Unravelling the Neoproterozoic accretionary history of Oman, using an array of isotopic systems in zircon

Abstract

The Omani basement is a critical window into the Neoproterozoic tectonic geography of the Mozambique Ocean and the amalgamation of Gondwana. It is located east of the juvenile arc terranes of the Arabian–Nubian Shield, yet the relationship between the two is not well understood. Magmatic and detrital zircon samples were analysed from four main basement terranes: Mirbat, the Huqf, Jebel Ja'alan and Al Jobah. The U–Pb (zircon) ages from igneous samples give ages between 838 and 765 Ma. The Lu–Hf and oxygen isotopes show that the zircons are juvenile (ɛHf(t) values 10.5–8.7), with low δ¹⁸O values (c. 2–6‰). Detritus from sediments in Mirbat, the southernmost basement outcrop, preserves a main age peak at c. 786 Ma, with Lu–Hf between +6.05 and +12.64. Lu–Hf isotopic data for Proterozoic detrital zircons from Jebel Ja'alan suggest that this region was depositionally connected to a source yielding both evolved Tonian and Neoarchean to Paleoproterozoic detritus. These sources could correlate to the terranes in India and South China, which record similarly low δ¹⁸O values. These data support a model in which Oman formed in its own tectonic domain, accreting onto the Neoproterozoic active margin of a continent.