东海冲绳海槽天然气水合物成矿地质条件与资源潜力

冲绳海槽位于东海的东部,区内天然气水合物调查研究程度低。本文分析了冲绳海槽的区域地质背景和天然气水合物调查研究现状,根据已有资料和前人研究成果,分析了研究区天然气水合物形成的地形地貌、水深、温度、热流值特征,地层、沉积、构造、气源等条件,以及区内存在天然气水合物的地球物理、地球化学和其他证据,在此基础上推测区内天然气水合物成藏存在4种可能的地质类型。即成岩型、断裂构造型、底劈构造型和滑塌型。研究认为,冲绳海槽天然气水合物资源潜力巨大。

Formation Conditions and Resources Potential of Gas Hydrate in the Okinawa Trough of the East China Sea

Located in the east part of the East China Sea, the Okinawa trough is one of the areas with possible gas hydrate potentials in the East China Sea. However, little work has been devoted to this problem except for some preliminary surveys and discussions. According to the geological, geophysical and geochemical data from several cruises and various publications and on the basis of an analysis of geological factors which control gas hydrate development as well as much evidence for possible development of gas hydrate in the Okinawa trough, this paper points out that there are probably 4 kinds of hydrate deposit types in the study area, i.e., diagenetic, fault-controlled, diapir-controlled and sliding controlled hydrate deposits. The geological factors which control the development of gas hydrate include tomography, geomorphology, water depth, temperature of sea bottom and sedimentary layers, heat flow, sedimentary sources, sedimentary thickness, source rock, sedimentation rate, structure feature, local structure etc., and the evidence indicating the development of gas hydrate might include BSR, blanking zone, negative polarity of BSR Wave, lower layer-velocity response on seismic migration profile, CH4 anomalies in shallow-surface layer and sea-bottom water shown by geochemical investigation, and temperature-increasing anomalies detected by satellite-based thermal infrared remote sensing. In addition, authigenic minerals such as pyrite and carbonate, gas seepage, and CO2-hydtrates were observed. All these data provide valuable evidence in search for mineral resources of gas hydrate in the Okinawa trough of the East China Sea. The authors hold that the reason for lack of gas hydrates discovery here as compared with other seas is mainly due to the relatively lower exploratory level.