南海陆坡天然气水合物成藏的构造环境

STRUCTURAL CIRCUMSTANCE OF GAS HYDRATE DEPOSITION IN THE CONTINENT MARGIN,THE SOUTH CHINA SEA

南海是西太平洋最大的边缘海之一,其复杂的构造演化,形成了构造特征迥异的南海陆缘,有利于天然气水合物的发育。南海地区在中中新统以上发育了上中新统、上新统和第四系3套地层,3套地层所对应的地质时期的沉降速率在纵横向上的差别均较为悬殊,总体而言,南海第四纪整体沉降速率较大,为天然气水合物压力场环境的形成提供了有利条件。南海复杂的构造背景形成了丰富多彩的构造地质体,特定的构造地质体与水合物形成关系密切。这里讨论了滑塌体、泥底辟、增生楔等构造地质体在南海的分布情况,分析了上述构造体与气体水合物地震标志BSR之间的关系,以及特殊构造带在南海的展布规律,提出了特殊构造带中天然气水合物的成藏模式。

The South China Sea is one of the largest marginal seas in the West Pacific,which has four continent margins greatly different in structural history.The four margins are all in favor of gas hydrate deposition.There are upper Miocene,Pliocene and Quaternary overlying the middle Miocene,and their subsidence rates are very different from each other.In general,the rate for Quaternary is the largest,favorable for the formation of the pressure field of gas hydrate.Plentiful and various geological structures are formed in complicated structural environments in the South China Sea,which provides advantageous condition for gas hydrate accumulation.The distribution of slumps,clay diapirs and accretional wedges in the South China Sea was discussed,and the relationship with the seismic symbol of gas hydrateBSR(Bottom Simulating Reflector)was also studied.And the special structural belt(SSB)was discussed in detail:the characteristic, distribution and the model in which gas hydrate forms.