五大连池火山区气体地球化学特征

Geochemistry of gases from Wudalianchi volcanic district,northeastern China

根据泉（池）水中气体的组分和同位素组成，讨论了五大连池火山区气体的来源和运移。１９９７年８月从五大连地火山区泉（池）中采集了９个气、水样品，同年９月测定了游离气和水溶气的气体组分、Ｈｅ同位素比值和ＣＯ２的Ｃ值。气体以ＣＯ２为主，多数样品的ＣＯ２体积分数大于８０％。Ｈｅ和ＣＨ４的体积分数变化范围大，分别为０．７×１０－６～３８０×１０－６和４．０×１０－６～１８０×１０－６。３Ｈｅ／４Ｈｅ比值分布在１．０Ｒａ～３．３Ｒａ之间（Ｒａ＝１．４×１０－６，大气对流层３Ｈｅ／４Ｈｅ比值）。４Ｈｅ／２０Ｎｅ比值均比大气中的高，分布在０．３５～１０１１之间。ＣＯ２的 １３ｃ（ＰＤＢ）值与地幔或岩浆ＣＯ２的值一致，为－９．６‰～－４．２‰。这些均表明，泉水为渗入地下的大气降水，经过不同深度和不同岩层渗流出露地表；气体为幔源组分和地壳组分的混合物，利用二元混合模型估计，至少１３％～３７％的Ｈｅ源于地幔；ＣＯ２可能为幔源岩浆脱气后残留的ＣＯ２；Ｎ２、Ｏ２和Ａｒ主要为大气来源；研究区地球深部气体和热仍在大量地向地壳浅层和地表逸散。

The origin of gases in springs, pools and well from Wudalianchi volcanic district isdiscussed based on molecular and isotopic compositions of the gases. Nine gas and watersamples were collected from bubbles and water of springs and pools in the district, northeasternChina in August of 1997. The molecular components were measured with MAT 271 massspectrometer, and helium isotope ratios with VG5400 MS, and 13C with MAT 251 MS inLanzhou Institute of Geology. The gases are rich in CO2, and the volume fraction of CO2 of mostsamples is more than 80% . The volume fractions of He and CH4 have wide ranges of 0. 7 ×10-6 ￣ 380 × 10-6 and 4 × 10-6￣ 180 × 10-6, respectively. Helium isotopic ratios are in therange of 1. 05Ra to 3. 1 Ra. 4He/20Ne values are between 0. 35 and 1011 which are largerthan that in atmosphere. 13C (PDB) values of carbon dioxide range from - 9.6‰ to - 4. 2‰.In summary, spring water was derived from meteoric water which permeated the ground,migrated through different aquifers in different depths and went up to gush on the surface. Thegases are a mixture of mantle- and crust-derived ones, and at least 13% ￣ 37% of He may bederived from the mantle. CO2 may be residual gas from degassing of mantle-derived magma.N2, O2 and Ar are mainly of meteoric origin. Gases and thermal energy in deep level of thestudied district have been escaping in large quantities to the shallow crust and the surface.