新构造活动的生态地质环境效应讨论——以扬子西缘西昌市为例

扬子西缘西昌市的环境变迁和地质灾害与新生代构造活动密切相关。该地区的新构造运动主要经历了5个阶段: ①青藏运动阶段(N_1-2, 11.6~3.6 Ma),强烈向东挤压,形成一系列的复式褶皱系,断裂带以挤压走滑活动为主; ②伸展断陷阶段(N₂—Q₁, 3.6~1.0 Ma),断裂带以斜张走滑活动为主,活动强度较弱,形成安宁河谷等断陷盆地; ③元谋运动阶段(Q_1-2, 1.0~0.6 Ma),进一步向东挤压,地壳逆冲增厚,早期褶皱山系加速隆升; ④构造松弛阶段(Q₂, 0.6~0.126 Ma),在安宁河谷等地区再次发生断陷作用; ⑤共和运动阶段(Q_3-4, 0.126 Ma至今),左旋走滑活动为主,褶皱山系整体缓慢剥蚀和抬升。西昌市的新构造运动具有强烈性、差异性、振荡性、继承性和新生性等特征。新构造运动导致了该区现今地貌格局,控制了山河湖泊的分布,形成了独特的局部气候,对土壤、植被等生态环境的影响十分显著。新构造运动也直接或间接地控制着本区地质环境的演化以及地质灾害和地震的发育。

Discussion on the eco-geo-environment effects of Neotectonic activities: A case study of Xichang City in western Yangtze block

The environmental changes and geological disasters in Xichang City of western Yangtze block are closely related to the Cenozoic tectonic activities. The Cenozoic tectonic movement in this area is divided into five stages. ① During the Qinghai-Tibet movement stage (N_1-2, 11.6~1.0 Ma), the strata were strongly squeezed to the east to form a series of compound fold systems, and the fault zone was dominated by compressional strike-slip activity.② During the extensional fault depression stage (N₂—Q₁, 3.6~1.0Ma), the fault zone was dominated by oblique strike-slip activity and the activity intensity was weak, forming faulted basins such as Anning river Valley.③ During the Yuanmou movement stage (Q_1-2, 1.0~0.6 Ma), the strata were further squeezed eastward to thicken the crust by thrusting, and the early fold mountain system accelerated uplift. ④ During the tectonic relaxation stage (Q₂, 0.6~0.126 Ma), the fault subsidence occurred again in the Anning river valley and other areas. ⑤ During the Republican movement stage (Q_3-4, 0.126 Ma to present), the left-lateral strike-slip activity was dominant, and the fold mountain system was slowly denudated and uplifted as a whole. The Neotectonic movement in Xichang City has characteristics of strong intensity, difference, oscillation, inheritance and neogenesis. And it led to the present geomorphological pattern in this area and controlled the distribution of mountains, rivers and lakes, which formed a unique local climate and had great impacts on soil, vegetation and other ecological environment. Besides, the Neotectonic movement also directly or indirectly controls the evolution of geological environment, and the development of geological disasters and earthquakes in this area.