Geological Characteristics And Tectonic Significance Of Niuxinshan Granite In East Hebei Province

The Niuxinshan granite is located at the junction of Qianxi County and Kuancheng County,Hebei Province,China.Niuxinshan granite is not only the host rock of Niuxinshan gold deposit,but also the metallogenic parent rock of gold deposit.Therefore,it is of great significance to study it.This article takes Niuxinshan granite as the research object.Through detailed field geological survey and sample test and analysis,the geology,geochemistry and chronology of Niuxinshan granite are studied and the diagenetic age,genesis,tectonic environment and significance of the granite are discussed.The conclusions are as follows:(1)Nearly NE-SW distribution,Niuxinshan granite is a small complex rock mass,which is composed of red potassium feldspar granite and white monzonitic granite.The edge of the Niuxinshan is red medium-coarse-grained porphyritic potassium feldspar granite,and the center is white medium-fine-grained monzonitic granite,which intrudes into the red granite.The distribution of Niuxinshan granite is controlled by the superposed fold of the NE fold of Yanshanian and NW fold of Archean basement.(2)Niuxinshan granite belongs to the series of peraluminous-high potassium calcalkaline granite rich in silicon and potassium.It is enriched in large ion lithophile elements(LILE)K and Rb,depleted in Ba and Sr,and depleted in high field strength elements(HFSE)such as P,Ti,Nb,U and Yb,where P is strongly depleted.The fractionation of heavy and light rare earth elements is not obvious,showing a strong negative anomaly of Eu and magma evolution has undergone the crystallization and separation of plagioclase.The study of Pb isotopes shows that the granite source rocks come from the lower crust,which is mainly the product of partial melting of the lower crust rocks.(3)LA-ICP-MS zircon U-Pb isotope dating results show that the weighted average age of the red potash feldspar granite is 170.8±0.58,and the age of the blue-gray monzonite is 165.3±0.89Ma,indicating that the red potash feldspar granite was formed older than the blue-gray monzonitic granite,and the emplacement age of the rock body belongs to the Jurassic.(4)The structural diagram shows that Niuxinshan granite belongs to intra-plate granite and post-orogenic granite and basically belongs to A-type granites.The tectonic setting is the transition from post-collision stage to post-orogenic stage,which is the northern margin of the North China Plate.Under the background of the closed collision of the oceanic crust,the in-situ stress relaxes,and the internal plate tension occurs.Under this tension background,the rock mass intrusion occurs and a large-scale granite body is formed.This is also the transitional stage from regional extensional structure to the Yanshan intracontinental orogeny.