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
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摘要
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 Jurassic magmatic rocks distributed sporadically in the south of Lhasa terrane are considered to be the magmatic records of the early subduction of the Neo-Tethys. In addition, Xiongcun porphyry copper system was associated with the magma. Therefore, research on the Late Triassic-Jurassic magmatic can help to evaluate its metallogenic potential. This paper reports LA-ICP MS zircon U-Pb age and in situ Hf isotopic compositions of the granodiorite in the northwest of Xigaza. The obtained U-Pb zircon age of the granodiorite is 175~180.1 Ma. Zircon Hf isotopic compositions of the granodiorite displayεHf(180.1 Ma)=(+13.4), which shows the characteristics of mantle source with an affinity 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 potential for exploration of the porphyry Cu-Au system.
The Late Triassic-Middle Jurassic magmatic rocks distributed sporadically in the south of Lhasa terrane are considered to be the magmatic records of the early subduction of the Neo-Tethys. In addition, Xiongcun porphyry copper system was associated with the magma. Therefore, research on the Late Triassic-Jurassic magmatic can help to evaluate its metallogenic potential. This paper reports LA-ICP MS zircon U-Pb age and in situ Hf isotopic compositions of the granodiorite in the northwest of Xigaza. The obtained U-Pb zircon age of the granodiorite is 175~180.1 Ma. Zircon Hf isotopic compositions of the granodiorite displayεHf(180.1 Ma)=(+13.4), which shows the characteristics of mantle source with an affinity 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 potential for exploration of the porphyry Cu-Au system.
引文
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[19]Kang Z,Xu J,Wilde S A,et al.Geochronology and geochemistry of the Sangri Group Volcanic Rocks,Southern Lhasa Terrane:Implications for the early subduction history of the Neo-Tethys and Gangdese Magmatic Arc[J].Lithos,2014,200/201:157-168.
[20]耿全如,潘桂棠,王立全,等.西藏冈底斯带叶巴组火山岩同位素地质年代[J].沉积与特提斯地质,2006,26(1):1-7.
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[24]魏友卿.藏南叶巴组火山岩的年代学、地球化学及岩石成因[D].中国地质大学(北京)硕士学位论文,2014.
[25]黄丰,许继峰,陈建林,等.早侏罗世叶巴组与桑日群火山岩:特提斯洋俯冲过程中的陆缘弧与洋内弧?[J].岩石学报,2015,31(7):2089-2100.
[26]Liu Y,Gao S,Hu Z,et al.Continental and Oceanic Crust Recycling-induced Melt-Peridotite Interactions in the Trans-North China Orogen:U-Pb Dating,Hf Isotopes and Trace Elements in Zircons from Mantle Xenoliths[J].Journal of Petrology,2010,51(1/2):537-571.
[27]Liu Y,Hu Z,Gao S,et al.In situ analysis of major and trace elements of anhydrous minerals by LA-ICP-MS without applying an internal standard[J].Chemical Geology,2008,257(1/2):34-43.
[28]Anderson T.Correction of common lead in U-Pb analyses that do not report204Pb[J].Chemical Geology,2002,192(1):59/79.
[29]Ludwig K R.User’s manual for Isoplot 3.00:a geochronological toolkit for Microsoft Excel[M].2003.
[30]吴元保,郑永飞.锆石成因矿物学研究及其对U-Pb年龄解释的制约[J].科学通报,2004,49(16):1589-1604.
[31]S?derlund U,Patchett P J,Vervoort J D,et al.The176Lu decay constant determined by Lu-Hf and U-Pb isotope systematics of Precambrian mafic intrusions[J].Earth and Planetary Science Letters,2004,219(3):311-324.
[32]Wu F,Ji W,Liu C,et al.Detrital zircon U-Pb and Hf isotopic data from the Xigaze forearc basin:Constraints on Transhimalayan magmatic evolution in southern Tibet[J].Chemical Geology,2010,271(1/2):13-25.
[33]郎兴海.西藏雄村斑岩型铜金矿集区成矿作用与成矿预测[D].成都理工大学博士学位论文,2012.
[34]Miller C,Thoni M,Frank W,et al.Geochemistry and tectonomagmatic affinity of the Yungbwa ophiolite,SW Tibet[J].Lithos,2003,66(3):155-172.
[35]Xu J,Castillo P R.Geochemical and Nd-Pb isotopic characteristics of the Tethyan asthenosphere:implications for the origin of the Indian Ocean mantle domain[J].Tectonophysics,2004,393(1):9-27.
[36]Mcdermid I R C,Aitchison J C,Davis A M,et al.The Zedong terrane:a Late Jurassic intra-oceanic magmatic arc within the Yarlung-Tsangpo suture zone,southeastern Tibet[J].Chemical Geology,2002,187(3/4):267-277.
[37]曲晓明,辛洪波,徐文艺.西藏雄村特大型铜金矿床容矿火山岩的成因及其对成矿的贡献[J].地质学报,2007,81(7):964-971.
[38]Hébert R,Bezard R,Guilmette C,et al.The Indus-Yarlung Zangbo ophiolites from Nanga Parbat to Namche Barwa syntaxes,southern Tibet:First synthesis of petrology,geochemistry,and geochronology with incidences on geodynamic reconstructions of Neo-Tethys[J].Gondwana Research,2012,22(2):377-397.
[39]Aitchison J C,Badengzhu,Davis A M,et al.Remnants of a Cretaceous intra-oceanic subduction system within the Yarlung-Zangbo suture(southern Tibet)[J].Earth and Planetary Science Letters,2000,183(1/2):231-244.
[40]张立雪,王青,朱弟成,等.拉萨地体锆石Hf同位素填图:对地壳性质和成矿潜力的约束[J].岩石学报,2013,29(11):3681-3688.
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