgression of the proto-Tethys onto the decaying Neoproterozoic orogen. We studied the detrital zircon U–Pb–Hf from core samples of arkose from different parts of the Zenifim Formation in order to constrain the composition of its provenance and to obtain the Late-Neoproterozoic detrital fingerprint of the ANS.The proximal alluvial fan and plain facies is dominated by a remarkable concentration of U–Pb detrital zircon ages between 0.6 and 0.7Ga with a peak around 0.63Ga, alongside a few older grains (0.8Ga and 0.9Ga). Pre-Neoproterozoic detrtital zircons are absent. The youngest detrital zircon population peaks at 0.60Ga. The entire inventory of detrital zircons yielded positive ɛHf values between +11 and +5, generally overlapping ɛHf values of Neoproterozoic rocks of the northern ANS. It is notable that little indication for the exposure of the Cryogenian rocks of the ANS is represented by the detrital zircon signal in the alluvial fan deposits, a feature indicating the prevalence of Ediacaran granitoids in the provenance. Towards the north, the youngest detrital zircons in the sea marginal facies concentrate at 0.58Ga implying this part of Zenifim Formation is among the youngest Late Neoproterozoic sedimentary units in the northern ANS. The detrital zircon signal exhibits a preponderance of Neoproterozoic-aged detrital zircons peaking at 0.6Ga and 0.75–0.8Ga, but Grenvillian-like age peaks at 0.92, 1.0 and 1.1Ga are also identified. Additionally, a small number of 1.8, 2.1 and 2.6Ga-aged zircons, and a few Late Neoproterozoic detrital zircons with negative ɛHf values also occur. Erosion of basement rocks in the northern ANS was generally capable of accounting for most of the detrital zircon spectra in the sea marginal facies, but we point out two other potential sources. Our preliminary investigations indicate that dike swarms that invaded the northern ANS in the mid Ediacaran carry abundant inherited pre-Neoproterozoic zircons and Neoproterozoic-aged zircons with negative ɛHf values. The presence of such zircons in post −0.58Ga sediments, subsequently to the major diking phases, can thus be accounted for, at least partly, by the erosion of dikes and associated volcanics. Likewise, a northern provenance that resided within the Cadomian realm or laterally along the Gondwana margin could also play a role in delivering zircons of this type to the sea marginal facies of Zenifim Formation.