深部物质运动的气体地球化学特征

根据氦同位素地球化学资料讨论了中国东部和云南腾冲地区上地幔的脱气。尽管地球脱气作用主要发生在地球形成时的十亿年间，但是后期的脱气作用仍是影响大气圈演化的主要因素。在两种力学性质不同的构造带──中国东部大陆裂谷和位于欧亚板块与印度板块缝合带的腾冲火山区，采集了天然气样，并分析了气体组分和氦同位素组成，较高的３Ｈｅ／４Ｈｅ值和地质、地球物理资料表明天然气和温泉气中的氦相当一部分是来自上地幔。来自上地幔的氦和其他气体自第三纪以来不断在气藏中聚集或向大气中逃逸。伴有源于上地幔的岩浆活动的地幔脱气是深部物质运动的具体表现形式，它对新生代气候演变可能有直接影响。

MANTLE DEGASSING-A GASGEOCHEMICAL FEATURE OF DEEP-EARTH-MATTER MOVEMENT

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.