Study on Genetic Mechanism of Geothermal System in Arxan Area based on Integrated Geophysical Method

Abstract

Arxan area is a famous enrichment area of groundwater thermal resources in China. The tectonic movement in the area is intense and the magmatic activity is frequent. The exposed temperature of hot spring groups suffers great differences. In order to reveal the regional geothermal geological characteristics and put forward the genetic model of geothermal water, the integratede geophysical methods of satellite gravity, magnetotelluric (MT) and controlled-source audio MT (CSAMT) are used to detect Yinjianggou hot spring, and the geophysical field characteristics of Arxan area are obtained. Regional geological, hydrogeological and geochemical data are combined and used for the comprehensive geological interpretation, indicating that the hot spring in Arxan area is a low medium temperature geothermal systems of convective type: (1) It belongs to a low and medium temperature hot water geothermal system, because no special heat source such as magma chamber is found in the area. (2) The heat source, thermal reservoir and caprock in the geothermal system were formed in the late Jurassic. Large-scale volcanic activities entrained mantle materials to the near surface. The groundwater underwent components exchanging in heat diffusion, forming a heat fluid with high mineralization. (3) There is a nearly vertical tension torsion secondary fault underground in Yinjianggou area. Driven by hydraulic pressure difference, the thermal fluid migrates upward along the structure, exposes at the caprock break, and forms a medium low temperature hot spring after mixing with shallow fissure water.