Discussion on heat source mechanism and geothermal system of Qinghai Gonghe-Guide Basin

The Qinghai Gonghe-Guide Basin together with the alternatively distributed mountainous region shows characteristics that the conductive geothermal resource of the basin has high geothermal gradient, the granite occurs in the bottom of borehole for geothermal exploration, and the convective hot springs in the basin-edge uplift fracture are in zonal distribution and with high-temperature geothermal water. There are still some divergences about the heat source mechanism of the basin. In this paper, queries to the view of mantle-derived heat source have been put forward, coming up with geochemical evidences to prove that the radiogenic heat of granite is the heat source within the mantle. Additionally, temperature curve is drawn based on the geothermal boring and geochemical geothermometer has been adopted for an estimation of the temperature and depth of the geothermal reservoir, it has been found that the surrounding mountains belong to the medium-temperature geothermal system while the area within the basin belongs to the high-temperature geothermal system with the temperature of borehole bottom reaching up to 175-180 ℃. In this paper, discussions on the problems existing in the calculation of geothermal gradient and the differences generated by the geothermal system have been carried out.