青藏高原泛非—早古生代造山事件研究重大进展藏北安多地区花岗片麻岩锆石LA-ICP-MS U-Pb定年
LA-ICP-MS U-Pb dating of zircon from granite-gneiss in the Amdo area, northern Tibet, China.
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摘要: 安多花岗片麻岩出露于藏北安多县城以南约30km，构成聂荣微陆块上聂荣岩群的主体岩性。聂荣微陆块呈大透镜体夹持在藏北冈底斯-念青唐古拉板片与羌塘-三江复合板片之间的班公湖-怒江板块缝合带内。所采样品黑云母二长片麻岩锆石CL图像具明显的韵律环带，Th/U比值范围为0.63~1.04，平均为0.85，具有典型岩浆锆石的特征。获得片麻岩中锆石LA-ICP-MS U-Pb原位同位素年龄488.0Ma±4.2Ma。定年结果表明，安多花岗片麻岩原岩侵位于泛非期，证实聂荣微陆块受到晚泛非热运动的影响，为解决聂荣微陆块基底性质和构造演化问题提供了重要的年代学依据。
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关键词:
- 青藏高原 /
- 安多地区 /
- 片麻岩 /
- 泛非期 /
- 锆石LA-ICP-MS U-Pb定年
Abstract: Amdo gneiss which exposed in south of Amdo County about 30km, in the northern Tibet constitutes the major lithologic of Nierong Group on Nierong microcontinent. Nierong was a large micro-lens gripping Gangdise-Nyainqentanglha plate of northern Tibet and Qiangtang-Sanjiang composite plate in the Bangong Co-Nujiang River suture zone. The CL images of biotite-monzonite-gneiss zircons show distinct oscillatory zoning. Th/U ratios range from 0.63 to 1.04 with an average of 0.85. Gneiss zircons LA-ICP-MS U-Pb in situ isotopic age is 488.0±4.2 Ma. Dating results show that the Amdo gneiss protolith was emplaced in the Pan-African period, and verifies that Nierong microcontinent was effected by the late Pan-African thermal motion. This study provides an important chronological evidence for basement properties and tectonic evolution of the Nierong microcontinent. -
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