Study of structure and morphology of zircons in pelitic migmatites in Hamedan, Touyserkan and Boroujerd regions, Sanandaj-Sirjan zone

Several outcrops of migmatitic rocks (metatexite to diatexite) developed in the northern part of the Sanandaj-Sirjan zone (Hamedan, Touyserkan and Boroujerd). Two types of inherited zircons (2590 to 190 Ma) and metamorphic zircons (180 to 160 Ma) are found in the mesosome of migmatites. As the cathodoluminescence images display, inherited zircons are euhedral to subhedral with oscillatory zoning, and are jagged their margins in some cases. Metamorphic zircons as thick form grains are characterized by the lack of magmatic zoning and the presence of ghost texture, growing on the margins of the inherited zircons as a thin sheath.  In some cases, metamorphic zircons are found as single crystals without any inherited nuclei. As the structural evidence suggests the process of recrystallization formed metamorphic zircons and their elements were moved under sub-solidus conditions. During migmatization, on one hand, the presence of fluid phase due to partial melting, gave rise to the formation of metamorphic zircons showing oscillating zoning and on the other hand, it has precluded the deformation due to shearing in the internal structure of these phases.  Metamorphic zircons, belonging to 180 Ma, and younger are possibly nucleated through the Jurassic period thermal-dynamic metamorphism.