Strain partitioning in the Kahdan shear zone: Microstructural and kinematic evidence from the SE Sanandaj-Sirjan zone, Zagros orogeny

• Published in: Journal of structural geology 2022-12, Vol.165, p.104759, Article 104759
• Main Authors: Shafieibafti, Shahram, Keshavarz, Saeede, Zarei, Saeed
• Format: Article
• Language: English
• Subjects: Finite strain; Kinematic vorticity number; SE Sanandaj-Sirjan zone; Shear zone; Zagros
• ISSN: 0191-8141; 1873-1201
• DOI: 10.1016/j.jsg.2022.104759

Microstructural, vorticity and strain analyses, combined with geological field observations are fundamental tools for retrieving information about kinematics of deformation in crustal-scale shear zones. The Kahdan shear zone is located in the SE part of the Sanandaj-Sirjan metamorphic zone within the Zagros orogen, SW Iran. The Zagros Orogen that formed due to the oblique convergence between the Afro-Arabian plate and the central Iranian plateau. Three-dimension strain analyses show that finite strain ellipsoids shape is oblate (K = 0.38–0.89). Vorticity analysis on mylonites yielded arithmetic mean maximum (Wm max) and mean minimum values (Wm min) of 0.83 and 0.72, respectively (63–47% simple shear). Higher values of Wm and Rxz estimated adjacent to the shear zone boundaries and gradually decrease toward the central part of the zone. Our yielded results show a non-unified spatial variations of vorticity and strain values in the deformed metasandstone (Late Jurassic to Early Cretaceous) of the Kahdan shear zone. Vorticity analyses and noncoaxial indicators indicate that this zone experienced general shear deformation. The horizontal shortening of ∼13–27% measured perpendicular to the shear zone boundaries. Based on yielded results, this area provides a good example of strain partitioning in a ductile shear zone. •This study presented significant information of deformation at the Kahdan shear zone.•Noncoaxial indicators show top to the SE-sense of shear.•This area has experienced sub-simple shear deformation.•Higher simple shear recorded near to shear zone boundaries compared to the central parts.•The results confirm that deformation in this area controlled by transpression tectonics.