Research On Volcanic Rock Lithofacies Of Baiyingaolao Formation In Zhenglanqi Area,Inner Mongolia

In this paper,the volcanic rocks of Baiyingaolao Formation in Zhenglanqi area of Inner Mongolia are studied in terms of petrology,petrography,zircon U-Pb dating and petrochemistry.On this basis,the lithofacies division and volcanic cycle of the Baiyingaolao Formation are divided,and the Mesozoic tectonic environment in this area is further discussed.Research indicates:The lithology of the Baiyingaolao Formation in the study area is mainly medium-acid volcanic clastic rocks,a small amount of lava and a small amount of volcanic clastic rocks;The zircon U-Pb dating results show that the Baiyingaolao Formation in the study area is formed at(140.61±0.53)Ma,which is the product of Early Cretaceous;The geochemical characteristics of rocks show high silicon,rich aluminum and low magnesium,titanium and phosphorus,which are similar to the composition of A-type granite;The analysis results of rare earth elements and trace elements show that the high field strength elements Nb,Ta,Hf and Ti are relatively depleted,and the large ion lithophile elements Rb,K and LREE are relatively enriched;Among them,Sr,P and Ti show strong negative anomalies,which are similar to the low Ti,Sr rhyolite and II-type rhyolites of the Daxinganling division;The petrographic analysis results show that the volcanic activity is dominated by the explosive phase,with a small amount of effluent and volcanic-sedimentary facies,during this period,the volcanic activity was strong and the eruption time was long,which was a strong period;According to the relationship between volcanism and geotectonics,as well as the cyclicality of volcanism,according to the classification scheme of supercycly-giantcycle-cycle-rhythm-layer,it is proposed that the Baiyingaolao Formation belongs to the Yanshan Movement-Pacific Ocean supercycle,and the Baiyingaolao-Meiletu giantcycle,among them,the Baiyingaolao-Meiletu giantcycle is further divided into 4 cycles and 10 rhythms;The tectonic environment analysis shows that the tectonic setting of volcanic rocks may be the extensional tectonic setting after orogenic formation under the subduction mechanism of the Paleo-Pacific plate.In conclusion,this paper systematically studies the volcanic rocks of Baiyingaolao Formation in Zhenglanqi area.On the one hand,it provides chronological evidence for thestudy of plate subduction in the Daxinganling area,on the other hand,it is of great significance to study the dynamic mechanism of the formation of Mesozoic volcanic rocks,at the same time,it also provides a theoretical basis for the exploration of volcanic reservoir in this area,which has theoretical and practical significance.