关键词: 东沙海区, 地质构造, 天然气水合物, 似海底反射波, 沉积作用, 活动断裂

Abstract: The geological and tectonic characteristics for generating gas hydrate in the Dongsha continental slope of the South China Sea were analyzed.It is suggested that tectonics and sedimentation play the important roles in the generation of methane hydrate.The range of occurrence of bottom simulating reflector(BSR) in the Dongsha continental slope of the South China Sea was mapped by means of some high-resolution seismic data.The BSR clearly appeared on the seismic profiles of the lower slope,whereas it was few discovered in the upper slope.The BSR was mainly distributed in the transition zone between the continental crust and oceanic crust southwestward the Dongsha Islands.The background of the region was characterized by the passive continental margin.The BSR were distributed in the range of debris flow and turbidity sedimentation.This means that debris and turbidity are sufficiently high to allow the vertical transport of large volumes of methane and to form the gas hydrate.The occurrence of BSR was resulted from anomaly overpressure fluid including gas and water,because of the rapid sedimentary rate revealed by ODP drilling and piston cores during the Late Cenozoic.The high heat flow values indicate that the active tectonics and deep crust fluid in the region benefit to the generation of gas hydrate.Otherwise,few BSR and gas hydrate occurred in the upper slope,because of the thin sedimentary layers and serious tectonic erosion.

Key words: South China Sea, geological structure, gas hydrate, bottom simulating reflector, sedimentation, active fault