Advances in Earth Science ›› 1994, Vol. 9 ›› Issue (3): 48-52. doi: 10.11867/j.issn.1001-8166.1994.03.0048

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Du Jianguo,Wang Xianbin,Xie Hongsen   

  1. State Key Lab. of Gasgeochemistry, Lanzhou Institute of Geology,Chinese Academy of Sciences, Lanzhou  730000
  • Received:1993-12-08 Revised:1994-01-10 Online:1994-05-01 Published:1994-05-01

Du Jianguo,Wang Xianbin,Xie Hongsen. MANTLE DEGASSING—A GASGEOCHEMICAL FEATURE OF DEEP-EARTH-MATTER MOVEMENT[J]. Advances in Earth Science, 1994, 9(3): 48-52.

The paper discusses upper-mantle degassing in East China and Tengchun district of Southwestern China based upon data of helium-isotope geochemistry. Even though earth degassing mainly occurred in beginning 1000 Ma of the Earth history, mantle degassing is an important factor affecting atmosphere evolution since then. Mantle degassing is one of manisfestations of deep-earth-matter movement. Gas samples were collected from production gas-oil wells and hot springs. The gas-oil wells distribute in continental rift valley. East China,and the hot springs occur in Tengchun volcanic district where belongs to the collision zone between the Eurasia plate and India plate. Molecular component and helium isotope composition were analyzed 3He/4He ratios of natural gas have arrange of 0.2 Ra to 5.2 Ra (Ra stands for 3He/4He ratio of atmosphere). 3He/4He ratios of the hot springs are from 0.5 Rato to 5.1 Ra. Higher values of helium isotope composition and geological and geophysical data indicate that helium in the natural gases and hot-spring gas is partially derived from upper mantle.It can be considered that helium migrating from upper mantle have being accumulated in gas reservoir or escaped to atmosphere since Paleocene Epoch according to the time of gas reservoir formation and Quaternary volcanicity in Tengchun district. Larger 3He/4He ratios have a close relation to magmatite originated from upper mantle. It can be concluded, therefor, that upper in continental rift valley East China and Tengchun volcanic district is in a stage of stronger degassing in Cenozoic Era.Upper mantle degassing may be one of the most important factors affecting Cenozoic evolution of atmosphere and environment.

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