Magmatic evolution recorded by phenocrysts in volcanic rocks southeast of Isfahan

Abstract

Late Miocene–Pliocene calc-alkaline volcanic rocks are exposed southeast of Isfahan in the Urumieh-Dokhtar magmatic belt. Volcanic rocks consist of lava flows and domes, chiefly basaltic andesites, andesites and dacites. Minerals in the volcanic rocks exhibit degrees of disequilibrium features. Plagioclase as dominant mineral in these rocks generally displays reverse and oscillatory zoning; sieve or dusty and clear populations, cores are unusually Ca-rich. Hornblende and biotitephenocrysts have reaction rims indicating disequilibrium growth during late stage crystallization. Quartz phenocrysts are corroded and embayed and a few show augite reaction rims. Criteria such as: a) development of sieve textures in plagioclase b) reaction rims in mafic minerals c) reverse zoning and heterogeneity of plagioclase rims d) the resorbed and embayed phenocrysts; support magma mixing as an important process in the evolution of these rocks.