周口店黄院东山梁构造变形特征及其地质意义

Structural Deformation in the East Ridge of Huangyuan,Zhoukoudian and Its Geological Significance

针对周口店黄院东山梁一带青白口系和下古生界构造变形进行的详细解剖分析一直未见有文献报道。通过对东山梁构造变形现象进行反复多次的详细观察,发现东山梁中段寒武系张夏组鲕粒灰岩层位重复出现,但鲕粒未发生变形,经追索表明该层位存在逆冲断层重复和破坏;同时,东山梁南段采石场掌子面可见青白口系景儿峪组薄层大理岩和寒武系府君山组灰岩构成的小型斜歪倾伏褶皱,上覆寒武系馒毛组中发育由NNE向SSW推覆的逆冲褶断,使部分层位缺失,褶断带内岩石存在韧性变形等构造现象。这一观测成果修正了前人研究认为东山梁一带只存在大量折叠层、而断层发育欠佳的认识,也为北京西山地区区域地质演化研究提供了一定的科学佐证。

Detailed analysis of the structural deformation in the Qingbaikouan and Lower Paleozoic erathem in the East Ridge of Huangyuan has not been reported. A recent field observation yields that the oolitic limestone in Zhangxia Formation in the middle of East Ridge occurs repeatedly with its ooides insignificantly deformed, leading to a new detection of thrust faults in Zhangxia Formation. In addition, a small-sized inclined plunging fold, which is composed of the Cambrian Fujunshan Formation and the Qingbaikouan System Jing＇eryu Forma- tion outcroping on the excavating face of a quarry in the East Ridge, is characterized by fault contact between one of its limbs and Cambrian Manmao Formation over it. The fault thrust SSW-ward causing the absence of cer- tain strata as well as ductile deformation in wall rocks. These phenomena rectify the previous view of single- stage structural deformation dominated by folds in the East Ridge of Huangyuan, and a new hypothesis of multi- stage deformation starting with folding followed by fault thrusting is put forward. The hypothesis is valuable for a better understanding of the regional structural evolution in West Hills of Beijing.