Isotopic and geochemical evidence for mantle and crustal contributions to geothermal fluids in Southern Jiangxi Province, China

摘要

Relative He, Ar, N2 and CO2 contents as well as helium, neon and carbon isotopes of geothermal gases are applied to identify contributions of crustal and mantle volatile components to geothermal fluids in the southern Jiangxi Province, SE-China. The δ13C values of CO2 for the CO2-dominant type geothermal gases are -5.5‰ to -4.4‰ (PDB) showing that these-type gases are derived from a magmatic inorganic origin. The helium isotopic compositions of these geothermal gases range from 1.36 to 2.11 Ra, indicating that the helium may be partly from a mantle source. The δ13C values of CO2 for the N2-dominant type geothermal gases are - 12.6‰ to -23.7‰ (PDB), suggesting that the CO2 is a mixture of organic and inorganic sources. The 3He/4He ratios of the N2-dominant gases are from 0.05 to 0.13 Ra, representing input of radiogenic 4He in the crust rocks of the area. The 4He/20Ne-3He/4He relations and CH4/3He as well as CO2/3He ratios of geothermal gases are also discussed.