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

Document Type: Research Paper


Department of Geology, University of Zanjan, University Blvd., Zanjan, 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 the
orthogneiss and crop out in the external limbs of the antiformal dome. Two main deformational episodes have been documented in the
schists and marbles. The first episode (D1 phase) produced S1 foliation, whereas the second episode (D2 phase) produced a penetrative
S2 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) occurred
during 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 highpressure
metamorphic assemblage (M1 stage), documented in the Chadegan complex, were formed during the subduction stage, while
the D2 deformation phase and M2 metamorphic blastesis were recorded during the exhumation stage; probably they occurred before
the end of Cretaceous.