中文摘要：

从岩相学特征、岩石组合、岩石化学、稀土元素、微量元素、大地构造环境等诸多方面分析清迈带洋脊/洋岛玄武岩的东侧分布的晚二叠世—早三叠世（P2—T1）火山岩认为其具有陆缘弧火山岩特征。火山岩组合为玄武安山岩-安山岩-流纹岩;火山岩系列以钙碱性系列为主,拉斑系列次之;火山岩的化学成分以高Al2O3为特征,稀土模式为轻稀土富集右倾斜型;微量元素大阳离子元素富集,普遍富U,Th亏损Ti,Cr和P;岩石化学投点均落在岛弧火山岩区,与中国澜沧江带陆缘弧火山岩投点相一致。该陆缘弧火山岩带与清迈带的洋脊/洋岛型火山岩构成了成对分布的洋脊火山岩-弧岩浆岩带,指示清迈带洋壳向东俯冲。

英文摘要：

The characteristics of Late Permian—Early Triassic（P2—T1） continent marginal arc-volcanic rocks on the eastern side of the ocean-ridge/oceanic island basalts in the Chiang Mai belt were analyzed on the basis of REE,trace elements and geotectonic setting.These volcanic rocks consist of basaltic andesite,andesite and rhyolite,belonging to mainly calc-alkaline series with minor tholeitic series.Chemical compositions of the volcanic rocks are characterized by high content of Al2O3.REE distribution patterns are of the LREE-enrichment of rightward incline type.Large cation elements are highly enriched and the U and Th are also enriched contrast with the depleted Ti,Cr and P.Petrochemical plot falls within the field of island-arc volcanic rocks,in consistency with the projected points of continental marginal arc-volcanic rocks in the Lancangjiang belt,China.These continental marginal arc-volcanic rocks,together with ocean-ridge/oceanic island-type volcanic rocks in the Chiang Mai belt,constitute the ocean-ridge volcanic rock-arc magmatic rock belts distributed in pairs,indicative of eastward subduction of the oceanic crust in the Chiang Mai belt.This result is of great importance in exploring the evolution of the paleo-Tethys in the Chiang Mai belt.