Evolution of deep parent fluids of geothermal fields in the Nimu–Nagchu geothermal belt, Tibet, China

•Quartz geothermometers are suitable for Yangyi and Yangbajing.•Multicomponent geothermometry yields more reasonable temperatures for diluted waters.•Na/K and K/Mg results could represent the deep reservoir and mixing temperatures for Gulu.•Intermediate and high temperature reservoirs of any one geothermal field are within the same hydrothermal system.•Enthalpy vs. chloride plot provide insights on the cooling processes of deep parent fluids.