Chronology And Geochemical Characteristics Of Early Cretaceous Volcanic Rocks In Jiyuan Area,Northern Da Hinggan Mountains

This paper,the volcanic rocks of Baiyingolao Formation and Manitu Formation in Jiyuan area are selected as the research objects.Based on the summary and field investigation of the previous research data,the types,ages and geochemical characteristics of the collected rock samples are analyzed in all aspects.The age,genesis and tectonic movement background of the samples are discussed,which is the Mesozoic volcanism and tectonic movement background in Jiyuan area.The tectonic environment provides strong evidence.The LA-ICP-MS dating results show that the volcanic rocks in Jiyuan area were formed in the early Cretaceous.The age of the volcanic rocks in Baiyingaolao Formation is 112.8±0.8Ma,and Manitu Formation is 128.2±0.4Ma.The chemical data of Baiyingaolao Formation show that the content of high silicon?75.74%⁸2.87%?,total alkali?Na₂O+K₂O=6.65%⁸.71%?,CaO content is between 0.01%and 0.02%,and MgO content is between 0.01 and 0.03%.The curve in the pattern distribution diagram inclines to the right,and EU is negative.?REE is between 146.7×10^-66 and 853.15×10^-6,the average value is 328.4×10^-6,with high LREE/HREE fraction[?La/Yb?_n=1.13⁵.46,the average value is 2.98].They are riched in Rb,U,Th,K,Zr and depleted in Ba,Sr,Ti.The chemical composition is similar to A-type granite,which originated from partial melting of lower crust rocks.The chemical data of Manitu Formation show that SiO₂ is between 68.87%and73.9%,total alkali?Na₂O+K₂O?is between 7.6%and 9.17%,CaO content is between0.69 and 0.94%,MgO content is between 0.21 and 2.26%.The sample have the characteristics of high silicon,rich alkali,aluminum and low content of magnesium and calcium,which belongs to high-K calc-alkaline peraluminous rocks.The curve in the pattern distribution chart inclines to the right and Eu is negative.?REE is between186.2×10^-6 and 210.4×10^-6,the average value is 200.3×10^-6,with high LREE/HREE fraction[?La/Yb?_n=16.31¹8.80,the average value is 17.49].They are riched in Rb,Th,U,K,Ba,and depleted in Nb,P,Ti.The chemical composition is similar to I-type granite,which originated from partial melting of lower crust rocks.