Genesis And Geochemistry Characteristics Of Dianzhong Formation Volcanic Rocks Of Linzizong Group In The Cuoqin Area, Tibet

The Linzizong Group volcanic rocks is an important part of Gangdisetectonic-magmatite belt in Tibet, which is a product of magmatism of the transformprogress from syn-collision to post-collision.Between the syn-and post-collision,abundant information from the end of Subduction of the Neotethys to collision andpost-collision of India and Eurasian Plate was recorded. The study area is located inthe south Tibet Autonomous Region, the western section of the Gangdise belt,belonging to south Gangdise magmatic arc tectonic units. This article discusses thecause, differentiation and evolution characteristics, tectonic environment of theDianzhong formation. which is the lowest member of Lin Zizong group volcanicrocks, through to Dianzhong formation petrological and geochemical system study ofdistribution of large in survey area. The author detailedly contrast study theDianzhong formation with the formation in eastern and middle Gangdise.Study results showed that Dianzhong Fm volcanic rocks in coqen area is a set ofrhyolite, dacite-oriented pyroclastic rocks.Major Elements indicates that the volcanicrock is a peraluminous high-K calc-alkaline and calc-alkaline combination rock series,and has the characteristics of collisional orogenic. The emergence of shoshonitesuggests that the end of the oceanic lithosphere’s subduction and the start ofintracontinental convergence. Peraluminous rocks suggest that Magma Source hasmuch to do with the continental crust. The large ion lithophile of trace Elements (Rb、Th、K、La、Ce、Nd) are enrichment while high field strength elements (Nb、P、Ti) losses, which reflect the characteristics of island arc magmatism. Variousanomalies and ratio analysis revealed that the volcanic magma from the mantle mixedwith crustal material even mixed with the earth’s crust material in the source region.In the process of upwelling, there are also plenty of crust material mixed into themagma,eventually the magma evolved into an acidic magma.The magma sprayed thesurface and became a lot of acid rock.Rare earth element distribution curves arerightist smooth type. Negative Eu abnormal is glaringly, Ce abnormal is light. Thedistillation of LREE overtops HREE.Compare with middle and estern Gandise, the Dianzhong Fm volcanic rocks instudy area have many special features, such as a relative high degree of Acid、Potassium、aluminum, differentiation completely, large quantity of REE, more crustalmaterial. The comparative analysis of constant and trace element characteristicsshows that the Indian plate and the Eurasian plate collision pattern started at westernsection and gradually spread to the middle, and then the eastern section.From the perspective of time, the Magmatism of the Dianzhong Fm volcanicrocks started in the late Cretaceous, actived at about20Ma. The western part’s activetime was earlier than the eastern part’s, which showed the collision started from thewestern part. The peak of the collision was about65-60Ma, causing large areas ofmagma sprayed, producing a large area of Dianzhong Fm volcanic rocks.