| Zhejiang section of Wuyi metallogenic belt,attaching to the northeast area of Wuyi metallogenic belt,is one of the most important metallogenic areas in Zhejiang Province.With high degree of exploration,low degree of research and less breakthroughs,especially the controversial source of ore-forming material,the prospecting direction of the region is restricted.In this paper,Pb isotopes of main strata and metamorphic rocks,magmatic rocks in Zhejiang section of Wuyi metallogenic belt were measured.Combined with previous studies on the Pb isotope data of typical deposits in the study area,the ore-forming materials in the study area are mainly related to Yanshanian magmatism.Based on the discussion of the metallogenic tectonic environment during the Yanshanian,the magmatic process is clarified that since the Cretaceous,the mantle component of the magma source areahas been gradually increased with the changes of the times.The research results have important theoretical and practical significance for further prospecting in the study area.The main achievements of this study are as follows:(1)On the basis of previous studies,through the analysis of the strata,tectonics and the exposed state of magmatic rocks in the study area,collating the distributive characteristics of regional deposits and their types,the regional tectonic features and evolution were deeply studied.According to the tectonic thermal events and metamorphic deformations in the tectonic evolution of the Zhejiang section of Wuyi metallogenic belt,this thesis finally draw a conclusion that the ore deposit distribution is most relevant to regional strata,faults and rock mass.(2)The Analysis on the Pb isotopic data of 22 metamorphic basement,29 magmatic rocks and 5 typical ore deposits in this area show that the Pb isotopic compositions of the metamorphic rocks have obvious characteristic of the upper crust source.The Pb isotopes of magmatic rocks vary during the different period,but it is mainly composed of above crust and orogenic belt lead.At the same time,the Pb isotopic composition of ore in the typical deposit in the study area is dominated by orogenic(mixed)Pb,with some of the deeper source(lower crust or mantle)Pb involved.In addition,the Pb isotopes of ore Pb are similar to those of the Yanshanian magmatic rocks.The Yanshanian magmatism may be the dominant metallogenic factor and provide the most important metallogenic material.(3)The geochemical anomaly of soil and stratigraphic distribution indicate that:the Au,Ag,Pb and W in the studied area are related to the volcanic-intrusive effects during the late Yanshanian early stage(145-115Ma),and Cu,Sn and Mo are related to the lava-intrusion effect as mantle-derived materials increase in the Late Yanshanian late stage(115-100Ma).Therefore,the source of ore-forming materials in this area is mainly Yanshanian magmatism.(4)Study on more than 70 samples of 11 Yanshanian rock samples using geochemical analysis method.Zircon U-Pb geochronology indicate that intrusive rocks in Yanshanian late period early stage(145-115Ma)are mainly distributed in the west of Lishui-Yuyao fault region.Intrusive rocks in Yanshanian late period late stage(115-100Ma)are mainly distributed not only in the East of Lishui-Zhoushan fault,but also extending to the north west from the west of Suichang-Songyang to the Jiangshan-Shaoxing fault.Geochemical analysis show that Al-Saturation Index of Yanshanian is mainly quasi-aluminum-persalane and the distribution of rare earth element chondrules in the intrusive rocks is obviously negative in Ba,Sr and Eu(Eu/Eu*=0.03-0.86).Content of microelements Nb,Ta is low,and intrusive rock mainly own the characteristics of A-type granite plate extension.This result show that,although there have no intrusive rocks in some age and the distribution gradually moved eastward,the tectonic environment is unified.In addition,Sr-Nd isotopes indicate that magmatic mantle source material gradually increases with age.(5)According to the latest results of recent plate rebuilding and the seamount K-Ar age,it can be studied that from 145 to 100Ma,the paleo-Pacific plate subducted generally along northwestward and westward beneath the lithosphere in the south-eastern China and the subduction direction did not change significantly.During the process,the oceanic plate itself undergoes the process of detachment,rotation and retreat.Mantle material,after melting crustal substance at low velocity in lower crust,intruded into the upper crust through deep fracture and eventually formed the Late Yanshanian magmatism.(6)Under the late Mesozoic Paleo-Pacific subduction mechanism,with the combined effect of pre-existing faults and regional crust low velocity layer,the study area was affected by massive volcano eruption and magmatic intrusion of deep faults control.Finally,it formed 145-115Ma series of Au,Ag,Pb and W controlled by faults,volcanic bodies and invaded bodies.With the retreat and steepening subduction of the Paleo-Pacific plate,increasing source material of the mantle,so that formed a Mantle Source-related Cu,Sn,Mo series(during 115-100Ma). |
PDF Full Text Request