The nature of fluids during pegmatite development in metamorphic terrains: Evidence from Hamadan complex, Sanandaj-Sirjan metamorphic zone, Iran

Abstract

In the Sanandaj-Sirjan zone of metamorphic belt of Iran, the area south of Hamadan city comprises of metamorphic rocks, granitic batholith with pegmatites and quartz veins. Alvand batholith is emplaced into metasediments of early Mesozoic age. Fluid inclusions have been studied using microthermometry to evaluate the source of fluids from which quartz veins and pegmatites formed to investigate the possible relation between host rocks of pegmatites and the fluid inclusion types. Host minerals of fluid inclusions in pegmatites are quartz, andalusite and tourmaline. Fluid inclusions can be classified into four types. Type 1 inclusions are high salinity aqueous fluids (NaCl eq >12 wt%). Type 2 inclusions are low to moderate salinity (NaCl eq <12 wt%) aqueous fluids. Type 3 and 4 inclusions are carbonic and mixed CO 2 -H 2 O fluid inclusions. The distribution of fluid inclusions indicate that type 1 and type 2 inclusions are present in the pegmatites and quartz veins respectively in the Alvand batholith. This would imply that aqueous magmatic fluids with no detectable CO 2 were present during the crystallization of these pegmatites and quartz veins. Types 3 and 4 inclusions are common in quartz veins and pegmatites in metamorphic rocks and are more abundant in the hornfelses. The distribution of the different types of fluid inclusions suggests that CO 2 fluids generated during metamorphism and metamorphic fluids might also contribute to the formation of quartz veins and pegmatites in metamorphic terrains.