دگرگونی مجاورتی در هسته دگرگون شاهیندژ (SMC)- شمالغرب ایران؛ تعیین دما و فشار و شواهد بافتی برای پدیده ذوب بخشی در متاپلیتها

Contact metamorphism in the Shahindezh Metamorphic Core (SMC), which is occurred due to intrusion of Pichaghchi granodiorite during Laramian orogeny (Upper Cretaceous), is studied here. The well deve loped mineral parageneses at the aureo le is quatz + plagioclase + biotite + cordierite ± chlorite ± K-feldspar ± muscovite ± andalusite ± sillimanite ± garnet. Pressure and temperature of the contact metamorphism at the SMC for andalusite + cord ierite -bearing assemblages (the most common paragenesis at the aureole) are estimated -3.5 ± 1.5 kbar and 500 ± 50°C using THERMOCALC computer program. Also the exact pos ition of the muscovi te + biot ite breakdown reaction at the PT space, is calculated. Temperature for muscovite-biotite breakdown was about 650 ± 40°C at 3.5 kbar. The calculated position of the reaction curve, is in good agreement with publ ished experi mental data. The metape lites at the north-eastern part of the SMC contain hi gh-temperature assemblage quartz + biotite + garnet + sillimanite + plagioc lase ± cordierite ± K-fe ldspar. The mineral assemblages and reaction textures in the aureole rocks record temperature about <750 °C at the si llimanite -cordierite zone and pressure - 4 kbar, detennined using petrogenetic grids. In the partially molten rocks garnet porphyroblasts are associated with coarse-grained quartz. Cord ierites occurred both at the rims of res idual garnets crystallized during regional metamorphism and in the matrix. All cordierites are altered to pennite. Fibrolite inc lusions in the matrix cordierites are common.