Environmental Isotope Evidence of Geothermal Water Recharge in Xi’an Southern Sag

The supply of Xi’an depression southern abdominal deep and shallow underground hot water was studied with environment isotope method, the results showed that Xi’an depression abdominal shallow geothermal water points were mainly distributed near the line of atmospheric precipitation, only two points had diverged, meaning that they were accepted from modern precipitation and ancient precipitationin the north of Qinling Mountains, while the deep geothermal water with the tritium content was less than 1 TU and the average value of ¹⁴C dating was more than twenty thousand, meaning that it was accepted from ancient precipitation recharge before Holocene in the north of Qinling Mountains. The result showed that the deep and shallow underground hot water inflowed from the southwest direction. The range of the recharge height was 839 m-1746 m. The annual average temperature was 0.69 ℃ when the deep and shallow underground hot water received recharge. The recharge environment was the pore and fracture type underground hot water system.