Structural, micro-structural and kinematic analyses of the duplex thrust system related to the gneiss dome of the slate belt and Zagros hinterland-fold-and-thrust belt: the Sourian and Tutak metamorph

The Zagros hinterland fold-and-thrust belt left eye-catching features during its evolutionary episodic processes. The Tutak gneiss dome is one of the features consist of exhumed middle crust along a channel. It is including Sourian and Tutak metamorphic complexes, which are lied on its edges and core respectively. Whereas several studies conducted at the Tutak gneiss dome, they do not cover structural nature of the dome, completely. Therefore, main purpose of the research is revealing clues about formation mechanism of the Tutak gneiss dome through structural and microstructural observations, structural relationship analyses, and cross section. Based on field observation data at least three main deformation phases concordance to the multiphase regional deformation of the Zagros hinterland fold-and-thrust belt, impressed the Tutak gneiss dome during its evolution. Multiple generation folding and overprinting them by later phase had produced a variety of fold interference structures. The Jian and Sourian major thrusts had controlled the crustal flow of Tutak gneiss dome along a hybrid channel with producing a duplex thrust system. According to the presented cross section, we proposed a thrust-related gneiss dome in form of a duplex structure as formation mechanism of the Tutak gneiss dome. Also, Quartz c-axis fabrics, finite strain and kinematic vorticity number analyses were used to investigate deformation characteristics of the Sourian and Tutak metamorphic complexes. The opening angle of the quartz c-axis fabric patterns was used to determine the deformation temperature which implies amphibolite facies conditions (532.72 ± 21.36° C) for ductile deformation. The kinematic vorticity number varies from 0.69 to 0.93, which indicates that the metamorphic rocks of the Tutak gneiss dome was facilitated by contribution of both pure shear (39%) and simple shear (61%) deformation components within a sub-simple shear regime. During evolution of the Tutak gneiss dome, NW-SE foliations with commonly SW and NE dipping accompanied by mostly NW-SE plunging and subordinate NE-SW plunging stretching lineations which both indicate more extension along NW-SE trend that resulted a prolate elliptical wedge in map view. Structural and vorticity analysis suggest that the Tutak gneiss dome has experienced dome formation followed by thrust stacking rather than the two deformations occurring together and a protracted progressive deformation through a decreasing temperature regime.