Geochemistry,zircon U-Pb Geochronology And Implication For Tectonic Setting Of The Bozhushan Granite In Southeastern Yunnan Province, SW China

The Bozhushan area(Research Area)is located in the western margin of the South China fold system and the central part of the Southeast Yunnan Ore-Concentration Area,which is an important part of the magmatic-metallogenetic belt in the western part of South China.All the known tungsten-silver-tin polymetallic ore deposits in the research area are closely associated with the Bozhushan granite pluton.They all formed in the Late Yanshannian period,same to the Bozhushan granite which was a complex rock mass formed by the multistage magmatism.Through the research on petrological characteristics,zircon U-Pb dating,whole rock geochemistry and Sr-Nd isotope geochemistry of the Bozhushan granite,this paper discuss the formation age,petrogenesis and the relationship with mineralization.The main conclusions can be drawn as follows:1.Our new zircon U-Pb date indicate that the intrusion age of Bozhushan pluton dates back to the Late Cretaceous,a short period of time ranging from 87.33 to 91.17 Ma.The Zirconic U-Pb dating of Bainiuchang granite samples are(89.06±0.92)Ma,(90.50±1.0)Ma and(91.17±0.77)Ma respectively,with the Tuanshan samples(87.33±0.33)Ma,(89.49±0.41)Ma,and the Huazidong samples(88.60±0.82)Ma,(88.94±0.77)Ma.2.The main rock type of the Bozhushan granite is biotite monzogranite,characterized by shoshonite series.Most of the sample plot in the metaluminous to weakly peraluminous granites field,and the others in the strongly peraluminous granites.All the samples have similar REE and trace elemental geochemistry,showed in the diagrams of primitive mantle-normalized trace element concentrations and chondrite-normalized rare earth element distribution patterns.They all show moderate negative Eu anomalies,positive Rb,Th,La Nd anomalies and negative Ta,Nb,P,Ti anomalies.3.The Bainiuchang granite is totally rich in ore-forming elements such as Ag,W,Pb,Zn.The Guanfang and Huazidong granite is rich in W,Pb,Zn.Therefore,the Bozhushan granite provides the important metallogenetic material source for mineralization.4.Based on the results about whole rock geochemistry and Sr-Nd isotope geochemistry,together with the regional background,this paper considers that: The Bozhushan granitoids are geochemically considered as S-type granite.And associated with the change of the Paleo-Pacific Plate subduction in Late Cretaceous,the formation of the Bozhushan granite is related to a collision and post-collision geological environment under active continental margin.And the Bozhushan granitoids evolve from the parental magmas which is indicated a crustal source,under a probable original temperature of 751.9-852.7? by calculating the Zr saturation temperature.