Study of zircon crystals: an implication to determine of source, nature and temperature of crystallization in rhyolitic magmas

The zircon crystallization is a function of temperature, composition and water content of magma, also its crystal shape and size depends on velocity of crystallization and Zr saturation, then we have focused on the study of zircon crystals in Hormuz rhyolites from four salt domes in different localities (Gachin, Bandare Moallem, Hormuz and Larak Islands) based on the morphology study. The most of studied zircons are plotted in the P3 and P4 areas and the less lie in the P5, P2 and S15 domains. Crystals morphology, lack of hydrozircon overgrowth and apatite or monazite inclusions in zircons indicating that they have crystallized from an I-type rhyolitic magma. Zircon morphology pointing on moderately alkaline and dry nature of parental magma. Based on morphology, zircon saturation temperature and whole-rock geochemistry calculation, the minimum temperature of zircon crystallization is ranging from 750 to 840˚C. Coexistance of euhedral elongated zircons with wide and short zircon crystals indicate the super-saturation of Zr in the responsible magma from early stage, which is also confirmed by thin zonation features.