Characteristics And Formation Mechanism Of The Mesozoic Volcanic Rocks From In Wuliyasitai Area,Inner Mongolia

In this thesis,the research of petrology and geochemistry have been carried out on the volcanic rocks in the Mesozoic Volcanics in Wuliyasitai area of Dongwuqi.This paper studies the chronology of volcanic rock,too.Provides precise chronology of the volcanic rocks of the data,this paper expounds the formation of volcanic rocks in the studied area and analyzes the forming tectonic background.The volcanic rocks of Wuliyasitai area are mainly rhyolite,dacite,andesite,etc.It is a set of acidic volcanic rock,The LA-ICP-MS Zircon U-Pb dating of the rocks is 131.6±1.8Ma-153.2±0.6Ma,which indicates its eruption in the Late Jurassic-Early Cretaceous.They have SiO2 contents of 56.15%-77.52%,as in the acid-acidic volcanic rock;Al2O3 contents of 11.13%-17.15%;TFe2O3 contents of 0.81%-8.07%,MgO contents of 0.17%-3.27%,Magnesium iron content is low;TiO2 contents of 0.04%-2.06%,the low of Ti;The alkali(Na2O+K2O=5.89-10.91%);and sodium(Na2O/K2O=0.12-1.7),The content of K higher than Na.All the samples of the volcanic rocks are characterized by the enrichment of LILE,depletion of HFSE,have less basic compatible components(Cr,Co,Ni)and Mg#,which show the magma derived from the lower crust.Primitive mantle-normalized spidergram for the rocks,the volcanic rocks are characterized by the enrichment of LILE and LREE,Loss of Nb features with high field strength elements.The ratio of Rb/Sr?Ti/Zr and Ti/Y shows that volcanic rock has the characteristics of the shell source magma.Most of the sample falls into the source area by diagrams of(La-Yb)N vs.? Eu and diagrams of Ca-Fe-M,it also suggests that formed by the partial melting of crustal rocks,There may be an mantle source of Manitu Formation.The geochemical features of rhyolites areconsistent with A-type granite.Comprehensive analysis shows that the Mesozoic rocks formed,which should be the result of lithospheric extension after the closure of Mongol-Okhotsk Ocean.