东沙群岛西南海区泥火山的地球物理特征

多道反射地震和CHIRP浅地层剖面显示在南海东沙群岛西南陆坡和白云凹陷东部陆坡之间的深水(600~1 000m)陆坡上矗立着一系列高出周围海底50~100m的丘形地质体,其内部地层发生褶皱,反射波呈现杂乱和空白,海底声波屏蔽严重。浅地层剖面还显示丘状构造带有气体羽状构造,从海底进入水体高达50m。海底沉积取样分析表明,这些海丘区的表层分布着生物成因的致密碳酸盐结核。可以推断东沙西南的丘形地质体就是泥火山带,并且可能是一个重要的水合物潜在区。东沙西南海区泥火山表现出构造挤压和带状分布的特点,不同于南海北部神狐和九龙甲烷礁已发现水合物区的非泥火山,也不同于全球其他典型被动大陆边缘的泥火山特征,其构造成因和水合物潜力有待进一步研究。

Geophysical features of mud volcanoes in the waters southwest of the Dongsha Islands

There exist a series of submarine mounds (50 to 100 m higher above the surrounding seafloor) on the deepwater (600 to 1000 m) slope area between the southwestern Dongsha Islands and the eastern Baiyun sag, revealed by some Multi-channel seismic reflection and CHIRP subbottom profiles. The strata within these mounds have suffered folding and showed chaotic or weak reflections and seriously acoustic masking effects. CHIRP subbottom profiles also showed gas plumes up to 50 m have been developed within the mounds, which reflect there may exist ongoing muddy volcanism. Sedimentary studies showed that some biogenic carbonate nodules distributed on the surface of the mounds. Based on evidences mentioned above, it can be inferred that these mounds southwest of Dongsha Islands are mud volcanoes which may be an important prospecting area for gas hydrates. These mud volcanoes showed characteristics of tectonically compression and banded distribution, which are different from gas hydrate-bearing non-mud volcanoes in the Shenhu area and the Jiulong Methane Reef area and mud volcanoes in other typical passive continental margins in the world. The origin and the potential for gas hydrates of the mounds southwest Dongsha islands are still in debate, and need to be further studied.