莺歌海大型走滑盆地构造变形特征及其地质意义

Tectonic deformation features and petroleum geological significance in Yinggehai large strike-slip basin, South China Sea

在系统整理大地构造资料的基础上,研究莺歌海盆地隐蔽式走滑构造变形及其与沉积、超压、油气运移之间的关系。研究发现:(1)左行走滑伸展派生的局部张性破裂主要发育在距今10.5 Ma之前,这些破裂在东斜坡大型鼻状凸起大量分布,并在晚期流体超压作用下幕式活化,成为盆地斜坡地区油气垂向运移的主导通道;(2)右行走滑伸展有利于沉积速率增大和区域欠压实盖层形成,其派生局部张性破裂作用是底辟发育的诱发动力,而底辟发育又进一步放大局部张性破裂发育规模;(3)左行走滑作用在距今10.5 Ma开始减弱,产生北部挤压、南部旋转伸展(北挤南伸)的构造运动,造成盆地北部河内凹陷地层抬升剥蚀、南部莺歌海凹陷碎屑岩供应量激增,最终导致莺歌海凹陷在东、西非对称斜坡地貌上分别形成迁移式斜坡水道化海底扇和叠置式海底扇。

The subtle strike-slip tectonic deformation and its relationship to deposition,overpressure and hydrocarbon migration were studied on the basis of systematic sorting of tectonic data.(1)The local T(tension)fractures derived from sinistral strike-slip process were formed before10.5Ma,large in number in the nose structure of the eastern slope,and reactivated episodically under the effect of fluid overpressure in the late stage,they served as dominant vertical hydrocarbon migration paths in the slope area of basin.(2)The dextral strike-slip extension was conducive to the increase of depositional rate and formation of regional under-compacted seal,and induced generation of local T fractures which triggered the development of diapirs;in turn,the development of diapirs made T fractures grow in size further.(3)The sinistral strike-slip process weakened after10.5Ma,causing tectonic movement characterized by compression in the north and rotational extension in the south,and the uplift and erosion of strata in Hanoi sag and a surge in clastics supply for south Yinggehai sag.Finally,migrating slope channelized submarine fans and superimposed basin floor fans were developed respectively on the asymmetrical east and west slopes of the Yinggehai sag.