地幔源气体的CO2／^3He特征及其地质意义

THE CO_2/~3He RATIO IN MANTLE-DERIVED GASES AND ITS IMPLICATION

全球范围内的洋中脊玄武岩 (MORB)玻璃及气泡具有均一的CO2 /3He比率(CO2 摩尔数与3He摩尔数之比 ) ,为 ( 2～ 7)× 1 0 9,这表明通过洋中脊体系释放的幔源气体具有基本恒定的CO2 /3He比率。地幔脱气的机理研究表明 ,MORB中的该比率反映的是初始MORB岩浆的挥发份特征 ,而气泡在MORB岩浆中的成核、生长和上升的活动过程所造成的CO2 -3He的分离是很有限的 ,这说明幔源气体具有特征的CO2 /3He比率。匈牙利潘诺尼亚盆地等一系列的研究实例表明 ,幔源气体的CO2 /3He比率特征能够可靠地估计地幔脱气的通量 ,并为大陆地区构造拉张背景下的地幔脱气研究提供了一个可靠的约束条件。

It was found that CO\-2/\+3He ratio in the gas from glasses and vesicles of MORB is constant, (2-7)×10\+9, indicating that the CO\-2/\+3He ratio in mantle\|derived gases that released worldwide through the Mid\|Ocean Ridge is characterized as being constant. Mechanism studies show that this CO\-2/\+3He ratio is not the result of magma activity and it indeed reflects the volatile composition of the initial magma. So it provides a reliable tool for constraining the flux of mantle\|derived CO\-2, which is especially useful for the study of mantle\|derived CO\-2 in the continental extension area.\;