Comparison of Fluid Activity Within Metapelitic and Carbonate Rocks of the Cheshin from Contact Aureole of the Alvand Batholite, Hamadan

Field relations and petrographical features, shows that formation of the metapelitic and carbonate rocks of Hamadan in Western Iran was poly-metamorphic. The intrusion of the Alvand Batholite (Jurassic age) into pelitic and calcareous host rocks has produced metamorphic rocks in the Cheshin area containing, sillimanite hornfels, marbles and calc-silicate rocks. Mineral assemblages in the metapelitic and calc-silicate rocks are different, peak metamorphic assemblages of these rocks respectively are garnet, biotite, staurolite, aluminosilicate minerals (kyanite/ sillimanite), muscovite and quartz but calc-silicate assemblage are garnet, diopside, wollastonite epidote and amphibole, which usually take place by contact metamorphism. Using multiple equilibria, temperature (~600-630 ºC), pressure (~2-4 kbar), and fluid composition (XCO2 as low as 0.17) have been calculated for the formation of the calc-silicated rocks. The results show good agreement with those from other metapelitic rocks. P-T results indicate that contact metamorphism conditions occur in pyroxene hornfels facies in this part of the Hamadan crust.