Petrogenesis of Duoxiasongduo masses in Yulong Cu(Mo)ore belt:Constraints from zircon U-Pb geochronology and petrogeochemistry
The formation genetic mechanism and dynamic background of in the Yulong Cu(Mo)ore belt remain controversial.In this study,we present a systematic dataset of whole-rock major and trace elements,zircon U-Pb dating and in situ zircon Hf isotopes,to constrain the petrogenesis of masses in the Duoxiasongduo area.The Duoxiasongduo mass is composed of monzogranite porphyry and alkali feldspar granite porphyry.Monzogranite porphyry is mainly composed of potassium feldspar,plagioclase and quartz,and alkali feldspar granite porphyry is composed of potassium feldspar and quartz.Petrogeochemical analysis shows that both of the rocks belong to high-K calc-alkaline to shoshonitic intrusions with high alkali and potassium.Moreover,these rocks are depleted in high field strength elements(HFSE,e.g.,Nb and Ti),but enriched in the large-ion lithophile elements(LILE,e.g.,Rb,Th and U)and Pb.Rare earth elements(REE)content ranges from 145.04×10-6 to 290.91×10-6.The ratio of LREE/HREE is relatively high(6～37).Eu varies from weak negative anomalies(Eu/Eu*=0.66～0.84)in the early stage to moderate negative anomalies(Eu/Eu*=0.35～0.39)in the late stage.The zircon U-Pb dating results show that the monzogranite porphyry and alkali feldspar granite porphyry crystallized at 38.3±0.6 Ma and 37.8±1.0 Ma,respectively.Both of them were formed in the same age,belonging to the Himalayan age,indicating that there was an important magmatic hydrothermal Cu-Mo mineralization event in the Eocene in the Duoxiasongduo area.The εHf(t)values of the zircons from the two types of rocks range from+1.3 to+2.6.Combined with the geochemical characteristics of elements and isotopes,the Duoxiasongduo ore bearing porphyry may be the product of juvenile basaltic lower crust which was derived from depleted mantle,which was possibly formed controlled by the Jinshajiang strike-slip fault system induced by the collision between the Indian Plate and the Eurasian Plate.
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