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

The Chadegan metamorphic complex is a WNW-ESE- trending antiformal structure located in Sanandaj-Sirjan structural zone, Iran.The inner core of the structure is made of orthogneiss, containing eclogitic lenses. Schists and marbles lie structurally above theorthogneiss and crop out in the external limbs of the antiformal dome. Two main deformational episodes have been documented in theschists and marbles. The first episode (D1 phase) produced S1 foliation, whereas the second episode (D2 phase) produced a penetrativeS2 axial plane foliation, F2 folds, and a mylonitic fabric. Relicts of a high-pressure metamorphic mineral assemblage (M1) (phengite+garnet + sodic-calcic amphibole) have been documented along S1 foliation. A later amphibolite-facies metamorphism (M2) occurredduring D2 deformation phase. P-T estimates for M1 stage give an average pressure of 1.6 GPa and an average temperature of 550 °C,whereas M2 stage has been constrained at P = 0.34 – 0.48 GPa and T = 508 - 575 °C. D1 deformation phase and the associated highpressuremetamorphic assemblage (M1 stage), documented in the Chadegan complex, were formed during the subduction stage, whilethe D2 deformation phase and M2 metamorphic blastesis were recorded during the exhumation stage; probably they occurred beforethe end of Cretaceous.