Paragenetic equilibration and T-X CO2 estimation for formation of calc-silicate rocks from Jolbar area, south of Urmia

Siliceous dolomites of the Jolbar area are metamorphosed during the intrusion of the Balestan alkali granite, Early Cenozoic. The main observed mineral paragenesis is Cal+Tlc+Srp±Tr±Di. Talc is the first mineral which is formed at the contact aureole and accompany the other calcareous minerals and some detrital quartz produced serpentine as a common mineral at the area. We plotted the position of chemical composition of the calcsilicates on the compatibility diagrams of the SCM system. Almost all of the samples are located on the Cal-Srp (Atg) tie line which shows that the above paragenesis was in the equilibrium with the whole rock chemistry. Considering that no olivine or brucite are crystallized and assuming 2kbar pressure for contact metamorphism, the highest estimated temperature at the aureole was 500±50 ºC. Serpentine is stable in the calc-silicate rocks, only if the composition of the present fluid is enriched by H2O. Therefore the X CO2 of fluid at the Jolbar area is considered to be <0.05.