Hydrogeochemical Processes And Genesis Machenism Of High-temperature Geothermal System In Gudui,Tibet

The Gudui geothermal field is located in the eastern part of the Himalaya block in the Qinghai Tibet Plateau,which is part of the Tethyan Himalaya belt.The geothermal resources is rich in this field.The highest iso-depth temperature of Mainland China is discovered in a geothermal well here.However,the development and utilization of geothermal resource is impeded by the limited research and survey of this field.The bottleneck is that the origin of thermal storage is not clear,it is urgent to reveal the genesis mechanism of geothermal source,transport,storage and coverage.This work combined related information and data of stratum and tectonic structures,collected water samples in typical areas,characterized the geochemical features of deep geothermal fluids according to monitoring and analyzing results.The geothermometer was adapted to identify deep geothermal processes,determine sources of geofluids and estimate the temperature of geothermal reservoirs.The hydrogeochemical path was modeled with PHREEQC to reproduces the geochemical process involved in the migration of geofluids.Geophysical inspections and drilling explorations conducted verified these analysis.Most geothermal water in this study area are type ofCl,HCO3-Na,Cl-Na.Concentrations of Na,TDS,F,Li,SiO2,in general positively related with that of Cl,indicating intrusion of deep thermal fluid in Gudui geothermal area.Hydrogen-oxygen stable isotopes measurements showed the underground water was mainly recharged from meteoric water: snowmelt at the elevation higher than 5000 m.HCO3 was originated from dissolutions of carbonate minerals,sulfates were leached from sediments.Determination of some nuclear explosions in thermal water by using tritium isotope value 3H,the circulation is not in depth.Main component analysis of gas-phase samples showed that CO2 was mainly generate in deep formation,and N2 originate from atmosphere.He isotopic analysis and gas component triangle diagram indicated its crust origin.Geothermometers showed the hottest geofluid could reach 260?.Inverse modeling calculations showed that the water-rock interactions induced mutual material and energy exchanges during its horizontal migration.Based on these results,the genesis mechanism of Gudui geothermal field was proposed as: intense tectonic activity may cause the uplift of partial melt in the crust,forming a good heat source;north-south regional Voca-Cuona deep fault provided channels for deep heat transferring to the shallow strata provide;local faults and fractures across each other formed channels for energy and mass transfers,broken zones formed geothermal reservoirs.The total potential explorable resource was estimated as 9.83×1015J.