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

Abstract

The Chadegan metamorphic complex is a WNW-ESE- trending antiformal structure located in Sanandaj-Sirjan structural zone, Iran.<br />The inner core of the structure is made of orthogneiss, containing eclogitic lenses. Schists and marbles lie structurally above the<br />orthogneiss and crop out in the external limbs of the antiformal dome. Two main deformational episodes have been documented in the<br />schists and marbles. The first episode (D1 phase) produced S1 foliation, whereas the second episode (D2 phase) produced a penetrative<br />S2 axial plane foliation, F2 folds, and a mylonitic fabric. Relicts of a high-pressure metamorphic mineral assemblage (M1) (phengite+<br />garnet + sodic-calcic amphibole) have been documented along S1 foliation. A later amphibolite-facies metamorphism (M2) occurred<br />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,<br />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<br />metamorphic assemblage (M1 stage), documented in the Chadegan complex, were formed during the subduction stage, while<br />the D2 deformation phase and M2 metamorphic blastesis were recorded during the exhumation stage; probably they occurred before<br />the end of Cretaceous.