Deformational phases in the Balvard metamorphic complexes, southeast of the Sanandaj-Sirjan Zone

At the northeastern margin of the southern part of the Sanandaj-Sirjan Zone (SSZ), northeast of Sirjan, two metamorphic assemblages belong to the SSZ’s basement exposed. The first complex is ZardKuh and the next is Hossein Abad-e-Souch which is situated in the north and east of the city of Balvard, respectively. The two metamorphic complexes underwent the greenschist and amphibolite facies, juxtaposed few different tectonic units such as the Dehshir-Baftophiolitic mélange and the Sardooieh volcanic assemblage, and were thrusted over the Neogene deposits. These complexes have preserved the deformational history of the region much better than the other tectonic units. Field studies accompanied by oriented sampling as well as micro-tectonic investigations provide us the role of four deformational phases in the tectonic evolution of the studied area. The first two phase of the D1 and D2 are characterized by the remnants of micro- to meso-scale isoclinal folds. Inasmuch as the whole of the metamorphic rocks were recrystallized, therefore, both of these deformational phases must be happened before or at same time as the Jurassic or older metamorphic event/s. A widespread, post-metamorphic, plastic deformational phase (D3) was occurred in the entire metamorphic rocks and part of the non-metamorphic rocks of the region. This mylonitic process of rocks may be originated in an extensional tectonic event and associated Eocene magmatism. Subsequently, another transpressional tectonic regime linked to the Arabian-Eurasian collision was the main responsible of the brittle fractures and micro-faults in the complexes; this could be synchronous with the thrusting of the metamorphic rocks onto the Neogene sediments.