Geological And Geochemical Characteristics And Geodynamic Settings Of The Tiezhai Complex In Linqu,Western Shandong

Western Shandong is a part of the North China platform,which is located in the southeastern margin of the North China Craton,experiencing multiple tectonic movement and extensive distribution of intrusive rocks.The general evolution trend of main magmatic types is basic?neutral?acidic?alkaline.In this paper,the rock geochemistry,mineralogy and zircon chronology of the 4 representative rocks of the Mesozoic complex in Linqu,western Shandong Province,are selected to determine the genesis of the complex rock mass,and the preliminary study of the dynamic background of the formation of complex rock and the indication significance of the complex rock to mineralization.The geochemical study of the whole rock shows that the Tiezhai complex has geochemical characteristics of quasi-Al,silicon-rich,alkali-rich and high Mg~#values.The total amount of rare earth is lower than 200?g/g,Sr and Ba content are high.The rare earth fractionation of the olivine in the base of the complex rocks is not obvious,and the Eu positive anomaly(?Eu=1.39).Neutral rocks have significant LREE enrichment[(La/Yb)n=10.24~42.65]and negative anomalies of high field strength such as Nb,Ta and Ti,and there is no abnormal characteristic of the Eu,which shows the geochemical characteristics of the adakite-like rocks.The zircon LA-ICP-MS U-Pb age of grey quartz monzonite porphyry was129±1.7Ma,2520±30Ma inherited zircon age;The zircon LA-ICP-MS U-Pb age of light red quartz monzonite porphyry was 125±1.6Ma.The results show that the Tiezhai complex rocks are formed around 125Ma and coincide with the peak of magmatic activity in the eastern part of North China Craton.Mineralogical studies have concluded that the hornblende in the hornblende inclusions in the grey quartz monzonite porphyry of the Tiezhai complex are the magnesiohastingsite,and the hornblendite enclaves is formed by crystallization differentiation.The plagioclase oscillatory zoning indicates that the grey quartz monzonite porphyry formed in the shallow phase of rapid cooling,and diorite formed in the relative static deep phase.According to the study of rock geochemistry,it is concluded that the original magma of the Tiezhai complex is originated from the partial melting of the enriched mantle,and the involvement of the ancient crustal material.Before the formation of such magma,in the lithosphere mantle,there has been a partial melting of continental crust material to the mantle of the olive rock metasomatism,the metasomatism of the mantle occurred in partial melting,the melt through crustal assimilation and fractional crystallization(AFC)that formed the Tiezhai complex.This paper summarizes the geodynamic model of magmatic rock evolution in western Shandong,the Tiezhai complex formed in the climax of the lithospheric thinning/Cratonic destruction in the Early Cretaceous,coincided with the massive magmatic activity stage of the North China Craton,and the dynamic process is the extrusion-to-stretch transition process.