, s.keshavarz2007@yahoo.com
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This study investigates deformation in the Chai kour metamorphic complex, located in the Sanandaj-Sirjan metamorphic belt, using structural, microstructural, and strain analyses. Field observations show that this area has been affected by a complex deformation system resulting from the interaction of three deformation phases. The structural and microstructural analyses conducted provide evidence for the activity of a transperssion in this region. Presence of diverse structures, including asymmetric folds, sheath folds, and asymmetric boudins, all indicative of intense and heterogeneous deformation conditions. At the microscopic scale, the identification of sigma and delta porphyroclasts, S/C fabrics, and fish-shaped micas not only confirms a dextral shear sense (top-to-the-SE) but also provides valuable insights into the temperature conditions prevailing in the region. Quantitative strain analyses using the Fry and Flinn methods demonstrated that the strain ellipsoid in this area exhibits a clear tendency toward plane-flattening strain. K values (0.51-1.18) and D values (1.1-2.22) indicate significant heterogeneity in strain distribution across the region. The calculated vorticity number (0.75–0.83) revealed that the deformation flow in the region was predominantly non-coaxial, with a simple shear component playing a more dominant role than pure shear. Examination of quartz and feldspar microstructures, including subgrain rotation (SGR) and grain boundary migration (GBM) recrystallization, suggests a temperature range of 400–650 °C for the main deformation event, consistent with amphibolite facies conditions. Additionally, the presence of quartz blg recrystallization and brittle structures like book-shelf in feldspars indicates the occurrence of late-stage deformation under lower temperature conditions. These findings are in complete agreement with the region's tectonic setting within the framework of oblique convergence between the Eurasian and Arabian plates.
Keywords: mylonite, strain partitioning, shear zone, Sanandaj-Sirjan metamorphic belt, transpression.
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