Isotope Geochemistry with Implications on the Genesis of Alkaline Bicarbonate Water Along the Himalayan High-temperature Geothermal Belt

Abstract

Himalayan geothermal belt is marked with more than 1,750 hot springs together widespread fumaroles, geysers, steaming ground and large piles of sinters. The tectonic background is the collision between the Indian and Eurasian continents after the closing of the ocean Tethys in the Cenozoic and the continuous compression thereafter has created such a hot orogeny at high elevations. The alkaline bicarbonate water dominates in these hot springs except those in Tengchong volcanic geothermal field and a few magmatic geothermal fields, such as Yangbajing. It is proposed that the geothermal water has experienced a relative rapid circulation in the hot thickened crust after being recharged by precipitation. This is the reason for the fact that thermal waters of most high-temperature geothermal systems show little or no oxygen isotope shift. Furthermore, according to the isotopic composition of δ13C-CO2 contents and the helium gas isotopic ratio, it is proposed that the crustal CO2 is product of metamorphic limestone that was formed in the Tethys oceanic basin. The excess bicarbonate ion due to the dissolution of large amount of metamorphic CO2 has produced alkaline bicarbonate water along the Himalayan high-temperature geothermal belt.