南海北部陆缘盆地形成的构造动力学背景

Tectonic dynamics of northern continental margin basins in South China Sea

南海北部陆缘盆地处于印度板块与太平洋及菲律宾海板块之间,但三大板块对南海北部陆缘盆地的影响是不同的。通过对三大板块及古南海演化的研究,可知南海北部陆缘地区应力环境于晚白垩世发生改变。早白垩世处于挤压环境,晚白垩世以来转变为伸展环境并且不同时期的成因不同。晚白垩世—始新世,华南陆缘早期造山带的应力松弛、古南海向南俯冲及太平洋俯冲板块的滚动后退导致其处于张应力环境。始新世时南海北部陆缘裂陷盆地开始产生,伸展环境没有变,但因其是由太平洋板块向西俯冲速率的持续降低及古南海向南俯冲引起的,南海北部陆缘盆地继续裂陷。渐新世—早中新世,地幔物质向南运动及古南海向南俯冲导致南海北部陆缘地区处于持续的张应力环境;渐新世早期南海海底扩张;中中新世开始,三大板块开始共同影响着南海北部陆缘盆地的发展演化。

Northern continental margin basins in South China Sea are located among Pacific Plate, Indian Plate and Philippine Sea Plate; these plates had different impacts on these basins. The study of the evolution of the three plates and paleo-South China Sea showed that the stress environment had been changed in the late Cretaceous in northern continental margin area. The stress environment was compressional in the Lower Cretaceous and had been changed into extension in the Late Cretaceous. The cause of extensional environment was different since the Late Cretaceous. Extensional environment was caused by stress relaxation of eogenetie orogen in South China continental margin area, by southern subduction of paleo-South China Sea and by rollback of the subducting Pacific slab from the late Cretaceous to the Paleocene, and the early rift basin began to form in continental margin in northern South China Sea. Continued reduction of western subduction rate of Pacific slab and southern subduction of Paleo-South China Sea formed the same stress environment in the Eocene and rift basins formed continually. Southern movement of mantle materials and southern subduction of Paleo-South China Sea formed the extensional environment from the Oligoeene to the Early-Miocene and seafloor spreading of South China Sea began in the Early Oligocene. The three plates affected these north continental margin basins in South China Sea together since the Middle Miocene.