青藏公路沿线地表渗漏气体地球化学特征及来源  

Geochemistry and Origins of Gas Discharging Along Qinghai-Tibet Highway,Northern Qinghai-Tibet Plateau

作　　者：黄华谷[1,2] 罗敏[2] 张鹏[3] 吴青柏[3] 陈多福[2] 

机构地区：[1]广东省地质调查院,广东广州510080 [2]中国科学院广州地球化学研究所,广东广州510640 [3]中国科学院寒区旱区环境与工程研究所,甘肃兰州730000

出　　处：《天然气地球科学》2014年第6期874-881,共8页Natural Gas Geoscience

基　　金：中国科学院西部行动计划项目(编号:KZCX2-XB3-03);中国科学院广州地球化学研究所"135"前沿领域项目(编号:Y234021001)联合资助

摘　　要：CO2和CH4渗漏在地球表面是一种普遍的地质现象，这些释放的温室气体不仅对全球气候变化和碳循环产生重要影响，而且可以示踪其来源及构造活动信息。对青藏公路沿线地表渗漏气体的组分、CO2和CH4碳同位素以及He同位素组成进行了分析，结果显示该区渗漏气体主要有N2型和CO2型2类。N2型渗漏气体主要分布在北麓河、布查湖和沱沱河东侧，N2含量均超过75％，CO2和CH4含量分别为3．45％～20．91％和0～3．58％。CO2型渗漏气体主要分布于二道沟南侧、沱沱河支流和唐古拉山兵站附近，CO2含量均超过96％。所分析的渗漏气体的CO2／3He值、CH4／3He值、δ13CCO2值和δ13C1值显示布查湖渗漏CO2和CH4均为生物成因，无幔源CO2和He；北麓河和沱沱河东侧渗漏CO2和CH4可能均为非生物成因，幔源CO2含量超过50％；二道沟南侧、沱沱河支流和唐古拉山兵站附近的CO2型气体中CO2主要为幔源无机成因，其中唐古拉山兵站渗漏气体中还伴有幔源CO2还原形成的微量非生物成因CH4。所有渗漏气体中He均是以壳源为主，幔源He仅占2．15％～5．66％。以上的结果表明研究区大量幔源无机CO2的释放，可能与班公湖-怒江缝合带和可可西里-金沙江缝合带这2条深大断裂带以及藏北新生代火山活动有关，但有限的幔源He输入可能与断裂带深部的开放性程度较低有关，反映了该区处于挤压的构造环境和地壳增厚的地质背景，或者是由于较高壳源放射性成因He的混入而“稀释”了慢源He所致。CO2 and CH4 play a significant role in the global climate change and carbon circulation and can be used to monitor their origin and tectonic activity. In this paper, we carried out investigations on the gas compositions,carbon isotope ratios of CO2 and CH4 ,and He isotope compositions from the Qiangtang Basin and its adjacent areas. Our results show gas samples from Beiluhe,Bucha Lake, and eastern Tuotuo River are N2-rich with N2 over 75o%. The contents of CO2 and CH4 are only 3.45%-20.91% and 0-3.58%,respectively. CO2/3 He and CH4/3He and carbon isotopic values of CO2 and CH4 suggest that both CO2 and CH4 from Bucha Lake are biotic without mantle-derived CO2 and He,whereas those of Beiluhe and eastern Tuotuo River are abiotic. Southern Erdaogou Depot,branch of Tuotuo River, and Tanggula Mountain Dep- ot are enriched in CO2 with more than 96%. The CO2 was at least partially originated from mantle,trace a- mount of CH4 was abiotic and derived from mantle-derived CO2 ; He was primarily originated from crust with only 2.15 %-5.66 % of mantle-derived origin. These results show that the emitting of large quantity of mantle-derived CO2 is likely to be ascribed to the presence of Bangong Lake-Nujiang River, Hoh Xil-Jinsha River sutures and the Cenozoic volcanism in northern Tibet. Nevertheless, the estimated small fraction of mantle-derived He may result from the low opening degree at the bottom of fault zones and possibly reflect a geological setting of strong extrusion and an increase in crustal thickness.

关 键 词：气体渗漏 碳同位素 氦同位素 来源 青藏高原 

分 类 号：TE122.113[石油与天然气工程—油气勘探]