According to the control of Paleozoic present structure in North China, the faults in this area are divided into deep boundary faults. The first-order fault controls the uplift and depression areas; Secondary faults control or partially control the depression and uplift of the block; Inside the fault depression and fault uplift is a Tertiary fault (Table 2-6-2). Now the boundary deep faults and main faults are described as follows.
Table 2-6-2 Paleozoic Fault Elements in North China
sequential
I. deep boundary fault
1. Zhangjiakou-Pingquan fault
The fault is located at the northern boundary of the work area, with its middle section slightly protruding to the south, and the overall strike is near east-west, roughly extending along the line of 41north latitude, with a length of about 450km.
According to previous studies, the late Archean to Proterozoic should be the fault occurrence period. In Mesoproterozoic, an aulacogen trough with Jixian-Kuancheng as the center was formed on the south side of the fault, with a maximum sedimentary thickness of nearly 10,000 meters. The north side of the fault is relatively uplifted, which is basically a coastal zone, and the sedimentary thickness in most areas is less than 1000 meters. Therefore, Mesoproterozoic is an important fault contemporaneous period. In Paleozoic, the whole fault line showed different activities of the southern depression and the northern uplift, which blocked the northward invasion of Cambrian-Middle Ordovician and Middle Carboniferous-Permian epicontinental seas on the south side. At the end of Paleozoic, due to the influence of compressive stress on the north side, thrust deformation from north to south was caused, accompanied by the intrusion of acid magma. In Mesozoic, the inherited activities of faults were intense and frequent. First, a series of Jurassic small piedmont depressions were formed along the fault line, which accumulated to form continental coal-bearing basins, and then volcanic eruptions were widespread. From Cretaceous to Cenozoic, the fault activity was weak, and only local areas accumulated molasse-like formations.
Therefore, the fault was formed earlier, which obviously controlled the spatial distribution of sediments in Mesoproterozoic and Paleozoic, the structural strike and sedimentary characteristics of Yanshan uplift in Mesozoic.
2. Lishi fracture
The fault is located at the western boundary of the working area, mainly distributed in the east of the Yellow River and the west of Luliang Mountain, along the east path 1 10 15'. The working area is about 600km long. Macroscopically, the fault is huge in scale and extends far away, which is the dividing line between the North China Craton Basin and the Ordos Craton Basin. The overall strike of the fault zone is nearly north-south, but it is NNE or NNW locally. Faults are not simple faults, but are composed of several fault planes and tectonic rock belts between them. From south to north, it is composed of several sections with different characteristics and properties, and each section is basically connected by a pinch-out and lateral line. At the end of Triassic, the segments of the fault were connected into a whole, which greatly controlled the deposition and tectonic evolution on both sides. Sedimentation changed from Paleozoic to early Middle Triassic, with thick east and thin west, and thin east and thick west. Structurally, a complete large-scale sedimentary basin, Ordos Basin, has been formed in its west, with weak internal tectonic activity. In the east of the fault, there are some scattered small inland basins. Relatively speaking, the structure is much more complicated. Through analysis, the fault was formed earlier, which had certain influence on the deposition on both sides of Paleozoic. At the end of Triassic, due to the strong circum-Pacific tectonic activity, the Kula-Pacific plate subducted to the Eurasian plate, forming a northeast structural belt in North China. Lishi fault may be the western boundary of the area strongly influenced by this activity, and its eastern plate is strongly thrust westward at a high angle, while the tectonic activity in Ordos basin is weak westward.
3. Tancheng-Lujiang Fault
Located at the eastern boundary of the working area, the fault is a deep and large fault system, which runs through the eastern part of China and spreads to the northeast. The fault in the work area is as long as 1300km, connecting with Shenyang Yilan-Yitong deep fault in the north, passing through Qinling fold belt in the south and inserting into Jiangxi. The middle section of this fault runs from Changwei, Shandong Province to Wuhe, Anhui Province, commonly known as Yishu fault zone. It consists of four major faults: Changdian-Dadian, Anqiu-Juxian, Yishui-Tangtou and Tang Wu-Gegou. It has a second graben and a first basement, and its Mesozoic thickness can reach more than 3,000-6,000 meters ... The graben belt formed by the merger of two faults in southern Linyi extends southward. Huge Jurassic-Cretaceous sediments, mainly red clastic rocks and volcanic rocks, are accumulated in the graben and Hefei depression on the west side controlled by it, and the maximum thickness can reach about 7000m. The northern part of the fault is also two faults that pass through Bohai Sea and Liaodong Bay and continue to extend northward. The palaeozoic gap in the Dongerbao fault area of Liaohe River reached more than 4,000 meters. According to the analysis of existing data, the Tanlu fault may have formed earlier and was later influenced by the Kula-Pacific plate activity. At the end of Triassic, it was strongly active and twisted to the left, with the characteristics of horizontal thrust and strike-slip with the east plate facing north and the west plate facing south. The maximum translation distance reaches 2 10km (according to Xu Jiawei), and the magma and volcanic activity along the fault zone are strong. In Cenozoic, due to the change of regional stress field, the fault twisted to the right, resulting in dozens of thick Paleogene fault basins and several large faults parallel to the Tanlu fault in Bohai Bay area.
4. Luanchuan-Queshan-Fei Zhong Fault
This fault is located at the southern boundary of the working area, which is the boundary fault between the North China Basin and the Qinling fold belt. It is distributed in the northwest direction with a total length of 650km.
The northern part of the fault belongs to North China stratigraphic area and the southern part is Qinling stratigraphic area. These two areas are different in stratigraphy, paleontology, sedimentary facies and construction, metamorphism and structural characteristics. There are obvious differences in aeromagnetic anomalies. The aeromagnetic field in North China is a gentle positive and negative magnetic field area, and the Qinling area is a beaded positive and negative alternating magnetic anomaly area in the northwest. At the same time, from the gravity anomaly map, it can be seen that Luanchuan-Queshan-Fei Zhong area presents a dense gradient mutation zone. On the north side of the fault, there are thick intermediate-basic and intermediate-acid eruptive rocks in the early Mesoproterozoic. There are mixed granites in the fault zone, gabbro, granite porphyry, syenite porphyry, trachyte, Yanshanian granite and intermediate-acid small rock mass in Wuwang period and Jinning period. It reflects that the fault was active in Zhongtiaoshan period, Wuwang period, Jinning period and Yanshan period, and the nature of fault activity in each period was different.
Second, the primary fracture
1. Baodi-Luanhe fault
The fault is located in the northern part of the work area, starting from Huairou in the west, and entering Bohai Sea in Baodi and Luannan in the east longitude, with an east-west distribution and a length of about 320km. Many places along the line are flattened by NNE or NW faults, which is the boundary between Yanshan uplift area and Bohai Bay depression area.
The uplift plate on the north side of the fault, Quaternary and Neogene covered Mesoproterozoic or Paleozoic, and no Paleogene or Paleogene was found thin. The west of the fault is called Baodi fault, and the lower wall of Paleogene in Wuqing area on the south is more than 6000m thick, which is the northern boundary of Paleogene Jizhong depression. The eastern part of the fault is called Luanhe fault, and the bottom fault distance of Upper Paleozoic is 5000m, which is the northern boundary of Paleogene Huanghua Depression. The thickness of Paleogene on the south side of the fault is 3000 m m, which mainly controls Mesozoic and Paleogene deposits. It is speculated that the eastern part was formed in Mesozoic, but the main formation period is Cenozoic. This fault is also the dividing line of structural lines in different directions in the north of the work area. The structural line on the south side of the fault is nearly NNE, and the structural line on the north side is nearly EW.
2. Taihang East Fault
The fault is located in the middle of the work area and distributed in the northeast, with a total length of about 640km. From north to south, it can be divided into three faults: Huairou-Laishui, Dingxing-Shijiazhuang and Xingtai-Anyang, which are the dividing lines between Shanxi uplift and Bohai Bay depression.
Huairou-Laishui (Huang Zhuang-Gao Liying) fault in the northern section, the upper wall of which is Mesoproterozoic and covered by Quaternary; The footwall developed in Mesozoic, and the Tertiary system was thin. The fault zone obviously controls the Mesozoic-Cenozoic sedimentation.
The Dingxing-Shijiazhuang fault in the middle section is roughly distributed along the Beijing-Guangzhou railway, with a length of about 200km. The upper wall of the fault is Archean and Mesoproterozoic, covered with thin Neogene and Quaternary, and its thickness gradually increases from west to east, and it is 400 ~ 600 m near the fault. There is a thick Paleogene layer in the footwall of the fault, the thickest of which is over 5000 m; It has been confirmed by drilling that there are Jurassic-Cretaceous strata in Shijiazhuang area, and the thickness can reach 4000 meters.
Xingtai-Anyang fault in the southern section, from Luancheng in the southeast of Shijiazhuang to the south, passes through Gaoyi, Xingtai, Handan and Cixian to Xinxiang, with a total length of about 300km. The fault strikes nearly north and south, and it is a normal fault that dips eastward. The fault along the rising wall is a large anticline structure with gentle west and steep east. Archean and Proterozoic crystalline basement constitutes the core of Zanhuang area in the north, followed by Mesoproterozoic and Paleozoic in the two wings. The descending plate of the fault belongs to Mesozoic and Cenozoic, and it thickens from north to south in turn, reaching the thickest of more than 4000 meters in Tangyin area.
Generally speaking, the fault shows a gradient abrupt zone with heavy and dense magnetism. Shijiazhuang, Beijing and the southern section may have been formed in Mesozoic. In Cenozoic, it was connected into a large-scale regional fault that traversed north and south evenly.
3. Lanliao Fault
The fault is located in the middle of the working area, and the south section of the fault extends in the northeast direction, turning from north to northwest, which is called Qihe-Guangrao fault in Shandong Province. Lanliao fault, with a total length of 480 kilometers, is the dividing line between Bohai Bay Depression and Luxi Uplift.
The southern part of the fault is basically a normal fault with a drop of 3,000-4,000m, with a maximum drop of 6,000-7,500m. There is a huge Cenozoic cover above the Mesozoic remnants in the footwall, with the thickest reaching more than 5,000m. The upper wall lacks the Mesozoic and Paleogene, and only the Neogene with a thickness of several hundred meters directly unconformity covers the Paleozoic. A small amount of basic and acidic volcanic rocks are distributed near the fault. The gravity field and magnetic field show dense gradient abrupt zones. According to the sedimentary characteristics, magmatic activity and tectonic deformation, the Liaocheng section of the fault may have been formed in Mesozoic, and it was strongly extensional during the late Yanshan-Himalayan period, and the fault extended southward to the vicinity of Lankao.
The northern part of the fault (Qihe-Guangrao fault) is a normal fault that descends to the north, with a thick deposition in the descending Pangu system and a thin deposition in the ascending wall. According to the analysis, it may have been formed in Cenozoic, which controlled the sedimentary thickness of Paleogene to some extent.
4. Jiaozuo-Shangqiu fault
The fault is located in the south of the working area, generally in the northwest direction, and distributed along Jiyuan, Jiaozuo, Lankao and Shangqiu, with a total length of about 500km. The fault is basically a normal fault dipping to the south, with a maximum drop of 6000m, which is the northern boundary of Nanhua North Depression.
This fault cuts Archean to Jurassic in the west of Jiaozuo. A dynamic metamorphic rock belt of tens to hundreds of meters is formed along the fault, and secondary faults parallel to it are developed on both sides of the fault, which gradually descend from north to south, forming the boundary between the mountain area and the basin, with a relative height difference of nearly 1000 meters. The fault basically controls the Mesozoic and Cenozoic sediments in the east of Jiaozuo, and most areas in the north of the fault lack Mesozoic and Paleogene sediments. The Mesozoic-Cenozoic sedimentary thickness in Jiyuan-Kaifeng area in the south is several thousand meters.
Jiaozuo-Shangqiu fault is the dividing line between two tectonic lines in different directions in the south of the work area. To the north of the fault, the structural line is NNE or nearly NNE; The south side of the fault is nearly east-west or northwest. The difference of geophysical fields is also obvious. The magnetic field in the north of the fault is NNE or nearly NNE; The magnetic field in the south of the fault extends almost east-west. Through analysis, the fault may have formed earlier, and the activity was strong during Yanshan-Himalayan period.