The Geochemical Characteristics And Tectonic Setting Of Volcanic Rock In Baiyingaolao Formation From Xiwuzhumuqin Area Inner Mongolia

The article studied the goegoly, geochemistry and Zircon U-Pb ages of thevolcanic rocks in Baiyingaolao Formation from Xiwuzhumuqin area Inner Mongolia.The author summarized the petrological and geochemical characteristics,determinedthe formation age,dicussed the the volcanic magmatic and analyzed the tectonicsetting of the volcanic rocks.The rock types of Baiyingaolao Formation include Rhyolitic tuff,Rhyoliticignimbrite, Tuffaceous sandstone, dacite, rhyolite.All these rocks give priority toeruption facies volcanic rock and overflow facies and sedimentary facies account foronly a small number of them.The zircon U-Pb dating result of volcanic rocks is131-134Ma, indicating that the acid volcanic rocks of Baiyingaolao Formation wereformed in Early Cretaceous.The result of major elements show that the volcanic rocks are characteristicdby high silica, alkali,lower magnesium, titanium, phosphorus,whith close to theaverage composition of the world A-type granites. They belong to alkaline seriesaccord to alkalinity rate. The result of trace elements and rare earth elements showthat all the rocks are characterized by depletion in HFSE like P, Ti,Nb, Ta, etc.,enrichment in LILE such as K、Rb and LREE.but the Ba and Sr are negative anomaly. All these Characteristics are equivalent with the low Ba-Sr rhyolite from DaHinggan Mountains defined by other researcher.Comprehensive analysis shows that the primary magma of the volcanic rocks inBaiyingaolao Formation from Xiwuzhumuqin area were derived from partial meltingof crustal rocks. The volcanic rocks were impacted by the Pacific plate whichsubducted to the Eurasian plate and formed in the extensional setting after thecompressive orogenic.