北京西山位于中朝陵台上。但是在古生代后期,西山中部发生了深大断裂而活跃化起来。使得在断裂带间地区的沉积建造构造变动岩浆活动及矿产分布等都接近了地槽区的型式。 西山最主要的深大断裂是沿百花山——妙峰山一带,以北东70°向横穿西山,长80公里,并向雨端延长,南部下陷,裂隙带大部被后来的堆积物和火山熔岩所掩埋。另一个是次要的,出露于房山城——坨里西——大灰廠——八宝山,向北东70°入于北京平原,裂隙带出露约四十里,北部下陷。这雨个断裂带使得西山中部逐渐下陷接受沉积,尤其是靠近断裂带,下陷幅度最大,沉积物最厚。 断裂深度达到矽镁层,在三叠纪末有大量玄武岩熔岩沿横穿西山的大裂隙上升溢出形成达二百余公尺厚的溶岩被。侏罗纪时有千公尺厚的安山岩流沿裂隙溢出,至白垩纪时又有厚达千公尺的酸性熔岩穹,并有多处酸性侵入岩。 西山的深大断裂,是从古生代后期开始,全部中生代都强裂活动着,在断裂带间的下陷地区,沉积着厚达四千七百公尺以碎屑物为主几乎全部含有火山物质的相变及厚度变化很大的中生代沉积物。加上上部古生代地层,總厚度超过了五千公尺。并且发生了强裂褶皱,断裂,变质及岩浆活动。 在断裂带所形成的下陷地区以外,没有上部古生代和中生代的沉积物,而这些下古生代主要是震旦纪地 Beijing Xishan is located in the cemetery in the North. However, in the late Paleozoic, a deep fault occurred in the middle of Xishan Mountain and became active. Which makes the tectonic alteration of magmatic activity and mineral distribution in the area between fault zones close to the type of the terrain area. The main deep fault of Xishan is along Baihuashan - Miaofeng Mountain area, crossing the Xishan Mountain at an angle of 70 ° to the east and 80 km long, extending to the rainy end and subsided in the south, where most of the rift zone is covered by later deposits Buried by volcanic lava. The other one was secondary and was exposed in Fangshancheng - Tuoli West - Dali Ash Plant - Babaoshan. It entered the Beijing Plain at 70 ° North East and the crevasse was about 40 miles out of the northern subsidence. This rain-prone fault led to the gradual subsidence of sediments in central Xishan, especially near the fault zone, with the largest subsidence and the thickest sediments. At the end of the Triassic period, a large amount of basaltic lava flows up and down along the large cracks that cross the Xishan Mountains to form a magma layer, reaching a depth of 200 meters. Jurassic a thousand meters thick andesite flow along the fissure overflow, up to the Cretaceous and thousands of meters thick acid lava dome, and a number of acidic intrusive rocks. The deep faults of Xishan started from the late Paleozoic, and all Mesozoic tectonic movements were active. In the subsidence area between the fault zones, almost 4,700 meters of detrital sediments were almost deposited with volcanic material Mesozoic sediments that vary greatly in phase change and thickness. Together with the upper Paleozoic strata, the total thickness exceeded 5,000 meters. And the occurrence of a strong crack fold, fracture, metamorphism and magmatic activity. Outside of the subsidence zone formed by the fault zone, there is no upper Paleozoic and Mesozoic sediments, which are mainly Sinian