青藏铁路沿线多年冻土区天然气水合物的地质、地球化学异常

通过对青藏铁路沿线多年冻土区重点地段野外冻胀、坍塌、冷泉冒气现象的观测及对低空大气、冷泉气体、表层冻土沉积物、地下冰等不同介质中气体的地球化学分析,发现部分冻土区如托纠山、昆仑山口、雁石坪等地区存在着明显的地质地球化学异常。这些气体地球化学异常可能主要是由青藏高原多年冻土区不同类型的断裂作用把深部气体带至浅部冻土沉积物中形成的,另一部分可能与浅部有机质转化成烃的作用相关,还有一部分可能与冰川发生位移造成的烃类气体聚集体重新分配有关;地质异常现象可能与该区构造热活动或天然气水合物形成的演化有关。对比前人的模拟计算结果,本次地质地球化学异常区的冻土厚度基本能满足天然气水合物形成的温压条件,这些异常可能与天然气水合物有关。

Geological and geochemical anomalies of gas hydrate in permafrost zones along the Qinghai-Tibet Railway, China

The authors made field observations of the phenomena of frozen mound upheaving, collapse and cold venting and performed geochemical analyses of gases in different media such as the lower atmosphere, cold spring gas, superficial frozen sediments and underground ice at key sites in permafrost zones along the Qinghai-Tibet Railway. Based on these observations and analyses, they found pronounced geological-geochemical anomalies in some frozen areas such as Tuojiu Mountain, the Kunlun Pass and Yanshiping. These gas geochemical anomalies were probably mainly produced by the rise of gas from the deep level to shallow frozen sediments via faults of different types in permafrost zones on the Qinghai-Tibet Plateau, and some of them are probably related to transformation of organic matter at the shallow level to hydrocarbon or to redistribution of gas accumulations caused by glacier displacement; the geological anomalies are likely to be related to tectonothermal activities or gas hydrate formation and evolution. A comparison with the previous modeling calculation shows that these geological and geochemical anomalies are situated in places where the permafrost depth is enough to meet the temperature and pressure conditions for the formation of gas hydrate, suggesting that these anomalies are possibly associated with gas hydrate occurrence in this region.