Zircon xenocrysts in Late Cretaceous magmatic rocks in the Kermanshah Ophiolite: link to Iran continental crust supports the subduction initiation model

Abstract

ABSTRACT Geochronological and geochemical data show that Late Cretaceous Zagros ophiolites were generated by forearc seafloor spreading during a subduction initiation event along the southwestern margin of Iran. These ophiolites define a ~ 3000 km long belt passing from Cyprus to Turkey, Syria, Iran, the UAE, and Oman. Ten samples of plagiogranites, amphibole gabbros and diorites of the Kermanshah ophiolite yield U-Pb zircon magmatic ages indicating ophiolite formation at 98 to 96 Ma. Some Kermanshah rocks also contain abundant zircon xenocrysts with age peaks (in order of decreasing size): Triassic (~247 Ma), mid-Paleoproterozoic (~2150 Ma), Late Paleoproterozoic (~1850 Ma), Late Ediacaran (~560 Ma), Early Cretaceous (~140 Ma), and Tonian (~850 Ma). Similar age peaks are seen in magmatic and detrital rocks of Iranian crust to the north. The xenocrysts have εHf(t) values from +6.3 to – 21.6, corresponding to depleted mantle Hf model ages (TDM) of 0.6 to 3.6 Ga. The xenocryst age peaks are similar to those of zircons in Iranian continental crust. The occurrence of zircon xenocrysts in the Kermanshah ophiolite suggests that this formed adjacent to the Iranian continent, as expected for Late Cretaceous subduction initiation.