A study of various occurrences of the AI2SiOs polymorphs in the rocks/veins of the Hamedan region, Iran: with special reference to origin of quartz-kyanitc veins

The study area is a part of so-called sanandaj-sirjan zone or zagros imbricate zone of the zagrosorogen. iran. the harncdnn region comprises a metamorphic sequence of low- to high-grade regional andcontact metamorphic rucks intruded by mafic, intermediate and felsic plutonic bodies. the sequencecomprises pelitic, psarnmitic, mafic. calc-pelitic and calc-silicate rocks. pelitic rocks are the most abundantrocks in the region which are mostly composed of slates, phyllites. mica schists. garnet-mica schists. garnetandalusite-(±sillimanite/±kyanite) schists, garnet-staurolite schists, mica hornfelses, garnet hornrelses.garnet-andalusite-(± fibrolite) hornfclses, cordieritc-t±andalusitc i hornfelses, cordierite-k-feldsparhornfelses and sillimanite-k-feldspar hornfelses. several interlayers of amphibolites and amphibole schistsalternate with pelitic rocks in the sequence. various types of ab.sio~-bearing silicic veins occur in theregion. isotope characteristics indicate metamorphic origin for some of them. in this study, we have definedthree different generations of kyanite according to their various geological characteristics, including: (1)metamorphic (randomly distributed and commonly co-existed with xillimnnitc/undalu.... ire), (2) stress-tsbcor)induced(pseudomorphs of kyanite after andalusite ill the shear zones) and (3) late-stage (hydrothermal ormetasomatic) kyarutes. the quartz-kyanitc veins/pods are late structures that are created by interactions withwall rocks. circulating al- and si-rich fluids may be responsible for formation of these veins/pods.