西藏纳如松多铅锌矿床成矿岩体形成机制:岩浆锆石证据  

Formation mechanism of magmatic rocks in Narusongduo lead-zinc deposit of Tibet:Evidence from magmatic zircon

作　　者：纪现华[1] 杨竹森[2] 于玉帅 申俊峰[1] 田世洪[2] 孟祥金[2] 李振清[2] 刘英超[4] 

机构地区：[1]中国地质大学地球科学与资源学院,北京100083 [2]中国地质科学院矿产资源研究所,北京100037 [3]武汉地质矿产研究所,湖北武汉430205 [4]中国地质科学院地质研究所,北京100037

出　　处：《矿床地质》2012年第4期758-774,共17页Mineral Deposits

基　　金：国家重点基础研究发展计划(973)项目(2011CB403100);"十一五"国家科技支撑计划项目(2006BAB01A04);地质调查计划项目(1212010918014)联合资助

摘　　要：纳如松多铅锌矿床位于拉萨地块中部隆格尔-工布江达断隆带中段,以发育隐爆角砾岩型和矽卡岩型铅锌矿化为特征。西矿段与矽卡岩型铅锌矿化相关的岩体为粗斑和细斑两种石英正长斑岩,对其锆石进行的U-Pb定年、稀土元素、Lu-Hf同位素和锆石群型特征分析表明,粗斑石英正长斑岩侵位于(62.54±0.77)Ma,细斑石英正长斑岩侵位于(62.47±0.91)Ma;锆石稀土元素具有相似的左倾配分模式和Ce正异常、Eu负异常,在U/Yb-Y图解上均落于陆壳锆石范围;粗斑石英正长斑岩的176Hf/177Hf介于0.282577～0.282803,εHf(t)变化于-5.58～+2.21,反映岩浆来源于地壳物质的部分熔融,并有地幔物质的加入;锆石群型特征显示粗斑和细斑石英正长斑岩为地壳地幔混合岩浆成因的花岗岩。上述结果说明纳如松多铅锌矿床的岩浆侵入与成矿作用发生于印度-亚洲大陆碰撞造山的主碰撞期。由于印度陆壳随回转的新特提斯洋壳板片一起向拉萨地块之下陡俯冲,并产生异常热源,诱发了地幔物质上涌和上覆地壳部分熔融,形成的地幔地壳混合成因岩浆经结晶分异演化后上升侵位,形成矿区内粗斑和细斑两种石英正长斑岩及相关的铅锌矿化。The Narusongduo Pb-Zn deposit,located in the Longgeer-Gongbujiangda fault-block uplift belt of middle Lhasa Terrane,is characterized by two types of mineralization,namely the cryptoexplosive breccia type in the eastern part and skarn type in the western part.The magmatic rock related to the skarn type mineralization includes two kinds of quartz syenite porphyries with coarse and fine phenocrysts respectively.The results of zircon U-Pb dating by LA-ICP-MS show that the age of quartz syenite porphyry with coarse phenocrysts is（62.54±0.77） Ma,while that with the fine phenocrysts is（62.47±0.91） Ma.The REE patterns of zircon from both porphyries have conspicuous fractionation with low ratios of LREE/HREE and distinct anomalies of negative Eu and positive Ce,with the zircons similar to continental zircons in U/Yb-Y discriminant diagram.The Hf isotopic compositions of zircon from the coarse porphyry display 176Hf/177Hf ratios ranging from 0.282577 to 0.282803 and εHf（t） values ranging from-5.58 to ＋2.21,suggesting that the magma was mainly derived from partial melting of the crust,with the mixture of some materials from depleted mantle in different proportions.The features of zircon group indicate that both quartz syenite porphyries are hybrid granites that origina-ted from the crust and the mantle.All the data above suggest that the emplacement and related mineralization of quartz syenite porphyries in the Narusongduo Pb-Zn deposit occurred in the main collisional stage of Indo-Asia continental collision,which resulted from the upwelling of mixed magma derived from partial melting of the asthenospheric mantle and overlying crust due to the tremendous heat and fluid flow released from the asthenosphere during the steep subduction of Indian continental crust with the roll-back of the subducted Neo-Tethyan oceanic slab.

关 键 词：地球化学 锆石U-Pb定年 锆石稀土元素 HF同位素 锆石形态 石英正长斑岩 纳如松多铅锌矿床 西藏 

分 类 号：P618.41[天文地球—矿床学] P618.42[天文地球—地质学]