Geological Characteristics And Tectonic Significance Of Volcanic Rocks Of Linzizong Group In Xietongmen Area,Tibet

The volcanic rocks of the Linzizong Group are widely developed from west to east on the southern edge of the Gangdese tectonic magmatic rock belt,which is the largest volcanic rock belt on the Tibetan Plateau.Previous studies focused on the eastern and western sections of the Gangdese belt.This paper focuses on the petrological characteristics,rock geochemical characteristics,and petrology of the volcanic rocks of the Linzizong Group in the Xietongmen area,which is exposed in the northern part of the Gangdese belt.And other studies to explore its structural background and formation environment.Through research,it is determined that the lithology of the Dianzhong Formation in the study area is mainly a set of middle base-intermediate acid volcanic rocks with volcaniclastic rocks.According to the main element characteristic results,it belongs to basalt-andesite-dacite-rhyolite-trachyandesite in type rocks.The distribution model of the volcanic rocks in the Dianzhong Formation presents a right-inclined curve enriched in light rare earths,with weak-moderate loss Eu,without Ce anomalies.The volcanic rocks of the Dianzhong Formation show the characteristics of enrichment of large ion philophile elements Rb and K,radioactive elements Th and U,and loss of Nb and Ti to different degrees.The annual wave group lithology is mainly composed of a set of thin-layer limestone,tuffy sedimentary clastic rocks,andesite,and volcanic clastic rocks,a small amount of rhyolite can be seen.The annual wave rhyolite is rich in SiO₂ and poor in FeO,MnO,Na₂O,K₂0,P₂O₅,Al₂0₃,Fe₂O₃,MgO and CaO.It belongs to the basic series of rocks,which are high-calcium-calcium basic series rocks and peraluminous rock.The distribution model of the Nianbo Formation volcanic rocks shows a weakly enriched right-inclined curve of light rare earth.Compared with the Dianzhong Formation,the degree of Ce loss is higher and the degree of rock differentiation is increased.The loss degree of Nb,P and Ti is enhanced.The volcanic rocks in the study area are all products of crust-mantle mixing,and have the characteristics of continental margin arc and orogenic belt environment.The early Dianzhong Formation showed that it was formed in the volcanic arc environment and was the product of the mixed source area.From the middle to the late period,it showed the transition environment formed in the volcanic arc to the same collision environment and was the product of the magma.The annual wave group shows that the volcanic arcs collide with each other,and the transitional environment after collision is the arc-type mantle source magma mixed into the crust.The U-Pb dating shows that the age of the Zhongzhong group in the study area is 64.15-61.9Ma;the age of the annual wave group is 53.7-52.87 Ma.It is inferred that the volcanic rock formation of the Linzi Zong group is closely related to the India-Asia continent collision,and the collision time is in the middle of the Dianzhong Formation,about 64-62Ma.