ORIGIN AND DISTRIBUTION OF CARBON-DIOXIDE GAS POOLS IN EASTERN CHINA

Carbon dioxide gas pools occur widely in the basins of eastern China. CO, gas-bearing beds are from the Teritary to Ordovician, and reservoi rs are sandstone, carbonates and volcanic;. The gases from these gas p ools contain CO2 of 62.86 parts per thousand - 99.55 parts per thousan d. In the Mesozoic-Cenozoic extensional basins, such as Songliao, Boha i Bay, Subei, Sanshui and Zhujingkou, the delta(13)C(CO2) values of CO 2 gas pools range from -2.65 parts per thousand to -8.83 parts per tho usand, mainly from -3.5 parts per thousand to -6.0 parts per thousand, He-3/He-4 ratios are 2.65R(a) to 4.96R(a). The regression equation of CO2 content and helium isotope ratio is CO2(%)=61.3852+7.9745R/R(a), correlation coefficient r is 0.9430, CO2 is mainly mantle-derived and magmatic origin. delta(13)C(CO2) value of CO2 gas from Well X in Yingg ehai Basin is -3.80 parts per thousand. He-3/He-4 ratio is 0.07R(a), C O2 is metamorphic origin. Mantle-derived and magmatic CO2 gases are di scharged from the cross areas of northeastern trending and northwester n trending faults in these Mesozoic-Cenozoic extensional basins, in th e shallow level, the CO2 gases migrate and accumulate along northeaste rn trending extensional faults. The activity of the Neogene to Quatern ary northwestern trending tectonic-magmatism zones in eastern China is another important discharge event for mantle-derived and magmatic gas es, which have great contribution to the CO, gas pools in this area. M etamorphic CO2 in the Yinggehai Basin is released by the dynamic metam orphism of shear fractures.