Abstract
Iran is located in the continental collision zone between Arabia and Eurasia and consists of several micro-continents with the affinity of Gondwana, and its drifting history has close connection with the evolution of Tethys oceans. The widespread Late Neoproterozoic (Ediacaran) to Cambrian (ca. 600-500 Ma) granitoids and gneisses that built up the crystalline basement of Iran are regarded as part of the Cadomian magmatic arc resulting from the subduction of the Prototethys along the northern margin of Gondwana. The Cadomian rocks yield variable zircon Hf isotopic results of εHf(T) values from +11 to -3 and Hf crustal model (TDMC) ages of ca. 0.9-1.7 Ga, implying that the magmas were formed by the melts of mixed depleted-mantle and Archean crustal sources. The Iranian micro-continents were then separated from the northern Gondwanan margin because of the birth of the Neotethys. The Carboniferous (349-311 Ma) A-type granitoids in northwestern Iran have well constrained the timing of initial phase of the Neotethyan opening, which yield zircon εHf(T) values from +5 to -1 and TDMC ages of ca. 1.0-1.4 Ga that suggest the formation of these rocks involving the reworked Cadomian basement. The Middle Jurassic (~165 Ma) granitoids, mainly exposed along the Sanandaj-Sirjan zone, represent the early stage of products triggered by the subduction of the Neotethys beneath Iran and show similar zircon Hf isotopic compositions of εHf(T) values from +5 to -3 and TDMC ages of ca. 0.9-1.4 Ga. The long-lasting Neotethyan subduction subsequently led to the occurrence of the Urumieh-Dokhtar magmatic arc with major activities during the Eocene to Oligocene (55-25 Ma), and this prolonged magmatic flare-up event has been widely identified across Iran and Armenia. The Eocene-Oligocene igneous rocks, along with other Miocene small-volume bodies, have dominantly positive zircon εHf(T) values from +15 to -2 and much younger TDMC ages of ca. 0.2-1.2 Ga, which indicate the significant contribution of mantle inputs in the magmatic genesis and the important growth of newly formed continental crust during the Cenozoic in this particular segment of the Neotethyan orogenic belt.
