Mineral chemistry and thermodynamics conditions of impure marbles formation from Neybaghi metamorphic complex, NE of Myaneh, Iran

A metamorphic rock complex consists of slate, phyllite, micaschist and marble with NE – SW shistosity has cropped out in Neybaghi area in the NE of Myaneh.  Impure marbles occur as thick and thin layers or massive bodies within the centeral area of this complex. Textural and mineralogical evidences, revealed two metamorphic stages.  The early stage is testified by the minerals such as pyroxene (diopside), epidote (clinozoisite), amphibole 1 (edenite-pargasite) and plagioclase 1.  The main stage have chlorite (clinochlore), phlogopite, amphibole 2 (tremolite) and plagioclase 2.  P-T-XCO2 have been estimated for the early and main stage of metamorphism by computing nonideal and asymmetrical fugacity and activity and programing in THERMOCALC software for fluid and solid phases.  The estimations give pressure, temperature and XCO2 of 9.5Kbar, 660°C and 0.35, whereas the main stage has been constrained at P=4.2Kbar, T=510°C, XCO2=0.4. The obtained P-T path shows that the Neybaghi marbles were formed under medium pressure condition and overprinted by a low pressure metamorphism.  This type of P-T trend can be formed in collisional tectonic regime.