Abstract
A combined study of single zircon U–Pb dating, Hf–O zircon isotopic analyses and whole-rock Nd isotopic compositions was carried out to infer the magma sources of Neoproterozoic post-collisional A-type granitoids in Saudi Arabia. U–Pb zircon dating of magmatic zircons of two samples from the Hadb adh Dayheen ring complex yielded ages of 625±11Ma for a hornblende–biotite granite sample, and 613±4Ma for a monzogranite sample. The granitic rocks show initial εNd values of +4.1 to +5.3 and εHf of +4.5 to +8.4 that are lower than those of a model depleted mantle (εHf ~+14 and εNd ~+6.5) and consistent with melting of subduction-related crustal protoliths that were formed during the Neoproterozoic assembly of the Arabian–Nubian Shield (ANS). Crustal-model ages (Hf-tNC) of 0.81 to 1.1Ga are inconsistent with depleted-mantle Nd model ages of 0.71 to 0.81Ga and indicate that the post-collisional Hadb adh Dayheen granites were derived mostly from juvenile crust formed in Neoproterozoic time. Single zircons data show a wide range in δ18O values from +3.2‰ to +6.4‰, possibly indicating crystallization of zircon from magma derived from magmatic rocks altered by meteoric water in a magma chamber–caldera system.
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•Hadb adh Dayheen granitic rocks are Neoproterozoic in age (625–613Ma).•The granitic rocks yielded εHf(t) of +4.5 to +8.4 and εNd(t) of +4.1 to +5.3.•Single zircon grains show a wide range in δ18O values of +3.2‰ to +6.4‰.•Hadb adh Dayheen rocks are consistent with melting of juvenile crustal protoliths.