Figure 2.2 Tectonic Outline Map of Henan Province
The geological characteristics of each structural unit are briefly described as follows.
1) North China landmass. The southern boundary is Luanchuan-Minggang ductile shear zone, and the basement is metamorphic rock series with different metamorphic degrees in Neoarchean and Early Proterozoic. The caprock includes Mesozoic-Neoproterozoic shallow-sea facies clastic rocks-carbonate rocks, Cambrian-Middle Ordovician Guang Hai carbonate rocks, Carboniferous-Permian marine-continental coal-bearing clastic rock series, Mesozoic-Cenozoic intracontinental rift basin deposits (mainly terrigenous clastic rocks and various genetic types of loose accumulations). There are three large-scale structural zones in the continental block: Jiyuan-Jiaozuo fault zone, which is a normal fault inclined to the south formed in Cretaceous; Sanmenxia-Lushan thrust belt is a north-south thrust nappe belt formed in Cretaceous. Machaoying-Queshan ductile shear zone is a multi-stage active structural zone. In the southern part of the landmass, Jinning subduction granite and post-Yanshanian orogenic granite are developed.
2) North Qinling fold belt. It is an active continental margin in the southern part of the North China Plate and a part of the Variscan-Indosinian fold belt. The northern part is the Kuanping Group, which is deposited in the rift of Mesoproterozoic continental margin. The middle part is Erlangping Group in the early Paleozoic rift ophiolite belt and Shishuyuan Formation and Xiaozhai Formation deposited with flysch in the late Paleozoic. In the south, there are Qinling Group deposited on the paleoproterozoic continental margin, Xiahe Group deposited on the Neoproterozoic continental margin, and marine carbonate xenoliths of the Paleozoic Yanlinggou Formation. There are two large tectonic belts between the above three parts: Waxuezi-maoji upper crust thrust belt, which is a late Paleozoic-Triassic southward nappe belt; Zhuyangguan-Dahe ductile shear zone is a multi-stage active tectonic zone on the crust. Paleozoic arc granite and collision granite are developed in this belt. The Zhenping-Guishan ductile shear zone in the southern margin of this zone is a multi-stage active ultracrustal tectonic zone.
3) South Qinling fold belt. It is a passive continental margin of the northern margin of the Yangtze plate and a part of the Variscan-Indosinian fold belt. This belt has Yangtze basement, and shallow sea facies developed from Sinian to late Paleozoic. There are three major structural zones in this zone: Xixia-Zhoudang ductile shear zone is an upper crustal structural zone, which separates the Guishan Formation from the Nanwan component; Neixiang-Shangcheng ductile shear zone is a super-crustal structural zone, which separates Nanwan Formation from Sujiahe Group. The Dadouling-Wan Hu structural belt is an upper crustal fault, which separates Sujiahe Group from Douling Group and Dabie Group. Neoproterozoic arc granite, collision granite, Caledonian and Variscan acid rocks and basic-ultramafic rocks are developed in this zone.
The evolution history of geological structure in Henan Province is quite complicated. Since the New Archean, it has experienced nine cycles of tectonic activity, including Songyang period, Zhongtiaoshan period, Wuwangshan period, Jinning period, Caledonian period, Variscan period, Indosinian period, Yanshan period and Himalayan period, which can be merged into six major tectonic development periods and finally formed the present structural features. Songyang cycle to Zhongtiao cycle is the development period of geosyncline, also known as the pre-orogenic stage. From Wuwangshan cycle to Indosinian cycle, geosynclines and platforms coexist, also known as orogenic stage; Yanshan cycle to Himalayan cycle is the development period of continental margin active belt, also known as post-orogenic stage.
Songyang cycle is a period of all-round crustal activity, and its volcanic deposits formed two continental cores, Hehuai and Tongbai-Dabie, through Songyang movement, and formed geosynclines in Songji area of the northern Hehuai continental core. To the south of Hehuai land core, the vast Qinling area around Tongbai-Dabie land core becomes a primitive geosyncline. Midvein cycle is a stage of rapid growth of continental crust. At the end of the cycle, midvein fold orogeny and two geosynclines were folded, and the basement of China-Korea paraplatform was formed in the north. The development history of the original dominant geosyncline has ended in the South Qinling area, and the oceanic crust active zone has been pushed to the South Qinling and its south. Most parts of Henan province have been transformed into continental crust, and the north-south differentiation was already obvious at that time. During the Wuwangshan cycle, the initial continental crust began to disintegrate under the influence of the violent activities of deep faults. The Hua Xiong area on the southern margin of the Sino-Korean paraplatform sank, forming a platform margin depression. Xixia-Nanwan area in the central part of the former Qinling fold system was rifted into a faulted geosyncline. The Wuwangshan movement made the Hua Xiong platform edge sag and fold, and the China-Korea paraplatform entered the platform evolution stage. After the Xixia-Nanwan fault depression geosyncline returned to the fold belt, the geosyncline moved southward to the South Qinling area, forming a depressed geosyncline. At the same time, the Erlangping-Liushanyan area in the northern Qinling Mountains is a faulted geosyncline. At the early stage of Jinning cycle, the optimal geosyncline and fault geosyncline developed simultaneously. Strong Jinning movement, the upper geosyncline of South Qinling folded and turned into geosyncline; The Erlangping-Liushanyan fault depression geosyncline began to fold after Caledonian movement. After Jinning Movement, the whole province of Henan ended the development history of oceanic crust and became continental crust. The late Jinning cycle-Variscan cycle is the evolution stage of the South Qinling geosyncline. The Variscan movement at the end of Carboniferous uplifted the folds of the South Qinling geosyncline and the North Huaiyin fault depression, and the inner Qinling geosyncline in Henan finally closed and turned into a fold belt uplift. Yanshan cycle is another important change period in the history of geological structure development in Henan Province. The strong Yanshan movement completely folded the cover of the paraplatform, ending the development stage of the paraplatform between China and North Korea and resuming its activities. At that time, there was not much difference between the Sino-Korean paraplatform and the Qinling fold system in Henan. Since the late Yanshan cycle, under the influence of the Pacific active belt, the western part of Henan Province has been uplifted into a mountain, and the eastern part has been rapidly subsided, forming a depressed basin, which has become an integral part of the active belt of the eastern continental margin of China, forming the structural and geomorphological characteristics of Henan Province.
Looking at the development and evolution of geological structures in Henan Province, there are the following rules: in terms of time, two tectonic movements, Zhongtiaoshan and Yanshan, are important turning points in the evolution process of nine tectonic stages. From old to new, they can be roughly divided into three tectonic development periods: geosyncline (Songyang-Zhongtiaoshan cycle), coexistence of geosyncline and platform (Wuwangshan-Indosinian cycle) and continental margin active belt (Yanshan-Himalayan cycle). There is a sudden change between each development period, and its starting and ending time is not consistent everywhere. Each development period has a unique development process, forming a unique sedimentary formation combination, magmatic rocks, structural deformation and minerals. From a spatial point of view, before Mesozoic, the geological structure of Henan Province was obviously differentiated, and the general trend of geosyncline backflow and continental crust growth was to advance from north to south in turn, but due to crustal extension and deep faults, local northward movement often occurred. Since Mesozoic, the east-west differentiation of geological structures in Henan Province is remarkable, with strong activity in the east and relative stability in the west, which reflects the unbalanced development of geological structures in Henan Province. During its evolution, deep faults played an important role in controlling its evolution (Henan Bureau of Geology and Mineral Resources,1990; Lin Dechao et al., 1998).