Based on the OBS data and the multi-channel seismic data collected in 2009 and 2011, the structure of crust in the north part of Southwest Sub-basin in the South China Sea is explored. Using two-dimensional ray tracing method to establish P velocity model, employing acoustic basement reflection, the reflections from the top interface of lower crust and the Moho are calculated in order to give the location of the velocity discontinuity interfaces. By employing refraction under the acoustic basement and the head wave from the mantle, the P wave velocitystructure of the entire survey line is pictured. The results showed that the depths of the top interface of lower crust and the Moho vary significantly. We inferred the southwest sub-basin rifting model, and concluded that there is a similarity in geological structure between the southwest safe-basin of South China Sea and Iberia-Newfoundland which is a typical non-volcanic margin. It is found that the two end member mechanical continental rifling models could not satisfactorily explain the souihwest sub-basin geological structure, while the elastic beam mechanics model can explain this rifting mode. Although in the lower crust of the northern part of southwest sub-basin there isn't large-scale magmatic activity, we inferred that a small amount of molten material may exist on the lop of Moho.%基于2009年和2011年采集的海底地震仪数据,辅以多道地震数据,对南海西南次海盆北缘的地壳结构进行了探索.利用二维射线追踪的反演方法建立测线上的模型.利用声学基底面的反射波,下地壳顶界面的反射波和莫霍面的反射波走时的反演勾绘了地层中的不连续界面,利用自声学基底面下的折射波和来自上地幔的首波来反演整条测线的P波速度结构.结果发现在下地壳顶界面和莫霍面都出现了较大的起伏,据此推断西南次海盆的张裂模式,并得到西南次海盆与非火山型的大陆边缘伊比利亚-纽芬兰的张裂具有一定程度上的相似性的结论.说明了大陆张裂的两种端元力学模型不能很好的解释西南次海盆的拉张模式,而应用弹性梁的力学模型可以解释这种拉张模式.虽然在西南次海盆北部陆坡区的下地壳中没有发现大规模的岩浆活动,但是得出在莫霍界面上方可能有小规模熔融物质存在的结论.
展开▼
