Host rock controls to thermal water chemistry induced from the global comparison

Under a framework of the Geothermal Implementing Agreement (GIA) of the International Energy Agency (IEA), chemistry of thermal water is compared among Iceland, Japan, South Korea and the USA. The pH value of thermal water in Iceland shows 9 or 10, that is evidently higher than those of other silicic crust countries. It is ascribed to the host rock controls that hydrothermal water only attacks anorthite in basalt. The boron and chloride components of thermal water in Iceland are significantly lower than those in Japan and the USA. Their variation ranges show that the boron component in Iceland is 1 magnitude lower than other two countries and the chloride component is 0.5 magnitudes lower. It is also explained by the host rock controls that the basaltic crust in Iceland is 1 magnitude lower in boron and 0.5 magnitudes lower in chloride than the silicic crust in Japan and the USA.