Mineralization And Petrogenesis Of Yanshanian Magmatic Rocks, Dabie Orogen

On the basis of field observations of the three study areas, ie. Xianghongdian(Gongdongchong Pb-Zn deposit) and Xiaotian-mozitan (Dongxi-longxing gold deposit)areas of North Huaiyang zone and Yuexi areas (Xichong Mo polymetallic deposit) ofNorth Dabie zone, petrography and zircon U-Pb dating are carried out to determine thetiming sequence of the magmatic rocks in the three study areas; both magmatic rocksclosely associated with mineralization and magmatic rocks have nothing to do withmineralization are selected to do the zircon in suit Hf isotopic research. Combiningwith the existing datas of chronology, major and trace elements, Sr-Nd-Pb isotope andzircon Hf isotope of the Mesozoic magmatic rocks in Dabie orogen belt, we try todiscuss the petrogenesis of different stages in the mining areas.LA-ICPMS zircon U-Pb dating of Mesozoic magmatic rocks, Yuexi area, range from133to125Ma, while133to128Ma for Xianghongdian area and131to127Ma forXiaotian-mozitan area. Combing with the existing chronology data of Dabie orogen,we conclude that Mosozoic magmatic rocks in Dabie orogen have a chronologyframwork as follow: early stage of143to130Ma, exhibit the characteristic of high-Kcalc-alkaline and have adakitic affinity; late stage of130to109Ma, show the trendingto alkaline rocks with occurrence of small amount of A-type granite around120Ma.Magmatic rocks of Yuexi area contain inherited zircons of Mid-paleoproterozoic(1850~2200Ma), Neoproterozoic (700~800Ma), Triassic and140~160Ma; while forXianghongdian area, North Huaiyang zone, inherited zircons exhibit not only ofMid-paleoproterozoic, Neoproterozoic (700~850Ma) and Triassic, but also of earlyPaleozoic (400~500Ma), late Mesoproterozoic and zircons near2500Ma, indicate adifferent source region compare to Yuexi area. Zircon Hf isotope suggest at least threesignificant crust growth are taken place in Dabie orogen, respectively3.0Ga,2.6Gaand1.8~2.1Ga.The tectonic setting in the Dabie orogen belt transformed from extrusion toextension after the continental collision of indo-chinese epoch to the late Jurassicperiod. Partial melting of thickened lower crust result by continental collision,generated the adakitic rocks before130Ma; large strike-slip motion of the Tan–Lufault near130Ma, might trigger the foundering of some fragments of theover-thickened lithosphere near the Tan–Lu fault, result the high Mg adakites of130Ma and granitic rocks as well as mafic rocks after130Ma. Among the granitic rocks after130Ma, the ones whose model age locate around1.8~2.1Ga closely related tothe mineralization in North Huaiyang zone.