南海东部古扩张脊的俯冲机制

SUBDUCTION OF THE PALEO-SPREADING-RIDGE IN EASTERN SOUTH CHINA SEA

南海东部古扩张脊处于欧亚板块和太平洋板块的汇聚地带,其东侧为马尼拉海沟、北吕宋海槽和西吕宋海槽,由于受到多个构造单元的相互作用,使其处于复杂的构造环境中。南海东部古扩张脊俯冲过程的研究对深入理解南海海盆构造演化、火山及地震活动等具有重要意义,同时也是今后南海构造研究的重要方向之一。在总结前人研究基础之上,探讨南海东部古扩张脊俯冲时间、俯冲深度及动力学过程。南海板块在16 Ma之后,由于菲律宾板块NW向仰冲的作用,使南海东部古扩张脊被动地沿马尼拉海沟进行俯冲,形成了现今马尼拉海沟中段的构造格局。古扩张脊俯冲深度为200~300km,并且在约100km处发生板片撕裂,造成古扩张脊两侧俯冲角度的不同。

The paleo-spreading-ridge of the eastern South China Sea,striking in NE50°,lying between the Eurasian plate and the Pacific plate（Philippine Sea plate）,is about 240 kilometers long from east to west and bordered with the Manila Trench,the North Luzon Trough and the West Luzon Trough to the east.Based on previous studies,this paper is devoted to the discussion of the subduction time,subduction depth and dynamic process of the paleo-spreading ridge.After 16 Ma,the paleo-spreading-ridge of the South China Sea was passively subducting along the Manila trench,forming the structural pattern of the middle segment of the Manila Trench.The depth of subduction was between 200-300 km,with slab tears happened at about 100 km,which resulted in the difference in subduction angle on both sides of the paleo-ocean-ridge.The subduction of the paleo-ocean-ridge is quite significant to the research of South China Sea＇stectonic evolution in the future.