Mineralogy, mineral chemistry and thermobarometry of the metamorphic complex of the Vehnan area in the west of Alvand (Hamedan)

The regional and  contact metamorphic rocks of the studied area are located in the west of Hamedan city and Alvand plutonic body as a part of the northern part of the Sanandaj-Sirjan belt. This metamorphic complex consists of slate, garnet mica schist, amphibole schist and tremolitite in regional metamorphic rocks and spotted schists, mica hornfels, epidote amphibole hornfels and cordierite hornfels in contact metamorphic rocks. The analyzed minerals in these rocks include biotite, garnet, staurolite, amphibole and cordierite. EMP chemical analyses indicate that the composition of garnet is almandine, the composition of biotite is siderophyllite and amphibole is actinolite. Staurolite has iron-rich composition and cordierite has intermediate composition (iron-magnesian). Thermometric calculations based on biotite in garnet staurolite schists show a temperature of about 555°C, and the temperature of about 511°C was determined by the garnet-biotite pair method. Due to the presence of staurolite and the absence of kyanite and other medium and high pressure minerals, the pressure of 3 to 4 kilobars is possible. The type of metamorphism of the study area is suggested to be related to a  subduction tectonic environment. The stability of the garnet + staurolite assemblage requires the presence of water in the environment.