Geochemistry of Thermal Waters of Continental Margin of Far East of Russia

Abstract

AbstractStudied waters belong to warm (T=30–50°C), alkaline (pH=8.9–9.3), low mineralized (TDS<235 mg/l) Na–HCO3 or Na–SO4–HCO3 thermal waters with high content of SiO2 (up to 81 mg/l) and F (up to 3.9 mg/l), occur on modern volcano–tectonic rejuvenated areas of Eastern Sikhote–Alin orogenic belt. Low 3He concentration as well as N2/O2 and N2/Ar ratios exclude influence of deep mantle fluid. New rare earth element data constrain our understanding of water–rock interaction occurring in the water source region. Meteoric origin of waters is proved by stable isotope values varying from −71‰ to −136.1‰ and from −10.8‰ to −18.8‰ for δ2H and δ18O respectively. REE patterns reflect high pH, resultfing from water–rock interaction and oxidative conditions. Calculations of deep aquifer temperature using Na–K and quartz geothermometers show 116.8–131.1° C and 82.2–125.8°C respectively. Presence of deep faults both with abnormal thermal gradient (∼45–50 K/km) define unique geochemical shape of thermal waters of Sikhote–Alin, area, where no present volcanic activity is registered.