(1) The southern and internal structural boundaries of the North Huaiyang structural belt.

The structural boundary between the North Huaiyang structural belt and the Tongbai-Dabie metamorphic complex uplift is considered to be the Mozitan-Xiaotian fault zone, and also the contact zone between the former Foziling Group, the former Luzhenguan Group and the Dabie complex. Xu Shu (1994) classified it as the collision suture zone between the North China plate and the Yangtze plate. In Henan Province, the tectonic position corresponding to this boundary should be the boundary zone between Sujiahe Group and Dabie Complex. According to the geological records of Henan (1989), the former Sujiahe Group is not integrated on the Dabie complex, and the boundary between the former Sujiahe Group and the former Xinyang Group is the Neixiang-Tongbai-Shangcheng fault. Therefore, these two faults are not one fault, but have different attributes, which are described as follows.

The Mozitan-Xiaotian fault zone (F2) starts from the north of Jiu Feng at the junction of Henan and Anhui in the west, reaches Mozitan in Huoshan County and Xiaotian in Shucheng County in the east, and is cut off by the Tanlu fault zone in Lujiang. The Dabie complex is located on the south side of the fault zone, and the north side is the Yuanluzhenguan Group, the former Foziling Group and the Carboniferous, cutting the continental volcanic basin of the Late Jurassic. There are mylonite belts and vitrified rocks with a width of 2 ~ 5 kilometers on the fault zone. The profile is inclined to the north, with an inclination angle of 50 ~ 80, steep on the top and gentle on the bottom, showing a wave shape. Because the mylonite in the fault zone was cut by vitrified rock, the mylonite in the early tectonic rocks fluctuated and the north wall of the fault showed the characteristics of multiple slips, which indicated that the fault had multi-stage activities. In addition, there are obvious manifestations in the field of geophysics. Recently, through the mapping study of1:50,000 area, new discoveries have been made: ① In the original Dabie complex distribution area on the SE side of the fault zone, the Foziling rock group was found in Liaoyewan, Guanzhuang and Shenqiao areas of Tongcheng. Generally, it is NWW strike, with a width of about 2 ~ 10 km, and it is distributed parallel to the south side of the fault zone. Author Jing et al. (Tong Jiafu et al.,1995; Qian Cunchao et al., 2000), a detailed study shows that there is a stable rock assemblage from bottom to top, which consists of dolomite marble (gravelly marble)-quartzite-banded biotite amphibole schist, which is equivalent to Xianrenchong Formation (marble)-Xiangyunzhai Formation (quartzite)-Zhufo 'an Formation (biotite amphibole schist with green curtain). The newly discovered Foziling rock group in Liaoyewan and Shenqiao has undergone strong deformation and transformation, and was wrapped by Dabie complex, and was later invaded and destroyed by granite. ② The fault zone extends eastward to Tongcheng, which is not obvious. The Dabie complex on the south side of the fault zone is indistinguishable from the deformed and metamorphic intrusions in the Yuanluzhenguan Group on the north side of the fault zone in terms of rock properties, structural deformation, formation age and inclusions, and the fault zone has gradually disappeared. To sum up, the Mozitan-Xiaotian fault zone is mainly a ductile-brittle fault zone formed in Mesozoic, which controls the distribution of Mesozoic continental basins. The discovery of the Foziling rock group on the south side of the fault zone and the discontinuity of the fault strike indicate that it belongs to a non-zonal structural interface, not to mention a plate collision suture zone.

In Henan, the fault zone equivalent to Mozitan-Xiaotian has not been confirmed. Neixiang-Tongbai-Shangcheng deep fault (F3) is located in the west of Nanyang fault basin and extends to Shaanxi. It is a Yangshan deep fault with the strike of 280 ~ 3 10 and the profile inclines to the north. The southern plate is the Douling complex, and the northern plate is equivalent to the original Xinyang Group, and its tectonic position corresponds to the Mozitan-Xiaotian fault zone. To the east of Nanyang fault basin, it is nearly east-west, inclining northward with an inclination of 45 ~ 85, and disappears eastward in Shangcheng granite body. The south panel is the original Sujiahe Formation and the north panel is the original Xinyang Formation. Because the former Sujiahe Group is equivalent to the former Luzhenguan Group, this fault zone not only cannot be connected with the Mozitan-Xiaotian fault, but also belongs to two faults with different stratigraphic units. Therefore, Tongbai-Shangcheng fault should be located in the north of Mozitan-Xiaotian fault. The mylonitization and schistosity zone of this fault zone is very wide. The author found a structural schist with a width of several thousand meters in Jigongtan area of Xinxian County, indicating the characteristics of northward sliding fault. However, stratigraphic cutting shows that it is not the southern boundary of the North Qinling structural belt, but a fault in the North Huaiyang structural belt. Therefore, it is the key to understand the nature of the contact relationship between the original Sujiahe Group and Tongbai Complex and Dabie Complex. According to the geological records of Henan Province (1989) and the geological data of1:200,000 new county sheets, it is confirmed that the original Sujiahe Group was not integrated on Tongbai complex and Dabie complex, but no exact sketch data was found. On the geological map of1:50,000 Tongbai map, it is considered that they are in ductile fault contact, but they are not specified. 1∶ 50,000 In the northern part of Xuanhuadian, the former Wan Hu Formation was classified as a structural melange, which contains eclogite blocks of different sizes, and this stratum still extends southward. After entering Xiongdian in the southern part of Xuanhuadian, the surrounding rock associated with eclogite is called the original Hongan Group (see Figure 2-6). It can be considered that the former Sujiahe Group at the junction of Henan and Hubei has been integrated, and its structural boundary properties with Tongbai complex and Dabie complex need to be further studied and determined. However, according to the data of1:50,000 Mu Zi store, it is found that the Dabie complex is in contact with the original Sujiahe Group in a ductile detachment fault, with a width of several kilometers and a gentle dip to the north, which may be equivalent to the Mozitan-Xiaotian fault zone.

It should also be noted that in the Tongbai area in the western section of the North Huaiyang structural belt, the boundary between the north belt (equivalent to the North Qinling structural belt) and the middle belt (equivalent to the North Huaiyang structural belt) is called the Tongbai-Songba fault zone (F 1), which enters Shaanxi in the west and is equivalent to the southern boundary of the Shangdan belt, and connects the Shangcheng-Shucheng fault zone and Zhang Guowei in the east (20065438+). The geological record of Henan is called Zhenping-Guishan-Meishan Fault (F4). According to relevant data, the fault zone is located in Tongbai and its west, that is, along both sides of Songba fault, forming the boundary between Tongbai complex and the original Xinyang Group in the south, Qinling complex and Erlangping Group and Fengdan Group in the north, which is considered as the boundary between the northern and southern Qinling tectonic belts. Extending eastward, its nature is unknown. Especially in Guishan-Meishan area east of Yang Zixin, through recent mapping and the author's research, it is found that: ① The breccia marble exposed in Caijiaao, Xinyang Shuixian Bridge, Mafan, Shangchengwaimiao and Jinzhai Chuanbanchong in Tongbai is considered as a tectonic melange zone because it contains a large number of structural blocks such as basic rocks and granites. According to the author's observation, the basic rocks, acid rocks and surrounding rocks in these structural blocks have obvious intrusive thermal alteration phenomenon (Figure 2-24), which can be considered as the product of structural fracture after intrusion. This gravelly marble stratum is stable, which has been determined as the northern wing of Zhufo 'an superimposed syncline by structural anatomy in North Huaiyang, Anhui Province, and is the same as the Xianrenchong Formation in the south, so it cannot be considered as a structural melange belt. ② Rock equivalent to Qinling complex was found in Mafan, Shan Zhinan, Henan Province, and deformed metamorphic granite with quite different complex was also found in Nanxiyuan, Jinzhai, Anhui Province. Therefore, it is necessary to re-understand the nature of metamorphic basement in the lower part of Beihuaiyang structural belt. ③ In Meishan (Jinzhai) area in the east of Guishan-Meishan fault zone, the original Meishan Group (now classified as the lower stratum of Foziling Group) was cut by a fault, which belongs to a brittle fault. To sum up, this fault zone may be the boundary between the surface geology and the deep structure of the lithosphere in the Qinling orogenic belt (Zhang Guowei 200 1), but the Guishan-Meishan fault in the east is only a fault in the North Huaiyang structural belt. In this regard, further research is needed.

Figure 2-24 Contact Relationship between Serpentine Ultrabasic Rock and Marble in Mafan Marble Stope, Guangshan County

① Basic-ultrabasic rocks; ② white marble; ③ Black marble; ④ Alteration zone