The Forming Mechanism Of Typical High-Temperature Geothermal Systems In Nimu-Naqu Geothermal Belt, Tibet

Study areas were located in Nimu-Naqu high-temperature geothermal belt, in the Middle-North section of Dangxiong-Yangbajing-Duoqingcuo activity structure. Various high temperature geothermal manifestations were distributed in study area, there were rich in geothermal resources in Tibet. However, the geothermal field of Yangbajing and Yangyi have been investigated and researched systematically. In the paper, we choose11untapped geothermal fields along Nimu-Naqu in Tibet. Collected and gathered hydrochemistry, hydrogen and oxygen isotopes data, geothermal gases and its isotopes data in the study area, comparison of other typical high-temperature geothermal systems in Himalaya geothermal belt. It was significance to improve the genesis of high-temperature geothermal systems and provide guidance on exploration and drilling in the area. From the heat source, geothermal fluid migration pathways, geothermal fluid sources and thermal storage area features four aspects, this article reasearched typical high-temperature system, obtained the following understanding:High-temperature geothermal heat source system in the study area was generally considered to be partial melting of the crust layer contributions. It was obviously that active faults and deep tectonic activity controlled geothermal activity. There was a close relationship with surface rupture, seismic activities, geothermal distribution in Qinghai-Tibet Plateau hinterland; they were relationship with the deep geological processes that have genetic relationship dynamics.Analysis hydrochemistry of geothermal fluids, the chemistry type of high-temperature thermal water were mainly Cl-Na or CIHCO3-Na, moderate and high-temperature thermal water were mainly HC03-Na, there was a positive correlation Cl, Li, F, SiO2, HBO2with Cl, indicated possible mixing of magmatic water. With chemical geothermometer of thermal water and gas geothermometer, estimated the geothermal reservoir temperature were90to270℃; there were25%to75%cold water mixed with thermal water, estimated with chlorine and silicon enthalpy diagrams.From stable isotopes data, thermal water showed mainly meteoric recharge, thermal water presence slight "Oxygen-18drift" in Dongweng, Ningzhong high-temperature geothermal fields, the phenomenon was obvious in Gulu geothermal field than other geothermal fields; the tritium contents were less than1TU in Ningzhong, Gulu and Luoma, mainly sub-modern water recharge, Yuela was8.4TU, inferred to modern water recharge, others were mixed sub-modern with recent hybrid water recharge. Analysis carbon and sulfur stable isotopic characteristics of thermal water, revealed carbon and sulfur sources in thermal water mainly from leaching of the deposited layer, atmospheric source increased with cold water mixed, most of between the two types, part of material may from deep source.Geothermal gases were mainly carbon dioxide and nitrogen; there was a good negative correlation between carbon dioxide and nitrogen. From carbon isotopes from carbon dioxide, helium isotopes and comprehensive index analysis, the source of gases was mainly from crust, however, monitored R/Ra values greater than1in Ningzhong and Yuzhai, there may be a significant release of mantle material phenomena, the proportion of mantle helium was2.73%to30.93%.The studies showed that high-temperature geothermal systems primarily for heat and thermal water components contribute partial melting body, with geothermal fluids upward migration process, there have been mixed precipitation composition of the atmosphere; Helium isotope data of geothermal gases showed emplacement of mantle-derived substances in Ningzhong and Yuzhai geothermal fields.Finally, comprehensive analysis of regional geological data, deep exploration, mainly geothermal field geophysical results and the analyze results of geothermal fluid geochemical, obtained high-temperature geothermal field’s genesis model in the study area, and proposed conceptual model of Yuzhai high-temperature geothermal systems, for the latter depth research and development and utilization provided an important scientific basis.