| 西藏东南缘早二叠世长英质凝灰岩锆石U-b年龄和Hf同位素特征 |
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| 引用本文： | 麦源君,朱利东,杨文光,解龙,童霞,郝金月,钟摇.西藏东南缘早二叠世长英质凝灰岩锆石U-b年龄和Hf同位素特征[J].地球科学,2021,46(11):3880-3891. |
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| 作者姓名： | 麦源君 朱利东 杨文光 解龙 童霞 郝金月 钟摇 |
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| 作者单位： | 1.成都理工大学沉积地质研究院, 四川成都 610059 |
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| 基金项目： | 国家自然科学基金项目41972118冈底斯-喜马拉雅铜矿资源基地调查项目DD20160015 |
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| 摘 要： | 西藏东南缘记录的唐加-松多古特提斯增生杂岩带对认识古特提斯洋晚古生代的构造演化提供了新的证据.针对该杂岩带中新发现的长英质凝灰岩开展了全岩主、微量元素，锆石LA-ICP-MS U-Pb定年和锆石Hf同位素组成的研究.结果显示冲尼凝灰岩喷发于278~275 Ma，具有较高的SiO2含量（63.47%~72.65%）、Al2O3含量（14.53%~21.31%），较低的K2O含量（1.30%~2.51%）和TiO2含量（0.50%~1.17%），MgO含量较低，介于0.92%~2.00%，Mg#范围在19.9~34.2（均低于40）.富集大离子亲石元素（LILE）、亏损高场强元素（HFSE）.锆石具有较高的εHf（t）值（+10.2~+14.4）和相对年轻的地壳模式年龄TDMc=351~621 Ma，认为冲尼凝灰岩是唐加-松多古特提斯洋向北俯冲背景下的新生地壳部分熔融的产物，洋盆俯冲消减的开始时代不晚于早二叠世，并且在早二叠世拉萨地体东南缘存在新生地壳生长事件.
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| 关 键 词： | 早二叠世 拉萨地体 Hf同位素 U-Pb年龄 唐加-松多古特提斯 岩石学 |
| 收稿时间： | 2020-11-21 |
Zircon U-Pb and Hf Isotopic Composition of Permian Felsic Tuffs in Southeastern Margin of Lhasa,Tibet |
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| Mai Yuanjun,Zhu Lidong,Yang Wenguang,Xie Long,Tong Xia,Hao Jinyue,Zhong Yao.Zircon U-Pb and Hf Isotopic Composition of Permian Felsic Tuffs in Southeastern Margin of Lhasa,Tibet[J].Earth Science-Journal of China University of Geosciences,2021,46(11):3880-3891. |
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| Authors: | Mai Yuanjun Zhu Lidong Yang Wenguang Xie Long Tong Xia Hao Jinyue Zhong Yao |
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| Abstract: | The Tangjia-Sumdo Paleo-Tethys accretionary complex belt, recorded in the southeastern margin of Lhasa, provides new evidence for the understanding of the Late Paleozoic tectonic evolution of the Paleo-Tethys Ocean. In this paper, it reports new data for the felsic tuff in this accretionary complex belt, including petrology, major and trace element compositions, zircon U-Pb age, and in-situ Hf isotopic compositions. U-Pb zircon dating indicates that the timing of eruption of the Chongni tuffs was ca. 278-275 Ma. They are characterized by relatively high SiO2 (63.47%-72.65%), and high Al2O3 (14.53%-21.31%), relatively low K2O (1.30%-2.51%), TiO2 (0.50%-1.17%), MgO (0.92%-2.00%), and Mg# (19.9-34.2). These tuffs exhibit LILE enrichment and HFSE depletetion. The zircons participating in the weighted age calculation have positive εHf(t) values of +10.2 to +14.4 and relatively young zircon Hf crustal model ages (TDMc=351-621 Ma). It agrees that Chongni tuffs were derived from the partial melting of the juvenile crust under the background of the northward subduction of the Tangjia-Sumdo Paleo-Tethys Ocean slab, and the beginning time of the ocean slab subduction is not later than Early Permian, before which there were the events that crust grew in the southeastern margin of Lhasa. |
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