Thermo-barometry of amphibole-plagioclase phenocrysts in volcanic rocks in the east of Kamu, north of Isfahan province (middle part of the Central Iranian volcanic belt)

The studied volcanic rocks، in the middle part of the Central Iranian volcanic belt (Urumieh-Dokhtar magmatic arc) belong to a vast magmatic province located in the north of the Bitlis-Zagros suture zone. Petrographically، these rocks show dacite to andesite composition and include phenocrysts of plagioclase، amphibole and biotite with a prevailing porphyritic texture in a matrix composing of feldspar، quartz، microlite and glass. Having a relatively invariable composition، plagioclases are all andesine. Amphiboles are calcic and tschermakite type. Estimation of temperature and pressure of crystallization resulted from graphically integrating amphibole and amphibole-plagioclase geothermo-barometry equations indicates that the amphibole-plagioclase phenocrysts were crystallized in the temperature range of 763-823 °C with average of 797 °C and in the pressure range of 2. 2-4. 5 kbar with the average of 3. 4 kbar. The maximum depth of crystallization is evaluated at 17 km in continental crust.