Strain pattern and vorticity analysis in the transpressional Kamandan area within the Sanandaj-Sirjan Metamorphic Belt, Iran

Abstract

New structural data on radiolarite and quartz mylonite rocks from the well-exposed Kamandan area are presented with the aim to shed light on the quantitative finite strain and vorticity analyses and strain partitioning along the Zagros transpression zone. Duplex structures, imbricate fans, thrust sheets and shear zones are well developed in the Kamandan region, located in the Sanandaj-Sirjan Metamorphic Belt, western Iran. Kinematic shear sense indicators associated with Kamandan shear zone show top-to-the-NE sense of ductile shearing deformation. Integrated quantitative finite strain and kinematic vorticity analyses of deformed rocks indicate deformation pattern and geometry. The strain parameter measurements vis. strain ratios and strain ellipsoid shape (k) show that radiolarite and quartz mylonite rocks have deformed in the constrictional to approximately plane-strain conditions. The quartz mylonite rocks highlight general-shear (sub-simple shear) deformation (Wm = 0.68–0.81) associated with the spatial increase in simple-shear component (47%–60%) from NE to SW. Our results of structural, strain, and vorticity analyses confirm a dextral transpression with strain partitioning into the pure-shear and simple-shear components in the Kamandan shear zone. Estimated Wm-values display the θ angle between the transpressional boundary and the maximum instantaneous strain axis (ISA) is the range from 63 to 69°. Accordingly, the oblique convergence angle (α) between the flow apophyses was estimated at about 35–48° that causes a horizontal shortening of ∼32–42% perpendicular to the boundaries of the Kmandan shear zone.