北京东部丰台顶一带地质构造特征

经过近期对燕山地区地质构造的调查研究 ,依据岩石、岩石组合、接触变质、矿化蚀变在空间上的展布、与燕山期侵入岩体的接触关系等证明 ,前人在丰台顶一带圈定的中生代潜 (次 )火山岩体 ,实际为陆相火山喷发 -沉积岩 ,属中生代早白垩世东岭台期酸性火山活动产物。在不足 4 0km2 面积中 ,发现了由多个构造推覆断片叠置而成的复杂构造堆叠体 ,卷入其中的既有太古宙片麻岩 ,也有中元古宙碳酸盐岩 ,还有中生代早白垩世东岭台期火山岩。其中 ,由东岭台组火山岩构成的 3个构造岩片夹于 4个由长城系、蓟县系碳酸盐岩构成的构造岩片之间。这些构造岩片具有不同的片内褶皱 (断片形成前的褶皱 )和岩片褶皱 (断片形成后的褶皱 )特征。以卷入叠覆构造的最高层位 -东岭台组为据判断 ,其为燕山晚期区域性收缩构造事件的产物。并由此预测 ,在北京东部大范围的中 -上元古宙沉积岩层中可能存在由碳酸盐岩构成的岩性相同产状相近的叠覆构造 ,亦可能在中 -上元古宙沉积层构成的推覆体下 ,隐伏有最高层位达下白垩统东岭台组的各时代地层和相关矿产。

Geology of the Area Around Fengtaiding Mount in the Eastern Part of Beijing Municipality

During our recent field mapping in Yanshan orogenic belt,a suit of acid eruptive rocks, which had been regarded as sub-volcanic or plutonic rocks for more than 30 years, were identified in the Fengtaiding area,Miyun County of Beijing. This volcanic suit belongs to Donglingtai Formation Formed in Early Creiaceous. In the area of less 40 km2 around Fengtaiding Mount, a very complex tectonic stack formed by several thrusting slices was recognized through geological mapping. The strata involved in the thrusting stack include Archaean gneiss,Mid-Proterozoic carbonate and the acid volcanic rocks of Early Cretaceous Donglingtai Formation.In geometry,the stack is composed of three slices of acid volcanics and four over-thrusting slices of Proterozoic carbonate.Meanwhile,both pre-thrusting and post-thrusting folds are recognized. The thrusting occurred in Late Yanshanian epoch because the newst strata involved in the deformation is Early Cretaceous Donglingtai Formation. Based on these observation and interpretation, we predict that the same style tectonic stacks may exist in the eastern part of Beijing Municipality where a lot of Proterozic carbonate strata expose. It is also very possible that some mineral resources within Mesozoic strata were covered by over-thrusting carbonate strata.