Stratigraphic Sequence And Tectonic Attribute Of Late Jura Volcanic Rocks In Hraoshan,Zhalantun,Inner Mongolia

The studied area is located in the volcanic eruption belt of Daxinganling area,with the Mesozoic rocks relatively well developed.The basic geologic study is very poor in this area,which leads to chaos of the strata division.By comparising the samples of different locations,this paper is aimed at explaining the characteristic of the volcanic rocks and the age definition,comparing with the adjacent areas-the north of Daxinganling area,Hailar Basin and North of Hebei-West of Liaoning area,and then discussing the facies of volcanic rocks and the tectonic setting of the volcanic rocks.Late Mesozoic rocks extensively outcropped in target area.This series of stratum is divided into three formations-Manketouebo Formation,Manituzu Formation,and Baiyingaolao Formation from bottom to top.The Manketouebo Formation is mainly consist of acid volcanic rocks,the Manitu Formation intermediate volcanic rocks,and the Baiyingaolao Formation acid volcanic rocks and volcanic classific sedimentary and so on.Considering the ages of zircon and the interrelations of different stratigraphic units,it can be draw that the volcanic rocks belong to Late Jurassic.This volcanic rocks are similar with the late Mesozoic rocks in North of Hebei-West Liaoning,but different with the late Mesozoic rocks in the north of Daxinganling area and Hailar Basin.The volcanic facies varies.It is pyroclastic flow facies at the bottom of the Manketouebo Formation,explosive facies in the middle,and eruptive sedimentary facies or sedimentary facies of volcanic lake on the top.It is mainly effusive facies at the bottom and explosive facies on the top in Manitu Formation.There are many faces in Baiyingaolao Formation:it is mainly pyroclastic flow facies,explosive facies and eruptive sedimentary facies or sedimentary facies of volcanic lake on the top,with sub-volcanic rocks intruded later.The late Mesozoic rocks is mainly belonged to between calc-alkali and K calc-alkaline.Rare earths distribution curve shows generally a rightward heeling form:light rare earths concentrate and heavy rare earths are of depletion.Based on the geochemical analysis results and geotectonic background,it can be concluded that Late Mesozoic rocks in studied area were formed in an extrusion tectonic environment,where the closure of Okhotsk ocean mainly resulted in the formation of this rocks,along with the pacific plate tectonics.