Metamorphic evolution of high-pressure Quartz Schists in the Zhan metamorphic complex, Sanandaj-Sirjan zone, Iran

Abstract

The study area is located at the Sanandaj-Sirjan zone in the west and north-west of Azna and north-east of Doroud, Iran. The Quartz-Schists are divided into two main groups: amphibole-quartz schist and garnet-quartz schist. Field and microstructural studies show several deformational phases. The D1 episode which is represented by S1, matches with M1 metamprphism and D2 deformation matches with M2 metamorphism. Sodic-amphibole, phengite, garnet and plagioclase are the minerals of M1 metamorphism stage; and calsic-amphibole, garnet, plagioclase, muscovite, biotite and chlorite are the minerals of M2 metamorphism stage. The estimated P-T using Thermocalc indicates that minerals paragenesis in M1 stages have average temperature of 633±76 ◦C and also pressure of 15.2±1 Kbar; and in M2 stages have average temperature of 588±41 ◦C and also pressure of 6.8±1 Kbar. Based on calibration methods, minerals paragenesis in M1 stages have average temperature of 621±5 ◦C and also pressure of 14-16 Kbar and in M2 stages have average temperature of 546±91 ◦C and also pressure of 8.7-8.01 Kbar. Based on calibrated curves and thermocalc measurement the stability range of mineral paragenesis in M1 are in echlogitefacies and the stablility of mineral paragenesis in M2 are in amphibolite facies. This complex generated in subduction zone (Tethys under central Iran) in late Triassic and exhumed in Cretaceous and thrusted on Zagros during collision between Afro-Arabi and central Iran micro continent in Miocene.