Dacitic rocks from the south of Julfa (eastern Azerbaijan): Amphibole and plagioclase thermobarometry and crystallization condition

The Oligocene dacitic volcanic rocks display widespread exposures in south of Julfa (eastern Azerbaijan). They generally show porphyritic to hyalo-porphyritic textures with major minerals of plagioclase, amphibole, quartz and biotite. Electron probe micro analyzer (EPMA) data indicates oscillatory zoning and chemical variation of amphiboles (pargasite and edenite). The plagioclase crystals are, chemically, andesine (An= 29-51%) which mostly display oscillatory zoning. Based on geobarometric calculations, plagioclase displays pressures of 5 to 8 kb and amphiboles demonstrate different pressure ranges of 1.5 to 3 and 5 to 9 kb. Moreover, geothermometric calculations of plagioclase and amphibole provide temperatures of 1020-1050 and 850-900 °C, respectively. On the basis of geobarometric results, crystallization and growth of the minerals took place in magmatic chambers of different levels. Some of the amphiboles nucleated in lower continental crust and subsequently grown during magma ascent in middle crust whereas some others crystallized in the upper continental crust. Therefore, existence of minerals of different levels inside the studied rocks could be related to magma mixing in shallow magma chambers.