There are some active bottom currents on the northern continental slope of the South China Sea (SCS). Reflection seismic profiles show that the bottom current channels occur in the water depth range of 1000 to 2700 m,...There are some active bottom currents on the northern continental slope of the South China Sea (SCS). Reflection seismic profiles show that the bottom current channels occur in the water depth range of 1000 to 2700 m,extending from the NE to the SW,leading to accumulation of discontinuous drifts with higher sedimentation rates on the eastern side of the channel. The stacking pattern of the layers sug-gests that these drifts propagated southwestward,following the direction of the bottom currents. One sedimentary drift to the southeast of the Dongsha Islands has the highest sedimentation rate of 97cm/ka in the last 12 ka. The sedimentary characteristics of the sediment layers indicate that these bottom currents are most likley caused by the water movement of a branch of the West Pacific Ocean Current,which enters the northern SCS via the Bashi Strait. Once formed,the bottom currents trans-port sediments along the northern slope of SCS southwestward and finally disappear into the central basin of the SCS. Due to the bottom current activity,the deep-sea sedimentary process in the northern SCS is complex.展开更多
Sponsored by the Chinese National Fundamental Research and Development Program in 2001,Guang-zhou Marine Geological Survey launched out a long geophysical survey from the northeastern part of the South China Sea (SCS)...Sponsored by the Chinese National Fundamental Research and Development Program in 2001,Guang-zhou Marine Geological Survey launched out a long geophysical survey from the northeastern part of the South China Sea (SCS),through the Luzon Arc,to the Huatung Basin and the Gagua Ridge. Based on high-resolution seismic data from this survey,combined with gravimetric and magnetic modeling,a systematic effort is made to the study of the regional geodynamics offshore southern Taiwan. By focusing particularly on precollisional tectonic interactions between adjacent geological units and their tectonic affiliations,this study can help reveal early arc-continent collisional processes that formed the Taiwan orogen. The construction of the Manila accretionary prism and its eastward progressive deformation indicate that the subduction of SCS have experienced multiple phases of increased activity. Active precollisional crustal shortening within the Northern Luzon Trough resulted in tilting of sedimentary layers at angles between 6° and 13°. But the shortening induced by tilting accounts for only a tiny part of regional total crustal compression. The eastern flank of the Luzon Arc appears to be more active than the rest,evidenced by active faulting and folding in the intra-arc basins on the eastern flank. Magnetic modeling/inversion shows that the Luzon Arc may have experienced multiple phases of magmatic activities,causing lateral magnetic inhomogeneity. Bouguer gravity anomalies and gravity modeling indicate that the Huatung Basin has anomalously higher crustal and upper mantle densities than those of SCS and the Luzon Arc. In addition,there is a large bathymetric difference between the Huatung Basin and the northeastern part of SCS basin. These observations argue against early hypothesis that the Huatung Basin and the northeastern part of SCS basin may once have belonged to one single oceanic crust,in part or in whole. The Gagua Ridge,as a sliver of uplifted oceanic crust,may be related to a transient northwestward subduction of the western Philippine plate. All evidences point to the argument that the region offshore southern Taiwan is experiencing multiple terrain amalgamation,which is a classical model for continental growth.展开更多
基金Supported by the National Natural Science Foundation of China (Grant Nos. 40276019 and 40238060)the National Key Basic Research Special Foundation Project of China (Grant No. G2000078500)
文摘There are some active bottom currents on the northern continental slope of the South China Sea (SCS). Reflection seismic profiles show that the bottom current channels occur in the water depth range of 1000 to 2700 m,extending from the NE to the SW,leading to accumulation of discontinuous drifts with higher sedimentation rates on the eastern side of the channel. The stacking pattern of the layers sug-gests that these drifts propagated southwestward,following the direction of the bottom currents. One sedimentary drift to the southeast of the Dongsha Islands has the highest sedimentation rate of 97cm/ka in the last 12 ka. The sedimentary characteristics of the sediment layers indicate that these bottom currents are most likley caused by the water movement of a branch of the West Pacific Ocean Current,which enters the northern SCS via the Bashi Strait. Once formed,the bottom currents trans-port sediments along the northern slope of SCS southwestward and finally disappear into the central basin of the SCS. Due to the bottom current activity,the deep-sea sedimentary process in the northern SCS is complex.
基金the Chinese National Basic ResearchDevelopment Program (Grant Nos. G2000047604 and G2000078501)
文摘Sponsored by the Chinese National Fundamental Research and Development Program in 2001,Guang-zhou Marine Geological Survey launched out a long geophysical survey from the northeastern part of the South China Sea (SCS),through the Luzon Arc,to the Huatung Basin and the Gagua Ridge. Based on high-resolution seismic data from this survey,combined with gravimetric and magnetic modeling,a systematic effort is made to the study of the regional geodynamics offshore southern Taiwan. By focusing particularly on precollisional tectonic interactions between adjacent geological units and their tectonic affiliations,this study can help reveal early arc-continent collisional processes that formed the Taiwan orogen. The construction of the Manila accretionary prism and its eastward progressive deformation indicate that the subduction of SCS have experienced multiple phases of increased activity. Active precollisional crustal shortening within the Northern Luzon Trough resulted in tilting of sedimentary layers at angles between 6° and 13°. But the shortening induced by tilting accounts for only a tiny part of regional total crustal compression. The eastern flank of the Luzon Arc appears to be more active than the rest,evidenced by active faulting and folding in the intra-arc basins on the eastern flank. Magnetic modeling/inversion shows that the Luzon Arc may have experienced multiple phases of magmatic activities,causing lateral magnetic inhomogeneity. Bouguer gravity anomalies and gravity modeling indicate that the Huatung Basin has anomalously higher crustal and upper mantle densities than those of SCS and the Luzon Arc. In addition,there is a large bathymetric difference between the Huatung Basin and the northeastern part of SCS basin. These observations argue against early hypothesis that the Huatung Basin and the northeastern part of SCS basin may once have belonged to one single oceanic crust,in part or in whole. The Gagua Ridge,as a sliver of uplifted oceanic crust,may be related to a transient northwestward subduction of the western Philippine plate. All evidences point to the argument that the region offshore southern Taiwan is experiencing multiple terrain amalgamation,which is a classical model for continental growth.
