中国一些地区温泉中天然气的地球化学特征及碳、氦同位素组成

中国一些地区温泉气的主要组分是CO_2或N_2,烷烃气含量低或无,同时含极微量的氦。温泉气的δ~(13)C_1主频率峰在-20‰至-22‰,说明温泉气的甲烷主要是无机成因的。温泉气的δ~(13)C_(CO_2)主频率峰在-4‰至-8‰,反映温泉气的CO_2也主要是无机成因的。δ~(13)C_(CO_2)值与CO_2含量正相关,其回归方程为δ~(13)C_(CO_2)(‰)≈0.966lgCO_2-6.354,δ~(13)C_(CO_2)值与N_2含量负相关,其回归方程为δ~(13)C_(CO_2)(‰)≈-3.193-0.109 N_2。根据氦同位素组成特点,可划分出幔源温泉气和壳源温泉气,前者R/R_a>1,后者R/R_a<1。     

Geochemical Characters, Carbon and Helium Isotopic Compositions of Natural Gas From Hot Springs of Some Areas in China

The main components of hot spring gases in some areas of China are CO2 or N2, and they have no or trace alkanes and very lower quantity of He . The δ13C1 values of hot spring gases mainly range from - 20‰to - 22‰ , which suggest the methane mainly be the inorganic origin in these gases. The δ13Cco2 values of hot spring gases are mainly from -4% to - 8%, so these carbon dioxides are also the inorganic origin. δ13Cco, values positively correlate with CO2 contents, their regression equation is δ13Cco2(‰)≈0. 966 log-CO2 - 6. 354; δ13Cco2 values negatively correlate with N2 contents, their regression equation is δ13Cco, (‰)≈ - 0.109N2 - 3.193. According to the helium isotopic compositions, we can distinguish mantle-derived hot spring gases from crustal hot spring gases, the former with R/Ra>1 and the latter with R/Ra<1.