Crustal structure of the northwestern sub-basin, South China Sea: Results from a wide-angle seismic experiment  

作　　者：WU ZhenLi LI JiaBiao RUAN AiGuo LOU Hai DING WeiWei NIU XiongWei LI XiBing 

机构地区：[1]Institute of Oceanology,Chinese Academy of Sciences,Qingdao 266071,China [2]Graduate University of the Chinese Academy of Sciences,Beijing 100049,China [3]The Second Institute of Oceanography,State Oceanic Administration,Hangzhou 310012,China [4]Laboratory of Submarine Geosciences,State Oceanic Administration,Hangzhou 310012,China [5]Institute of Geophysics,China Earthquake Administration,Beijing 100081,China

出　　处：《Science China Earth Sciences》2012年第1期159-172,共14页中国科学（地球科学英文版）

基　　金：supported by National Basic Research Program of China (Grant No. 2007CB411701);National Natural Science Foundation of China (Grant Nos. 40876035 and 91028006);Scientific Research Fund of the Second Institute of Oceanography, State Oceanic Administration (Grant No. JG200803)

摘　　要：The crustal structure of the northwestern sub-basin area of the South China Sea was modeled by inverting a wide-angle seismic survey line across the entire region and on both sides of its bounding continental margins. The survey line extended over 484 km. A total of 14 Ocean Bottom Seismometers (OBS) were deployed at intervals of 30 km to record air-gun array sources with a combined volume of 5160 in 3 . The crustal velocity structure of the northwestern sub-basin area was acquired through the integration of multi-channel seismic data. OBS data were processed and modeled initially using ray tracing inversion techniques. Results indicate that crustal thickness under the continental slope decreases from 21 to 11 km, crustal thickness of the northwestern sub-basin is 7.7 km, and the depth to the Moho ascends from 21 km under the upper continental slope to 11 km under the middle basin. The crust of the northwestern sub-basin is similar to that of the eastern sub-basin in its oceanic crustal structure. This structure has a thicker layer 1 (sedimentary layer) and a thinner layer 2. These characteristics are especially clear in the eastern sub-basin, which differs somewhat from typical oceanic crust. The tectonic geometry and velocity structure of the northwestern sub-basin and its margins comprise a symmetrical conjugate and indicate a pure shear mode with regard to the continental margin rifting mechanism. We did not find clear seismic signals from high velocity layers under the lower crust of the continental margin in the northern part of the northwestern sub-basin, which provides new evidence for the idea that the western part of the northern continental margin of the South China Sea constitutes nonvolcanic crust. Because the seafloor spreading period of the northwestern sub-basin was short, layer 2 might have experienced asymmetrical basalt magma flows, which may have blurred the magnetic anomaly lineations of the northwestern sub-basin.The crustal structure of the northwestern sub-basin area of the South China Sea was modeled by inverting a wide-angle seismic survey line across the entire region and on both sides of its bounding continental margins. The survey line extended over 484 km. A total of 14 Ocean Bottom Seismometers （OBS） were deployed at intervals of 30 km to record air-gun array sources with a combined volume of 5160 in3. The crustal velocity structure of the northwestern sub-basin area was acquired through the in- tegration of multi-channel seismic data. OBS data were processed and modeled initially using ray tracing inversion techniques. Results indicate that crustal thickness under the continental slope decreases from 21 to 11 km, crustal thickness of the north- western sub-basin is 7.7 km, and the depth to the Moho ascends from 21 km under the upper continental slope to 11 km under the middle basin. The crust of the northwestern sub-basin is similar to that of the eastern sub-basin in its oceanic crustal struc- ture. This structure has a thicker layer 1 （sedimentary layer） and a thinner layer 2. These characteristics are especially clear in the eastern sub-basin, which differs somewhat from typical oceanic crust. The tectonic geometry and velocity structure of the northwestern sub-basin and its margins comprise a symmetrical conjugate and indicate a pure shear mode with regard to the continental margin rifting mechanism. We did not find clear seismic signals from high velocity layers under the lower crust of the continental margin in the northern part of the northwestern sub-basin, which provides new evidence for the idea that the western part of the northern continental margin of the South China Sea constitutes non-volcanic crust. Because the seafloor spreading period of the northwestern sub-basin was short, layer 2 might have experienced asymmetrical basalt magma flows, which may have blurred the magnetic anomaly lineations of the northwestern sub-basin.

关 键 词：wide-angle seismic crustal structure South China Sea tectonic evolution 

分 类 号：P736.1[天文地球—海洋地质] P315.2[天文地球—海洋科学]