The Geochronology,Geochemisty Of The Jiudingshan And Baofengsi Porphyry In Dali Yunnan

There is a NW porphyry belt around the Jinsha River-Ailao Mountain Fault which is along the southeastern margin of Tibetan Plateau and the Collision boundary between India plate and Eurasian plate.In recent years,a large amount of copper and molybdenum deposits which are genetically related with porphyry belt were found in this belt.Many scholars have also done a lot of research on the genesis mechanism of the porphyry.Jiudingshan and Baofengsi rock mass were chose as the study area in this paper.By LA-ICP-MS zircon U-Pb dating analysis,Jiudingshan monzonite porphyry age is 35.3±0.2Ma(MSWD=0.43),Baofengsi monzonite porphyry age is 35.6±0.2Ma(MSWD=0.36).The geochemical analytical results reveal that the rock mass of Jiudingshan and Baofengsi are characterized by high K2 O and Na2 O contents,belong to high potassium calc alkaline-potassium rock series,and exhibit peraluminous features(A/CNK=1.13 to 1.72).The rocks are characterized by enrichment in light rare earth elements(LREE),and moderate Eu anomalies(?Eu=0.61~0.86).The rocks are also characterized by enrichment LILE(Rb?Th?U?K)and depletion in HFSE,and display the “TNT” anomalies.The porphyry in the study area is similar to the geochemical characteristics of large-scale magmatism in Yunnan Sanjiang.These similarities reveal the connection of their tectonic background,material source and diagenetic mechanism.Regional tectonic evolution and rock geochemical characteristics show that Magmatic magmatism is related to the sinistral strike slip produced by the collision between the India plate and the Eurasian plate.The samples collected from the study area are C adakite.The alkali rich magma originated from the melting of the thickened lower crust,and the addition of mantle material,the crust and mantle magma have been prominent mixing.