Jurassic Tectonic-Magmatic Evolution In The Southern Qinghai-Tibet Plateau

Through the use of 1:250,000 area tune,1:500,00 area tune/mine tune,the relevant scientific research report,published papers,dissertations and tutor team nearly 20 years accumulated research area chronology and petrochemical data,based on the fine division of the Jurassic magmatic rocks and the analysis of the rationality of the main chemical elements in the Jurassic related magmatic rocks in the study area,the petrochemical type?TTG and high Mg rock combinations were identified.And then from the perspective of rock assemblage and its evolution,the evolution of Jurassic tectonic magma is discussed,and the following basic understanding is obtained.?1?J₁ rock assemblage characteristics:T₁T₂ combination is mainly distributed in the eastern part of Lhasa-Linzhi sub-the Eastern part of Lhasa,and a small amount is distributed on the southern margin of the Pazhi-Zayuya sub-the Bomi County area.The G₁G₂ combination is mainly distributed in the PangduoChayu sub zone,and a small amount is distributed in Lhasa-Linzhi sub-the eastern part of Lhasa City.In the south of the Songduo fault zone,the TTG combined band with the combination of T₁T₂ and a small amount of G₁G₂ was formed.In the North songduo fault zone,GG combination zone is formed and the whole presents the features of the belt,edgewise composite and the central breakthrough.And then it indicated the early Jurassic period of the eastern oceanic crust of the YarlungZangbo River began to subduction northward.?2?J₂ rock assemblage characteristics:T₁T₂ combination is mainly distributed in the southern margin of Lhasa–Linzhi sub.The distribution of G₁G₂ is relatively dispersed,mainly distributed in the suburbs of the Chuoqin-Namucuo sub,the Shiquanhe-Bange sub,the Pangduo-Chayu sub and the Lhasa-Linzhi sub.A combination of T₁T₂ and a small number of G₁G₂ TTG combined bands were formed in the southern margin of the Lhasa-Linzhi sub in the Gangdise Formation,and the GG assemblage zone was formed in the northern Shenzha-Jiali area.And then it indicated that the mid-western oceanic crust of the Brahmaputra during the Middle Jurassic began to subduction northward.?3?J₃ rock assemblage characteristics:The distribution of T₁T₂ is relatively scattered,mainly distributed in Longgeer-GongbuJiangda sub,Lhasa-Linzhi sub and laguigangri sub.The distribution of G₁G₂ is relatively dispersed,mainly distributed in Cuoqin-Namucuo sub,Longgeer-GongbuJiangda sub and Laguigangri sub.Forming a TT combination zone in the Zhongba area;forming a TTG assemblage zone with a nuclear complex matrix in the eastern part of the laguigangri sub;forming a TTG zone in the southern margin of the Lhasa-Linzhi sub;forming in the western part of the Longueer-TTG combination zone;in the Shenzha-Jia Li area to form GG combination zone.And then it Indicated that during the Late Jurassic period,the YarlungZangbo River oceanic cranes entered a comprehensive subduction stage.?4?Understanding of tectonic magmatic evolution:combined with the basic characteristics of rock chemistry,TTG combination characteristics and magmatic activity characteristics,It is concluded that The eastern oceanic crust of the YarlungZangbo River began to subduct northward,and the subduction intensity was relatively large and relatively fast.During the Middle Jurassic period,The oceanic crust in the central and western part of the YarlungZangbo River began to subduct northward,and the subduction intensity was relatively weak and relatively slow.During the Late Jurassic period,the YarlungZangbo River oceanic oceanic crust were fully subducted northward,further deep melted and expanded,and the shallow fissures became weaker and magma activity became slower.