中文摘要：

通过对南海北部大陆边缘地壳结构分析，指出南海东北部存在下地壳高速层，大致分布在112°E～120°E，19°N～22°N的陆坡和拉张程度大的陆架地区，呈NEE向延伸，在海底地震仪剖面上最大的厚度有8km，向南海海盆方向减薄。通过对比综合分析认为，高速层物质组成是底侵作用形成的熔岩垫，由于伸展作用，南海海底扩张（30Ma）前后底侵作用形成了熔岩垫，并促使南海北部大陆边缘地壳抬升，导致区域性抬升剥蚀。

英文摘要：

Based on the study of the crustal structure, the authors point out that there exits a high velocity layer in the lower crust of northeast South China Sea, which distributes around continental shelf and rifted continental slope from 112°E - 120° E , 19° N - 22°N in NEE strike. The high velocity layer can reach as thick as 8 km according to the OBS data, its thickness reduces from the continental shelf to the South China Sea ocean basin gradually. From multidisciplinary analysis, the high velocity layer in lower crust is interpreted as magmatic underplating. It emplaced almost simultaneous with the South China Sea spreading around 30Ma, and gave rise to crust uplifting and erosion of the study area.