The Genesis Of Cuonadong Leucogranite In Southern Tibet

The Himalaya orogenic belt is a typical example of collisional orogenic belt,the high Himalaya crystalline rock series and the Northern Himalaya leucogranites belt are important parts of the Himalaya orogenic belt,Cuonadong leucogranite in Southern Tibetan is an important rock belt of Northern Himalaya leucogranite mineralization,the pluton is located on the eastern margin of the Northern Himalaya leucogranite belt,it is a product of the Himalaya orogenic belt formed by the collision between the India plate and Eurasia.In this paper,Cuonadong leucogranite as the research object,through field geological investigation,petrographic study of rocks,whole rock geochemistry and zircon U-Pb age analysis methods,the conclusions are as follows:Cuonadong leucogranite is divided into Two mica leucogranite,containing tourmaline two mica leucogranite and containing garnet two mica leucogranite,that three types of granites in space with certain lithofacies zonation:the edge phase is mainly fine grained two mica leucogranite,the transition phase is mainly medium grained two mica leucogranite,local development containing garnet two mica leucogranite and containing tourmaline two mica leucogranite,the intermediate phase is mainly coarse-grained containing tourmaline and garnet two mica granite,partial visible containing beryl and tourmaline granite pegmatite.Type of zircon in Cuonadong leucogranite were inherited zircon and magmatic zircon,The weighted average ages of zircon U-Pb was 21.88±0.92Ma,The main elements of granite composition:SiO₂=72.35%⁷7.38%,K₂O+Na₂O=7.66%⁹.39%,the average value of K₂O/Na₂O is 1.02 and A/CNK=1.006¹.17,the overall performance is rich silicon,rich Alkali,strongly peraluminous,poor calcium,titanium,magnesium,iron;Trace element composition changed greatly:Rb=43.2⁴32ppm,Sr=12.3¹07ppm,Ba=8.33³94ppm,rich large ion lithophile elements such as Rb,radioactive element such as U,Th,non active elements such as Nb,Ta,high field strength elements such as Hf,Zr,Y,loss large ion lithophile elements Ba,low field strength elements Sr,Weakly incompatible elements P,Ti;Amount of rare earth elements is low,La _N/Yb_N=1.26¹1.93,LREE/HREE=1.65⁷.98,for weak light rare earth enrichment type,?Eu=0.24⁰.72,the obvious negative europium anomalies,REE chondrite standardized type partition type curve is the right seagulls type.Upper limit of initial magmatic temperature of Cuonadong leucogranite is 628⁷92?,The average value is 691?,Among them,zircon saturation temperature of two mica leucogranite?The average value is 718??higher than containing tourmaline two mica leucogranite and containing garnet two mica leucogranite?The average value is 669??;The pressure of the two mica leucogranite is relatively dispersed and falls into the⁴00MPa zone,formation depth is¹3.3km,containing tourmaline two mica leucogranite and Containing garnet two mica leucogranite is relatively dispersed and falls into the 300⁴00MPa zone,Formation depth is 10¹3.3km;By discussing the source area of the rock and source rock properties that Cuonadong leucogranite is crustal origin,The partial melting of the source rocks from the crust,Mainly argillaceous rocks;The main formation mechanism of rock is formed by Muscovite dehydration melting reaction,among them,the formation of two mica leucogranite may be involved in biotite;The tectonic setting of Cuonadong leucogranite is the products of the metapelites dehydration result in partial melting in the background of the Post collision of India plate and the Eurasian tectonic;Through the analysis of relationship between Cuonadong leucogranite and Zhaxikang ore-field,found Cuonadong leucogranite in time and space is closely related to the Zhaxikang ore-field,the causes may provide such as Pb,Zn.Ore-forming materials for deposit formation,and provide ore-forming fluid for the Zhaxikang deposit mineralization stage I and Keyue deposit metallogenic stage.