Investigations on mineral chemistry and P-T estimation for formation of diopside, garnet and coexisting minerals in the calc- silicate hornfelses from the Alvand metamorphic aureole, Hamadan, West of Iran

Calc-silicate hornfelses are resulted from temperature excreted from the Alvand Batholith on the surrounding carbonate rocks. Metamorphic minerals in these rocks are vesuvianite garnet牘Ꞣ鲫ꌗꝻ tremolite/actinoliteꫦꮷ㾜橗⊵±epidote. Calc- silicate minerals occurred in two stages of prograde and retrograde metamorphism. Mineral chemistry of clinopyroxene and garnet in calc-silicate hornfelses determined by EPMA shows that these minerals are mainly diopside and grossular. Based on clinopyroxene-garnet thermometry with coexisting minerals such as tremolite/actinolite, quartz, . . . temperature of ~550˚C was calculated for metamorphism of the clac-silicate hornfelses. Pressure of metamorphism was estimated to be about 3.5 Kbar. Fluid composition in the calc- silicate hornfelses had XCO2 = 0.2 which indicates that during prograde metamorphism carbonate minerals reacted out and the amount of these minerals was reduced in the rocks.