Kinematic analysis of asymmetric boudins in the Doroud area, west of the Sanandaj-Sirjan zone
Subject Areas :
1 -
Keywords: General shear, Boudin, Vorticity, Transpressional flow, Zagros orogenic belt,
Abstract :
Structural data from asymmetric folds and granite-mylonite rocks in the Doroud region provide good indicators for quantitatively estimating the final strain, the tau number (Wk), and, ultimately, the kinematic analysis of the deformation pattern in the studied area. This region is part of the Sanandaj-Sirjan zone, located within the Zagros orogenic belt. Types of asymmetric domino and shear-band boudins in quartzite layers, which are deformed and associated with granite-mylonite, mica schist, and limestone, have been identified. Shear-band boudins exhibit a backward rotation, while domino folds exhibit a forward rotation, both showing a dextral shear direction. Mantled porphyroclasts found in the granite-mylonites also confirm the dextral shear direction. The mean kinematic vorticity number (Wm) was estimated using the methods of asymmetric boudin hyperbolic distribution and quartz c-axis pattern. The Wm calculated from these methods shows a combination of 30% to 48% simple shear component and 52% to 70% pure shear component. The results suggest that asymmetric boudins are an appropriate method for estimating the kinematic vorticity number. These quantitative analyses reflect the general shear deformation developed along the Sanandaj-Sirjan metamorphic belt, which has formed in a transpressional flow regime with shortening perpendicular to the shear zone boundary.