Age dating and thermometry of the zircon crystallization of the metagranites from the North Shahrekord Metamorphic Complex

The North Shahrekord Metamorphic Complex (NSMC) in the center of Sanandaj-Sirjan Zone includes metagranite bodies, which has been intruded in some metamorphic rocks, especially schists. The NSMC metagranites display metamorphic and distinctive ductile deformation characteristics. These rocks are composed of quartz, alkali feldspar, plagioclase, biotite, amphibole, epidote, garnet, zircon, allanite, titanite, apatite and magnetite. Ages of the NSMC metagranites by zircon U–Pb shows the age of 523.92 [+ 5.03 – 5.73] Ma, and the whole rock Rb–Sr isotopes represents the age of 504 ± 47. The ages of NSMC metagranites (middle Cambrian) are younger than the Late Neoproterozoic - Lower Cambrian granitoids of the Sanandaj-Sirjan Zone, the NSMC metagranites are formed in the post-collisional setting, while the older granitoids are mostly related to volcanic arc. According to the morphology and shape of zircon crystals in NSMC metagranites, most of zircons are placed on S19 and S15 areas in morphology classification of zircon crystals, therefore, the granite magma of the area has hybrid (crust and mantle) origin. The crystallization temperature of metagranites, according to zircon morphology studies, is 750 to 850 °C, based on Zircon saturation calculation method, is 753.2 to 828.5 °C, and based on the graphical method (results of total rock chemical analyses), is 760 to 830 °C.