山西太原西山东缘(晋祠-平泉)构造变形特征及其地质意义

Structural Features of the Eastern Margin of the Xi Mountain in Taiyuan,Shanxi Province and its Geological Significances

太原西山地区位于山西吕梁山‒太行山中部,其构造变形特征对于深入认识华北克拉通中部造山带中‒新生代构造演化过程及分析该地区水文地质条件具有重要意义。本次研究对太原西山东缘的晋祠‒平泉一带进行详细构造解析及相关构造模型分析。研究结果显示,以石炭系本溪组‒奥陶系峰峰组的区域不整合面为构造分界面,太原西山东缘奥陶系碳酸盐岩与石炭系‒二叠系碎屑岩的构造样式具有明显差异性。碳酸盐岩层主要发育近S-N向箱式褶皱及断层,碎屑岩层主要发育NE-SW向宽缓褶皱,NE-SW向断层对二者进行叠加改造。上述构造样式的垂向差异性是力学性质不同的岩层在区域构造演化过程中差异性变形的结果。综合分析表明,太原西山地区S-N向和NE-SW向构造形迹形成于华北克拉通中部燕山期陆内造山作用的不同阶段,其区域应力场表现为早期近E-W向(或NWW-SEE向)挤压和晚期NW-SE向挤压,具有“顺时针”演化特征。将野外观测结果与水文钻孔数据相结合,初步构建研究区的构造模型。模型结果显示,近S-N向断层和NE-SW向断层为研究区内主要断裂体系,直接控制了节理等次级裂隙的产出特征,对于太原西山地区的古岩溶作用、岩溶地下水强径流带和强富水区的分布具有明显控制作用。

The structural features of the Xi Mountain in Taiyuan,which is located between the Lüliang Mountain and the Taihang Mountain in Shanxi province,are of great significance to understand the Mesozoic to Cenozoic tectonic evolution of the central orogenic belt of the North China Craton as well as the regional hydrogeology.In this contribution,detailed structural analyses and modeling have been carried out on the eastern margin of the Xi Mountain in Taiyuan.Our results show that the Ordovician carbonate strata and the Carboniferous-Permian clastic strata,which are separated by a regional disconformity between the Carboniferous Benxi Formation and the Ordovician Fengfeng Formation,have quite different structural patterns.The S-N-trending box folds occur in the Ordovician carbonate strata,while broad,NE-SW-trending folds exist in the Carboniferous-Permian clastic strata.This different structural patterns of these two strata can be attributed to their difference in mechanical properties.These two structural sub-layers are cut and influenced by the later NE-SW-trending faults.These structures in the Xi Mountain may be formed during different tectonic stages of the early Yanshanian in the intra-continental orogeny,the central part of the North China Craton.The stress fields in the study region underwent a clockwise rotation,with nearly E-W(NWW-SEE)compression in the early stage,and followed by NW-SE compression in the late stage.Combined with the field observations and regional hydrogeological investigations,a structural model is established.This model shows that,as the major fracture systems in the study region,the S-N-trending and the NE-SW-trending faults directly control the occurrences of joint systems,the distributions of paleo-karsts and groundwater runoff zone and water-enriched regions around the Xi Mountain.