The Oka hydrothermal system, East Sayan mountains

The western flank of the Baikal Rift Zone contains the Oka hydrothermal system of the “volcanogenic type,” which is related to the occurrence of basaltic volcanism. It consists of springs for the discharge of thermal and subthermal waters confined to the intersections of faults of various settings at the boundary of two major lithospheric blocks. Helium isotope data were used to find heat flow for all springs of the hydrothermal system; this heat flow is comparable with that across the bottom of the Baikal southern basin. Predicted hydrotherm temperatures were calculated at the depths of their generation using silica and cation thermometers. The average depth of generation of the springs that form the Oka hydrothermal system is 2.8 km, which is 1.1 km nearer to the ground surface than the h of the hydrothermal occurrences around Lake Baikal. The spatial coincidence between the location of the hydrothermal system and the area of young volcanism provides evidence of a common source of heat, while the thermal parameters of the system, its gas and chemical compositions, correlate with the age of the volcanism.