Investigations of deformation in west of Silvana mica schists, southwest of Urmia: Implications for tectonic structures and microstructures

The outcropping mica schists from the Silvana region, which are a component of the Silvana colored mélange complex, are situated southwest of Urmia. This region is located in the northwesternmost part of the Sanandaj-Sirjan metamorphic belt. Mica schists can be classified into three sub-types based on petrographic studies: muscovite schists, biotite-muscovite schists and fibrolite-biotite-muscovite schists. Mylonitic zone can be identified by the presence of mylonitic foliation and microstructures such as mica fish, dynamic recrystallization, asymmetrically tailed porphyroclasts, kink bands, and microfolds. The Silvana mylonites are categorized as low to medium grade mylonites based on textural and microstructural evidence. According to the structural and microstructural relations, the study area appears to have been impacted by three main phases of deformation. The first phase can be characterized by a transpressional deformation regime, leading to the formation of S1 foliation in mica schists. The dextral main simple shear component can be attributed to the second phase. During this phase, S2 foliation, mylonite zones and various folds and microfolds were developed. Ultimately, multiple fractures and microfaults were caused by the third phase of brittle deformation that affected the study area.