滇西北德钦-中甸一带温泉逸出气体的地球化学特征

Geochemical Characteristics of Hot Spring Gases from the Deqin-Zhongdian Area,Northwestern Yunnan,China

为探讨滇西北地区德钦-中甸一带温泉气体的地球化学特征及其来源,对采集到的18个温泉逸出气体样品的化学组分和氦、碳同位素组成进行了分析。结果显示,德钦-中甸一带CO2含量偏高且主要沿金沙江断裂和德钦-中甸断裂分布,平均CO2的释放量为80.6%;气体样品的^3He/^4He值为0.06-0.74Ra,中甸地区的下给茨喀和天生桥温泉为研究区高幔源氦释放区,分别达到7.6%和5.0%;中甸地区碳同位素也表现为幔源的特征,δ^13CCO2变化范围为-1.94‰--5.95‰。与已有的深部探测结果对比,研究区幔源氦释放较高的中甸地区（下给茨喀温泉、天生桥温泉）主要位于软流圈上涌区（四川黑水-金川-道孚-雅江-稻城）南端的边缘地带,因而幔源氦释放不显著。

In order to investigate the geochemical characteristics and origin of hot spring gases in the Deqin-Zhongdian area of northwestern Yunnan,the chemical components,He and C isotopic ratios of 18 samples of hot spring gases have been analyzed. The results show that the CO2 contents of gases of hot springs in the Deqin-Zhongdian area are relatively high.Especially,those gases of hot springs mainly distributed along the Jinshajiang and Deqin-Zhongdian faults contain average CO2 contents of 80. 6%,with^3He/^4He values varying from 0. 06 to 0. 74 Ra. The Xiageicika and Tianshengqiao hot springs in the Zhongdian area contain high contents of He released from the mantle source,with He contents of up to 7. 6% and5. 0%,respectively. The C isotopes of hot spring gases in the Zhongdian area also have characteristics of mantle-derived carbon with their δ^13CCO2 values varying from-1. 4‰ to-5. 95‰. Compared with the existing deep detection results,the Zhongdian area（ the Xiagei and Tianshengqiao hot springs）,where the release of mantle derived helium is relatively high in the study area,is mainly located in the edge zone at the southern end of the asthenosphere upwelling zone（ the HeishuiJinchuan-Daofu-Yajiang-Daocheng belt in Sichuan Province）,so the release of mantle derived helium was not very significant.