Investigating the progressive dynamothermal metamorphic evolution of metabasites from the Qori complex (NE Neyriz) using phase diagrams

The Qori metamorphic complex in the northeast Neyriz (Sanandaj-Sirjan zone) formed due to the different metamorphic phases during the Jurassic to Cretaceous as a result of the subduction of the Neotethys oceanic crust beneath the Iran microplate. The whole-rock compositions revealed that some of the complex units formed from the metamorphism of basic protoliths. Petrographic investigations showed that the metabasites contain assemblage actinolite + zoisite + plagioclase + chlorite + epidote + quartz ± titanite in the lowest metamorphic grade (green schist facies) that was replaced by hornblende + plagioclase + garnet + clinopyroxene + quartz ± titanite assemblage at the peak of the metamorphism (lower granulite facies). Based on the thermodynamic phase diagrams (pseudosection) calculated for these rocks, the metamorphism at the green schist facies occurred at T < 550 C° and P < 5 kbar, while the peak condition occurred T and P 640 to 750 C° and 6.5 - 10 kbar, respectively. The other phase diagrams indicate that the low MgO content in the protolith and CO2</sub> content in the metamorphic fluid played an important role in the formation and stability of the metamorphic assemblages observed in the metabasites of the Qori metamorphic complex.