Crustal Structure of the Northwest Sub-Basin of the South China Sea and Its Tectonic Implication
Crustal Structure of the Northwest Sub-Basin of the South China Sea and Its Tectonic Implication
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发表时间：
2012
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通讯作者：
Ao Wei
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作者：
Ao Wei
南海中国海北部陆缘深部地壳结构蕴含着南海北部陆缘裂谷过程的关键信息。通过对南海西沙地块和南海西北次盆地(NW次盆地)NEE向广角反射和折射洋底地震仪资料的采集，获得了386公里长的地震剖面(OBS2006-2)，这是迄今为止唯一一条平行于NW向次盆地扩张脊的剖面。利用射线追踪模拟方法获得了OBS2006-2沿线的地壳结构，得到了速度、构造和构造的信息速度结构表明，从西沙地块(约1-2公里)到西北次盆地(约2-3公里)，沉积物厚度逐渐增加。莫霍面由典型的南中国陆缘(约27公里)向洋壳(约12公里)变化。上地幔顶部的速度为7.8-8.0公里/秒。未发现高速层和低速层。西沙地块与西北次盆地过渡带有大量的岩浆活动。可能与NW次盆地的初始伸展有关，模型在220-370公里范围内的部分为洋壳，而在0-220公里范围内的西部可能为变薄的陆壳，Pn震相异常推断的NW次盆地的展布脊下可能存在残余岩浆。
Deep crustal structure in the northwest sub-basin contains the key information of the rifting process of the northern continental margin of the South China Sea(SCS).A 386km-long seismic profile(OBS2006-2)with wide-angle reflective and refractive ocean bottom seismometer(OBS)data was acquired across Xisha block and the Northwest sub-basin(NW sub-basin) of the SCS in NEE direction,which is the only profile hitherto parallel to the expanding ridge of the NW sub-basin.The crustal structure along OBS2006-2has been obtained by using ray-tracing simulation method(RAYINVR),which yields information on the velocities,tectonics,and geophysical properties.Our velocity structure indicates that sediment thickness increases from Xisha block(about 1-2km)to NW sub-basin(about 2-3km).Moho interface changes from typical continent margin of South China(～27km)to oceanic crust(～12km).The velocity at the top of upper mantle varies from 7.8to 8.0km/s.No high velocity layer and low velocity layer have been identified.Voluminous magmatism in transition zone between Xisha block and NW sub-basin,is possibly related to the initial extending of the NW sub-basin.The part of model in the domain of 220-370km would be of oceanic crust while the western part in the domain of 0-220km may be of thinned continental crust.Residual magma may exist under the speading ridge of the NW sub-basin deduced by the anomaly of Pn seismic phase.