云南哀牢山构造带仰宗流纹斑岩锆石U-Pb年龄、地球化学特征及其构造意义

孙崇波; 李忠权; 王道永; 许远平; 李滔; 赵云川

云南哀牢山构造带仰宗流纹斑岩锆石U-Pb年龄、地球化学特征及其构造意义

Petrogeochemistry and zircon U-Pb chronology of the Yangzong rhyolite porphyry along Ailao Mountain tectonic belt

摘要

摘要: 对云南绿春县仰宗流纹斑岩进行了锆石U-Pb年龄、岩石地球化学分析。LA-ICP-MS锆石U-Pb测年显示，仰宗流纹斑岩年龄为263.1±2.3Ma，形成于晚二叠世。岩石地球化学分析显示，仰宗流纹斑岩SiO₂含量为71.08%~80.26%，全碱（Na₂O+K₂O）含量为4.67%~8.67%，且Na₂O＜K₂O；岩石轻、重稀土元素存在一定的分馏，负Eu异常明显（δEu=0.05~0.57），相对富集Rb、Th、U、Ni、Cs、Zr、Hf、As、K等元素，亏损Sr、Ta、Ba、Cr、Zn、W等元素。结果显示，仰宗流纹斑岩形成于碰撞期后的陆内构造环境，表明哀牢山构造带的古特提斯支洋或弧后盆地在晚二叠世（263.1±2.3Ma）可能已经闭合。

Abstract: This paper presents bulk petrogeochemistry and zircon U-Pb dating results for the Yangzong rhyolite porphyry in Luchun County, Yunnan Province. LA-ICP-MS zircon U-Pb dating results show that the Yangzong rhyolite porphyry was formed in the Late Permian (263.1±2.3Ma). The Yangzong rhyolite porphyry is characterized by SiO₂ content of 71.08%~80.26%, alkali (Na₂O+ K₂O) 4.67%~8.67%, and Na₂O＜K₂O. It is enriched in LREE and Rb, Th, U, Ni, Cs, Zr, Hf, As, K and depleted in Sr, Ta, Ba, Cr, Zn, W with negative Eu anomalies (δEu=0.05~0.57). According to the diagrams, the Yangzong rhyolit porphyry was formed in the tectonic environment of island arc-continent or continental-arc collision, indicating that the branch of Paleo-Tethys Ocean or arc basin in Ailao Mountain tectonic belt might have been closed in the Late Permian (263.1±2.3Ma).

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