The Geochronology,Geochemistry Of The Yongsheng Porphyry In Yunnan Province

The lithology in Jinshajiang-Ailao Mountain area is complex,the lithology and the strata are well developed.Yongsheng county in Lijiang of western Yunnan,is located in the west of Jinghe-Chenghai fault and in the east of Jinshajiang belt.The alkali-rich porphyries is distributed in the form of rock pearls,which is an important part of the Jinshajiang-Ailao Mountain Aalkali-rich porphyry belt.Alkali-rich porphyries in Zhanhe county and Yangpin county have high contents of biotite,quartz and feldspars.By means of field geology survey,petrography,whole rock geochemical data analysis,Sr-Nd isotopes analysis,zircon LA-ICP-MS U-Pb ages and Hf isotopes analysis in this area,the space-time framework of Cenozoic magmatic rocks in the study area is replenished and enriched.Furthermore,it enriches the mineralogical and geochemical aspects of the alkali rich porphyry in western Yunnan,and provides temporal and material constraints for the crust mantle interaction in this area.In addition,the research results of this paper are compared with the previous research results,and the internal relations and differences are analyzed to deepen the understanding of the regional alkali rich porphyry and tectonic setting,which provides deep constraints for the study of the geological tectonic evolution and mineralization in the region.A total of 15 samples were selected for this analysis.Combined with hand specimen and microscopic characteristics,it is obvious that the rock has porphyritic structure.Phenocrysts are biotite,quartz,two kinds of feldspar?potash feldspar,plagioclase?and hornblende.There is one sample showing xenoliths,indicating the intrusion of material from the lower crust.The geochemical analytical results reveal that the rock mass are characterized by high K,LILE and LREE,low HFSE and HREE,obscure Eu abnormal.The K₂O+Na₂O mean value of this sample is 8.92%,the mean value of K₂O/Na₂O is0.97%,and the Peraluminous?A/CNK mean value is 0.99?,indicating that the sample belongs to high potassium calc alkaline-potassium rock series.The REE distribution pattern is right tilting type,and Eu-Anomaly is not obvious,indicating that less plagioclase is in source area.Even in geochemical diagramming,it is considered to be a small rock mass exposed to the same rock mass,which belongs to the product of the evolution of the homologous magma and has a similar diagenetic background.Porphyry are shallow intrusive rocks,which are of great significance for the environment and material carrying in the source region.The zircon age of the alkali rich porphyry magma obtained in this paper is 33.17Ma³4.39Ma in the peak period of the magmatic activity of the Jinshajiang-Ailao Mountain rich alkali porphyry zone?45³0Ma?.Combined with geochemical data,it is considered that it is similar to the composition and genesis of other alkali rich porphyry zones on the tectonic belt?such as the Jianchuan and Ma Chang Qing rock mass?.The mechanical conditions are consistent with the source area characteristics,all of which are continental arc environment,and have a mixed source area of crust and mantle,that is,under the background of dynamic properties of the India Eurasian plate collision period after the collision period,the continental arc environment after the orogenic period makes the thickened lower crust and upper mantle material partially melted and form the Yongsheng alkali-rich porphyry.