Geochemistry,Geochronology And Petrogenisis Of Hongshan Complex In Southern Taihang Mountain

Southern Taihang Mountains is located in the southern part of the central zone,North China Craton,which is an important part in study of Mesozoic Magmatic Activity and tectonic evolution.Hongshan is the only alkaline complex which is studied as a whole in the past.Based on the detailed field observations,the rock type and magmatic evolution sequence of the complex is recognized.Meanwhile,Combined with the dated U-Pb ages,this paper offers petrological,t geochemical,zircon U-Pb geochronological and zircon Hf isotope data to constraint the genesis,formation age as well as the magmatic evolution.As a typical intrusive complex,which is consisted of syenitoid,concealed explosive,porphyry and veins emplaced terminally,the Hongshan complex is the main component of the eastern rock belt in Southern Taihang Mt.The syenitoids accounted for about 93%of the total rocks which has the characters of homologous and invasion multiply.It is consisted of coarse grained syenite,medium grained syenite,fine grained syenite,syenite porphyry and trachyte porphyry.The chemical compositions of the coarse grained syenite,medium grained syenite,fine grained syenite and the syenite porphyry in this study shows that the syenitoids have a characteristics of rich of silica and alkali.In the TAS diagrams,all the samples were felled within the scope of the syenite.The?REE has a large variation range(18.50×10^-6?179.79×10^-6)and shows a characteristics of rich LREE but defective HREE(LREE/HREE=6.94?13.10,(La/Yb)N=5.09?16.28),besides,the Eu shows unconspicuous abnormity(?Eu=0.88?1.21).Morever the standard trace element spider shows a characteristics of rich LILEs(Rb,Th,U,K)but depleted HFSEs(Nb,Ta,Ti).Combined with the previous results and the zircon U-Pb ages of the 2 samples in this paper(129?131Ma),the instrusive time of the Hongshan complex is confirmed of 128Ma to 135Ma,which is belong to early Cretaceous.Zircon Hf isotopic compositions are all negative values with a great range and the Hf crustal model ages focus on 1.1?2.6Ga,which is indicating partial melting of the enriched mantle.It is the North China Craton destruction that caused the spartial melting of the enriched mantle of the Taihang Mountain in Mesozoic,forming an alkali rich magma.Emplaced in the lower crust,the magma had crystallization differentiation of mafic minerals pyroxene and hornblende which accompanied with the slight contamination of the lower crustal material,and ultimately formed the Hongshan complex.