Abstract
The Xi’an Depression of the Weihe Basin, located in the transition zone where the North China, Qinling and Yangtze plates collide with each other, is an important area of geothermal energy utilization in China. Studies of heat flow and thermal sources are of great significance to the exploration and development of geothermal resources in this area. In this paper, six temperature logs boreholes, and 14 thermal conductivity samples have been used to study the geothermal gradient and terrestrial heat flow in the area. The results show that the geothermal gradients of Xi’an Depression range from 20.8 C/km to 49.1 C/km, with an average of 31.7 ± 5.0 C/km. The calculated heat flow is 59.4–88.6 mW/m2, and the average value is 71.0 ± 6.3 mW/m2, which indicates a high thermal background in the area. The high anomalous zones are near the Lintong-Chang’an Fault zone in the southeast, the Weihe Fault in the north, and the Fenghe Fault in the central Xi’an Depression. These deep and large faults not only control the formation of the Xi’an Depression but also provide an important channel for the circulation of groundwater and affect the characteristics of the shallow geothermal distribution. The temperature of the Moho in the Xi’an Depression ranges from 600 to 700°C, and the thermal lithosphere thickness is about 90–100 km. The characteristics of lithospheric thermal structure in Xi’an Depression indicate that the higher thermal background in the study area is related to lithospheric extension and thinning and asthenosphere thermal material upwelling.
Highlights
Except that the shallow temperature is affected by climate or convection of groundwater, the temperature curve generally increases linearly with depth, indicating that the heat transfer method is Geothermal gradient is the rate of temperature change with depth and is the crucial parameter for calculating the heat flow value
This paper selected relatively stable temperature intervals and used the least-square regression method to calculate the geothermal gradients for different layers, and the correlation coefficients are all above 99% (Table 3)
The heat flow values in Xi’an Depression range from 59.4 to 88.6 mW/m2, and the average heat flow is 71.0 ± 6.3 mW/m2, which is significantly higher than the average continental heat flow of 60.4 ± 12.3 mW/m2 in China (Jiang et al, 2016)
Summary
The Weihe Basin is situated between the southwestern margin of the North China Plate and the Qinling Orogenic Belt (Figure 1). It is a half-graben rift basin controlled by its southern and northern bounding faults and filled with 7,000 m Cenozoic sediments (Rao et al, 2014). Based on the results of geology, tectonics, geophysics, and geochemistry, etc., Heat Flow and Thermal Source previous studies have been conducted on the characteristics of the geothermal field (Rao et al, 2016; Ren et al, 2020), the characteristics of underground hot water (Qin et al, 2005a; Ma et al, 2008b) the evaluation of geothermal resources (Mu et al, 2016; Zhang et al, 2020), and the characteristics of the thermal structure of the lithosphere in the Weihe Basin (Rao et al, 2016; Liang et al, 1992)
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