شيمي كاني و دما - فشارسنجي سنگهاي رسي موجود در هسته دگرگون در دما بالا - فشار متوسط شاهنيدژ )SMC( شمال غرب ايران‌

HT-MP metamorphism at the Shahindezh Metamorphic Core (SMC) - NW Iran; Mineral chemistry and thermobarometry of metapelites

On the basis of microstructural evidence it is clear that SMC metapelites have experienced at least two regional (RM 1, RM2) and one contact metamorphism (CM). During RM2, several porphyroblasts including kyanite, andalusite, staurolite, cordierite, garnet and fibrous sillimanite have grown in the mica - schists. In order to estimate the PT condition of metamorphism of metapelites, we used cation exchange and multi-equilibrium methods. Temperature of RM2 estimated using, Grt - Bt and Grt - ChI thermometry 650 - 700°C. Also PT conditions are calculated by THERMOCALC computer program which is based on multiequilibrium reactions. Kyanite - staurolite - cordierite - bearing mica - schists are metamorphosed at pressure -5 - 7 kbar and temperature -650 ± 50°C. Thermal gradient at the SMC is considered to be - 40 °CIkm. This thermal gradient is similar to those from continent-continent collision settings.