Geochemical Characteristics of Gases from the Wudalianchi Volcanic Area, Northeastern China

Abstract

Abstract The origins of gases in springs, pools and wells from the Wudalianchi (WDLC) volcanic area are discussed based upon molecular and isotope compositions of the gases. Nine gas and water samples were collected from bubbles and water of the springs and pools in the WDLC volcanic area, Northeastern China, in August 1997. The molecular components were measured with a MAT‐271 mass spectrometer (MS), helium isotope ratios with a VG‐5400 MS, and δ13C with a MAT‐251 MS in the Lanzhou Institute of Geology. The gases are enriched in CO2, and most of the CO2 concentrations are over 80% (V). The helium and methane concentrations have relatively wide ranges of 0.7 to 380×10−6 and 4 to 180×10−6, respectively. The 3He/4He ratios are between 1.05 Ra and 3.1 Ra (Ra = 1.4×10−6); the 4He/20Ne values are between 0.45 and 1011, larger than the atmospheric value (0.32). The δ13C (PDB) values of carbon dioxide range from −9.6 to −4.2%%. These geochemical data demonstrate that the spring water is from aquifers at different depths, and that helium and carbon dioxide are derived from the mantle, and are contaminated by crust gases during deep fluid migration. Also, there are larger fluxes of deep‐earth matter and energy in the WDLC volcanic area.