The study of petrogenesis, mineral chemistry and thermobarometry of contact metamorphic rocks from aureole of Alvand body, Hamedan

There are various contact and regional metamorphic rocks، from low to high grade in contact of the Alvand plutonic body. These rocks have undergone regional dynamothermal metamorphism and in the later stage due to heat and fluids derived from the body have been subjected to contact metamorphism. Hornfelses from the east and the north-eastern part of the Alvand aureole have sedimentary protolith of shale type. In the studied hornfelses، garnets are almandine-rich; composition of biotite is sidrophyllite and of the plagioclase varies from albite to andesine. Based on thermometric cation-exchange method of garnet-biotite pair، using different calibrations، the obtained temperature for cordierite-free hornfels، is about 580 °C and for the cordierite-bearing hornfels 566 °C. In barometry with GPBQ system، calculated pressure for hornfelses is strongly consistent with pressure obtained from multiple equilibrium curves for these rocks and was estimated to be about 2. 9 to 3. 6 Kbar. The obtained temperature and pressure using composition from rim of minerals in cordierite- and aluminosilicate-bearing rocks، with multiple equilibrium curves and THERMOCALC software represent temperature of about 650 °C and pressure of 3 Kbar.