| 西藏冈底斯北缘尼玛地区帮勒村一带寒武纪火山岩LA—ICP—MS锆石U—Pb年龄及其地球化学特征 |
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| 引用本文： | 潘晓萍,李荣社,王超,于浦生,辜平阳,查显锋.西藏冈底斯北缘尼玛地区帮勒村一带寒武纪火山岩LA—ICP—MS锆石U—Pb年龄及其地球化学特征[J].中国区域地质,2012(1):63-74. |
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| 作者姓名： | 潘晓萍 李荣社 王超 于浦生 辜平阳 查显锋 |
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| 作者单位： | 中国地质调查局西安地质调查中心西安地质矿产研究所,陕西西安710054 |
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| 基金项目： | 中国地质调查局地质大调查项目《青藏高原前寒武纪地质、古生代构造一古地理综合研究》（编号：1212010610102） |
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| 摘 要： | 青藏高原南部中国境内是否存在寒武纪地层一直是地质界关注的焦点。研究表明．冈底斯北缘西藏尼玛县控错南帮勒村一带，原划的前震旦纪念青唐古拉岩群为一套浅变质的拉斑系列双峰式火山岩。通过高精度LA—ICP—MS（激光剥蚀等离子体质谱）锆石微区原位u—Pb同位素测年，获得其中变流纹岩“Pb／“u年龄加权平均值为（536．4±3．6）Ma，确定该套火山岩形成于 旱寒武世。地球化学分析表明，变玄武岩富集LREE、L1LE、部分HFSE，Nb、Ta、Zr、Hf等亏损，Zr／Nb比值（2．53～3．61）低；变流纹岩明显富集LREE、LILE、Th、HFSE，具有Eu负异常和sr、Nb、Ta、Ti负异常。同时，变玄武岩的gNd（t）为负值（一2．80~一4．56）。源区为富集地幔端元EMll。反映其源区为岩石圈和软流圈相互作用的产物，并遭受了地壳物质的混染。综合分析认为该套火山岩形成于陆缘裂谷环境．为冈底斯北缘存在寒武纪裂解作用提供了佐证。
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| 关 键 词： | 冈底斯北缘 寒武纪 双峰式火山岩 LA—ICP—MS锆石u—Pb测年 地球化学 |
Pan X P,Li R S,Wang C,Yu P S,Gu P Y,Zha X F. Geochemical characteristics of the Cambrian volcanic rocks in Banglecunarea on the northern margin of Gangdise,Nyima County, Tibet. |
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| PAN Xiao-ping,LI Rong-she,WANG Chao,YU Pu-sheng,GU Ping-yang,ZHA Xian-feng.Pan X P,Li R S,Wang C,Yu P S,Gu P Y,Zha X F. Geochemical characteristics of the Cambrian volcanic rocks in Banglecunarea on the northern margin of Gangdise,Nyima County, Tibet.[J].Regional Geology of China,2012(1):63-74. |
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| Authors: | PAN Xiao-ping LI Rong-she WANG Chao YU Pu-sheng GU Ping-yang ZHA Xian-feng |
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| Institution: | Xi＇an Institute of Geology and Mineral Resources, China Geological Survey, Xi＇an 710054, Shaanxi, China |
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| Abstract: | Geologists show much concern over the problem whether there exist Cambrian strata in southern Tibetan Plateau. The ＂Nyainqentanglha Rock Group＂ originally classified as pre-Sinian strata consists of epimetamorphic tholeiitic series bimodal volcanic rocks in Banglecun area, Nyima County, on the northern margin of Gangdise. The Z~Pb/Z38U weighted average age of （536.4＋3.6） Ma was obtained by in-situ LA-ICP-MS zircon dating of the meta-rhyolite, which proves that this volcanic rock was formed in early Cambrian. The results of geochemical analysis show that the meta-basalt is enriched in LREE, LILE and some HFSE and depleted in Nb, Ta, Zr, Hf, and yields low Zr/Nb ratios （2.53~3.61）. However, the meta-rhyolite is obviously enriched in LP,.EE, LILE, Th, HPSE, and depleted in Eu, St, Nb, Ta and Ti. Meanwhile, the meta-basalt yields a negative eNa（t） （-2.80-4.56）, and the magma was enriched in mantle source EM]I, which may suggest that the magma resulted from the interaction between the lithosphere and the asthenosphere and experienced crustal contamination. Based on a comprehensive analysis, the authors hold that the volcanic rocks were formed in a tectonic setting of continental margin rift, which offered evidence of the breakup on the northern margin of Gangdise in Cambrian. |
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| Keywords: | northern margin of Gangdise Cambrian bimodal volcanic rocks LA-ICP-MS zircon U-Pb dating geochemistry |
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