Sedimentary Geological Characteristics And Tectonopalaeogeographic Significance Of Huashan Group In Dahongshan,Northern Hubei Province

The Huashan Group in Dahongshan,Northern Hubei Province,is a structural melange of the Jinning orogenic belt on the northern margin of the Yangtze Block.It is an important geological record of the Precambrian structural evolution of the Yangtze Plate and has important geological environmental implications for its research.The Dahongshan melange stratigraphy contains various combinations of materials from different sources,different ages,and different properties.There are different understandings about the origin,depositional environment,and the structural background of the different combinations of materials in the melange.The predecessors have done a lot of chronological and geochemical work on basic rocks in Huashan Melange,but there is still no systematic research on sedimentary rocks in the melange and clastic rocks in the matrix of melange.Therefore,in this paper,systematic petrology,geochemistry and detrital zircon chronology studies have been carried out on the sedimentary rocks in the melange rocks in order to analyze the paleoenvironment and provenances of the sedimentary rocks in the Huashan Group,and to discuss the ancient tectonic settings on the northern margin of the Yangtze plate in the Jinning period.Based on the analysis of sedimentary characteristics,rock material composition and deformation combination characteristics of the non-Smithian strata in the orogenic belt,siliceous rocks and volcanic tuffs,Turbidite,ophiolite(fragmented),basaltic and carbonate rocks,pebbles,and sand-debris Dolomite and argillaceous slate,conglomerate,and miscellaneous sandstone,and many different combinations of rock types were identified in the Huashan Group structural melange zone of the Dahongshan area in the northern margin of the Yangtze block.These rocks have turbidity flow,depth flow,traction flow,and chemical deposition and other deposition features.This paper focuses on the systematic petrology and geochemistry of the Huashan melange in the combination of the Lvlin-Taiyangsi profile carbonate group,the siliceous rock group,the Dahongshan top turbidite and the Nanfengya-Daya profile sandstones.Detrital zircon chronology study was conducted on the clastic rocks in the melange and the following conclusions were drawn:1)The siliceous rocks in the Huashan Group are formed in an acidic,medium salinity water environment and are biochemical cause,rather than hydrothermal cause.It is speculated that the tectonic setting formed by siliceous rocks is shallow-sea to deep-sea sedimentary environment on the continental margin;The dolostones in the Huashan group melange are formed in a shallow burial environment where oxygen enrichment is low and salinity is smaller than normal seawater,and they are consistent with the lithofacies characteristics of the Dagushi Group,the Taiyangsi Formation,the Luohanling Formation,and the Chenjiachong Formation,forming in a relatively stable passive continent.The marginal environment is presumed to be the debris from the Dagushi group that was involved with other materials in the subduction process.The sandstones turbidite in the Huashan melange are formed in the pre-arc basin and belong to the active continental margin island arc environment.The source of the sandstone turbidite is the felsic source and is deposited in the pre-arc basin.The Nanfeng-Daya sandstones were developed at Ocean island-Seamountain,and were presumed to be formed on the mainland island arc and the oceanic island arc environment.2)The youngest age peak of the four detrital zircons in the Huashan Group is 850 Ma,which indicates that the sedimentary age is less than 850 Ma.The age peaks of 850 Ma,2050 Ma,and 2650 Ma in the four detrital zircon age profiles are similar to those of the detrital zircon ages in the Dagushi group.The Huashan Group may be characterized by dual source which come from the magmatic arc and the continent.The source may be Dagushi Group and the Sanligang-Zhoujiawan Island arc of about 840-870 Ma.3)The Huashan Group is a set of rocks that formed on the active continental margin,the oceanic basin,and the passive continental margin.They converged in the Dahongshan area during the subduction of the Yangtze Block of the Jinning Period and the Tongbai-Dabie Block.In the non-Smithian strata,the material may originate from oceanic islands,intra-oceanic arcs,pre-arc basins,fractured lands,and marginal sea environment.