Study On The Geological Background Of Hydrothermal Activities In North Tibet

Tectonic position of the study area is located between Bangonghu-Nujiang suture zone and Yarlung suture zone, hydrothermal activities are concentrated in this region. In the study area, the hydrothermal activities in southeast are stronger than northwest, and the entire Tibetan plateau trend. Active tectonic systems control the distribution of hydrothermal activities, while the distribution of earthquakes and lakes are closely related. The earthquake epicenter and the intensity contour lines are consistent with the distribution of active tectonics. Study area and the surrounding lakes’long axis preferred orientation is 60°, and the active tectonic lines of this region are in the same direction. The study of seismic activities and lakes will be helpful to understand the mechanism of hydrothermal activities, seismic and hydrothermal activity may be two different ways of energy release, and they do not exist in isolation.Heat source mechanism is the core issue of hydrothermal activities, which is the thermal structure of the crust and upper mantle. Geophysical data indicates that the crust of the Tibetan plateau generally have one to two low-velocity and high-conductivity layers, be interpreted as a crust of fractional melting layers. Majority of scholars believe that the fractional melting layers are the heat source of hydrothermal systems. Heat flow value measured points are very limited. Nowadays the shallow where does not have a strong hydrothermal display areas crust may also has a greater value than the global average heat flux value inside 63mV∕m~2.Assume that the hot spring water and steam are hated in deep and exposed at the surface, and then they can help us to understand the information of deep earth. Rongma hot spring and Jiwa hot spring are hydrochemically of HCO3-Na type; Yangbajing and Gulu hot spring are hydrochemically of Cl-Na type. The HCO3-Na type hot water generally occurs in low-temperature geothermal systems, which formed in a high background heat flux value fault zone by deep circulation. The Cl-Na type hot water mostly appears in high temperature geothermal systems with magmatic heat source. The helium components of Yangbajing gas samples indicate that there are mantle-derived substances. The temperature of the deep geothermal reservoirs are calculated more than 200℃, the deep geothermal reservoirs are estimated about 2㎞. The major water charging supply of the hot springs is atmospheric precipitation. The strong hydrothermal activity area and the adequate water supply area are closely related, that is they match well.The hydrothermal activities produced sinters and hydrothermal rocks, the products record the complete information of the hydrothermal activities, in-deep study on sinters and hydrothermal rocks will be contribute to analyze the generation , development and evolution of hydrothermal activities correctly. The dating data of the southeast part in study area shows that hydrothermal activities mainly had happened in four periods, and their ages is 500～470ka., 400～350ka., 270～200ka., and 150ka～0 respectively. The study area’s northwest part is lack of dating data, however, compared with the southeast part by using the relative geological ages we will find out that the beginning age of hydrothermal activities in northwest was earlier than the first period in southeast, which was older than 500ka.