| 西藏班公湖-怒江缝合带西段中特提斯洋盆的双向俯冲:来自岛弧型花岗岩锆石U-Pb年龄和元素地球化学的证据 |
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| 引用本文： | 杜德道,曲晓明,王根厚,辛洪波,刘治博.西藏班公湖-怒江缝合带西段中特提斯洋盆的双向俯冲:来自岛弧型花岗岩锆石U-Pb年龄和元素地球化学的证据[J].岩石学报,2011,27(7):1993-2002. |
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| 作者姓名： | 杜德道 曲晓明 王根厚 辛洪波 刘治博 |
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| 作者单位： | 1. 地质过程与矿产资源国家重点实验室,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 |
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| 基金项目： | 本文由国家重大基础研究发展计划项目(2011CB403103)、国家"十一五"科技支撑计划项目(2006BAB01A 05)和中国地质调查局青藏专项(1212010818097)联合资助. |
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| 摘 要： | 笔者调查发现西藏班公湖-怒江缝合带西段狮泉河-改则-洞错蛇绿岩带北侧和拉果错蛇绿岩带南侧都有岛弧型花岗岩岩基产出。这些岩体岩性上以中粒花岗闪长岩为主,岩石化学上明显富集大离子不相容元素(LILE) Rb、Th、U、K、Pb,亏损高场强元素(HFSE)Nb、Ta、Ti,具有岛弧型岩浆岩的本质特征,指示着班公湖中特提斯洋盆存在双向俯冲。锆石U-Pb LAICPMS定年结果显示岩体在不同构造位置年龄并不一致,位于狮泉河-改则-洞错蛇绿岩带北侧的嘎拉勒和改则北两个岩体锆石206Pb/238U加权平均年龄分别为155.6±1.1Ma(MSWD=1.7)和142.15±0.35Ma(MSWD=2.9),位于拉果错蛇绿岩带南侧的扎布耶北岩体的锆石206Pb/238U加权平均年龄为134.07±0.77Ma(MSWD=1.8),表明班公湖中特提斯洋盆向北俯冲发生在晚侏罗世,而向南的俯冲发生在早白垩世,两者相差约8Ma。岛弧花岗岩浆都是由地幔楔部分熔融而成,岩浆源区经历过来自俯冲板片的沉积物熔体的交代。不同岩体的源区沉积物熔体的交代比例不同:扎布耶北岩体最多,大体在12%~16%之间;嘎拉勒岩体次之,在9%~13%之间;改则北岩体最少,为5%~10%。
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| 关 键 词： | 岛弧型花岗岩 锆石U-Pb年龄 双向俯冲 班公湖-怒江缝合带 西藏 |
| 收稿时间： | 2011/3/16 0:00:00 |
| 修稿时间： | 2011/5/26 0:00:00 |
Bidirectional subduction of the Middle Tethys oceanic basin in the west segment of Bangonghu-Nujiang suture, Tibet: Evidence from zircon U-Pb LAICPMS dating and petrogeochemistry of arc granites |
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| DU DeDao,QU XiaoMing,WANG GenHou,XIN HongBo and LIU ZhiBo.Bidirectional subduction of the Middle Tethys oceanic basin in the west segment of Bangonghu-Nujiang suture, Tibet: Evidence from zircon U-Pb LAICPMS dating and petrogeochemistry of arc granites[J].Acta Petrologica Sinica,2011,27(7):1993-2002. |
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| Authors: | DU DeDao QU XiaoMing WANG GenHou XIN HongBo and LIU ZhiBo |
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| Institution: | State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Science and Mineral Resources, China University of Geosciences, Beijing 100083, China;Institute of Mineral Resources, CAGS, Beijing 100037, China;State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Science and Mineral Resources, China University of Geosciences, Beijing 100083, China;Institute of Mineral Resources, CAGS, Beijing 100037, China;State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Science and Mineral Resources, China University of Geosciences, Beijing 100083, China |
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| Abstract: | Through geological surveys in Tibet, the authors have discovered arc granite batholiths both in the north side of Shiquanhe-Gerze-Dongcuo ophiolite zone and in the south side of Laguocuo ophiolite zone in the western segment of Bangonghu-Nujiang suture zone. These granite bodies are lithologically dominated by mid-grain granodiorite, and petrochemically rich in large-ion incompatible elements(LILE, e.g. Rb, Th, U, K, Pb)and depleted in high field strength elements (HFSE, e.g. Nb, Ta, Ti), and show essential characteristics of arc magmatic rocks, indicating there were bidirectional subduction of the Bangonghu Middle Tethys oceanic basins. Zircon U-Pb LAICPMS dating results show these granite bodies have different ages. In the north side of Shiquanhe-Gerze-Dongcuo ophiolite zone, the zircon 206Pb/238U weighted average ages of Galale and Gerze-north bodies are 155.6±1.1Ma(MSWD=1.7)and 142.15±0.35Ma(MSWD=2.9), respectively. And in the south side of Laguocuo ophiolite zone, the age of Zhabuye-north body is 134.07±0.77Ma(MSWD=1.8). These ages show that the northward subduction of the Bangonghu Middle Tethys oceanic basin occurred in Late Jurassic, whereas the southward subduction occurred in Early Cretaceous, with an about 8Ma delay of the latter. The arc granitic magma was all generated by partial melting of mantle wedges, and the magmatic sources have undergone metasomatism of sedimental melts from subducted plates. Proportions of sediment melts involved in different granite bodies are variable. The Zhabuye-north body has the highest proportion of from 12%~16%, followed by the Galale body (9%~13%), and the Gerze-north body is the lowest (5%~10%). |
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| Keywords: | Arc granites Zircon U-Pb LAICPMS ages Bidirectional subduction Bangonghu-Nujiang suture Tibet |
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