The term fault metamorphic belt was put forward by Professor Mo Zhusun in 1962. It is a deep fault zone in the northeast direction in Guangdong Province, and it is also an important rock-controlling and ore-controlling structural zone. Over the years, many experts and scholars from geological teams and teaching and scientific research units have done research work in this field to varying degrees, and gained a lot of geological knowledge and achievements, thus gradually deepening the research in this field.
1. 1962 Understanding and achievements of Mo Zhusun and others.
The term Wuchuan-Sihui fault metamorphic belt was put forward, which is still in use today. Located on the eastern edge of Yunkai Uplift, it includes the vast areas east of Wuchuan-Lubu and west of Bajia-Sihui. It sinks southwest into the South China Sea, and may pass through Qingyuan, Yingde and Nanxiong graben northward. It is composed of large and small faults, and the fault direction is NE-NNE, forming a long and narrow fault metamorphic belt. The fault metamorphic belt is also an important metallogenic belt in Guangdong Province, and tungsten, tin, copper, lead, zinc, arsenic and pyrite have good prospecting prospects.
2. 1979 Qiu Yuanxi's Guangdong Structural System Diagram and Description.
Wuchuan-Sihui fold fault zone is located in Wuchuan-Sihui line in Guangdong Province. Extending north and east to Xiniu area in northern Guangdong; The southwest is concealed under the Cenozoic strata near Wuchuan City, and continues to cross the Qiongzhou Strait to the south, entering Lingao County and ending in Changjiang County and Dongfang County. It can be traced back to 700 kilometers, and it is one of the main structural zones of New China in Guangdong.
The main structural components of the fold fault zone include regional large faults, dynamic metamorphic belts, magmatic belts, various folds and tectonic basins. Generally, it extends in the direction of 20 ~ 30 northeast. The northeast end is about 10km wide and the southwest end is 50km wide, which is slightly like a trumpet in space.
Some people think that the fault is a deep fault zone and may be connected with the Tancheng-Lujiang fault zone.
The formation of this fault zone can be traced back to the early Late Paleozoic. After the Indosinian movement and Yanshan movement, it suffered a strong transformation. Up to now, the activity has not stopped. It is a long-term and repeatedly active fold-fault structural belt. Most of the older structural components in this belt (Cathaysian system) were strongly reformed and merged by the late Neocathaysian structure, and the original signs were difficult to identify, so it was called the early and late Neocathaysian reconnection. It should be pointed out that in the reconnection composite fold-fault zone, the structural characteristics of these two stages can be distinguished locally.
3. 198 1 wuchuan-sihui fault zone's geological characteristics and metallogenic relations.
At the meeting, two opinions were mainly put forward on the division of fault zones. One view is that the Chengdong fault and the Beimian-Shi Qi fault are located on the east and west sides of Yangchun basin, respectively, and their fracture properties and ore-bearing properties are very similar, so they should be classified as a group of faults and not belong to Wuchuan-Sihui fault zone; Another point of view is that this belt is a deep and large fault zone, which may be connected with the Tanlu fault zone, and its distribution range should be large rather than small, so the Beimian-Yi Shi fault and Yong Cheng fault should be included in this range.
4. 1982 Chen tingguang et al., "Geological Characteristics and Metallogenic Relationship of Wuchuan-Sihui Fault Zone in Guangdong Province"
The scope, distribution, shape and extension of the fault zone are studied in detail, and it is considered that the fault zone extends to the south China sea coast in the southwest and Qingyuan in the north. As a whole, it shows a 40-degree direction, forming a belt-shaped fault system with northeast diffusion and southwest convergence. It bends many times and looks like an inverted horn. According to the data of Guangdong Geophysical Exploration Team Yang, the plan of gravity and magnetic field in western Guangdong shows that there is a cascade belt in Wuchuan, Sihui and Qujiang. The gravity fields on both sides are obviously different, and the gravity field in the whole region is divided into two parts: high in the east and low in the west. Near the boundary line of gravity field, a series of local aeromagnetic anomalies distributed in the northeast are concentrated, and their overall positions are basically consistent with the boundary line of gravity field. In addition, the thickness profile of the crust passing through the fault is calculated by using the gravity data measured by the South China Sea Geological Survey Command. There is one in the north, starting from Huaiji and Guangning in the north and going to Foshan through Sihui. According to the calculation, the maximum thickness of the crust in the northwest of Sihui can reach 34.9km, and the thinnest near Foshan is only 3 1.3km, with a difference of 3.6km. In the south line, the deepest part of the fault passing through the west side can reach 34.6km, and the thinnest part in the southeast side is 32. 1km, with a difference of 2.5km. It is considered that this fault zone meets the Tancheng-Lujiang fault northward through Shaoguan. According to the characteristics of two gravity anomalies in the fault zone, basic dikes are exposed along the fault zone, which is considered as a deep fault in the crust. Through the study of the combination relationship between structural characteristics and fault zones, it is considered that it is one of several famous NE-trending fault zones in Guangdong Province and an important part of Cathaysian structural zone in western Guangdong. The fault zone consists of more than ten regional large faults, a dynamic metamorphic belt sandwiched between them, and a spiral structure supporting NW-trending faults and derivatives.
It is pointed out that the fault zone is closely related to pyrite, tungsten, tin, iron, copper, lead, gold and silver deposits, and that Shijie arc, Tiantang arc and Zhaoqing arc control three porphyry deposits respectively.
As for the time of tectonic activity, the report clearly points out that the fault zone began in Ordovician, and it was active in Caledonian and Indosinian, and it underwent strong transformation in various scenes of Yanshan movement until modern activities did not stop. It is a long-term and repeatedly active fold-fault structural belt.
5. 1982 Regional Geology of Guangdong Province
The fault zone is an important deep fault in Guangdong province, which is more than 800 kilometers long and has an overall shape of 20 ~ 40. Impact width 15 ~ 20km. The fault zone runs from Wuchuan to the north through Yangchun and Guangning, and connects with Renhua-Yingde fault. It is divided into two branches near Shaoguan. One branch is connected with Jiangxi Dayu-Xingguo-Chengnan deep fault along Nanxiong Basin, which Ren Jishun called Wuchuan-Xiaoshan fault zone. The other branch is inserted into Zhuchuan, Jiangxi Province, and connected with the Tancheng-Lujiang fault zone along the northern extension of the Ganjiang River. The southwest section is also obviously divided into two branches, one of which lurks under the Leiqiong fault depression after entering Wuchuan and inserts into the Beibu Gulf near Wushi Port in Haikang; The other branch weaves into the sea along Yangjiang and enters Dazhuzhou Island. This fault is the dividing line of the secondary structural units in western Guangdong. Ruyuan and Wengyuan are the dividing lines of the fourth-grade tectonic units in northern Guangdong. The southwest opening of the fault zone is trumpet-shaped, which is a multi-cycle tectonic, magmatic and metamorphic belt.
Geophysically, the fault zone is the interface of different gravity, magnetic field and Moho surface, reflecting that the east side is a local uplift area of the upper mantle, and the Moho surface is buried at a depth of 26km. The west side is the upper mantle depression area, and the Moho surface is 28 kilometers deep. In aeromagnetic survey, it is a local magnetic anomaly zone with northeast distribution, and its position is equivalent to gravity cascade zone. Therefore, some fault zones have reached the upper mantle, corresponding to the evolution series of mantle-derived heteromorphism and synlava magma.
Generally speaking, the activity and early formation of this fault zone may be related to Yunan movement, which was formed in Ordovician; The rise of Indosinian movement led to ductile shear, dynamic thermal metamorphism, migmatization and magmatic emplacement. Yanshan movement is strong and magma intrusion is frequent. In the early stage, it was dominated by Yangtze series (quite syntectic) magma, which was related to iron, copper, lead, zinc and other deposits. The late stage is mainly characterized by Nanling series magma, which is related to tungsten, tin and uranium deposits. There was activity until recently.
6. 1984 Qin mutao et al. Study on metallogenic conditions and prospect prediction of gold deposits in western Guangdong.
According to reports, the fault zone starts from Wuchuan in the south and ends at Sihui Kevin·Z (south-central section) in the north, with a total strike of 30 ~ 40 and an inclination of 40 ~ 70 to the north or southeast. The fault zone is mainly composed of 16 faults and three dynamic metamorphic belts, and a single fault is several kilometers to 100 kilometers. It is a wide regional ductile-brittle deep fault zone, which extends in gentle waves on the plane and has the characteristics of left-handed flying geese. The secondary fault is parallel to the main fault and has low-order torsion structure. The activity began in Ordovician and is still active today. There were magmatic activities in Indosinian and Yanshanian, many granites invaded along the fault zone, and ultramafic rocks distributed along the fault zone. Geophysical (△T) characteristics show that the fault zone is the boundary of magnetic fields in two different regions, and the local magnetic anomalies are distributed in strips. The gravity field is characterized by discontinuous distribution of cascade zones, which are high in the east and low in the west, and are paired local abnormal zones. According to the gravity data calculated by "South China Sea Geological Survey Command", the difference of crust thickness between the two sides is 2.5 ~ 3.6 kilometers. Geologically, it is located in two different terrane splicing zones. Moho surface on both sides of the fault zone is shallow in the east and deep in the west, which runs through the crust and belongs to a deep fault beyond the crust.
Second, research progress and new achievements
On the basis of predecessors' work, this paper carefully analyzes and studies predecessors' understanding and achievements on fault zones. Through the field investigation and indoor research work of this topic, the contents that are considered to be in line with the objective reality are affirmed, and the parts that are not well understood are supplemented and improved as much as possible, thus obtaining a more comprehensive understanding and results.
1. Distribution scale
Wuchuan-Sihui fault zone is a deep fault zone belonging to Cathaysian tectonic system along the southeast coast of China, and its division and extension have always been the focus of controversy. This study basically agrees with Chen Tingguang (1982), and makes the following supplementary explanations:
The (1) fault zone extends to both ends. In the past, many experts only confined the fault zone between Wuchuan and Sihui. In our opinion, it is impossible for such a super crust to tip over in just over 300 kilometers, just because the north extension is cut off by Fogang's east-west tectonic magma belt, making its structure invisible. We agree with the viewpoint of regional geology in Guangdong Province, which is connected with Renhua-Yingde fault to the north (this book calls it the northern section). With regard to the problem of extending northward after arriving in Shaoguan, the author comprehensively analyzes a large number of geological and geophysical field data and some field investigations in this area. It shows that the main fault passes through Renhua, the Yangtze River and Dong Tang, and there is a magnificent composite structural belt in the early and late Cathaysian period, and the width of mylonite belt is more than 100 meters (see later). Consistent with the views of Chen Tingguang and others (1982) and the regional geology of Guangdong Province (1988), Yang Minggui of Jiangxi Bureau of Geology and Mineral Resources also agrees with this view, that is, it connects with Ganjiang fault via Suijiang River to the north, and then extends to the north to continue with Tanlu fault. As for whether there is a branch extending northeast through Nanxiong basin, we think that the following problems are difficult to solve due to the lack of current data: ① the fault zone is sharply eastward, that is, northeast; ② Most of the main fault zones pass through Yanshanian granite and Cretaceous-Tertiary red beds; ③ The main faults are mostly torsional and a few are tensile. From the above three points of view, its performance reflects the Taishan-style structural characteristics of the new China summer system, and also shows the Chinese elements. As for the existence of Cathaysian structure, it is hard to say now. As for the southward extension of the fault zone, we think that the fault zone extends southward to Wuchuan and Wuyang, hidden under the Cenozoic strata, and then extends southward to the coast of the South China Sea, and is intercepted by the east-west fault in Lei Qiong.
(2) The scale of the fault zone. The fault zone is 550 kilometers from south to north, from Wuchuan coast to Guangdong-Jiangxi border. The distribution width of the main fault is10-30km, the influence width is 50-60km, and the maximum width is 70km.
2. Form of appearance
Faults are arranged in a goose shape from northeast to left, with an overall strike of 30 ~ 40, inclined to northwest or southeast, and an inclination angle of 40 ~ 70. There are gentle waves on the plane, and the secondary faults parallel to the main fault develop, which is a wide and deep fault zone. The above viewpoints are basically consistent with the early understanding of Qin Mutao and others (1994). As for the shape of the whole belt, we think it is more appropriate for Chen Tingguang (1982) to describe it as an inverted horn, which is wide in the north and narrow in the south, showing a northeast trend.
3. Fracture combination
According to Chen Tingguang's understanding (1982), the fault zone is composed of 22 regional main fault zones, 4 dynamic metamorphic (shear) zones sandwiched between them, and the matching NW-trending faults and derived spiral structures, forming a huge fault zone with complex fabric.
4. Fracture characteristics
It is an inherited composite fault zone and a deep compression-torsion fault.
5. Physical field characteristics
According to the data of Geological Survey Headquarters and Guangdong Geophysical Exploration Team Yang (198 1), the fault zone is a gravity cascade zone, which is the boundary of magnetic fields in two different regions.
6. Magmatic activity
We think that the regional geology of Guangdong Province (1988) is well described, and it is a multi-cycle tectonic magmatic metamorphic belt. In addition to a large number of intermediate-acid magma intrusion along the fault zone, Qin Mutao and Yuan also proposed that it is distributed along ultramafic rocks.
7. Metallogenic relationship
According to the previous understanding of mineralization, combined with some recent data and research results, the following understanding is put forward.
The (1) fault zone is closely related to pyrite, tungsten, tin, molybdenum, iron, copper, zinc, gold, silver, arsenic and uranium deposits.
(2) There are mainly three ore-controlling forms of the fault zone: ① the deposits controlled by the fault zone or its low-order structure, such as pyrite deposits controlled by the late cycle of Sinian system (Dajiang Ping), syngenetic deposits or stratabound pyrite deposits in late Paleozoic basins (Xiniu and Hongyan), and uranium deposits in Mesozoic and Cenozoic fault basins (Nanxiong Basin165438+); ② Mylonite-type gold deposits formed by dynamic diagenesis and mineralization in ductile shear zone; (3) Endogenous metal deposits related to various granitic magmatic activities in Yanshanian period.
(3) Granites of different genesis in Yanshanian controlled different metallogenic series, among which Nanling series (I series) granite controlled tungsten, tin, lead, zinc, silver, arsenic and uranium deposits. The Yangtze series (Ⅱ series) granites control iron, copper, lead, zinc, silver, gold, sulfur and molybdenum deposits.
(4) Porphyry deposits controlled by the fault zone are a major feature of this area: all kinds of porphyries are mainly produced in Yanshanian period, and intermediate-acid porphyries are relatively early, which are known as associated copper-molybdenum polymetallic deposits, and acid porphyries are mostly produced in the late stage, mainly associated with tin-molybdenum deposits; Porphyry deposits are obviously controlled by low-order cyclic structures; Porphyry deposits have certain zonation, which are copper, molybdenum, copper, sulfur, zinc, lead, silver and gold in turn from inside to outside. Those with well-developed structures often form a "trinity" porphyry deposit with internal rock mass, contact zone and surrounding rock.
Three. Evolution table of main cognitive achievements (table 1- 1)
Table 1- 1 Wuchuan-Sihui Fault Zone Main Understanding Achievements Evolution Table
sequential