SHANDERMAN ECLOGITES FROM NORTHERN IRAN, P-T PATH AND PALEOTETHYS GEODYNAMICS FROM SUBDUCTION TO EXHUMATION

Shanderman eclogites and related metamorphosed ophiolitic rocks mark the site of closure of Paleotethys ocean in northern Iran. Eclogitic mafic rocks have experienced different stages of metamorphism during subduction and subsequent exhumation. Mineral formed during prograde stages are preserved as inclusions in peak metamorphic garnet and clinopyroxene. The rocks have experienced blueschist facies metamorphism on their prograde path. They are metamorphosed in the eclogite facies at the peak of metamorphism. The eclogites has simple paragenesis of omphacite, garnet (pyrope-rich), paragonite, zoisite, glaucophane and rutile. Based on textural relations, post peak stages can be divided into amphibolite and greenschist facies. Pressure and temperature estimations on eclogite facies minerals (peak of the metamorphism) revealed pressures of 15-20 (kbar) at a temperature of ~600 °C. Pre-peak blueschist facies yield pressures lower than 11 kbar and temperatures of 400-460°C. Average pressure and temperature of post-peak amphibolite and greenschist stages were 5-6 kbar, ~ 470 °C and 2-3 kbar and 273-320 °C, respectively. The estimated pressures and temperatures indicate a clockwise P-T path for the rocks. The peak pressure indicates that the eclogites formed by Paleotethys oceanic crust subduction to a depth lower than 75 km in northern Iran. The PT path indicates subduction of the Paleotethys oceanic crust, subsequent collision between the Central Iranian and the Turan blocks and eventually exhumation of the high-pressure rocks.