(1) Panxian-Songtao-Cili fault zone
The fault zone is distributed in the northeast, which may extend to Jiujiang or even further along the northern foot of Mufu Mountain in the northeast, and the south and west extend to the Shizong-Maitreya fault zone connecting Yunnan, that is, the Shizong-Songtao-Cili-Jiujiang fault zone in the region, which is also the northern sub-zone of the Jiangnan orogenic belt divided by us. Regional geophysical data show obvious gravity gradient zones.
The Mesoproterozoic strata exposed in the northwest of the fault zone are in high-angle unconformity contact with the overlying Neoproterozoic strata. Compared with Danzhou Group, Banxi Group deposited in the early Neoproterozoic is obviously in a relatively stable tectonic environment. From Sinian to Middle Triassic, it was basically shallow platform deposit, and gradually became continental deposit from Late Triassic. There is no other magmatic activity except Permian continental overflow tholeiite. Fold deformation mainly occurred in Yanshan period, and the fold basement reflecting the formation of Wuling movement has always been a stable area except for local uplift.
Between the Mesoproterozoic strata exposed in the southeast of the fault zone and the overlying Neoproterozoic strata, there is a transition from low-angle unconformity to false conformity, transitional deposits (Jiangnan type) and active deposits (South China type) from Neoproterozoic to early Paleozoic, and oceanic tholeiite magma overflows into Neoproterozoic. Late Paleozoic fault block activities led to the sedimentary differentiation of basins and platforms, and there was intermittent overflow and intrusion of basic magma in the trough-basin area. After the Early Triassic, it gradually turned into continental deposits from southeast to northwest. The deformation after Wuling period includes Caledonian period, Yanshan period and Himalayan period, and there are folds and thrust nappes. Magmatic activity is dominated by intermediate-acid intrusive rocks, with regional metamorphism and certain changes in plane. Almost all discovered hydrothermal gold deposits (spots) are located in the southeast of the fault zone, and some other minerals also have such regional characteristics. For example, diamonds from Hunan and Guizhou, including the source of water system excavation, are located in the southeast of the fault zone.
(2) Luocheng-Taojiang fault zone
It is distributed in the northeast, and the northeast section bends to the northwest. The east of Taojiang River is staggered by the NW-trending Nanxian-Liling fault zone, and moves southward to the northern boundary of the central Jiangxi tectonic melange belt near Liuyang. The southwest section extends from Sanjiang to the south and west to the vicinity of Luocheng, that is, the Luocheng-Longsheng-Taojiang-Jingdezhen fault zone in the region, and it is also the central Asian belt of the Jiangnan orogenic belt.
Geophysical data show that it is a lithospheric fault, and the difference between the two sides of the lithospheric bottom boundary is more than 80km (Li Jingping, 1996), and the electrical characteristics and gravity field characteristics are significantly different. Neoproterozoic basic volcanic rocks and basic-ultrabasic intrusive rocks are distributed along its two sides, and the changes of sedimentary facies in early Paleozoic are controlled by them. Caledonian and Yanshanian intermediate-acid intrusive rocks and Indosinian-Yanshanian lamprophyres are intermittently distributed on both sides of the fault zone.
On both sides of the fault zone, the thrust-fold structural combination is extremely developed, indicating that the early Neoproterozoic strata thrust on the Sinian system and the Cambrian system. In Neoproterozoic and Mesoproterozoic strata, there are also large-scale reverse folds and strike thrust faults, and there are strong cleavage and complete structural metasomatism in some areas, reflecting the characteristics of ductile deformation, and various brittle deformations are quite developed in the later period.
The Congjiang-Tongdao fault zone and Rongjiang-Huitong fault zone, which are arranged in parallel on the north and south sides of the fault zone, also develop ductile, transitional shear zones and brittle faults superimposed later. Among them, the gravity data of Congjiang-Tongdao fault zone presents a high-density interfacial depression zone (Yuan Kuirong, 1992), which extends to the south and west near Nandan; Rongjiang-Huitong fault has two seismic sources, local magnetic anomalies are discontinuous, and the axial distribution directions of folds are different. The northwest fold axis is northeast, and the southeast fold axis is northeast, with an included angle of about 30.
(3) Beihai-Pingxiang-Shaoxing fault zone
The general strike is northeast, the middle section is curved to the northwest, and it extends into Hangzhou Bay to the north east longitude, which is the south Asia belt of Jiangnan orogenic belt, and the two sides of this fault zone are quite different.
The exposed early Paleozoic strata are all active "South China type" sediments with strong fold thrust nappe and multi-layer gently dipping ductile shear zone. After the relative stability from Late Paleozoic to Early Triassic, orogenic uplift occurred at the end of Triassic, ending the marine sedimentary history, and a small amount of continental lake basin deposits were retained in Middle Triassic. The folds and faults formed by Yanshan movement developed, and the strain gradually weakened to the northwest. From Caledonian to Yanshanian, the intrusion of acid magma gradually increased, and the magmatic activity characterized by remelting granite reached its peak in Yanshan, forming a huge granite belt in South China. The stratum level and degree of regional metamorphism are also very high. Generally speaking, the southeastern part of the fault zone has typical characteristics of orogenic uplift zone.
On the northwest side of the middle section of the fault zone, geophysical data reveal that the thickness of the lithosphere is obviously increased, the bottom boundary is steep to the northwest, and the lithosphere centered on the Xiangzhong depression is thickened, showing a structural weakening zone.