Investigation of mineral chemistry and geothermobarometry of plagioclase, pyroxene and amphibole phenocrysts of Hossein Abad volcanic rocks (southeast of Abhar)

The Hossein Abad area is located 120 km southeast of Zanjan. The volcanic rocks in this area belong to Eocene and younger a ges. Volcanic rocks include dacitic, trachyandesite and andesitic lavas, as well as tuff. Volcanic rocks have quartz, alkali feldspar, abundant plagioclase, pyroxene and amphibole. The alkali feldspar is Sanidine and plagioclases are oligoclase and andesine. The Porphyritic, microlithic porphyritic, glomeroporphyritic and poikilitic textures are predominant in these rocks. Examining the mineral chemistry of rocks in the study area shows that the clinopyroxenes are diopside and augite. Amphiboles in these rocks are magmatic and calcic with the chemical composition of pargasite. Based on magmatic diagrams, rocks in studied area are alkaline. According to the thermobarometric diagrams, these rocks have formed at temperature and pressure ranges of 700-750℃ and 5-6.5 kbar respectively. These values correspond to the depth of middle-lower crust. The rocks are formed in the active continental margin.