Jiangshan is located at the junction of Yangtze plate and South China plate, adjacent to Jiangshan-Shaoxing deep fault, and is the eastern edge of Zhejiang-Anhui Paleozoic basin. During the Indosinian movement, due to the subduction of the Pacific plate to the Eurasian plate, this area was strongly compressed in the southeast direction, and Indosinian folds and faults in the northeast-southwest direction and other associated and derived structures were formed in this area, forming the structural framework of this area (Figure 1.5).

1.4. 1. 1 folded structure

The folds in this area are linear parallel fold groups. The axial direction is about 30 ~ 45 northeast. The axial plane tends to the southeast. From southeast to northwest, the fold strength gradually weakens, and the fold types change from isometric fold, inverted fold and oblique closed fold to vertical open fold in turn. The main folds in this area are briefly described as follows.

◎ Xishan anticline: it starts from Lianhuachi in the south, passes through Xishan, and extends northeast to the north of Zhengcun village in Zu Feng township, with a total length of more than 8 kilometers, and the axis of the anticline is 25 ~ 30 northeast. The axial plane is inclined to the southeast, with an inclination angle of about 60, and the attitude of the two wings is roughly parallel, similar to an isometric fold. The center leans to the south and west. According to field data, mathematical calculation and stereographic projection calculation, the occurrence of wheel hub is 206 ∠ 30. The stratum forming the core is Tang Zhi Formation, and the southeast wing is normal wing. The exposed strata are Leigongwu Formation, Xifengsi Formation, Tanghe Formation, Bianbian Formation and Lower Ordovician in turn. The northwest wing is an inverted wing. Due to the destruction of Xishan thrust fault, the wing strata are covered by the upward thrust anticline core, and the Tang Zhi Formation in the northern and middle parts of Xishan is in direct contact with Changwu Formation, Yejiatang Formation and Outangdi Formation. There is a longitudinal silicified breccia belt near the ridge line of the positive wing of the inverted anticline, and the rocks on both sides are generally silicified to varying degrees, so that silicified rocks are exposed in a large area on the southeast slope of Xishan Mountain. In addition, the whole Xishan inverted anticline is staggered by a group of transverse (or oblique) faults with the strike of about 3 10 ~ 320, which destroys the continuity of the whole inverted anticline.

◎ Shitoushan-Huafen inversion syncline: it starts from the south of Xianantang in the south, extends to Shitoushan and Huafen in the northeast, and descends the mountain, with a total length of more than 5km, and the axial direction is roughly parallel to the Xishan inversion anticline. The stratum where the core is formed is Dingjiashan Formation, and the strata with exposed wings are Shitoushan Formation, Outangdi Formation, Yejiatang Formation and Changwu Formation in turn. The southeast wing is an inverted wing, connected with Xishan anticline, and its occurrence is steep (125 ∠ 70); The northwest wing is a normal wing with a gentle occurrence (135 ∠ 40). A concealed reverse fault with the same occurrence and nature as Xishan reverse fault developed near the turning end of the inversion wing, resulting in stratum loss. The whole inverted syncline is basically concealed under the Quaternary, and only the exposed core strata are seen in Xianantang and Shitoushan. The landform is negative.

Figure 1.5 Structural Outline of Jiangshan Training Area

1. Sinian system; 2. Cambrian-Ordovician; 3. Carboniferous-Permian; 4. Cretaceous; 5. anticline; 6. Syncline; 7. Silicified breccia zone and silicified zone; 8. Reverse failure; 9. Translation errors; 10. Fault of unknown nature; 1 1. unconformity line; 12. Granite

◎ Wu Jialong anticline: It starts from the southern foot of Lianhua Mountain in the south, extends to the northeast, passes through Xinpeng, Wu Jialong and the bottom of Outang, and pinches out near the pond head. The total length is more than 5km, the anticline axis is about 40, the hub is nearly horizontal and the posture is stable. The inclination angle of the southeast wing is about 45, the inclination angle of the northwest wing is 65, and the axial plane is inclined to the southeast with an inclination angle of about 80. Tumorous marl of Iwayama Formation is exposed from the core, and Huangnigang Formation and Changwu Formation are symmetrically exposed from both wings in turn. The angle between the wings is about 70, and the turning end is curved. Small folds, cleavage and irregular stone sausages are developed in the core of the new shed, and small reverse faults can be seen. It was destroyed by several transverse and oblique faults along the axis of the anticline. On the plane, the width of the anticline core changes, staggered on both sides of the fault.

◎ Canopy syncline: It extends from the south to the south of Longtou, passes through the canopy and Dengtang in the northeast direction, and pinches out at the bottom of Ominoyama, with a total length of more than 4km. The axial direction is about 40, and the hub is slightly inclined to the southwest direction of 220, with the inclination less than 5, the inclination of the southeast wing is 40 ~ 60, and the inclination of the northwest wing is relatively slow, generally less than 40. The axial plane is almost vertical. Changwu Formation is exposed at the core, and Huangnigang Formation and Yanwashan Formation are symmetrically exposed at the two wings in turn. Syncline consists of two secondary synclines and one secondary anticline. In Gong Ling, Dengtang and other places, Huangnigang Formation and Yanwashan Formation are exposed at the core of the secondary anticline due to the destruction of vertical undulation of transverse faults and the influence of topography. In the big faucet, the secondary anticline just passes through the top of the big faucet. Due to the gentle occurrence near the turning end, the Huangnigang Formation in the core is exposed along the Dalongtou area on the mountainside, and the long axis direction of the stratigraphic boundary is northwest, showing an "8" shape. If we only consider the plane shape of the boundary without considering the occurrence, we will often mistakenly think that the axial direction of the fold is northwest.

Laohushan syncline: Laohushan is a broad syncline as a whole and a fold of Shitoushan Formation. The syncline axis is about 20 NNE, the hub tends to the southwest and the axial plane tends to the southeast. The southeast wing has a steep occurrence with an inclination of about 80, while the northwest wing has a slow occurrence with an inclination of about 25. The limestone in the southeast wing is in fault contact with Yanshanian rock mass.

1.4. 1.2 fault structure

(1) failure

Faults are well developed in this area. According to their trend, they can be roughly divided into three groups: northeast, northwest and northwest. Among them, NE-trending faults are a group of strike (vertical) reverse faults, which are parallel to the axial direction of folds and the overall strike of strata. The NW-trending fault is perpendicular to the fold axis and the overall strike of the rock strata, and it is a group of inclined (horizontal) faults dominated by normal faults. The NW-trending fault obliquely cuts the fold axis and the overall strike of the rock strata, and it is a group of positive left-lateral translation faults dominated by left-lateral translation and the footwall descends.

◎ Xishan strike reverse fault: it develops on the reverse wing of Xishan anticline, starts from the south side of Lianhuachi in the south, reaches 180 highland in the west, turns northeast to Jiangshan Chemical Plant along the western slope of Xishan, goes downhill, and continues northward near Zhengcun, Zu Feng Township. The whole fault extends in a slightly inverted "S" shape, with a total length exceeding 7.5km. In the main section of Xishan Mountain, the fault strike is about 25. The fault plane tends to the southeast with an inclination of 55 ~ 60. The Tang Zhi Formation in the core of Xishan inversion anticline is exposed in the upper wall of the fault, and the strata exposed in the lower wall of the fault are Changwu Formation, Yejiatang Formation and Outangdi Formation. The fault distance of strata is greater than the sum of the thicknesses of Cambrian and Ordovician strata. The fault is gentle and wavy along the strike, and the fracture zone is narrow. Adjacent fault cleavage develops near the footwall section, and the cleavage strike intersects the fault plane strike at a small angle, while the former has a large dip angle. According to this analysis, the fault is mainly caused by the upward movement of the upper wall and has a slight left-lateral translation property. Due to the difference of weathering resistance between the two sides of the fault, the landform is characterized by obvious steep footwall topography near the fault line, forming a fault cliff.

Xishan reverse fault is cut off by a group of oblique (or transverse) faults, and the fault line is discontinuous, which shows translation and dislocation in plane.

◎ Hejiashan strike reverse fault: it starts from Zhujiawu in the south, extends to Hejiashan and Shangnantang in the northeast, and continues to extend to the northeast, concealed in Quaternary. The total length is more than 4 kilometers, the fault strike is about 40, and it tends to the southeast with an inclination of about 60. Timely conglomerate and sandstone in the upper member of Lououtangdi Formation are exposed on the upper wall, with occurrence of141∠ 53; The limestone of Shitoushan Formation is exposed in the footwall, with occurrence of 135 ∠ 54. The dip angle of fault plane is the same as that of rock plane, and the former is greater than the latter. Stratigraphic repetition is shown in both plane and profile. There is a fault fracture zone with a width of nearly 10M on the side wall of Hejiashan-Ganghou Expressway, which is filled with fault breccia and fault mud. The strata near the footwall fracture zone are broken, the occurrence is chaotic, and the dip angle of the overall trend is slowed down, and a basic dike is invaded along the bed. There is obvious traction phenomenon in the hanging wall strata. According to traction bending and stratigraphic repetition, it is judged that the fault is a reverse fault with hanging wall.

◎ Wu Jialong oblique right-left translation fault: it starts from the south of Wu Jialong and extends to the east of Zhengjiawu along the NW direction, with a total length of about 2km. On-site measurement shows that the fault plane attitude is 66 ∠ 80. The bandwidth of faults and fractures varies, generally less than1m. There are fault breccia and fault gouge in the area, and the breccia is mostly pointed and angular, with different sizes, no directional arrangement and no foreign bodies, and some broken rocks are loosely cemented. The rocks on both sides of the fault zone are broken, but there is no compression schistosity. The fault obliquely cuts the Wu Jialong anticline, with a horizontal offset of nearly 200 meters along the strike. The exposed width of the core of Wu Jialong anticline on both sides of the fault changes obviously, and the exposed width of the core (upper wall) of NE anticline is narrow. According to the occurrence of the two wings of the anticline, the vertical component of the footwall descent is about 120M, and the lateral angle of the slip line of the footwall on the fault plane is about 3 1.5. The fault is a positive left-lateral translation fault.

In the eastern part of Wu Jialong Village, near the footwall of the main fault, there are several small faults with similar occurrence and properties to the main fault, which are staggered to the left in the plane and form stepped faults in the profile.

Majiatang oblique right-left translation fault: it starts from Majiatang in the south and extends to the bottom of Outang in the northwest, with a total length of about 1km and a fault strike of 345. Inclined to the northeast, with an inclination of nearly 90 degrees. The rock that the fault passes through is broken, and the landform along the broken zone shows the negative topography of the valley. Near the bottom of the Outang River, the Yejiatang Formation on the northeast (upper) wall of the fault has obvious traction phenomenon, and the rock occurrence near the fault is 98 ∠ 43. Away from the fault, the stratum attitude gradually tends to be normal (143 ∠ 52). The fault effect reflected in the plane is that the geological boundary has moved to the left by about 700M m. The influence on the profile is the decline of the northeast plate. The faults that cause this effect can be left-lateral translation faults, normal faults with descending northeast wall, or oblique sliding faults with horizontal component of left-lateral displacement and vertical component of hanging wall descent. According to the comparison with other faults in the same direction in the area, and the phenomenon that Yanwashan Formation and Huangnigang Formation in the core of Wu Jialong anticline on the north side of the fault are not exposed to the surface, it is considered that the fault is a positive left-lateral translation fault with left-lateral translation as the main factor and vertical displacement as the auxiliary factor.

On the southwest side of Majiatang fault and south of Jiangjianong, a small fault with the same occurrence and nature is also developed.

◎ Dianbatou-Bi Chang side translates to the left-normal fault: it starts from Bi Chang in the south, extends to the north of Dianbatou in the northwest, and continues to extend to the northwest, with a total length of 1.5km or more. The fault crosses the compound syncline of the field shed, with a strike of 320 ~ 330, and the fault fracture zone is wide. Gully landform is formed along the fault zone, and the floating soil is thick, so it is speculated that the fault tends to the northeast. The fault plane is nearly vertical. Observed near Dianbatou, the fault has a long-distance left-lateral horizontal displacement effect. In the south of Bi Chang, the fault is buried in the Quaternary, and may have cut through the Wu Jialong anticline, but the horizontal displacement effect of the axis of the anticline is not obvious. In addition, near the upper longwall, the stratum occurrence of Panyanwashan Formation in the southwest of the fault is gentle and the outcrop width is very large, and its structural position is just near the turning end of the secondary syncline core of Tian Peng compound syncline. Compared with the northeast plate of the fault, the horizontal dislocation in the core of the secondary anticline is not obvious. Therefore, the fault is mainly vertical displacement. The old stratum exposed by Nanxi plate is the rising plate. It is a sinistral translation normal fault. In addition, it is inferred from the phenomenon that the axis of Wu Jialong anticline has no obvious dislocation, and the width of the core of the two anticlines of the fault has no obvious change, and the fault has the nature of a hub fault, and the footwall drop at the northern end is greater than that at the southern end.

The footwall subsidence in this area is mainly left-handed displacement, and there are also Jin Mu Wu-Lianhuashan fault and Dianbatou-Chang Gung fault, all of which strike around 330.

◎ Transverse (including oblique) faults in Xishan: A group of transverse (including oblique) faults developed in Xishan inversion anticline with strike of 3 10 ~ 340. On the plane, the fault displacement effect has left line and right line, and for the same fault, the horizontal dislocation of structural lines with different occurrences is also different. The smaller the dip angle, the greater the horizontal offset of the tectonic line. For example, the horizontal offset of the fault line of Xishan reverse fault is greater than the stratigraphic boundary and silicified zone. Although there is no engineering exposure, no exact data of fault plane occurrence, and no direct evidence of fault displacement such as scratches, steps and friction mirrors on the fault plane, it can be considered that the transverse fault in Xishan cannot be a simple translational fault or a fault dominated by translation, but a left-lateral translational-normal fault with certain translational properties. When the fault plane is inclined to the northeast, the plane displacement effect of the fault is staggered to the left, and when the fault plane is inclined to the southwest, the plane displacement effect of the fault is staggered to the right.

(2) Joint

Joints are small fracture structures with no obvious relative displacement along both sides of the fracture surface, and they are the most basic products of tectonic movement. No matter what the nature and intensity of tectonic movements are, joint structures may be formed and preserved, which provides reliable basis for reconstructing the orientation of paleotectonic stress axis and restoring paleotectonic stress field.

Joint structures are well developed in Jiangshan area. Shear joints are well developed in different lithology, and tensile joints are mainly found in limestone and thick layered sandstone, and calcite veins or time-dependent veins are often filled.

Through the study of joint structure in Jiangshan area, it is found that this area has experienced at least five obvious tectonic movements since early Paleozoic. The orientation of principal stress axis in each tectonic movement period is: early and middle Caledonian, σ 16 1.2 ∠ 57, σ 2239 ∠ 66. 1, σ 330.6 ∠ 9.4; In late Caledonian, σ1170 ∠18.3, σ 20 ∠ 84, σ 3263.7 ∠ 6.8; Indosinian period, σ1126.6 ∠ 21.1,σ 23 15 ∠ 7 1.3, σ 3220.6 ∠. In the early Yanshan period, σ 1 135.6 ∠ 28.4, σ 2296.6 ∠ 72.7, σ 345 ∠13; In the middle and late Yanshan period, σ 1222.9 ∠ 1.5, σ 210.6 ∠ 84.9, σ 3316.4 ∠/kloc-0. Among them, the action mode of tectonic stress in Indosinian period and early Yanshan period is right-lateral horizontal shear, and the action mode of tectonic stress in late Yanshan period is mainly σ3.

(3) cleavage

Cleavage is a secondary plane structure, which divides rocks into parallel and dense thin slices or slices in a certain direction. There are two types of cleavage in Jiangshan practice area, one is flow cleavage and the other is fracture cleavage.

◎ Flow cleavage: It is an easy-to-cleave fragile surface composed of parallel flaky, tabular or oblate minerals or aggregates. It is the result of plastic flow of rock in the rheological process of metamorphic solid and the flattening, elongation, rotation and recrystallization of internal components of rock under strong extrusion. The flow cleavage in Jiangshan practice area mainly exists in argillaceous rocks that are strongly compressed, such as the fault zone and its two sides of reverse faults and translation faults, as well as the core and wing of anticline. The flow cleavage plane is generally perpendicular to the direction of the principal compressive stress axis, and the acute angle with the principal sliding plane points to the sliding direction of the disk. Flow cleavage is developed near the fault zone of Changwu Formation in the footwall of Xishan reverse fault. The cleavage plane is slightly curved, the micro-cleavage stone is lenticular, the cleavage strike intersects with the fault strike at a small angle, and the cleavage plane has a large dip angle. It shows that Xishan reverse fault is accompanied by sinistral oblique thrust fault. In the argillaceous rocks at the bottom of Yanwa Mountain in the core of Wu Jialong anticline near Xinpeng, there are not only irregular small fold thrust faults, but also unstable flow cleavage. The angle between the cleavage plane and the rock surface is small, which reflects that the overlying strata near the core slide from the anticline wing to the turning end. In addition, the flow cleavage of oblique bedding can also be seen in the coal seam at the bottom of Yejiatang Formation and its roof and floor shale on the eastern slope of Fangjiashan.

Cleavage refers to a group of dense shear fracture surfaces in rocks, and the development of fracture surfaces has nothing to do with whether minerals in rocks are arranged in parallel. Its mechanical properties and genesis are the same as those of shear joints, and it belongs to brittle-ductile shear fracture deformation. The difference between them lies in the size of observation scale, and the interval between two cleavage faults is generally several millimeters to several centimeters. When the interval is more than a few centimeters, it is called a joint. There are two kinds of cleavage in this area, but the most typical one is interlayer cleavage. In the fold wing between soft and hard rock layers, the flow cleavage with a small angle to the bedding plane is formed in the soft rock layer, and the cleavage with a large angle to the bedding plane is formed in the hard rock layer, which shows cleavage refraction in the profile.