| The study area is located in Guangfeng District,Shangrao City,Jiangxi Province.The geotectonic location belongs to the Shaoxing-Jinhua ancient magma arc in the Jiangshao-Chenzhou-Qinfang suture zone.The rock type of the Nantuo Formation in South China has always been known as"morraine conglomerate",but field geological surveys show that the rock type of the Nantuo Formation in Guangfeng area,Jiangxi Province may be pyroclastic rocks rather than moraine conglomerates.On the basis of field geological survey and literature review,this paper has carried out the research on the petrographic,mineral chemistry and chronological characteristics of the Nantuo Formation"morraine conglomerate"in Guangfeng area,discussed the origin of the"morraine conglomerate",and obtained the following results and knowledge.Field geological surveys and petrographic studies have shown that the"morraine conglomerate"of the Nantuo Formation in Guangfeng area is actually breccia tuff.The breccia tuff of the Nantuo Formation in Guangfeng area has two colors,purple-red and gray-green,with breccia tuff texture and massive structure.The clastic components are mainly carbonate breccia,carbonate rock debris,quartz crystal debris and volcanic ash matrix.Field geological surveys and petrographic studies have shown that the purple-red breccia tuff is the original cause,while the gray-green breccia tuff is the result of fluid metasomatism of the purple-red breccia tuff.The filling of high temperature hydrothermal fluid causes the recrystallization of carbonate breccias,and the fluid is rich in magnesium and has strong reducibility.The Fe3+in the breccia tuff matrix is reduced to Fe2+and The calcite in the purplish red breccia tuff was metasomatized into dolomite,and the filling metasomatism of the fluid also led to the occurrence of illitization in the breccia tuff.The chronological research results of the breccia tuff in Guangfeng area show that the weighted average age of magmatic zircon is 776±15Ma.This paper believes that 776±15Ma can represent the age of formation of the purple-red breccia tuff of the Nantuo Formation in Guangfeng area,Jiangxi Province.The existence of breccia tuff in the Nantuo Formation in Guangfeng talc mining area indicates that a volcanic eruption occurred in this area.As the floor of Guangfeng talc mining area,the determination of the formation time limit of breccia tuff in the Nantuo Formation in Guangfeng talc mining area has indicative significance for controlling the ore bed,and can be used as the lower boundary marker of the ore bed,which has guiding significance for the exploration of talc ore.After petrographic and chronological studies,the petrogenesis and the age of the formation of breccia tuff of the Nantuo Formation in Guangfeng talc mining area is determined,which can provide a basis for further exploration of rock types and genesis of the Nantuo Formation in Qinhang area. |
