Study of the zircon morphology and internal structures as a tool for constraining magma source: example from granitoid bodies in the northern Sanandaj Sirjan zone (SW Saqqez)

The granitic intrusives in southwest Saqqez are located in the northern Sanandaj Sirjan zone. These granites can be divided into mesocratic and leucocratic granites. The external morphology and internal structures of zircon from these granites have been investigated employing the classic Pupin method supplemented by electron microscope analysis. The zircon crystallization is a function of temperature, chemical composition, water content of magma, velocity of crystallization and Zr saturation of magma. So, we have focused on the study of zircon to evaluate the chemical characteristic of these bodies. The minimum temperature of crystallization in mesocratic granite based on morphology of zircon crystal ranges from 784 to 847°C and for leucocratic granite ranges from 704 to 785°C, which show good correlation with calculation of saturation temperature of zircon (755 to 866°C for mesocratic granite; 755 to 832°C for leucocratic granite). Crystal growth {101} in most of zircon crystals in case study indicating I-type source of magma. Also, crystal growth {100} shows high temperature which confirm the result of thermometry. Also, absent of apatite and monazite inclusions in zircons and intergrowth hydrothermal zircons indicating dry I-type magma which correspondent with geochemical data, mineralogical survey and field observation.