北部湾盆地演化及局部构造成因机制研究

On the Evolution Process of the Beibu Gulf Basin and Forming Mechanism of Local Structures

为解决北部湾盆地区域构造演化及成因机制研究不足,局部构造认识存在差异等问题。文中利用二维、三维地震,结合重力、钻井等资料,阐明了北部湾盆地构造演化过程,明确了典型构造发育的成因机制。结果表明:(1)北部湾盆地具有两坳一隆的构造格局,即北部坳陷带、南部坳陷带和中部隆起带。控凹边界断层为大型低角度拆离正断层,分割变质核杂岩与上盘岩石,其中下盘穹隆状变质核杂岩由地壳中-高级古老变质岩及晚期岩浆岩组成(包括被拆离断层切割的含糜棱状岩石的剪切带,如碎裂岩、角砾岩、糜棱岩和片麻岩等);(2)受断裂伸展拆离,同时叠加晚期伸展应力旋转,乌石凹陷东区发育大型断层掀斜反转构造;(3)新提出"三明治"式地层充填模式下发育的顺层剪切走滑构造的形成机理。"三明治"式刚柔性岩石呈层状分布,在反转掀斜及后期应力场旋转叠加力的作用下,地层非常容易失衡,特别是在其界面处(刚柔界面、柔性界面内部)存在明显的物理力学差异性,二维层状滑动面摩擦阻力非常小,极易造成岩石的顺层剪切走滑。

In order to further understand the tectonic evolution and mechanism of the Beibu Gulf Basin,this study analyzes the process of tectonic evolution of the basin and the mechanism of typical structure development using 2 D/3 Dseismic,drilling and Bouguer gravity anomaly data.The results show that（1）the basin is characterized by two depressions and one rise,i.e.north depression,south depression and middle rise.The faults controlling the boundary of depressions in the Beibu Gulf Basin are large low-angle normal faults,separating metamorphic core complexes in footwall from hanging wall rocks.The metamorphic core complexes in footwall consist of the middle-and high-grade ancient metamorphic rocks and the late magmatic rocks,such as kataclasite,breccia,mylonite and gneiss in mylonitic rock-bearing shear zones.（2）A large inverted structure in the eastern part of Ushi depression was formed due to spreading detachment of faulting,superimposed by late stress rotation of the low-angle normal faults.（3）A formation mechanism of＂Sandwich strata filling＂mode is proposed for formation of bedding shearing strike-slip structure.The ＂Sandwich＂-mode flexible rocks occur as layers,which are subject to losing balance due to superposition effect of reversal tilting and late stress field rotation.Especially on the interfaces of the rigid or flexible rocks or within flexible interface exist distinct physical and mechanical difference,and the lower surface friction resistance of two-dimensional layered sliding surface can easily result in bedding shearing strike-slip.