洞庭盆地第四纪构造演化特征

摘要

通过地表观察和第四系钻探,以地貌和沉积为基础,对洞庭盆地及周缘地区第四纪构造活动特征进行了研究.认为第四纪洞庭盆地的构造演化经历了3个阶段.早更新世一中更新世中期洞庭盆地处于断陷阶段,区域构造活动的主要表现有:①盆地及次级凹陷边界受NNE、NW、EW和SN向等4组正断裂控制;②各次级凹陷强烈沉降并接受沉积,沉降中心位于凹陷内部或中央而远离边界断裂:断裂上盘局部可具明显沉降;③随着盆地逐渐扩张,断陷活动向东、西边缘迁移;④盆地断陷活动具幕式特征,总体可分为为早更新世早期、早更新世晚期和中更新世早一中期等3个裂陷幕;⑤盆地北面的华容隆起具明显构造沉降,盆地周缘其它隆起及盆地内部的赤山隆起具有脉动式抬升;⑥赤山隆起构造较稳定期和构造抬升期分别对应于安乡凹陷缓慢沉降期和快速沉降期.中更新世晚期以来洞庭盆地处于坳陷阶段,其中中更新世晚期洞庭盆地整体抬升并遭受剥蚀,在盆地东缘和西缘产生倾向盆地的构造掀斜,局部第四系变形形成褶皱;晚更新世一全新世洞庭盆地主体产生坳陷沉降并接受沉积,盆地周缘部分地区存在小幅度抬升.上述不同阶段构造活动特征可以通过盆地及周缘深部物质迁移以及板块尺度的物质运动和挤压来解释.%On the base of studies on the landforms and Quaternary deposits through detailed geologic mapping and borehole data, writers probed into the tectonic activities of the Dongting basin and its adjacent areas. Three stages of Quaternary tectonic evolution in the Dongting basin may be distinguished.Early Pleistocene-late Middle Pleistocene is a faulting－subsiding period for the Dongting basin, when there were tectonic movements as follows： ① the basin and its secondary sags were controlled by four groups of normal faults, i. e. , NNE-, NW-, EW- and SN-trending faults; ② every secondary sag subsided violently and received deposits with interior subsiding center far from boundary faults; ③ the faulting subsidence moved toward east and west margin of the basin for gradual expanding of the basin; ④ the faulting subsidence of the basin possessed episodic characteristics and can be divided into three faulting－subsiding episodes, i. e., early Early Pleistocene, late Early Pleistocene and early－middle Middle Pleistocene;⑤the Huarong uplift subsided observably, while other uplifts around the Dongting basin experienced pulsative rises; ⑥steady and rising period of the Chishan uplift corresponded with slow and rapid subsiding period of the Anxiang sag, respectively. The Dongting basin entered into a depressional phase since late Middle Pleistocene. The basin rose and were denuded in late Middle Pleistocene, while there occurred tectonic tilt on the east and west margine of the basin, and folds in Quaternary deposits were formed in part areas; Main body of the basin subsided for depression and received deposits during Late Pleistoncene－ Holocene, while there existed clear rise in part areas around the basin. These tectonic activities in different periods can be interpreted by deep matter transfer of the Dongting basin and its periphery, and by movement of the plate-scale material and compression.