幔源CO_2演化及CO_2气成藏实例分析

幔源CO2是当今地球科学研究中的前沿领域之一,具有重要的研究价值。处于超临界态的地幔流体具有很强的溶解和扩散能力,是地球内部能量与物质向外传输的重要载体。地幔流体中的挥发分以H2O和CO2为主,全球许多CO2气藏中的气体具有幔源特征,与地幔流体密切相关,但地幔流体与CO2气藏之间的关系研究则显得不够。本文分析了地幔流体的组成、性质与影响因素,结合济阳坳陷断裂构造、岩浆发育特征,阐述地幔流体上升和演化过程,认为地幔流体中溶解各种形式CO2气为气藏形成提供物质来源,断裂活动则为岩浆上侵和气体的运移、聚集提供了通道和空间。CO2气藏勘探的有利区块应该不仅仅局限于坳陷内,在坳陷边缘或者外部,新生代晚期的碱性岩浆侵入活动,不同方向断裂发育交汇地区均是气藏勘探的有利地区。

Origin and evolution of mantle-derived CO_2: A case study of CO_2 gas pool in Jiyang depression

The study of mantle-derived CO_2 is one of the frontiers in Earth science and is hence of great significance. Mantle fluids in supercritical state possess high dissolving and diffusing capacity and serve as an important transporting carrier of energy in Earth' s interior, with their chemical composition being mainly H_2O and CO_2. Many scholars believe diat mantle fluids play an important role in the ore-forming process, but research on their relation with the CO_2 gas pool is very insufficient. Along with the magma rising, the relatively insoluble CO_2 gas will be the first to release with the temperature and pressure reduction of the magma, and the favorable tectonic environment is likely to form the CO_2 gas pool. Many of the world's regional magmatic activities and fractures have formed CO_2 gas reservoirs. This paper analyzed properties and influencing factors of mantle fluids exemplified by the study of magma and fault characteristics of Bohai Bay basin in eastern China, and discussed the ascent and evolution process of mande fluids. The authors believe that mande degassing may be the main material source of CO_2, and diat fault activities provide passageways and space for magma uprising and gas migration and accumulation. The favorable sites in search for potential CO_2 gas pools lie in magmatic activities on basin margin and intersections of faults of different directions.