The Geochronology And Geochemistry Of Triassic Granitoids Of Zhangjiakou Area From The Northern Margin Of The North China Craton

Zhangjiakou region locates in the north of the North China Craton, western part ofthe famous Yanliao tectonic zone, the area exposed more intrusive pluton.Geochronology and geochemistry of the Triassic granitoids were studied. Preliminaryreached a certain understanding:(1)In the study area,Zhonga’liwusu rocks formd in Early Triassic(250.7±6.2Ma). TheMiddle Triassic rocks include Jiangjialiang(246.1±4.4Ma), Xinfangzi(250±16Ma),Wanshigou(238.6±4.4Ma) and Shanda(241.4±2.9Ma). The Late Triassic rocks includeDaolahudongcun(224±17Ma),Sanguxicun(222.1±2.6Ma,232.3±2.5Ma),Zhangerlinzi(237.9Ma) and Wenjiacun(228.2±2.9Ma).(2)Wanshigou rocks and Shanda rocks show high Si,Al,low MgO style.Yb and Y arelean,Sr is relatively high. LREE is enriched. Fractionation of HREE and LREE isclear.It has no obvious Eu negative anomalies.They are typical Adakite.Thisrepresents the thickened crust.(3)Daolahudongcun rocks,Sanguxicun rocks and Zhangerlinzi rocks have high SiO2and alkali.They are poor in CaO, MgO. They are enriched in Ga,HFSE and REEexcept for Eu. They show strong positive Sr、Ba anomalies. They have obviousnegative Eu anomalies in the REE patterns. REE distribution patterns show the typicalright-wing " Seagull ", showing the characteristics of a-type granites. A-type granitesoccur within the region on behalf of the environment into the extensional.(4) According to the various possible causes of rock in the study area, combined withits Nd isotopic characteristics of each rock,we inferred that the material of the rocks inthe study area mainly comes from ancient lower crust recycling.