The major, minor and rare earth elements (REE)‍ variations in hydrothermal alteration zones in the volcanic rocks of the west of Naein ophiolite (Central Iran)


Departments of Geology, Faculty of Sciences, University of Isfahan, Isfahan, Iran


The study area is located 39 km northwest of Naein and is a part of the Urumieh- Dokhtar volcano plutonic arc. The volcanic and pyroclastic rocks have been altered by hydrothermal fluids. According to field studies and petrographic observations the predominant rock types are basaltic andesite, andesite, dacite, rhyolite, tuff and ignimbrite which are related to the Eocene volcanic activity period. According to mineralogical and geochemical studies there are four different alteration zones including propylitic, phyllic, argillic and silicic. Furthermore, using the satellite data processing the existence of the hydrothermal alteration zones are established which the most widespread one is argillic. The REE's behavior displays different patterns in various alteration zones. The negative Eu anomaly in the argillic zone points to the presence of clay mineral. The silica bearing samples are highly depleted in REE content due to whole destruction of host rock minerals, decreasing of PH and increasing of fluid/ rock ratio. Base on mass changes during hydrothermal alterations processes, there are depletion and enrichment of some elements in alteration zones. Incidentally enrichment is determined in propylitic zone and silicic zone show the most depletion.