Petrography and Geochemistry of Quaternary travertines in the Ab-Ask region, Mazandaran Province- Iran

The travertine deposit springs are located on the southeast of the Damavand Volcano, 85 km northeast of Tehran Province. The deposits of these springs mainly outcropped with cascade, hill, conical, layered, calcareous Tufa and Fissure-Ridges morphologies. Travertine studies have usually been conducted based on field observations, geochemistry and hydrology. The tectonic activity of the region, faults and fractures have provided some channels for the rise of CO2-rich hydrothermal fluids. The present study was carried out based on field, geochemical and hydrological surveys. The results of thin section and SEM analyses show that photosynthetic microorganisms such as blue-green algae and diatoms play a key role in the formation of these travertines. Field studies alongside with petrographic characteristics revealed presence of crystalline crust, rafts, foam, laminated and tufa lithofacies. The mineralogy of these lithofacies is calcite. There is a significant enrichment in δ13C values of all travertine types due to decarbonation of limestone. Based on the isotope, performed on travertines of the region, the linear trend observed between δ13C and δ18O values is attributed to the mixture of two or more different fluids. This enrichment is attributed to the de-carbonation of limestone, algae activities and rapid de-gasification of hot springs.