Thermobarometry Chelvan igneous rocks using amphibole, biotite, plagioclase, pyroxene minerals, north of Shahrekord, Sanandaj-Sirjan zone.

Abstract: The area is in 45 kilometers north of Shahrekord and near the city of Chelvan in the middle part of the Sanandaj-Sirjan structural zone. The stratigraphic column of the area consists of: Cretaceous carbonates, Jurassic shales and sandstones, and volcanic rocks. The petrographic observation of volcanic rocks indicate the presence of igneous rocks of the andesite, andesite-basalt and basalt types with the main minerals olivine, pyroxene, plagioclase and amphibole, along with biotite and minor and opaque minerals that have a dominant microlitic porphyry and porphyry texture. The results of the chemical analysis of pyroxene phenocrysts indicate the presence of augite-type pyroxenes with a chemical composition spectrum of Fs 12.52-17.38 En 42.71-Wo 36.92-39.67, which were formed in the temperature range of 1200 to 1300 degrees Celsius and a pressure range of 6 to 10 kilobars. The amphiboles are magnesian-hornblende type that crystallized at a pressure of 2.7 to 5 kilobars and a temperature of 720 to 800 degrees Celsius. The micas of this area are primary magmatic magnesian biotites that were formed at a temperature of 580 to 680 degrees Celsius, and the composition of plagioclases fluctuates from oligoclase to labradorite, indicating the crystallization temperature 700-800 degrees Celsius. The combination of mineral chemical analysis data of the Chelwan igneous rocks indicates the tectonic setting of calc-alkaline magmas that formed in a subduction zone.