Geochemical characteristics of soil gases Rn， Hg and CO₂ and their genesis in the capital area of China

The concentration and flux of soil gases were measured at 35 profiles across 18 faults in the capital area of China from June to July of 2015， and the geochemical characteristics and sources of soil gases Rn， Hg and CO₂ in the area were also investigated. The results showed that the average concentrations of Rn， Hg and CO₂ varied from 3.2 to 45.0 kBq/m³， 3.9 to 24.9 ng/m³ and 0.154% to 2.175%， respectively. The average flux values of Rn， Hg and CO₂ ranged from 3.8 to 152.1 mBq/(m²·s)， 0.1 to 42.6 ng/(m²·h) and 8.5 to 89.4 g/(m²·d)， respectively. There is an obvious spatial distribution feature of soil gases that both the concentration and flux values in the eastern region were higher than those in the western region within the studied area， which could be attributed to the increased tectonic stress， the decreased crustal thickness， the increased thickness of sediments and earthquake activity from west to east. These spatial geochemical characteristics in the studied area might be mainly controlled by the upper crustal material structure， deep gas supply and seismic activity， and also additionally affected to some degree by the natural environment and soil types.