Mineral chemistry and petrogenesis of the dacitic volcanic rocks from the Arvaneh cone, SW Bostanabad-East of Sahand Volcano

The Arvaneh volcanic cone at eastern part of the Sahand volcanic complex is located on SW of Bostanabad city. This cone having lava composition as dacite, dacitic andesite and rhyodacite, is formed eletted to young volcanic activity of the Sahand volcanism. Having various colours and textures form dominant composition of the lavas in the Petrographycally phenocrysts are plagioclase+hornblende+biotite±quartz±K-feldespar. The dominante texture of the investigated rocks are hyaloporpyre and microlitic porphyre. Plagioclase are andesine and labradorite at the core and rim, respectively. The biotites are classified as Mg-bearing biotites on the basis of Si and FeO/(FeO+MgO) contents. The investigated biotites, having Mg/(Mg+Mg+Mn as 0.52-0.61, indicate relatively high oxegn fugacity corresponding to calc-alkaline magmatic series. Compositionally, the amphiboles are calcic indicating their crystallization related to subduction tectonic setting. Amphibole composition is supporting high fugacity of oxegen in the related magma. Petrogenesis of the lavas from Arvaneh cone are determined as active continental margion on the basis of biotite and amphibole mineral chemistry. Crystallization T-P are determined as 700-800 0C and 3-6 kbar respectively. On the basis of estimated pressures, it seems that oncet of phynocryst crystallization has been started from depth of 18 Km in the continental crust in the area.