(1. State Key Laboratory of Geological Action and Mineral Resources of China Geo University, Beijing100083; 2. Key Laboratory of Lithospheric Structure, Deep Process and Detection Technology of China Geo University, Ministry of Education, Beijing100083; 3. Fujian Geological Survey and Research Institute, Fuzhou 350003)

Metamorphic basement strata in central Fujian are mainly composed of Proterozoic, Mesoproterozoic and Neoproterozoic-Early Paleozoic. Mesoproterozoic metamorphic strata include Longquan Group and Mamianshan Group. According to the metamorphic deformation characteristics and isotopic chronology, Mamianshan Group should be Longbeixi Formation, Dongyan Formation and Daling Formation from bottom to top. The greenschist series of Dongyan Formation constitutes the main body of Mesoproterozoic stratigraphic records and is directly related to massive sulfide deposits widely distributed in this area. Dongyan Formation is mainly a set of ancient volcanic sedimentary formations dominated by greenschists. Its main lithologic types include greenschist, marble, quartzite and granulite, with diverse components. Green schist shows the characteristics of submarine volcanic eruption. Petrochemistry shows that the original rock of greenschist should be basalt. Metamorphic rocks mainly belong to dacite and rhyolite. These characteristics reflect that the Dongyan Formation has the characteristics of bimodal volcanic rocks and was formed in continental extensional environment. The REE characteristics of greenschist also show the characteristics of continental tholeiite. The distribution of trace elements shows that the protolith of the metamorphic rock group is similar to the intraplate alkaline basalt of oceanic island and continental rift. Therefore, the Mesoproterozoic in central Fujian may be in an intraplate rift environment. Based on the analysis of the characteristics and prospecting methods of this kind of deposits, the prospecting criteria of this kind of deposits are summarized, and the prospecting prospects of the central Fujian rift and the Chong 'an-Shicheng rift are preliminarily analyzed.

Keywords: central Fujian; Mesoproterozoic; Dongyan Formation; An ancient rift valley; Mamianshan Group

Central Fujian is located at the intersection of Wuyishan Uplift, Yongmei Late Paleozoic Depression and Eastern Fujian Volcanic Fault Zone (Figure 1). Its main body is located in the exposed area of Precambrian metamorphic basement to the west of Zhenghe-Dabu fault zone and the volcanic basement uplift belt to the east. In recent years, many lead, zinc, copper, silver and gold deposits have been discovered in this area. There are more than 20 geochemical concentrated anomaly areas in the whole area, and these high anomaly areas are highly consistent with the exposed area of metamorphic basement including dongyan formation and the "skylight" of metamorphic basement located in volcanic rock area. The discovery and study of ore deposits related to Precambrian paleotectonic environment in central Fujian greatly promoted the prospecting process in this area. The study of massive sulfide deposits in ancient rift environment has been going through more than 20 years, but the research time in central Fujian is short and the research foundation is weak. Based on the existing work results and the main basic geological problems in geological survey, the main problems restricting the prospecting in this area are as follows: (1) For the explored and evaluated mining areas, the stratigraphic sequence and structural ore-controlling characteristics are the main problems in expanding the prospecting; Further integration of geophysical and geochemical remote sensing data and information to evaluate regional mineral resources is the key to the progress of prospecting work; Theoretical breakthrough is also an important aspect to avoid detours, so we should pay attention to perfecting the regional metallogenic law, and make clear the distribution space of primary layered deposits and the superposition mechanism of late structure, metamorphism and magmatic hydrothermal solution.

This paper is one of the achievements of the geological survey mineral resources evaluation project "Study on the Metallogenic Regularity of Lead-Zinc Deposits in the Rift Valley in Central Fujian" (project number: 2003 10200064). In this paper, the stratigraphic sequence, original rock assemblage, petrochemistry and geochemical characteristics of Mamianshan Group and Dongyan Group are mainly studied, and on this basis, the paleotectonic environment of Meso-Neoproterozoic in central Fujian is discussed, and the metallogenic prognosis is studied.

1 Neoproterozoic mamianshan group stratigraphic sequence

Mamianshan Group, as the main component of the Neoproterozoic metamorphic basement in central Fujian, together with Longquan Group in Zhejiang and Tieshajie Group in Jiangxi, became the representative stratum of the middle Neoproterozoic in Cathaysian ancient land, and its tectonic environment obviously controlled the massive sulfide Pb-Zn-Cu deposits deposited by submarine jet at the same time. However, the normal stratigraphic sequence and spatial overlapping relationship of Longbeixi Formation, Dongyan Formation and Daling Formation, which are components of Mamianshan Group in central Fujian, are still unclear, resulting in a chaotic pattern of Longbeixi Formation. Through field profile investigation, these typical strata are selected for metamorphic deformation research, and it is concluded that the metamorphic strata folds of Longbeixi Formation and Dongyan Formation are mainly small rheological folds in space. After many transformations, the metamorphic degree is deeper and stronger than that of Daling Formation, but the metamorphic degree of Daling Formation is not high and the deformation is weak. Therefore, it can be considered that the normal stratigraphic sequence of Mamianshan Group in the central Fujian rift should be Longbeixi Formation, Dongyan Formation and Daling Formation from bottom to top, which provides a scientific basis for further prospecting in this area.

Figure 1 Geotectonic Location Map of Rift Valley in Central Fujian and Its Adjacent Areas

In order to determine the age of bimodal volcanic activity in Mamianshan Group strata related to mineralization and verify the stratigraphic sequence obtained by field observation of structural metamorphism and deformation. In this study, the metamorphic rocks of Longbeixi Formation, Dongyan Formation and Daling Formation widely exposed in Jian 'ou area were selected for high-precision ion probe zircon U-Pb dating. The selected samples are taken from the typical stratigraphic profile in this area and are representative. Under the microscope, zircon is magmatic zircon and the product of ancient volcanic activity. The SHRIMP zircon U-Pb ages of Longbeixi Formation, Dongyan Formation and Daling Formation are 825Ma, 800Ma and 750Ma, respectively. It can be clearly concluded from the above tree rings that the metamorphic strata of Mamianshan Formation are Longbeixi Formation, Dongyan Formation and Daling Formation from bottom to top, which are the products of Neoproterozoic.

2 Ore-bearing Stratigraphic Sequence of Dongyan Formation of Mamianshan Group

2. Distribution characteristics of1

Dongyan Formation is mainly exposed to the north of Dongyan in Jian 'ou and Meixian in Youxi County, and consists of two metamorphic belts composed of northeast greenschist and marble lens (Figure 2). The exposed thickness is generally 300 ~ 400 m, and the extension is greater than 140km. The western part of the study area is exposed to the surface in a large area due to Caledonian uplift, and the eastern part is concealed under Yanshanian volcanic rocks in a large area due to late rifting, and only exposed in sporadic areas in the form of basement "skylight".

Fig. 2 Distribution map of metamorphic rock series in central Fujian. [ 1]

2.2 Stratigraphic sequence

Dongyan Formation is the main component of metamorphic rocks of Mamianshan Group, in which there are many volcanic interlayers. Previous studies have shown that the protoliths of greenschist and granulite are basic volcanic rocks (continental tholeiite) and acidic volcanic rocks formed in continental extensional environment, respectively, which constitute bimodal volcanic rocks. However, the understanding of the stratigraphic sequence of dongyan formation is still very shallow. Through the observation and sampling analysis of several borehole cores in Yan Feng mining area, it is found that the green schist of Dongyan Formation often appears alternately with gray-light gray granulite, schist and marble, with 6 lithologic sections and 3 rhythms. Microscopically, each lithologic profile shows the typical structure of volcanic rocks, and the petrochemical composition is also consistent with basic and acidic volcanic rocks. It shows that the rock formation in central Fujian is not the product of simple volcanic cycle, but has experienced many bimodal volcanic cycles. It may be due to a large number of volcanism that great heat and ore-forming materials are provided for mineralization in this area, which also shows that Dongyan Formation is not only a ore-hosting space, but also an important source of ore-forming materials.

Member 6 of Dongyan Formation: (Yang Qi) albite granulite mixed with thin (translucent) epidote, containing 1 ~ 2 Pb-Zn layer. The thickness is greater than 70m.

The fifth member of dongyan formation: epidote and epidote diopside mixed with thin marble, containing 1 ~ 4 layers of lead, zinc and silver deposits. The thickness is about 60m.

The fourth member of Dongyan Formation: albite granulite, albite schist mixed with thin mica schist, lenticular marble and green diopside, with a layer of 2 ~ 3m thick banded timely marble at the top. It contains 1 ~ 2 layers of lead and zinc. The thickness is about 140 ~ 280m.

The third member of Dongyan Formation: epidote, green diopside, actinolite schist and sodalite epidote, with lenticular marble and sodalite porphyry in the middle and upper part, containing 2 ~ 4 layers of lead-zinc (silver) ore and copper ore locally, with a thickness of 150m.

The second member of Dongyan Formation: albite granulite, albite (potassium) feldspar granulite, adamellite and granulite. The upper part is medium-thick layered marble with 1 ~ 3 Pb-Zn (mineralized) layer locally. About 250 meters thick.

Member 1 of Dongyan Formation: thick layered marble and green curtain diopside, containing multiple layers of lead, zinc and silver deposits. Thickness is greater than 100 m.

The three rhythms formed by the above six lithologic sections represent three cycles of basic-acid volcanic eruption and deposition, each cycle begins with basic volcanic eruption and ends with acid volcanic eruption and deposition. During intermittent volcanic eruption, especially in the later period of each cycle, marine carbonate deposits often appear. Pb-Zn-Ag deposits are mostly found in greenschists, indicating that mineralization is closely related to basic volcanic eruption and sedimentation.

3 Petrological characteristics of metamorphic rocks in Dongyan Formation

Dongyan Formation is mainly a set of ancient volcanic sedimentary formations dominated by greenschists. Its main lithologic types include greenschist, marble, quartzite and granulite, with diverse components.

Green schist is a typical rock in the middle and upper part of Dongyan Formation, including sodalite schist and green curtain sodalite schist. The tabular albite phenocrysts have obvious mottled structure, almond-shaped structure and hollow skeleton crystal structure, which show the characteristics of rapid condensation and diagenesis due to submarine eruption. Metamorphic rocks are mainly biotite plagioclase granulite and sodalite granulite, which are interbedded in greenschist.

4 Petrochemical

The average content of SiO _ 2 in the metamorphic rocks of Dongyan Formation is 57.99%, indicating that magmatic rocks account for a large proportion, and the content of SiO _ 2 in most samples is between 40% and 60%. Most samples belong to basalt area, picrite basalt area and trachyte basalt area (Figure 3), so the original rock of greenschist should be basalt. Metamorphic rock samples are mainly distributed in dacite and rhyolite areas, and only a few samples appear in normal andesite areas. The discriminant function diagram shows that most samples are distributed in intraplate tholeiite, intraplate alkaline basalt and a few volcanic arc basalts, which reflects that Dongyan Formation is mainly formed in continental extensional environment and belongs to alkaline tholeiite series formed in continental extensional environment.

Five kinds of rare earth elements

The total amount of rare earth in greenschist varies greatly, from 84.09× 10-6 to 474. 16× 10-6. The ratio of LREE/HREE is 4. 17 ~ 8.47, mostly 4 ~ 6, with an average of 5.97, indicating that LREE is highly enriched, with the ratio of La/Yb of 5.6 ~ 16.2 and the ratio of Eu/Sm of 0. 1 ~ 0.35, which is light. The value of δEu varies from 0. 1 ~ 0.38, and the europium is quite abnormal. The distribution pattern of rare earths shows a strong right deviation, which indicates that the green schist of Dongyan Formation is a normal metamorphic rock, which is very similar to the characteristics of volcanic rocks in continental extension environment. Some samples have REE geochemical characteristics of tholeiite and alkaline basalt, and both light and heavy rare earths have increased.

There is a significant difference between light and heavy rare earths, but the light rare earths increase rapidly, so the slope is large. The comparative study of REE distribution patterns (Figure 4) shows that REE distribution patterns of greenschists are very similar in general and have the characteristics of basalt under tensile conditions. The LERR/HREE values of the metamorphic rocks of dongyan formation mostly vary from 4 to 6, and the light and heavy rare earths are obviously differentiated, which should belong to continental tholeiite.

Fig. 3 Classification map of metamorphic volcanic rocks in central Fujian (according to Le Maitre et al., 1989).

Six kinds of trace elements

The normalized trace element distribution map of greenschist trace element mid-ocean ridge basalt (MORB) in Dongyan Formation shows that all elements are basically enriched in different degrees relative to MORB. The left half of the curve shows a small "uplift", with the intermediate elements Nb and Ta slightly deficient and the tail elements Ti and Y slightly lower, which indicates that the original rocks of this metamorphic rock group have the characteristics of tholeiite in continental rift, and are not obviously contaminated by crustal materials, similar to the intraplate alkaline basalts in oceanic islands and continental rift.

7 diagenetic paleotectonic environment

The results of petrology, petrochemistry and geochemistry show that the Dongyan Formation, the surrounding rock stratum of massive sulfide lead-zinc deposit, is a set of ancient volcanic sedimentary formations dominated by greenschist+granulite+marble. The protolith of greenschist is mainly intraplate tholeiite, which is composed of high alkaline tholeiite and transition basalt between tholeiite and alkaline basalt, and is in a extensional environment within the continent. Green schist and granulite constitute bimodal volcanic rocks. Therefore, the tectonic setting for the formation of the metamorphic protolith of Dongyan Formation is the rift environment within the continental plate.

8 Geological characteristics of the deposit

The massive sulfide lead-zinc deposit in the rift valley in central Fujian occurs in the Dongyan Formation of Mamianshan Group in Neoproterozoic. Some large and medium-sized massive sulfide lead-zinc deposits have been found in the metamorphic rocks of Mamianshan Group to the west of Zhenghe-Dabu fault, or in the "skylight" of metamorphic rocks of Mamianshan Group in Mesozoic volcanic rock area to the east of Zhenghe-Dabu fault. The former is a large lead-zinc deposit in Bawaiyang, Jian 'ou, and the latter is a large lead-zinc deposit in Dingjiashan, Youxi and Yan Feng. The ore-bearing rock series is Neoproterozoic marine volcanic-sedimentary metamorphic formation: the ore-bearing strata are mainly composed of greenschist, granulite, marble and quartzite. According to the characteristics of residual structure, structure and lithologic combination, the recoverable original rocks are mainly limestone, marine volcanic rocks, tuff and pyroclastic rocks. The deposit has obvious stratabound characteristics: lead-zinc bodies all occur in the rock section of Dongyan Formation, and the overall occurrence is layered, which accords with the characteristics of submarine volcanic eruption sedimentary deposits; Lead, zinc and sulfur (pyrite+pyrrhotite) ores have clear metamorphic micro-bedding; It has a good common mineral assemblage consistent with submarine volcanic eruption sedimentary deposits; Some traces of syngenetic fault activity have been found in ore-bearing rock series. Such as breccia ore and syngenetic fault breccia. Therefore, it can be determined that the main lead-zinc deposits in central Fujian are massive sulfide deposits of submarine volcanic jet deposition (Neoproterozoic)-metamorphism (Caledonian)-hydrothermal superimposed transformation (late Yanshan).

Fig. 4 Distribution pattern of rare earth elements in metamorphic volcanic rocks of Middle East Fujian Formation; The standardized data of chondrites are quoted from Sun & McDonough (1989) [2].

9 characteristics of post-superposition transformation

Since the formation of Cathaysian ancient land, the rift zone in central Fujian has experienced a geological evolution history of nearly 65438±0800ma. The massive sulfide deposits formed in Mesoproterozoic also experienced a long-term evolution process. Accompanied by strong tectonic deformation and transformation, regional metamorphism and magmatism superposition. This transformation makes the primary ore deposit (mineralization) disappear (structural uplift and denudation), or destroy (thickening of ore body fold structure and fault dislocation), or overlap (hydrothermal solution enriched primary ore or formed new types of ore deposits after magmatic period), or surface oxidation. This post-transformation involves two main aspects: deposit preservation and post-enrichment. The central Fujian rift is located in the Mesozoic magmatic active zone along the southeast coast, and the reformed mineralization is very developed. The late transformation of the early deposit is mainly manifested in three aspects: first, metamorphic transformation, which mainly experienced regional metamorphism in Jinning period; The second is the superimposed transformation of hydrothermal solution after magmatic period, which was mainly formed in the late Mesozoic and dominated in the later transformation; Thirdly, the structural transformation caused the deformation and displacement of early ore bodies. The superimposed transformation of magmatic hydrothermal solution is obvious in the whole area, but it is more obvious around the mining area. Due to the superposition of hydrothermal alteration, the characteristics of metamorphic rocks in mining areas are obviously different from those in regional metamorphic rocks. Generally speaking, altered minerals are developed in the mining area, such as diopside, epidote, chlorite, sericite and garnet. Field investigation and microscopic observation show that hydrothermal superposition mainly occurs in three main parts in the later period: first, obvious skarn deposits are formed near the contact zone of rock mass, in which a large number of altered minerals such as garnet and pyroxene occupy the surrounding rock, and at the same time, epididymitization and other alterations are formed around it; Second, there are ore bodies in the fault zone, mainly NNE faults and their derivatives, such as NWW fault in Yan Feng and NNE fault in Shuiji. In addition, the transformation of early ore minerals by late hydrothermal solution can also be found in early (Neoproterozoic) layered and layered ore bodies, which is initially considered to be formed by the superposition and replacement of late hydrothermal solution infiltrating metamorphic schists. The preliminary study shows that the hydrothermal superimposed transformation in the later stage has obvious distribution law, and the northern and eastern parts of the study area have strong superimposed transformation, strong alteration, thickening of ore bodies and rich grade.

10 prospecting criteria and prospecting prospect

The discovery of massive sulfide-type lead-zinc deposits in the rift valley in central Fujian is an important achievement of the transformation of prospecting ideas from magmatic hydrothermal and metamorphic hydrothermal vein deposits to stratabound deposits since the investigation of Wuyishan metallogenic belt. Up to now, large and medium-sized massive Pb-Zn (polymetallic) deposits have been discovered in Dingjiashan, Yan Feng, Dongkeng, Jianou Bawaiyang, Shunchang Mountain, Pingnan Pandi (Daixi), Jianyang Shuiji and Zhenghe Xiashan, with a lead and zinc resource of 333+334 1 of nearly 5 million tons. The discovery of large massive sulfide deposits in the rift valley in central Fujian fills the gap in the genetic types of deposits in this area and lays an important foundation for further searching for similar deposits and expanding reserves in this area.

On a larger scale, the cracking of Neoproterozoic Cathaysian land is a common geological event. The discovery and study of massive sulfide deposits formed by submarine volcanic eruption deposits in central Fujian have certain guiding significance for finding similar deposits in South China.

According to the exploration process and geological characteristics of Xifeng Dingxijiashan, Jianou Bawaiyang, Jianyang Shuiji, Zhenghe Xiashan and Pingnan Pandi in the central Fujian Rift, it is concluded that (1) the Mesoproterozoic Dongyan Formation (a set of spilite-amphibole volcanic rocks erupted by submarine volcanoes and shallow marine facies flysch formation) is the most characteristic. The distribution area of Mesoproterozoic-Neoproterozoic Dongyan Formation, especially the metamorphic rock "skylight" in Mesozoic volcanic rock area of Mindong Rift Valley, is a favorable area for finding such deposits. (2) The swelling zone at the core of the anticline, which is composed of metamorphic rocks such as the Mesoproterozoic Dongyan Formation, is favorable for the accumulation of ore-forming materials and the formation of thick ore bodies, and is a favorable part for finding large-scale ore-rich bodies; (3) The alteration of surrounding rocks such as diopside, actinolite, tremolite and epidote are obvious prospecting indicators; (4) Iron hat is formed on the surface of this kind of deposit after oxidation, and the oxidized ore often presents skeleton-honeycomb structure and colloidal structure, and sometimes dispersed fine galena crystals can be seen, which is a direct sign for finding this kind of deposit; (5) The anomaly of Cu-Pb-Zn-Ag assemblage in river sediments and soil is banded, with large scale and high concentration, which can be used as a good prospecting indicator; (6) The magnetic anomalies related to pyrrhotite are in regular bands, which can be used as a sign for finding such deposits. The abnormal profile with high polarization and low resistance in greenschist is also a favorable prospecting site. (7) Ancient pits (caves) are indirect signs for finding such deposits.

According to the above prospecting criteria, combined with the geological, geophysical and geochemical survey results in central Fujian, it is considered that there are prospects for further prospecting in this area in the following aspects: (1) There are more than 20 geochemical anomaly concentration areas with Cu, Ag, Pb, Zn and Au as the main components in the metamorphic rock area of Mamianshan Group in Mesoproterozoic and Neoproterozoic, with ten mineralization points. Through the exploration and evaluation of a small part of them, more than 10 large and medium-sized massive lead-zinc sulfide (polymetallic) deposits have been discovered. There are still a large number of geochemical anomaly concentrated areas and mineralization points with similar metallogenic geological conditions and prospecting criteria, which need further work and are expected to find more large and medium-sized massive lead-zinc sulfide (polymetallic) deposits. (2) The Mesoproterozoic Longquan Group is basically the same as Mamianshan Group in central Fujian in Suichang-Qingyuan area in the north of central Fujian Rift, and it may also be a spilite porphyry formation formed by submarine basic-acid volcanic eruption and deposition in the Mesoproterozoic continental rift. There are also a large number of ore deposits, mineralization points and concentrated areas of geochemical anomalies of gold, silver, copper, lead and zinc with the same metallogenic geological conditions. Therefore, through in-depth investigation and evaluation, it is possible to find a number of large and medium-sized massive sulfide lead-zinc deposits. (3) On the other side (west side) of the Wuyishan uplift Suichang-Shunchang uplift in Wuyi-Yunkai fold belt, a meso-Neoproterozoic continental rift-Chong 'an-Shicheng rift has also developed. Wanquan Group (also spilite-quartz keratophyre formation), which is similar to Mamianshan Group, developed in this rift valley, experienced a similar geological structure evolution history, and also had a large number of deposits, mineralization points and copper, lead and zinc geochemical anomaly concentration areas. Theoretically, large and medium-sized massive sulfide lead-zinc deposits may also develop in this area. Among them, the massive sulfide lead-zinc deposit discovered in Xiyuan, Ninghua in recent years has preliminarily proved this inference. The analysis shows that the central Fujian rift (including southwest Zhejiang) and Chong 'an-Shicheng rift still have great potential to find massive sulfide-type lead-zinc (silver) deposits.

refer to

[1] Zhang Da, Wu, Ye Yujiang, et al. Paleotectonic setting of East Rock Group of Middle-Upper Proterozoic in central Fujian. Journal of China Geo University. 2004, 15 (1):29~35 (English)

Sun, Wen Fuhai, mcdonough. Chemical and isotopic systems of oceanic basalts: the significance of mantle composition and process. In: Saunders Law Firm, edited by Nori M J. Magma in ocean basin. Boston: Blackwell Science Company,1989,313 ~ 345.

Proterozoic paleotectonic background and lead-zinc mineralization prediction in central Fujian

Zhang Da 1 2, Wu Ganguo 1 2, Di Yongjun 1, Yu Xinqi 1, Jianhua Tao, Shi Jianji 3, Zhang Xiangxin 1, Wang Qunfeng 1

(1. State Key Laboratory of Earth Process and Mineral Resources, China Geo University, Beijing100083; 2. Key Laboratory of Lithospheric Structure and Rock Detection Technology, Ministry of Education, China Geo University, Beijing100083; 3. Fujian Geological Survey Institute, Fuzhou 350003)

Abstract: Metamorphic basement in central Fujian is mainly composed of Proterozoic, Mesoproterozoic and Proterozoic-Early Paleozoic strata. Mesoproterozoic metamorphic strata include Longquan Group and Mamianshan Group. According to metamorphism, deformation characteristics and isotopic chronology, Mamianshan Group is composed of Longbeixi Formation, Dongyan Formation and Daling Formation from bottom to top. As the main body of Mesoproterozoic, the greenschist of Dongyan Formation is directly related to the massive sulfide deposits in this area. Dongyan Formation is a set of ancient volcanic sedimentary formations dominated by greenschists. Rock types mainly include greenschist, marble, quartzite and felsic rock. Green schist shows the characteristics of submarine volcanism. The protolith of greenschist is basalt. The protoliths of felsic rocks are dacite and rhyolite. These characteristics indicate that. Its formation is the result of bimodal volcanism, which is formed in the extensional environment within the mainland. The REE characteristics of greenschists also indicate that they are continental tholeiite. Trace elements show that the protolith of metamorphic rocks is similar to alkaline basalt in ocean island or continental rift. Therefore, the central Fujian area may be an intraplate ancient rift in Mesoproterozoic. According to the characteristics and exploration methods of this type of deposit, the prospecting criteria of this type of deposit are summarized, and the prospecting prospects in the rift valley in central Fujian and Chong 'an-Shicheng rift valley are analyzed.

Keywords: central Fujian; Mesoproterozoic; Dongyan Formation; Ancient rift valley; Mamianshan Group