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Geothermal Characteristics and Formation Model of Hot Dry Rock In Gonghe Basin, Northeastern Tibetan Plateau
Gonghe Basin, located in the northeastern margin of Tibetan Plateau, has been one of the most geothermally active area in China. The discovery of Hot dry rock (HDR) in Gonghe Basin that makes it an ideal area for studying the formation model of HDR. However, due to a lack of overall understanding of the geological structure and temperature field in Gonghe Basin, there still exists some controversy on the formation model of HDR. Therefore, the geological structure and temperature field are described firstly based on a large number of geophysical exploration and drilling data in the region. Different areas in basin have obvious difference on the buried depth of crystalline basement. The maximum burial depth of the basement in the west is more than 7000 meters. However, it has been widely exposed to the surface in the eastern part. Similarly, there is a significant difference in the temperature field in the east-west direction of the basin. In Qieji area, which has the deepest buried depth of basement in the basin, the temperature at the depth of 5000 meters is lower than 167℃, and the average geothermal gradient is 30.8 ℃/km. In Qiaboqia area, where the buried depth of basement is shallow in the mid-east region, the temperature at the depth of 3350 meters generally reaches 180℃, the temperature gradient of sedimentary cover and granite crystal basement reaches 64.2℃/km and 40.5 ℃/km respectively. The geothermal in the eastern of basin is lower than that of Qiaboqia area at the same burial depth, and the temperature at the depth of 3000 meter still does not exceed 150℃. And then, the two-dimensional temperature field profile of the basin was obtained by numerical simulation combined with the measured thermophysical parameters. The simulation results show that the temperature field is coupled with the characteristics of basement burial depth. This phenomenon indicates that the formation of HDR in the basin may be related to differential uplift and denudation progress of the Gonghe Basin. Our research results deepen the understanding that partial melting is the main heat source of HDR in the past, and realize that uplifting and denudation process may be the internal dynamic mechanism controlling the formation of HDR.