滇西潞西地区晚寒武世岩浆构造热事件的新认识

THE LATE CAMBRIAN MAGMATIC TECTONIC THERMAL EVENTS IN LUXI AREA,WESTERN YUNNAN:A New Understanding

保山地块作为冈瓦纳大陆的重要组成部分,其西缘发育有以平河岩体为代表的大量早古生代侵入岩,但由于缺少野外调查资料,其地质意义存在长期争议.通过1∶5万区域地质调查,详实的野外接触关系证实平河岩体存在两期侵入岩.沉积作用及年代学、岩石地球化学等赋予了其新的地质意义.潞西地区早期侵入岩主要岩石类型为二长花岗岩,应用LA-ICP-MS获得锆石U-Pb年龄为488.3±3.9 Ma.通过主、微量元素分析,其岩石属高温富黑云母含堇青石过铝花岗岩,属高钾钙碱系列岩石,具中等负Eu异常稀土特征,属“南岭型”花岗岩.结合沉积作用和区域地质构造背景,认为该期侵入岩为晚寒武世保山地块与腾冲地块碰撞拼合后上地壳部分熔融产物.

A large number of Early Paleozoic intrusive rocks represented by Pinghe pluton are developed on the western margin of Baoshan block—an important part of Gondwana.However,due to the lack of field survey data,its geological significance has long been disputed.Based on the 1∶50000 regional geological survey,the detailed field contact relationship has confirmed the existence of two stages of intrusive rocks in Pinghe pluton,and sedimentation,chronology and petrogeochemistry have endowed it with new geological implication.The early intrusive rocks in Luxi area are mainly monzogranites,with the LA-ICP-MS zircon U-Pb age of 488.3±3.9 Ma.The major and trace element analysis results show that the rock belongs to high-temperature biotite-rich cordierite-bearing peraluminous granite of high-K calc-alkali series,with REE characteristics of medium negative Eu anomaly,classified as the Nanling type of granite.Combined with sedimentation and regional geological tectonic background,it is considered that the intrusive rock is the product of upper crust partial melting after the collision of Baoshan block and Tengchong block in the Late Cambrian.