Seawater-rock interaction at Ushishir volcano-hydrothermal system, Kuril Islands

摘要

Ushishir volcano is located in the middle of the Kuril Arc. The Ushishir crater, a closed bay connected with the ocean by a narrow and shallow strait is characterized by a strong hydrothermal activity. Boiling springs, hot pools, fumaroles and shallow submarine vents are manifestations of a magmatic-seawater hydrothermal system with the discharging solution similar in chemical and isotopic composition to the seafloor hydrothermal fluids. The main features of the Ushishir fluids are: (1) water has close to zero δD and a large oxygen isotopic shift (6 7‰); (2) high boron concentration (～70 ppm); (3) a significant uptake of Ca and Sr from the rock and Ca/Sr higher than that for seawater with ~(87)Sr/~(86)Sr ～0.7037, a bit higher than the rock value (0.7032). The measured onshore discharge of boiling water is ～5 kg/s; however, a large plume of the discoloured seawater releasing from the outer submarine slope of the volcano indicates a much higher total mass and heat output.