| 西藏那曲地区流纹岩LA-ICP-MS锆石U-Pb年龄和地球化学特征 |
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| 引用本文： | 彭智敏,耿全如,张璋,丛峰.西藏那曲地区流纹岩LA-ICP-MS锆石U-Pb年龄和地球化学特征[J].中国区域地质,2011(7):1050-1059. |
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| 作者姓名： | 彭智敏 耿全如 张璋 丛峰 |
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| 作者单位： | 中国地质调查局成都地质矿产研究所,四川成都610081 |
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| 基金项目： | 中国地调局青藏专项项目《西藏班公湖-怒江构造带基础地质综合研究》（编号：1212010818017）、《班公湖-怒江成矿带基础地质综合研究》（编号：1212011086068）; 国家自然科学基金项目《喜马拉雅东构造结地区雅鲁藏布江蛇绿岩地质年代学研究》（编号：40773001） |
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| 摘 要： | 对西藏那曲地区的中—晚侏罗世拉贡塘组流纹岩进行LA-ICP-MS锆石U-Pb测年,得出该流纹岩的时代为116.6Ma±0.81Ma,属早白垩世,与区域上多尼组和则弄群的时代一致,属同一地质事件的产物,说明该火山岩不属拉贡塘组,应不整合于拉贡塘组之上。流纹岩SiO2含量均值为71.01%,富集Rb、Th元素,亏损P、Eu、Ti元素,εHf（t）值集中在-0.030～2.277之间,平均值为0.75,对应的两阶段模式年龄为682～782Ma和1015～1175Ma,大于流纹岩的形成时代。流纹岩具同碰撞型火山岩的特征,不具传统岛弧环境的特征,构造环境可能存在两种可能：班公湖-怒江特提斯洋俯冲已经结束,进入陆-陆碰撞阶段,羌塘地块和拉萨地块开始碰撞;班公湖-怒江洋还未完全关闭,残留洋与拉萨地块发生碰撞。在碰撞的过程中,下地壳不断加厚并发生部分熔融形成酸性流纹岩。
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| 关 键 词： | 西藏那曲地区 班公湖-怒江洋 LA-ICP-MS锆石U-Pb年龄 地球化学 Hf同位素 |
Zircon LA-ICP-MS U-Pb ages and geochemical characteristics of rhyolite in Nagqu area,Tibet |
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| PENG Zhi-min,GENG Quan-ru,ZHANG Zhang,CONG Feng.Zircon LA-ICP-MS U-Pb ages and geochemical characteristics of rhyolite in Nagqu area,Tibet[J].Regional Geology of China,2011(7):1050-1059. |
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| Authors: | PENG Zhi-min GENG Quan-ru ZHANG Zhang CONG Feng |
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| Institution: | Chengdu Institute of Geology and Mineral Resources,China Geological Survey,Chengdu 610081,Sichuan,China |
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| Abstract: | This paper reports LA-ICP-MS zircon U-Pb ages of rhyolite from Middle-Late Jurassic Lagongtang Formation in Nagqu area,Tibet.The age of rhyolite is 116.6±0.81Ma,regionally consistent with the age of Early Cretaceous Duoni Formation and Zelong Group,which indicates products of the same geological event and suggests that this volcanic rock does not belong to Lagongtang Formation,and should unconformably overlie Lagongtang Formation.The average SiO2 content of rhyolite is 71.01%,with the enrichment of Rb and Th and the depletion of P,Eu and Ti.The εHf（t） values are concentrated on-0.030～2.277,0.75 on average,with the corresponding TDM2 crustal model ages being 682～782Ma and 1015～1175Ma,larger than the formation age of the rhyolite.The rhyolite is characterized by syncollision volcanic rock instead of by traditional island-arc volcanic rock.The authors hold that there exist two kinds of possible tectonic environments： The Bangong Co-Nujiang Tethys subduction had ended and entered into the continent-continent collision stage,and the collision between Qiangtang massif and Lhasa block began;the Bangong Co-Nujiang Ocean had not been completely closed,the collision between residual ocean and Lhasa block occurred,and during the collision,the lower crust continuously thickened and experienced partial melting to form acid rhyolite. |
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| Keywords: | Nagqu area Tibet Bangong Co-Nujiang Ocean zircon LA-ICP-MS U-Pb age geochemistry Hf isotopic composition |
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