• 责任者：Xie Yincai (State Key Laboratory for Mineral Deposits Research ; School of Earth Sciences and Engineering ; Nanjing University ; Nanjing 210093 ; China) ; Lu Jianjun
• 刊名：Acta Petrologica Sinica
• 出版年：2013
• 卷期：29(12)
• 关键词：铅锌矿床 ; lead-zinc deposit ; 花岗闪长斑岩 ; granodiorite porphyry ; 铀—铅计时 ; U-Pb dating ; 湖南 ; Hunan Province
• 页码：p.4186-4214
• 图表：14 illus., 4 tables, 294 refs.
• 分类号：1001
• issnNo：ISSN1000-0569
• isbnNo：CN11-1922/P

     Zircon U-Pb chronology, Hf isotope, whole rock geochemistry and Sr-Nd isotopes are reported for the granodiorite porphyry and the mafic microgranular enclave （MME） from the Baoshan Pb-Zn polymetallic deposit, southern Hunan Province. LA-ICP-MS zircon U-Pb dating yields crystallization ages of 156~158Ma and 155.21.4Ma for the granodiorite porphyry and MME, respectively, indicating they are coeval. The Baoshan granodiorite porphyry is metaluminous. This porphyry is enriched in LILEs such as K, Rb and U, depleted in Nb, Ti and P, and has an average Nb/Ta ratio of 11.3. It has initial 87Sr/86Sr ratios of 0.7095~0.7115, εNd（t） values of -7.3 to -5.0, t2DM（Nd） ages of 1.35Ga to 1.54Ga, and zircon εHf（t） values of -14.0 to -9.0. The MME is characterized by microgranular texture, oval-like shape, sharp contact with the host rock and darkly chilled margin, and contains needle-like apatite. It has low SiO2 （55.46%~57.30%） but high K2O （5.86%~6.90%）. This MME is enriched in LILEs such as Rb, Ba, Th and U, depleted in Nb, Ta and Ti, and has initial 87Sr/86Sr ratios of 0.7062~0.7063, εNd（t） values of -2.1~-1.9, zircon εHf（t） values of -12.1~-4.7, and relative high Nb/Ta ratio （average of 15.3）. The MME has higher compatible elements, such as Fe, Mg, V and Cr, than the granodiorite. The elemental and isotopic geochemistry suggests that the Baoshan granodiorite porphyry might have been formed by mixing of mafic and felsic member magmas. The mafic member is hydrous and K-rich mafic magma which might be derived from enriched lithospheric mantle source that had been metasomatized by subducting-sediment-derived melts. The felsic member was generated by partial melting of lower crust induced by the underplating of the hydrous and K-rich mafic magma. The MME might be derived from the mafic magma with minor addition of the felsic magma. The modeling using Sr-Nd isotopes shows that the mixture of 20%~30% mafic magma and 70%~80% felsic magma can generate the Baoshan granodiorite porphyry. Inherited zircon with age of 89220Ma has the εHf（t） and tDM（Hf） values of ＋6.0 and 1.21Ga, respectively, which is compatible with those of the Neoproterozoic arc magmatic rocks in the eastern Jiangnan Orogenic Belt. Therefore, the Neoproterozoic arc magma might have been involved in the formation of the Baoshan granodiorite porphyry, and the Neoproterozoic arc magma belt and continent-arc collision belt between the Yangtze Block and Cathaysia Block might extend southward from Pingxiang to Chenzhou-Linwu faults. In Early Yanshanian （190~150Ma）, the Nanling Range has undergone lithosphere extensional and thinning due to the subduction of the Paleo-Pacific Plate. The mantle-derived mafic magma underplating into the old lower crust resulted in partial melting of the crust. With the mixing of crust-derived and mantle-derived magmas, extensive granites were generated.