南海西南次海盆深部结构研究进展与展望

Investigation progress and prospect of the deep structure in the Southwest subbasin of the South China Sea

西南次海盆位于南海渐进式扩张的西南端,共轭陆缘结构和残留扩张脊保留完整,是研究南海深部结构和动力学机制的关键区域。前期研究发现,西南次海盆洋陆过渡带较窄、同扩张断层发育、地震反射莫霍面不清晰、具有慢速扩张等特征。然而,由于不同探测方法获取的地壳结构具有多解性,使得西南次海盆洋陆转换过程、慢速扩张洋壳结构与增生模式以及龙门海山岩石性质与地幔成因机制等基础科学问题尚存争议。为此本文建议在西南次海盆开展地质取样获取海山岩石样品,确定其年龄与性质,分析扩张后海山形成的深部动力过程;并对关键构造部署高精度的地震反射/折射联合探测,结合岩石物理分析,对西南次海盆进行构造成像和物质组成参数正反演,以实现壳幔尺度的地震学透视,为探索西南次海盆洋陆转换过程和洋壳增生模式提供重要的证据,以丰富和完善南海的动力学演化模式。

The Southwest sub-basin,located at the southwest propagating spreading tip of the South China Sea,features an intact conjugated continental margin and a central rift valley.The sub-basin is a key area for studying the deep structure and dynamic mechanisms of the South China Sea.Previous studies have found that the Southwest sub-basin has a narrow ocean-continent transition and is characterized by slow seafloor spreading rate with numerous syn-spreading faults and ambiguous Moho reflections.However,due to different crustal structures being acquired by diverse investigative techniques,the basic scientific issues such as the rift to drift transition pattern,the slow-spreading oceanic crust structure and accretionary process,the rock properties of Longmen seamounts and the genetic mechanism of mantle are still controversial.Geological sampling and a coincident deep seismic reflection/refraction experiment in the SCS\s Southwest sub-basin are required to address these problems.To understand the seamount\s deep dynamic process,take geological rock samples from the seamount and analyse their age and attributes.Additionally,to obtain the fine crustal structures,high-precision seismic reflection/refraction exploration is carried out in combination with petrophysical analysis,structural imaging,and forward inversion of material composition parameters to achieve crust-mantle scale seismological perspective.These studies will enrich and enhance knowledge about the procedure of continental oceanic transition and the pattern of oceanic crust accretion in the Southwest sub-basin.