新特提斯洋早期俯冲的岩浆岩记录及其成矿——西藏日喀则西北部花岗岩类锆石U-Pb年龄及Hf同位素

The magma records and mineralization of early subduction of Neo-Tethyan oceanic slab:Zircon U-Pb and Hf isotopic composition of granitoids in the northwest of Xigaza

拉萨地体南缘的晚三叠世—中侏罗世岩浆岩被认为是新特提斯洋早期北向俯冲的岩浆记录,并形成与之相关的雄村特大型斑岩-浅成低温热液铜-金矿床。对该时期岩浆岩成因背景的研究有助于评价其成矿潜力。选取拉萨地体南缘日喀则西北部花岗岩类进行锆石U-Pb测年及Lu-Hf同位素分析。花岗岩类LA-ICP-MS锆石U-Pb定年结果为175~180.1Ma,εHf(t)平均值为+13.4,显示幔源特征,为岛弧(洋内弧)背景成因,具有斑岩铜金成矿潜力。结合前人对拉萨地体南缘晚三叠世—白垩纪岩浆岩的研究,认为拉萨地体南缘未被剥蚀的晚三叠世—白垩纪火山岩中有可能保存有新特提斯洋俯冲形成的斑岩铜金成矿系统。

The Late Triassic-Middle Kumssic magmatic rocks distributed sporadically in th e sooth o f Lhasa terrane are considered tobe the magmatic records of the early subduction of the Neo-Tethys. In addition, Xiongcun porphyry copper system was associatedwi th the magma. Therefore,research on the Late Tr iassic-urassic magrmtic can help to evaluate its metaliogenic potential. This pa-per reports LA-ICP MS zircon U-Pb age and in situ Hf isotopic compositions of the granodiorite in the nor thwest of Xigaza. Theobtained U-Pb zircon age of the granodiorite is 175？ 180.1Ma. Z ircon Hfisotopic compositions of the granodiorite displayShGI80.lMa ） = （＋l3.4 ）,which shows the characteristics of mantle source with anaffinity for island arc which was capable of forming the porphyry Cu-Au system. Therefore,the Late Triassic-Cretaceous volcanic rocks in the south of Lhasa terrane have the potentil