| Abstract |
Southern Caspian Sea region is located in north of Iran. Gilan, Mazandaran and Golestan are three Provinces in this region. Geothermal activities in this area are directly related to tectonics and significant heat-generating rocks. The active tectonic zone of the Alborz Mountains along the southern coast of the Caspian Sea contains a diverse array of thermal springs. This paper presents a comparative analysis of the major geothermal systems in this region, integrating geological, tectonic, and hydrogeochemical data from four key areas: Gilan, Ramsar (in Mazandaran Province), Damavand (in Mazandaran Province), and Golestan. It is identified and characterized three distinct geothermal types: 1) Volcanic system (Damavand), defined by a magmatic heat source, mixed-anion chemistry, and high-enthalpy potential (T: ~150–280°C); 2) Tectonic system (Gilan and Golestan) characterized by fault-driven shallow circulation, immature Ca-Mg-HCO₃ waters, and low-enthalpy (T <45°C); and 3) Radiogenic system (Ramsar) that is distinguished by deep fault circulation, mature Na-Cl waters influenced by Caspian Sea intrusion, and high natural radiogenic from ²²⁶Ra and ²²²Rn. This regional synthesis highlights how variations in underlying heat source, fluid circulations, and host rock geology control the geochemical specification, resource potential, and environmental implications of geothermal manifestations across northern Iran. |