MESOZOIC AND CENOZOIC U-PB AGES AND MAGMATIC HISTORY OF GRANITOID BODIES IN THE NORTHERN SANANDAJ-SIRJAN METAMORPHIC ZONE, IRAN

The Sanandaj–Sirjan Zone (SSZ) is a sedimentary-metamorphic zone between a subduction-related magmatic belt (the Urumieh-Dokhtar magmatic zone) and the Zagros Fold-and-Thrust Belt of Iran. This area is considered as the suture between the Arabian microcontinent and Eurasia. The SSZ is one of the major structural and sedimentary zones of Iran, with more than 2000 km length along strike (NW-SE) from eastern Anatoly to Oman and contains both collision- and subduction-related granites. The SSZ can be divided in northern and southern parts based on tectonic, metamorphic and magmatic characteristics. The northern part experienced high temperature - low pressure metamorphism, and the southern part high pressure - low temperature. New U-Pb geochronology by the ID-TIMS method on zircon, from a number of plutons in the north of the SSZ refutes some earlier ages, and indicate a prolonged, multistage history of plutonism. I-type granites of the Boroujerd area yield mainly Jurassic ages of 168 to 170 Ma, but locally they are cut by a Late Eocene S-type granite with an age of about 35 Ma. Granitic rocks of the Hamedan region yield similar Jurassic ages of 168 and 165 Ma, whereas granite, granodiorite and gabbro from the Gorveh pluton are distinctly younger at 156 to 149 Ma. Two granites of an I-type intrusive complex at Saqqez provide vastly disparate ages of 109 Ma and 60 Ma, respectively, reflecting the long-term development of the complex. This episodic and multistage plutonic evolution reflects the protracted convergence history between Arabia and Eurasia with long-lasting subduction since the Jurassic followed by collision in the Tertiary.