^3He／^4He Ratios and Heat Flow in the Continental Rift—valley,Eastern China

3He/4He ratios and heat flow in the continental rift-valley,eastern China

Heat flow and the origin of helium in natural gases from fault basins of the continental rift-valley in eastern China are discussed in terms of helium isotope geochemistry.³He/⁴He ratios in natural gases from the rift-valley range from 2.23 × 10⁻⁷ to 7.21 × 10⁻⁶, which are directly proportional to the concentration of helium and ΣNHC/ΣHC ratio in natural gases. Geological and isotope geochemical data suggest that helium in natural gases consists predominantly of crustal radio-genic and upper mantle-derived helium. In a simple mixing pattern between crustal He and mantle-derived He, mantle-derived helium in natural gases would account for 10–60%. Calculated values for heat flow (Q) range from 59.7 to 82.4mWm⁻², of which about 60 percent in the rift-valley is derived from the upper mantle. Natural helium reservoirs would be found in the areas where the upper mantle uplifted greatly and heat flow is large in the continental rift-valley. The project is financially supported by the National Natural Science Foundation of China.