云南绿春黄草岭地区花岗岩SHRIMP锆石U-Pb年代学特征及地质意义

The granites from the Huangcaoling region, Luchun, Yunnan: SHRIMP zircon U-Pb chronology and geological implications

摘要: 金沙江-哀牢山缝合带系三江特提斯构造域东缘一条重要的古特提斯缝合带,其南段哀牢山缝合带闭合的时限及其岩浆活动响应,尚缺乏精确的年代学与岩石地球化学制约。本文对出露于哀牢山缝合带南部绿春地区黄草岭的花岗岩类进行了SHRIMP锆石U-Pb年代学与全岩主量、微量元素地球化学研究,获得花岗岩的形成年龄为249.8 ±4.3Ma。地球化学特征表明,该花岗岩具有K、Rb、U、Th和Pb正异常、Nb、Ta、Ti、Hf和Eu (0.29~0.37)负异常、过铝质与高钾钙碱质特征,属于S型花岗岩,形成于岛弧构造背景中。年代学和地球化学特征表明,哀牢山洋在早三叠世向西俯冲消减,绿春地区已出现成熟岛弧,并向陆-陆碰撞过渡。

Abstract: The present paper deals with the SHRIMP zircon U-Pb chronology, major and trace element geochemistry, and obtain a SHRIMP zircon U-Pb age of 249.8±4.3 Ma for the granites from the Huangcaoling region, Luchun, Yunnan. Geochemically, the granites in the study area display normal anomalies of K, Rb, U, Th and Pb, and negative anomalies of Nb, Ta, Ti, Hf and Eu, indicating the peraluminous, high-K cala-alkaline S-type granites formed in the island-arc tectonic setting. During the Early Triassic, there once occurred the westward subduction of the Ailaoshan Ocean, and the transition from the mature island arc to the continentcontinent collision in the Luchun region, Yunnan.