从柳江盆地前陆剖面平衡看“吴庄背斜”和“柳江向斜”的构造属性

Tectonic Attributes of the “Wuzhuang Anticline” and the “Liujiang Syncline” from Balanced Foreland Sections in the Liujiang Basin

摘要: 根据柳江盆地典型剖面的演化平衡剖面(剥蚀)恢复，认为柳江盆地可以分为西部冲段带系统、中部覆盖区系统、东部非覆盖系统三个区域性构造带，其中的西部冲段带系统可以在分为四个三级构造带。推覆褶皱区的形态整体上属于“断弯褶皱”，上部外来地体的覆盖范围达到5 km以上，覆盖了柳江向斜的大部分地域，经历大规模的覆盖、压陷及剥蚀后形成现代残留结构。柳江盆地西部的整体结构的核心属性应该是冲断带，是坡坪式构造的外来地块断弯褶皱作用的结果，西部冲断带分为寒武纪远程抬升系统、奥陶纪直立系统、石炭纪二叠纪冲断楔形系统三个部分构成。整体性的“宏观褶皱”属于断层相关褶皱。在冲断带的最西部存在向西倾斜的断阶导致了地层的系统性向西陷落和倾斜，形成和背斜体系的“地层向西变新”的整体性格局。黑山窑路线可以认为属于前陆压陷盆地结构中柳江单斜的“缩影”，反映呈现逐渐向西加强的压陷作用，柳江盆地的核心凹陷从属性上不是向斜凹陷，不属于和吴庄背斜共同组成的“背斜–向斜”组合型盆地，而是前陆压陷(单斜)凹陷，可称为“柳江单斜”。

Abstract: Based on the evolution equilibrium profile (erosion) restoration of the typical section of the Liujiang Basin, it is believed that the Liujiang Basin can be divided into three regional structural belts: the western erosion section system, the central coverage area system, and the eastern non-coverage system. Among them, the western erosion section system can be further divided into four tertiary structural belts. The morphology of the erosion fault zone is generally of the “fault-bend fold” type. The coverage range of the upper allochthonous terrane reaches more than 5 km, covering most of the area of the Liujiang syncline. After undergoing large-scale coverage, subsidence, and erosion, it forms the modern residual structure. The overall structure of the western part of the Liujiang Basin should be an erosion fault zone, which is the result of fault-bend folding of an allochthonous block in a ramp-flat structure. The western erosion fault zone is composed of three parts: the Cambrian long-distance uplift system, the Ordovician upright system, and the Carboniferous-Permian erosion wedge system. The overall “macroscopic fold” belongs to the fault-related fold structures. At the westernmost part of the erosion fault zone, there is a westward-sloping fault step, causing the systematic westward subsidence and inclination of the strata, forming an overall pattern of “strata becoming younger westward” in the anticline system. The Heishanyao route can be regarded as the “snapshot” of the Liujiang single anticline in the foreland subsidence basin structure, reflecting the gradually strengthening subsidence effect moving westward. The core depression of the Liujiang Basin is not an anticline depression in terms of its attribute, and does not belong to the “anticline-syncline” combined basin formed together with the Wu Zhuang Anticline, but is a foreland subsidence (single anticline) depression, which can be called “Liujiang Single Anticline”.