Geochemistry and Origin of Thermal Waters of the Kuril Islands (Russia)

Abstract

The Kuril Islands stretch for more than 1200 km from the Kamchatka Peninsula to Hokkaido Island. This area hosts active Pleistocene to Quaternary volcanism with more 30 active volcanoes. At least one hydrothermal system associated with volcanic structures can be found on each island. Differences in volcanic evolution, hydrological and geological conditions have led to differences in the conditions of formation and discharge of hydrothermal systems of the region. There are several hydrochemical types of thermal waters discharging on the islands. Acid sulfate waters (steam-heated waters) with temperatures up to 95 oC and TDS up to 5 g/L generated at near-surface levels of thermal fields of most activity volcanoes. At Paramushir, Shiashkotan, Urup, Iturup and Kunashir most of thermal manifestations are acid (pH less than 4) Cl-SO4 (SO4-Cl) waters showing temperatures of 30-90 oС with TDS up to 14 g/L. These waters are associated with hydrothermal aquifers inside volcano edifices and formed as the result of absorption of magmatic gases (SO2 and HCl) by ground waters. Another type of hydrothermal activity are the wide spread coastal hot and neutral springs situated as a rule within the tide zone and formed by mixing of the conductively heated groundwater with seawater. It have Na-Cl composition with temperatures 50-80 oC and TDS up to 15 g/L. Coastal neutral springs are on Shiashkotan, Russhua, Uturup and Kunashir islands. Thermal manifestations of Ushishir Island is formed by the absorption of magmatic gases by seawater. Ketoy volcano on the same island hosts a high temperature hydrothermal system with unusual boiling Ca-Na-SO4 neutral springs and steam vents. Deep Na-Cl waters are tapped by the geothermal wells drilled at thermal fields of big islands (Paramushir, Iturup, Kunashir). This study was supported by a grant # 20-17-00016 from the Russian Science Foundation.