Geochemical Characteristics And U-Pb Ages Of Mesozoic Granite In Louzidian Areas Of Southern Chifeng

Louzidian area within the southern Chifeng is located in the northern of North China Craton,and southern of Central Asian Orogenic Belt.A large scale of Mesozoic acid intrusion rocks,which is dominated by monzonitic granite and syenogranite present in the study area.In this paper,based on the analysis of petrographic,main elements,trace elements,isotope of U-Pb ages,together with field observation and regional geological background,and discuss the magma source area,tectonic environment and the dynamic background.The zircon U-Pb age of study granite are 220.4±1.9Ma?MSWD=0.54?,217.9±1.3Ma?MSWD=0.95?,204.3±2.3Ma?MSWD=5.4?.Constant element characteristics show that the Mesozoic granite in the study area is rich silica,rich alkali,AR and A/CNK range from 3.09 to 5.64 and 0.96 to 1.04,respectively.The granite within the study areas is characterized of quasi aluminum-peraluminous and high potassium calc-alkaline series.The relation between SiO₂ and Na₂ O is not obvious,the negative correlation between SiO₂ and K₂ O,Al₂O₃,CaO,TiO₂,MgO,P₂O₅ is obvious.The trace elements of the study granite which are rich in the content of large ionic lithophile elements such as Rb,Th,K,etc,and poor in the content of Ba,Ta,Nb,Sr,P,and Ti,which indicate the mineral differentiation of apatite,feldspar,and the differentiation of ilmenite oxides.The total of the rareearth elements ?REE change from114.05 to 399.96×10^-6 with an average of 216.53×10^-6,and above the earth crust ?REE value,the content of light rare earth elements?LREE?is between 73.76³29.28×10^-6,and the heavy rare earth elements?HREE?content is between 11.71⁷0.68×10^-6.REE are standardized in meteorites distribution curve which is tilted to the right,and the light rare earth enrich,the heavy rare earth and light rare earth fractionation is obvious,?Eu is0.14¹.00,the average is 0.53,the whole has weak negative Eu anomaly.The?87Sr/86Sr??of granite is 0.704538⁰.710634,with average value of 0.706165 between the continental crust range?0.706⁰.718?,?Nd?t?is low,which is-11.8^-5.7,two stage Nd model ages TDM2 were 1459¹712Ma.It is concluded that granites in the study areas are I type granites and are for med in subduction collision-post collisional tectonic background and derived from the ancient-Mesoproterozoic crustal material remelting and some mantle-derived subst ances added.This study will control tectonic evolution of the southern Chifeng and provide important information for the lithospheric stretching and thinning of the No rth China Craton.