Geochemistry and zeolitization of tuffs in Zarrin Dasht mining area (Firuzkuh, Central Alborz)

The Zarrin Dasht region is located in Tehran province, between Damavand and Firuzkuh cities. This region with 10 Km2 area belongs to Central-Alborz zone. On the base of petrographic and geochemical studies, the volcaniclastic rocks of the Zarrin Dasht area are trachyte, dacite, rhyodacite and rhyolite. Petrographic evidence as well as XRD analyses point to the presence of glass and crystallization quartz, clinoptilolite, analcime, natrolite, heulandite, montmorillonite, kaolinite, illite and chlorite. Texture of tuffs is vitrophyric. Based on the geochemical data, these rocks are calk-alkaline and metaluminous to peraluminous composition. Primitive mantle-normalized and chondrite-normalized trace elements and rare earth elements patterns indicate enrichment in LREE and LILE and depletion in HREE and HFSE with pronounced negative anomalies in Eu, Ba, Nb, Ti, Sr and P in the Zarrin Dasht samples. Samples position on the various tectonic setting discrimination diagrams demonstrate that these rocks were formed in environment related to subduction in active continental margins. Chlorites, are present in the rock context and also relatively filled cavities as amygdaloidal, while analcime was mainly distributed in the rock context. It seems these minerals are the result of recrystallization of volcanic glasses such as shard in the rock. Secondary minerals can be considered as a burial diagenesis and low-grade metamorphism in the studied tuffs that occurred under the upper floor pressure.