Study On The Characteristics And Genesis Of Volcanic Rocks Of Baoligao Formation In Abaga Qi,Inner Mongolia

Baoligaomiao Formatiom can be classfied into two members.The lower one is clastic rocks,the upper one is volaconic rocks.This paper researches on the petrographer,geochemisty and chronology of the volcanic rocks of Baoligaomiao Formatiom.It suggestes that the former lower volcanic rocks members is devided into three ones,the second member mainly consists of intermediate basic lava,the third member mainly consists of intermediate acidity lava and pyroclastic rocks,and the fourth member mainly consist of acidic volcanic clastic rocks.The U-Pb dating ages of the zircons from the typical volcanical rocks of the third member were measured.The U-Pb dating of the zircons shows that Baoligaomiao Formatiom's volcanic rocks occurred in Late Carboniferous.Major elements show SiO₂ ranges from 48.54wt%to 74.64wt%,TiO₂ranges from 0.15wt%to 2.53wt%,MgO ranges from 0.24wt%to 2.62wt%,Al₂O₃ rangs from 10.48wt%to 13.24wt%,Na₂O ranges from 3.05wt%to 5.69wt%,K₂O ranges from3.63wt%to 7.3wt%.Trace element shows depletion of Sr,Eu,Nb,Ta,and Ti.Enrichment of K,Rb,Th,U,Zr,and Hf.?RZZ=67.43²61.05,LREE/HREE=4.40¹0.69,La_N/Yb_N=2.96¹7.94.The average?RZZ is relative low with significant differentiation between LREE and HREE.Geochemical characteristics show that the volcanic rocks this area formed in an island arc settings or arc settings.Based on synthentical analyses,it suggestes that the volcanic rocks in the study area are with the characteristics of an island arc or a continental arc volcanic rocks,formed nearby subduction zone.