Abstract
The abundance and isotopic composition of He have been determined for a variety of natural gases (oil-field gases) in sedimentary basins in the continent of China. The 3He/ 4He and 4He/ 20Ne ratios range from 0.004 to 4.99 Ra (where Ra denotes atmospheric 3He/ 4He ratio = 1.4 × 10 −6), and from 100-39,000, respectively. Helium in the gas sample is composed of mantle-derived He and crustal radiogenic He. The high 3He/ 4He ratios were observed in the sedimentary basins which underwent Cenozoic extension in the eastern domain, such as the Songliao, Liaohe, North China, Subei, Sanshui and South China Sea basins. The basins where mantle-derived He is recognized are characterized by the presence of surface and subsurface volcanic rocks, high terrestrial heat flow, deep faults and thinned crust. On the other hand, regions which underwent pre-Tertiary extension such as the Jungar, Tarim, Tuba, Caidam and Yumen basins in the NW and tectonic loading such as the Ordos and Sichuan basins in the central domain are marked by almost pure radiogenic 4He of crustal origin and thus by an apparent absence of mantle-derived He, which coincides with complete lack of Cenozoic volcanics, low terrestrial heat flow and thickened crust. Such a 3He/ 4He distribution pattern clearly indicates that tectonic environment control the distribution of He isotopes in the continent of China.
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