The Hejiazhuang pluton is located in the South Qinling Tectonic Belt （SQTB） in the north side of the MianxianLueyang Su ture Zone, and consists dominantly of granodiorites. LAICPMS zircon UPb dating and LuHf isotopi...The Hejiazhuang pluton is located in the South Qinling Tectonic Belt （SQTB） in the north side of the MianxianLueyang Su ture Zone, and consists dominantly of granodiorites. LAICPMS zircon UPb dating and LuHf isotopic analyses reveal that these granodiorites of the Hejiazhaung pluton emplaced at 248 Ma, and show a large variation in zircon eHt（t） values from 4.8 to 8.8. These granodiorite samples are attributed to highK to midK calcalkaline series, and characterized by high SiO2 （66.6±70.0%）, A1203 （15.04±16.10%） and Na20 （3.74±4.33%） concentrations, with high Mg# （54.2±61.7）. All samples have high Sr （627±751 ppm）, Cr （553±73 ppm） and Ni （17.2182 ppm）, but low Y （5.42-8.41 ppm） and Yb （0.59-0.74 ppm） concentrations with high Sr/Y ratios （84.90±120.66）. They also display highly fractionated REE patterns with （La/Yb）N ratios of 18.93-4.0 and positive Eu anomalies （0＂Eu=1.102.22） in the chondritenormalized REE patterns. In the primitive mantle normalized spidergrams, these samples exhibit enrichment in LILEs but depletion in Nb, Ta, P and Ti. These geochemical fea tures indicate that the granodioritic magma of the Hejiazhuang pluton was derived from the partial melting of hybrid sources comprising the subducted oceanic slab and sediments, and the melts were polluted by the mantle wedge materials during their ascent. The emplacement ages and petrogenesis of the Hejiazhuang pluton prove that the initial subduction of the Mianlue oceanic crust occurred at 248 Ma ago, and the SQTB was still under subduction tectonic setting in the Early Triassic.展开更多
基金supported by National Key Technology R&D Program(Grant Nos.2011BAB04B05,2006BAB01A11)National Natural Science Foundation of China(Grant Nos.41072143,41072169)
文摘The Hejiazhuang pluton is located in the South Qinling Tectonic Belt （SQTB） in the north side of the MianxianLueyang Su ture Zone, and consists dominantly of granodiorites. LAICPMS zircon UPb dating and LuHf isotopic analyses reveal that these granodiorites of the Hejiazhaung pluton emplaced at 248 Ma, and show a large variation in zircon eHt（t） values from 4.8 to 8.8. These granodiorite samples are attributed to highK to midK calcalkaline series, and characterized by high SiO2 （66.6±70.0%）, A1203 （15.04±16.10%） and Na20 （3.74±4.33%） concentrations, with high Mg# （54.2±61.7）. All samples have high Sr （627±751 ppm）, Cr （553±73 ppm） and Ni （17.2182 ppm）, but low Y （5.42-8.41 ppm） and Yb （0.59-0.74 ppm） concentrations with high Sr/Y ratios （84.90±120.66）. They also display highly fractionated REE patterns with （La/Yb）N ratios of 18.93-4.0 and positive Eu anomalies （0＂Eu=1.102.22） in the chondritenormalized REE patterns. In the primitive mantle normalized spidergrams, these samples exhibit enrichment in LILEs but depletion in Nb, Ta, P and Ti. These geochemical fea tures indicate that the granodioritic magma of the Hejiazhuang pluton was derived from the partial melting of hybrid sources comprising the subducted oceanic slab and sediments, and the melts were polluted by the mantle wedge materials during their ascent. The emplacement ages and petrogenesis of the Hejiazhuang pluton prove that the initial subduction of the Mianlue oceanic crust occurred at 248 Ma ago, and the SQTB was still under subduction tectonic setting in the Early Triassic.
