Mineralogy and genesis of zeolitic succession of Sartakht area, SE - Semnan, north Central Iran

Zeolitic tuff succession, In the Sartakht area (Eocene) is located in the 20 km south east of Semnan, north Central Iran. Studies are based on thin sections, X-ray diffraction data, scanning electron microscopy (SEM), and ICP-ES, MS geochemical analysis. From mineralogical point of view, this succession is mainly composed of clinoptilolite, opal-CT, smectite, mordenite, orthoclase, and halite. Geochemical data confirm X-ray differaction studies and show that Na-K clinoptilolite and mordenite become more prominent at the base of the succession and toward the top, opal-CT and smectite increase. Based on trace element geochemical data, the composition of the unaltered tuff is rhyodacite to dacite. Glass and glass shards - the main constituent of these tuffs– are largely altered by diagenetic and saline, alkaline pore solution and SiO2, Na2O, K2O largely removed. They concentrate at the base of the succession. As a result, the zeolites at the base of the succession have high SiO2 and enriched in Na and K and toward the top, smectite, enriched in Ca, Mg, because of the low mobility of Ca, Mg is formed.