Petrotectonic Assemblage Of Northern Great Xingan Range Mesozoic Volcanic Rocks

The study area is located in the the Daxinganling orogen west of the northern section,in the multi-block flattening District.Daxinanling Mesozoic magmatic activity is the most intense in the region.The purpose of this paper is through the comparison of the sample in different location to explain the association of igneous rocks,magma evolution and tectonic environment.The large volcanic activities begin with Tamulangou volcanic cycle,which mainly along the large fault zone,and roughly formed around 160?150Ma,rock combination of a set of alkaline-K calc-alkaline intermediate and mafic volcanic rocks,such as basalt,basaltic trachyandesite and trachyandesite.Nb,Ta and Ti negative anomalies,Zr/Y ratio is much larger than 3;Nb/Ta ratio is usually in the 13.15 to 17.89,show the mixed properties of mantle and crust source.The tectonic discrimination diagrams show the study area is in the Board inside environment and the fault zone region is in the post-collisional tectonic environment.Manketouebo group,consitituted by calc-alkaline intermediate-acidic volcanic rocks,mainly rhyolite,rhyolitic tuff,formed roughly between 150-140Ma;low Sr-high-Yb characteristics,represent the low-pressure formation environment,and relative extrusion tectonic environment.Manitu group is a set of alkaline acidic volcanic rocks,the formation time of roughly 140Ma before;the sample ?Eu of the study area between 0.78 to 0.90,an average of 0.84,a weak negative anomaly,indicating that the deeper formation of the environment,is a sort of high-pressure trachyte;La/Nb ratios average 2.57;of Ba/Nb ratios average of 61.26;average Nd/Th ratio of 2.97;above show the properties of the crustal source.Baiyingaolao group was formed in between 13 0Ma-11 0Ma,K calc-alkaline acidic rocks,low Sr-high-Yb characteristics,represent the shallower formation environment;Meiletu group is a set of K calc-alkaline intermediate and mafic volcanic rocks,with TNT loss,Zr/Y ratio 7.11-35.76,Nb/Ta ratio 10.81?19.98,shows the attribute of the board and extensional environment.According to the study of Pacific plate and the Okhotsk Ocean evolution,and combined with the comprehensive analysis of the various layers of volcanic rock,the paper consider that the Tamulangou,Manketouebo and Manitu volcanic rocks'formation have direct relationship with the closure of Okhotsk ocean basin;the formation of Baiyingaolao and Meiletu volcanic rocks are relate to the Pacific plate,which subduct into the north china craton caused lower crustal delamination,and then generated large-scale volcano volcanism.