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)


دانشگاه اصفهان- دانشکده علوم - گروه زمین شناسی


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.