摘要
燕山期造山事件广泛影响东亚地区的构造演化,其启动时间与构造变形样式还存在较多的争议。侏罗纪宁武-静乐盆地位于华北克拉通中北部吕梁山地区,处在华北平原盆地与鄂尔多斯盆地之间,是吕梁山-太行山内部NE-SW走向的向斜盆地,为燕山期陆内造山作用的研究提供了例证。本文通过构造变形分析、平衡剖面恢复与生长地层碎屑锆石年代学分析,厘定了侏罗纪宁武-静乐盆地构造变形样式、原型盆地性质与生长地层开始形成的时间,探讨了燕山期构造变形的盆山耦合效应。其中,盆地北段西侧发育断展褶皱与对冲构造;盆地中段西侧发育断展褶皱与背冲构造,中段东侧发育断展褶皱;盆地南段西侧发育断展褶皱与叠瓦状逆冲构造。中侏罗统云岗组(J_2y)与上侏罗统天池河组(J_3t)为生长地层,记录了侏罗纪宁武-静乐盆地的生长与变形过程,反映了该地区燕山期造山事件的作用过程。前生长地层构造变形反映的侏罗纪宁武-静乐盆地地壳缩短率在盆地中段为26.2%,南段为58.6%。碎屑锆石定年研究限定了该地区燕山造山作用的启动时间为～168 Ma。由此认为,华北克拉通中北部是中生代燕山期造山作用最显著的地区之一,燕山期造山事件是纵贯华北吕梁山-太行山造山带崛起的主因。
The Yanshanian orogeny has affected extensively the tectonic evolution of the East Asia, however, the beginning and the deformation patterns of the event are still hotly debated. The Jurassic Ningwu-Jingle Basin, a NE-SW trending syncline basin in the northern central part of the North China Craton, provides an example for the study of the Yanshanian Orogeny. The Ningwu-Jingle Basin is located in the Lüliang-Taihang Mountains between the North China Plain Basin and the Ordos Basin. In this paper, the structural patterns and the prototype of the Jurassic Ningwu-Jingle Basin are determined through tectonic deformational analysis and reconstruction of balanced cross-sections, and the basin-mountain coupling effects of the Yanshanian Orogeny are discussed through detrital zircon U-Pb dating of the growth strata. Structural geological investigation reveals different structural patterns in different parts of the synclinal Ningwu-Jingle Basin. Fault-propagation folds occur in both the west and east limbs of the synclinal basin. In the west limb of the syncline, face to face compressive structures, back thrusts and imbricate thrusts, occur in the northern part,the middle part, and the southern part of the basin, respectively. The growth strata consist of the Middle Jurassic Yungang Formation(J_2y) and the Upper Jurassic Tianchihe Formation(J_3t), recording the obvious formation and tectonic deformation of the synclinal Ningwu-Jingle Basin resulting from the Yanshanian Orogeny during the Middle to Late Jurassic. Crust shortenings recorded by the pre-growth strata are ca. 26.2%(or ca. 13 km) for the middle part and ca. 58.6%(or ca. 34.6 km) for the southern part of the synclinal basin, respectively. Detrital zircon U-Pb dating constrains the oldest age of the Middle-Late Jurassic growth strata at ca. 168 Ma, which suggests the triggering of the Yanshanian Orogeny at ca. 168 Ma. It is considered that the Yanshanian Orogeny in the Middle to Late Jurassic led to the uplift of the Lüliang and Taihang Mountains in the northern central part of the North China Craton.