珠江口盆地珠二坳陷文昌组构造差异性与动力学成因机制

Differential structure and dynamic mechanism of Wenchang Formation in the Zhu Ⅱ Depression of the Pearl River Mouth Basin

通过统计珠二坳陷主要基底断层的要素特征,并计算典型断层的活动速率,系统地研究了文昌组沉积期研究区构造差异性,探讨了差异构造的动力学成因机制。结果表明阳江—一统暗沙东断裂带控制研究区西部开平—顺德凹陷和东部白云凹陷的构造差异性,主要表现在前新生代构造环境、新生代基底断裂走向、文昌组断层活动性和凹陷结构等方面。开平凹陷北侧和白云凹陷南侧控凹边界断层在新生代早期可能属于同一条初始断裂带。研究区东西部前新生代不同的岩石圈结构导致了文昌组构造动力学成因机制迥异:西部开平—顺德凹陷中生代处于火山弧区,较厚的上部地壳高度脆性破裂同时被大量沉积物充填,形成北断南超型窄半地堑结构;东部白云凹陷中生代位于弧前区,地壳韧性变形较强,文昌组沉积物源相对不足,形成南断北超型宽半地堑结构。云开低凸起作为构造调节带,对其两侧的差异性构造变形具有调节作用。

We have studied the differential structure of the Zhu II Depression and its dynamic mechanism during the deposition process of the Wenchang Formation in the Pearl River Mouth Basin, by tabulating the key features of the major basement faults and calculating their typical activity rates. The results indicate that the Yangjiang-Yitong Fault Zone controlled the development of the prominent structural characteristics that differentiate between the western Kaiping - Shunde and eastern Baiyun sags. These differential characteristics mainly reflects differences in the pre-Cenozoic tectonic environment, Cenozoic basement fault strike, fault activity and structural type. It is inferred that the two sag-controlling faults in the northern Kaiping and southern Baiyun sags possibly belong to the same initial fault zone during the early Cenozoic. Lithospheric structural variations on either side of the Yangjiang-Yitong Fault Zone led to different geodynamic mechanisms for the Wenchang Formation. The Kaiping - Shunde Sags are located in the pre-Cenozoic volcanic arc area, where the thick and brittle upper crust is highly fractured and filled with large amounts of sediments in the Wenchang Formation, displaying the structural type of a narrow half-graben which faulted in the north and overlapped in the south. Albeit, the Baiyun Sags are situated in the forearc area where the crust deforms mainly in a ductile mode, forming a wide half-graben which faulted in the south and overlapped in the north. The Yunkai Low Uplift, an accommodation zone between the two sides, played a role in regulating the differential deformation of the two sides.