Characteristics of neotectonic activity of Huichang fault

Ruijin-Huichang-Luotang arc fault is located in the southeast of Jiangxi Province, which is the western edge fault of Wuyishan ring structure and a part of Shaowu-Heyuan fault zone. The upper wall (east plate) of Huichang fault forms Huichang red basin, and the rich rock mass is rich in uranium and mineralization (Hecaokeng ore field), while the Zhulanbu rock mass in the lower wall (west plate) of Huichang fault is similar to the rich rock mass in formation age and rock geochemical characteristics, but there are few uranium deposits, which indicates that Huichang fault has an important influence on the formation and preservation of Hecaokeng ore field. Based on the geological facts observed in the field, this section puts forward a new understanding that Huichang fault is a new structure, which lays a foundation for discussing the ore-controlling effect of this fault and its important significance for uranium prospecting in Hecaokeng ore field.

1. Shaowu-Heyuan fault zone is an active seismic zone.

Shaowu-Heyuan fault zone, including Huichang fault, starts from fenshuiguan, the border between Fujian and Jiangxi in the north, passes through Shicheng, Ruijin, Huichang and Xunwu in Jiangxi, and reaches the source of Longchuan River in Guangdong, with a total length of more than 750 kilometers, a width of 10 km and a length of nearly 400 kilometers in Jiangxi. Fault zones can usually be divided into three sections, the northern section is Shaowu-Shicheng fault zone, the middle section is Ruijin-Xunwu fault zone, including Huichang arc fault zone, and the southern section is Longchuan-Heyuan fault zone. They are not end to end, but are arranged in the left column intermittently (Figure 6-9).

Figure 6-9 Distribution map of Shaowu-Heyuan fault zone and earthquake epicenter (according to Liu Daren, 2000)

According to the relevant data, the Shaowu-Heyuan fault zone has occurred Ms≥4.75 18 times, including Ms ≥ 6 earthquakes twice, namely, March 0962 1806+0654, March 38+0654 and March 38, the southern part of Huichang County, Ms ≥ 6 earthquakes.

Judging from the spatial distribution of seismic activity, the intensity and frequency of seismic activity in the northern part of Shicheng County, which is not affected by the combination of east-west structures, are low, and there are only two moderate earthquakes: Ninghua County 16565438+65438 and Shicheng County 12 on February 6, 0. There were 10 earthquakes in Shicheng-Xunwu section, 8 earthquakes in Longchuan-Heyuan section, and earthquakes of magnitude 6 or above 1 time. Since 1535, earthquakes have occurred from time to time in Shicheng-Xunwu section, but mostly between Ruijin and Xie Fang, and between Zhoutian and Liu Che (the earthquake occurred in the compound area of Shaowu-Heyuan fault zone and east-west structural zone), so the seismic activity in this section is scattered, characterized by slight earthquakes or a few moderate-strong earthquakes; Longchuan-Heyuan section has been relatively calm in history, and only in June 65438 +0953 1 October1Riheyuan, an earthquake of magnitude 4.57 occurred. Later, at the end of June 1959, a large number of microseisms occurred in Xinfengjiang Reservoir, which occurred in March 1962. By the end of 1979, 302,400 earthquakes have been recorded, including 12979 earthquakes with Ms≥ 1 (Ding Yuanzhang et al., 1982).

The Shaowu-Heyuan fault zone also obviously controls the distribution of hot springs. There are 35 hot springs in the whole belt, including the northern part of Xunwu County 17 and the Longchuan-Heyuan section 18. There is low to moderate warm water scattered in the northern section, and moderate warm water is relatively concentrated in the southern section (Liu Daren, 1988). The circulating depth of spring water is 500 ~ 5570 m (Liu Daren, 1995).

To sum up, the Shaowu-Heyuan fault zone is actually a seismic zone with moderate active frequency, and it is also the approximate western boundary of the southeast coastal seismic zone, with a focal depth of 5 ~ 15 km, belonging to a shallow seismic zone, and the focal depth tends to gradually deepen from this zone to the southeast coastal direction. The depth of Kangping plane in this area is only 20 kilometers, and the seismic activity belongs to shallow stress adjustment.

Two. Outcrop observation of Huichang fault

Huichang arc fault is an important fault in Ruijin-Xunwu section of Heyuan-Shaowu fault zone. It is an arc that bends eastward, with a total length of about 90 kilometers. The general trend is east, southeast or northeast, and the dip angle is moderate to small, which constitutes the western boundary of Huichang Red Basin.

Wuping Temple outcrops in the north of Wuyang Town, Ruijin City (Figure 6- 10), with the occurrence of 134 ∠ 52.5, and the main structural plane is smooth and wavy (Figure 6- 1). See also structural breccia (Figure 6-2). The width of silicified cracks in the structural footwall reaches 50m, and the silicon.

Fig. 6- 10 schematic diagram of Wupingsi outcrop of Huichang fault

The outcrop is located 5km northeast of Youshui Town, Huichang County, and the fault attitude is 1 14 ∠ 25. See the structural mud or schist zone of 20 ~ 100 cm (photo 6-3). Xiaoji Village, Junmenling Town, Huichang County is exposed, with the occurrence of 7 1 ∠ 44.5, and the width of structural cracks is about 30cm (photo 6-4). The breccia of structural breccia is angular, with a maximum of 6cm (photo 6-5).

Figure 6- 1 Smooth fault plane of Huichang fault

Figure 6-2 Water outcrop on the right side of Huichang fault

Discussion on Preservation Factors of Uranium Deposits in South China

Figure 6-3 Structural Breccia | (Location: Wuping Temple, Wuyang Town, Ruijin City)

Figure 6-4 Structural fracture zone

Third, traces of neotectonic activity of Huichang fault.

Huichang fault is located in Shaowu-Heyuan seismic activity zone, and there are a series of traces of neotectonic activity.

(1) The fault triangle is clear. Neotectonic movement is the main reason for the formation of modern tectonic landform pattern, and fault triangle is generally the product of neotectonic movement. There is an obvious fault triangle in Wuping Mountain, Wuyang Town, Heyuan-Shaowu Fault (Photo 6-6), which indicates that the fault has new structural characteristics.

(2) Wuping Temple in Wuyang is outcropped, with complex structural breccia, including phyllite, silicified rock and red siltstone breccia, which is angular (photo 6-2). The red siltstone breccia is the lithology of K2 stratum, and a yellow-brown film with a thickness of several millimeters can be seen on the structural plane, which indicates that the structure was formed after the late Cretaceous red bed and is the product of Neogene tectonic movement.

(3) There are three ground fissures on both sides of the fault, namely, the ground fissure in Baihua Garden of Dabu Village, Shazhouba Town, Ruijin City, the ground fissure in the south of Huichang County and the ground fissure in Tiger Village of Zhoutian Village. The ground fissures trace zigzag on the plane, wedge-shaped on the section, with steep dip angle (85), tensile or torsional mechanical properties, arranged in a left column, and the vertical depth is 30 ~ 40 cm. Ground fissures are mainly produced in Quaternary Pleistocene, Upper Pleistocene and Holocene alluvial eluvial layers, and go deep into purple argillaceous siltstone of Upper Cretaceous (Liu Daren, 1987). These phenomena indicate that Huichang arc fault is an active fault in Neogene (Neotectonic period).

(4) There are many hot springs along the fault, such as Xie Fang Hot Spring and Luotang Hot Spring, with the water temperature of 26 ~ 60℃.

Photo 6-5 Structural breccia

Figure 6-6 Fault Triangle