Isotope hydrology and geothermometry of the thermal springs, Damavand volcanic region, Iran

Abstract

The chemo-isotopic characteristics, geothermal activity and water origin of the 5 thermal and 7 non-thermal springs have been investigated in Damavand volcanic region, northern Iran. The Damavand thermal waters are characterized by outlet temperature values of 23 to 65 °C and the Ca–Cl or Ca-SO4 water types. Stable isotope values of 49 monthly precipitation samples from 5 stations at 2500 to 3200 m elevations were also measured in the study area and Damavand meteoric water line (DMWL) was drawn as δD = 7.64 × δ18O + 8.93 (R2 = 0.98, n = 49). It has a lower slope and intercept than the global meteoric water line (GMWL) due to isotope kinetic fractionation effects during precipitation. The δ18O = (−0.0018 × H(m.a.s.l.) − 3.12) equation was derived based on precipitation data. The reservoir temperature was estimated to be 110–135 °C based on different geothermometers. Damavand volcano can be considered as the main heat source for the thermal springs in the region. The conductive process along with the mixing of thermal waters with shallow cold groundwaters is the main cooling mechanisms. Almost, all the thermal waters fall near the LMWL and within prediction interval area, indicating meteoric origin and no significant effect of water-rock interaction. The Damavand geothermal reservoir is fed by local meteoric water from altitudes of 2500 to 4100 m and circulates at least 500 m deep, near the magma chamber.