Study on the Release of Deep Source CO2 in Western China
Yang Lizheng et al.(Chengdu University of Technology)
Base on the data of numerous hot springs in western China, the CO2 contents of hot springs are calculated, the sources of CO2 in hot water are discussed, the release process of CO2 in hotwater is analyzed, and the release quantities are estimated.
1.The CO2 content of hotsprings, which all occurred in carbonate rock strata, is relatively high. The maximum reaches 2575mg/L.The hot spring numbers, which CO2 content exceeds 500mg/L, make up 35% of the totals, mean value of CO2 content is 512.12mg/L in Tibet, 494.1mg/L in western Sichuan Province and 332.6mg/L in western Yunnan Province respectively. The statistical data indicate clearly that the CO2content in hotspring is abundant, and it is aproved that the hydrothermal activity zone in Tibet contains the richest CO2 content in China.
Fig.1 Scatter diagram of d18O,d13C
1.Yangbajin 2.Tengchong 3.Kangding
2.The carbon stable isotope data explain that the CO2 in hotspring mainly derived from inorganic CO2in the deep earth. The deep source CO2 has three different causes: (1)mantle-derived CO2, features a lower d13C value (-3‰~-6‰), Tengchong geothermal area in Yunnan Province is a typical CO2 release area of this kind (Fig.1); (2) metamorphic CO2, features a higher d13C value (around 0‰ or >0‰), typical region is located in Erdaoqiao, Kangding city, Sichuan Province (Fig.1); and (3) mixed origin CO2, features a middle d13C value (0‰~ -3‰), the percentage of metamorphic CO2 in Kangding hotsprings is very high, average value account for 49.3~86.9% of the whole, and mantle-derived CO2account for 13.1~50.7%.
3.In order to calculate the emission quantity of hotspring CO2, the paper put forward the concept of discharge modulus, it means that the emitted CO2 quantity of hotspring in unit time:
Mf = (Ch - Co)Q
Where Mf - Modulus of discharge(mg/L)
Q - Discharge of hotspring water (L/s)
Ch- CO2 content of hot water (mg/L)
Co- CO2 content of shallow seepage water (mg/L)
Based on the statistic results from about 700 hot springs, the emission quantity of deep source CO2 is 2.68´V