琼东南盆地半地堑特征及其动力学探讨

Characteristics of Half-Grabens in the Qiongdongnan Basin and Their Dynamic Implications

利用琼东南盆地的反射地震剖面等资料,对其中具有代表性的崖北、北礁凹陷等半地堑的几何学、运动学特征进行分析,划分出旋转半地堑、滚动半地堑和多米诺式半地堑系3种类型,认为半地堑经历了中始新世-早渐新世、晚渐新世-早中新世两个演化阶段,并且在时间上有东早西晚,空间上有"东西分块、南北分带"的特征。在盆地半地堑组合特征及区域构造分析的基础上,指出盆地的发育与演化主要受古太平洋板块俯冲带后撤、红河断裂的左行走滑和南海海盆扩张的联合作用影响,表现为裂陷前期(Tg-T7)主要受古太平洋板块俯冲后撤及红河断裂的左行走滑联合作用,后期(T-T)主要受南海海盆海底扩张作用影响;而盆地张裂是通过纯剪切作用完成的。

The Qiongdongnan basin is a Tertiary extensional basin developed on the north margin of South China Sea,with a main structural style of half-grabens.Three types of half-grabens,which are rotational,rollover and rotational,have been identified after analyzing the geometry of the half-grabens from the seismic sections in the basin.The half-grabens mainly experienced two evolutionary stages,which were from middle Eocene to early Oligocene and from late Oligocene to early Miocene.Meanwhile,the half-graben＇s evolution featured differently in time and space：1） it took place earlier in the east than in the west,2） it developed with zonation in NS direction and segmention in EW direction.The tectonic history of the basin shows two stages of extension based on the integrated research of half-grabens and regional tectonic dynamics.The first stage of extension （Tg-T7） may be related to the rollback of the Paleo-Pacific subduction plate in Late Cretaceous and sinistral slip of the Red River fault zone in the Eocene,The second stage （T7-T6） is mainly controlled by the south-northward seafloor spreading from 32Ma to 17 Ma of South China Sea.In addition,symmetrical distribution of the half-grabens and crust structure indicated the stretching style of the basin is pure shear.