Granulite facies metamorphism of the olivine bearing dolomitic marbles in Takab area, NW Iran

The Takab metamorphic complex in the NW of Iran, is located between longitude 4745' and 4705' E and latitude 3730' and 3630' N. The Takab complex, with Neo-proterozoic- Cambrian age, displays tectonic, lithological, stratigraphic and geochronological feathres (relative and isotopic dating) similar to those of the Central Iran Zone. Therefore, it is considered as a part of the Central Iran Zone with similar age (i.e. Neoproterozoic-Cambrian). The types of metamorphic rocks in the complex are gneiss, calc-silicate granulites, mafic granulites, migmatite, amphibolite, dolomitic marbles, pelitic schists, basic schists and serpentinized metaperidotites. The olivine- bearing marbles are derived by dolomitic marbles metamorphosed under granulite facies. Based on the appearance of olivine in paragenesis of the dolomitic marbles, the pressure and temperature of pick metamorphism is estimated at T≥800 C and P~8 kbar. The evidence for retrogression of the Ol-bearing dolomitic marbles is the presence of tremolite + dolomite assemblages after olivine. The infiltration of H2O-enriched fluids during retrograde metamorphism led to the formation of H2O-bearing minerals such as tremolite, zoisite and clinochlore as well as titanite in paragenesis of the dolomitic marbles.