geological structure

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The shape left over from the deformation and displacement of rock layers in the earth's crust due to crustal movement. Geological structures can therefore be divided into primary structures (primary structures) and secondary structures (secondary structures or tectonic structures) according to the time of their formation. Secondary structures are the main object of structural geology research, while primary structures are generally used as a benchmark to judge whether rocks are deformed and how they are deformed. Geological structure (referred to as structure): A general term for the shape of various components of the earth's crust or lithosphere and their mutual combination and facial features. The scale of geological structures, as large as thousands of kilometers, requires comprehensive analysis of geological and geophysical data and interpretation of remote sensing data to identify, such as lithospheric plate tectonics. Small ones, measured in millimeters or even microns, require the help of an optical microscope or an electron microscope to observe, such as mineral grain deformation, crystal lattice dislocations, etc. Guizhou is located within the South China Plate, between the East Asian Mesozoic orogenic belt and the Alpine-Tethys Cenozoic orogenic belt, spanning two tectonic units, the Yangtze continental block and the Nanhua active belt. In the known geological historical period of 1400 Ma, it has experienced five stages: Wuling, Xuefeng, Caledonian, Variscan-Indosinian, Yanshan-Hishan. The Xuefeng movement laid the foundation of the Yangtze continental block. The Guangxi movement caused the fold uplift in the southeastern Guizhou area to fuse with the Yangtze continental block. Later, it experienced rifting and subduction. The Yanshan movement established the basic structure of today's structure. Under the changing geostress conditions, the geostress field of multiple orogenies has formed three types of structural types: extrusion type, straight twisting type and twisting type, intertwining into a complex and changeable strain image. Its characteristics are: (1) The geological structure of Guizhou is an intraplate structure, and the main body of the structure is a thin-skinned structure. (2) The deformation is not very strong. The most complete and extensive structural style developed in Guizhou is the Jurassic fold belt. Duyun Sports: It was originally named by the Eighth Census Brigade of the Ministry of Land and Mineral Resources (1980) and refers to a crustal movement that occurred in central and southern Guizhou between the end of the Ordovician and the beginning of the Silurian. The performance of the movement is: In the central Guizhou area between the Bijie-Zunyi-Metan-Tongren connection and the Guiyang-Shibing connection, the middle and upper parts of the Upper Ordovician are generally missing, and the middle and upper parts of the Lower Silurian and different layers of the underlying Ordovician are pseudo-integrated. In many areas, such as near Wudang, Guiyang, the conglomerate layer or gravelly claystone at the bottom of the Silurian can be seen embedded in discontinuous surfaces that are several meters undulating. In the southern Guizhou area, the middle part of the Lower Silurian overlies different layers of the Ordovician, with hundreds of meters of missing strata. Basal conglomerate is common at the bottom of the Silurian, and weathering crust is seen in some areas. This is a large-scale lifting movement. Dushan uplift: Named by Wang Yue in 1994, it refers to the uplift movement between the Jiwozhai section of the Dushan Formation and the underlying Songjiaqiao section of the Middle Devonian Dushan Formation in the Dushan area. There is a weathered residual limonite layer at the bottom of the Jiwozhai section of the Dushan Formation in this area, and above it is bottom conglomerate. In addition, based on the regional comparison of trace fossil assemblages, it can be confirmed that the upper part of the Songjiaqiao section of the Dushan Formation has been weathered and denuded to varying degrees. The bottom of the Jiwozhai section lies directly on the uneven base. All these indicate that after the deposition of the Songjiaqiao section of the Dushan Formation, there was an extremely extensive and obvious upward movement of the crust. Guizhou-Guangxi Movement: Named by Zhao Jinke et al. (1959), it originally referred to the pseudo-integration between the Qixia Formation and the Maping Formation in Guangxi. In most areas of Guizhou, except for some areas, the Maping Formation and the overlying Liangshan Formation and Qixia Formation are pseudo-integrated, so this name is still used. According to my country's latest geological chronology, this movement occurred between the Middle and Lower Permian. Bihen movement: Named by Lin Shuji (1994). The named place is Qinglong Bihen Camp. There, obvious folds and faults occurred in the early Early Pleistocene strata (such as the Pingdi Formation), and the stratigraphic dip angle locally reached 50°~70°, but the overlying middle and late Early Pleistocene sediments were not deformed. The tectonic movement that will deform the sediments of the middle and late Early Pleistocene and the late Cenozoic before it is called Bihen movement. Based on the analysis of existing data, it roughly occurred about 1.5 to 1.2 million years ago. It was the most intense tectonic movement that occurred in the late Cenozoic era in Guizhou, and is roughly comparable to the "Yuanmou Movement" in Yunnan. This movement began a new period in which Guizhou's crust was tilted and uplifted from west to east. Guizhou Jura Mountain-type fold belt: The Jura Mountain-type fold belt is characterized by different deformation intensities of anticlines and synclines. Closed folds and open folds are alternately juxtaposed. The representative structures are barrier-type and trough-type folds. The Jurassic fold belt occupies most of the Yangtze continental block in Guizhou, and the strata involved in the fold belt range from the Mesoproterozoic to the Mesozoic. Although there are various fold styles, trough-type folds are the most developed and typical. It is composed of a series of tight synclines and gentle anticlines alternately arranged in parallel, arranged in a wild goose shape in plane and section. In a wide range, thrust faults parallel to the fold axis (mainly the anticline axis) are generally developed, and together with the above-mentioned folds, they form a fold-nappe structure. The occurrence of thrust surfaces is generally gentle, and sometimes there are flying peaks or structural windows. ； Some form dual structures or imbricate thrust sheets. In addition, another important type of fault in the area is the strike-slip (translational) fault that is obliquely intersecting with the above-mentioned folds and thrust faults. It forms a complex fault network with the above-mentioned thrust faults. In addition, on the sides of some large faults in the Jurassic fold belt in Guizhou, small extensional structures-skirt-shaped faults also developed, often appearing as half-graben basins, in which the accumulated late Cretaceous molasses have been slightly deformed, which is obviously a manifestation of the Himalayan movement. Gentle and open fold belt on the edge of Sichuan Basin: It belongs to the southern edge of the Sichuan Basin, and its scope is limited to Chishui and * Water and two cities (counties). The structural deformation in the area is relatively weak, and the formations are generally gentle, and some are even horizontal. The folding action is extremely slow. The folds, mainly composed of continental clastic strata from the late Late Triassic to the Late Cretaceous, are generally open. The main types are those with thin transverse curved roofs, and only some small-scale gentle anticlines and synclines, mainly distributed in the near east-west direction. Fault structures are also not developed, with only some small normal faults. According to Sichuan deep geophysical data, the basin base is a highly hardened early Precambrian crystalline basement. The above structural deformation is obviously a cover fold that stabilizes the upper part of the craton and is a Germanic-type fold in the foreland basin. Nanpanjiang orogenic fold belt: The Nanpanjiang area belongs to the southwest section of the South China activity zone. The strata involved in this zone range from the Upper Paleozoic to the Mesozoic, among which the terrigenous detrital complexes of the Middle and Upper Triassic are the most eye-catching. The main phase structural line is in the NW-NWW direction and is a tight fold and thrust fault. The most widely distributed middle and upper Triassic terrigenous clastic rocks have strong structural deformation. Continuous linear tight folds are common, regional plate cleavage is developed, and complex small and medium-sized structures, such as large supine folds, synclinal folds, fan-shaped folds and peaked folds are also common and very spectacular. It is worth pointing out that the deformation of the Triassic in this area is different from the general simple cleavage upright folds. Due to the complex lithology of this formation, a complex fold pattern is formed, including not only concentric-equal-thickness-box folds with no cleavage and little cleavage, but also sharp-edge folds with the same cleavage, as well as transition types between them. ； Along with fold cleavage and plate cleavage, refraction cleavage also appears. ； The inclination angle of the fold knots also changes in different parts. This shows that although the folds in the Nanpanjiang area are orogenic folds, they have certain particularities. Jiangnan basement fold-thrust belt: The southeastern Guizhou area southeast of the Zhenyuan-Kaili-Sandu connection is part of the Xuefeng Mountains, where the Precambrian epimetamorphic rock system is exposed in large areas. The traditional view is that: This is an ancient continent that has existed for a long time since the Precambrian, called "Xuefeng Ancient Continent" (i.e., the southwest section of Jiang Ancient Continent). Research in recent years has shown: ""Xuefeng Ancient Continent" did not exist from the Neoproterozoic to the Early Paleozoic. The current Xuefeng Mountain Area is roughly located from the front edge of the continental shelf of the Upper Yangtze Platform to the continental slope. The Caledonian movement at the end of the Silurian period folded the area into mountains and welded them with the Yangtze continental block. and rose into land (because of this, some geologists regard the Xuefeng Mountain area as part of the Caledonian Jiangnan Orogenic Belt). However, at that time, the area was not a separate ancient continent, but a part of the entire Upper Yangtze Ancient Continent. Soon seawater entered the area again. For most of the late Paleozoic and early Mesozoic era, it was still under the seawater, but it was exposed to the surface from time to time. The Indosinian turmoil at the end of the Triassic made the Xuefeng area become land and ended the marine sedimentation in the area. The Yanshanian period imbricated thrust toward the northwest, exposing the Precambrian system in large areas in this belt. The belt is characterized by basement involvement deformation, extensive development of cleavage, and the occurrence of deeper deformations such as double thrust structures. The western edge of this zone is a series of arc-shaped thrust faults that protrude from southeast to northwest. In Zhouxi south of Kaili, the Xiajiang Group pushes over the Permian, covering the entire southeastern flank of the syncline. The same frontal fault sees the Feilai Peak composed of the Lower Cambrian in Yuping. Similarly, the Gedong fault, which is parallel to the former in the interior of the belt, is also covered by the Sansui syncline with the Cambrian as its core. These materials indicate large-scale horizontal contraction in this zone. Field observations indicate that imbricated thrusting activity occurred before the Late White Epoch. Based on the distribution of internal sedimentary facies belts in different eras and comparison with the surroundings and the estimation of the thrust amount of the main fault at the front of the uplift zone, the Xuefeng uplift is a Huaiyuan terrane, and its displacement distance does not exceed tens of kilometers. Generally speaking, this belt is a Caledonian orogenic belt that was destroyed and transformed by the Yanshanian imbricate thrust. Liupanshui fault basin: It refers to a trough-shaped fault basin that spread northward along the present-day Weining, Shuicheng, Liuzhi, Zhenning and other places under the influence of the Emei Earth Fissure during the Late Paleozoic Era. Both sides of the basin are controlled by the Ziyun-Yadu Synsedimentary Fault and the Weining-Shuicheng Synsedimentary Fault respectively. In the basin, the Devonian, Carboniferous and Middle and Lower Permian are dark carbonate rocks, mudstones and siliceous rocks deposited in deep water, mainly containing plankton. The corresponding formations on both sides of the basin consist of light-colored carbonate rocks rich in fossil benthic organisms. This trough-shaped basin died in the late Permian. According to geophysical data, there are hidden volcanic rock masses distributed along the northwest-trending trough-shaped basin distribution area. The edge of the rift basin not only controls the distribution of lead-zinc deposits and hydrothermal siderite in the Devonian and Carboniferous systems, but also controls the distribution of the northwest-trending deformation zone formed during the Yanshanian period. Northwest-northwest deformation zone in western Guizhou (also known as Shuicheng-Ziyun deformation zone): It refers to the large-scale deformation zone extending from northwest to Weining, Shuicheng, Liuzhi, Zhenning and other places. This belt is about 250km long and 20~50km wide, with an overall trend of north 50° west to south 50° east. It consists of a series of inverted folds and thrust faults composed of the Upper Paleozoic, Triassic, and Jurassic, but their combinations are different in different sections. For example, in the Shazigou-Liuma section, the fold inversion and thrust directions are all to the south and west. ； In the Huangguoshu-Xiaojian segment, folds and thrust faults form a hedging pattern. It is worth noting that in addition to the compression characteristics, the northwest-trending deformation zone also shows left-lateral strike-slip characteristics. Leigongshan transitional shear zone: It refers to the brittle-ductile or ductile-brittle strong deformation zone in the middle and deep layers of the crust (10-15km) developed in Taijiang, Leishan, Sandu and other places, where shear deformation is the main force. According to Zhu Ailin et al. (1998), the transitional shear zone appears macroscopically as a series of dense cleavage zones extending NE30°-50° and arranged in parallel to each other in a wild goose shape. It also develops shear folds, shear lenses, SC structures, tensile lineations, bedding folds, rootless folds, sheath folds, etc. On the microscopic level, shear deformation is dominant, and the mineral composition changes accordingly, resulting in mylonitized rocks. In addition, the shear zone and surrounding rock transition from each other, and there is no obvious boundary between them. The shear zones in this area are mainly developed in rocks dominated by greenschist-phase sericite slate, silty slate, and tuffaceous slate. The original rock has heavy argillaceous and tuffaceous components, and the mineral particle size is small. After strong extrusion and shearing, although there is plastic deformation, there is no obvious grinding or thinning effect. This kind of rock with well-preserved original rock characteristics, no obvious reduction in grain size, and dense cleavage and flow structure appearing in a narrow zone is called mylonitized rock. According to relevant test data, this transitional shear zone was formed in the Caledonian period, with a depth of more than 14Km, a temperature of >350°C, and a confining pressure between 364-390Mpa.