提本文对云南墨江县扭只二长花岗斑岩进行了锆石U-Pb年代学、岩石地球化学分析。LA-ICP-MS锆石U-Pb测年显示扭只二长花岗斑岩年龄为（263.5±1.7）Ma，形成于晚二叠世。岩石地球化学分析显示：扭只二长花岗斑岩SiO2含量为55.30%~74.37%，全碱（Na2O+K2O）含量2.56%~7.57%，且Na2O＞K2O；岩石富集轻稀土，负铕异常明显（δEu：0.74~1.06），相对富集Sc、Co、Cs、As等元素，亏损Cr、Ni、Zn、Rb、Sr、Ba、Zr、Ta、Th、U、W等元素。根据图解显示扭只二长花岗斑岩形成于岛弧向陆陆碰撞或者陆弧碰撞的构造环境，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（（263.5±1.7）Ma）可能已经闭合。%This study presents bulk petrogeochemistry and zircon U-Pb dating results for the Niuzhi monzonitic porphyry in Mojiang, Yunnan. LA-ICP-MS zircon U-Pb dating results show that the Niuzhi monzonitic porphyry formed in the Late Permian (263.5 ±1.7Ma). The Niuzhi monzonitic porphyry is characterized by SiO2 content of 55.30%-74.37%, alkali (Na2O+K2O) 2.56%-7.57%, and Na2O higher than K2O. It is enriched in LREE and Sc, Co, Cs, As, and depleted in Cr, Ni, Zn, Rb, Sr, Ba, Zr, Ta, Th, U, W, with negative Eu anomalies (δEu 0.74-1.06). According to the diagrams, the Niuzhi monzonitic porphyry 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 Ailaoshan tectonic belt may have been closed in the Late Permian (263.5 ± 1.7Ma).
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