Gondwanan Eoarchean-Neoproterozoic ancient crustal material in Iran and Turkey: zircon U-Pb-Hf isotopic evidence
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The Sanandaj–Sirjan Zone is a basement culmination northeast of the Neo-Tethys suture in Iran. In this zone near Azna, granite has a magmatic zircon U–Pb age of 568 ± 11 Ma, with 900–800, ca. 2400, and ca. 3600 Ma inherited cores. The ca. 3600 Ma inherited zircon is the oldest crustal component yet detected in Iran. Near Chadegan, orthogneiss has a magmatic zircon U–Pb age of 637 ± 15 Ma, and carries ca. 1000 and 2000 Ma inherited zircons. Inherited 900–1000 Ma zircons have juvenile initial εHf values of ca. +8 to +9, whereas the younger 630 and 568 Ma magmatic zircons show lower initial εHf values; however, the 3600 Ma core has initial εHf = 0.0. A Neoproterozoic rim on the inherited 3600 Ma core has the most extreme initial εHf value of −18. The Hf isotopic data indicates generation of the magmatic protoliths from a mixture of juvenile Neoproterozoic and Archean sources. Previous studies showed that in Turkey the Central Anatolian Crystalline Complex is underlain by Neo-Eoarchean rocks, the Menderes Massif contains Neoproterozoic granitoids, and that central Iran’s basement and the northern Sanandaj–Sirjan Zone contain Neoproterozoic granitic rocks. This basement terrane is from Gondwana, and was transferred across Paleo-Tethys to dock against Eurasia’s southern margin. Occurrence in Iran and Turkey of Eoarchean crust raises the possibility of sinistral migration of this terrane in the closure of Tethys because the nearest known early Archean crust occurs in northeast India.