Mineral chemistry and P-T estimation of formation of cummingtonite and coexisting minerals in the calc-silicate rocks from the Takht-e-Soleyman area, NW Iran

The calcareous rocks in the Takht-e- Soleyman area (NW Iran) crop out in association with a variety of metamorphic rocks including amphibolites, granitic gneisses, pelitic schists and meta-ultramafic rocks. Retrogressive metamorphism of these rocks occurred during decompressional cooling during exhumation. Cummingtonite-bearing rocks resulted from retrogression of the calc-silicates in the area. Their dominant mineral assemblage is plagioclase + garnet + calcic – amphibole + ferromagnesian – amphibole + quartz + calcite ± titanite ± epidote. Calcic - and ferromagnesian - amphiboles were determined by petrographical observations and EMPA analysis. Hornblende and cummingtonite compositions dominate the analysed amphiboles. Formation of Ca-poor cummingtonite coexisting with calcite and calcic - hornblende in the retrograde calc - silicates of the Takht-e-Soleyman area is a rare petrological occurrence. Thermometric estimates using mineral compositions of cummingtonite co-existing with hornblende is in the range of 550 -600 ºC. Al in hornblende barometry yields a pressure of 6.5 ± 0.6 kbar, corresponding to medium pressure amphibolite facies