扬子西缘新元古代盐边群火山岩年代学及大地构造背景  

Geochronology and Tectonic Significance of Neoproterozoic Volcanic Rocks from Yanbian Group in Western Yangtze Block

作　　者：刘佩雯 张继彪 丁孝忠[1] 刘燕学[1] Liu Peiwen;Zhang Jibiao;Ding Xiaozhong;Liu Yanxue(Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;School of Civil and Hydraulic Engineering,Xichang University,Xichang 615000,China)

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]西昌学院土木与水利工程学院,四川西昌615000

出　　处：《地球科学》2023年第12期4508-4526,共19页Earth Science

基　　金：中国地质调查局地质调查项目(Nos.DD20221645)。

摘　　要：扬子板块西缘新元古代盐边群广泛发育一系列火山岩,其年代学和构造背景对理解扬子板块前寒武纪构造演化具有重要意义.本文获得盐边群乍古组、小坪组、渔门组和荒田组火山岩LA-ICP-MS锆石U-Pb年龄分别为934±5 Ma、863±4 Ma、843±7 Ma和797±9 Ma,精确限制了盐边群时代为934~797 Ma.荒田组玄武岩属于钙碱性N-MORB(正常型洋中脊玄武岩)系列,轻稀土相对亏损、重稀土相对富集,具有中等程度的Nb、Ta负异常和轻微的Ti负异常,εNd(t)值为3.8~4.9.荒田组玄武岩来自以石榴子石和尖晶石为稳定区的地幔橄榄岩10%~20%的部分熔融.构造背景判别图解指示荒田组玄武岩形成于活动大陆边缘弧前盆地.结合前人的研究成果,认为扬子西缘新元古代早-中期存在弧-盆地系统,扬子板块新元古代构造动力学背景应为活动大陆边缘洋-陆俯冲,板块俯冲开始的时间不晚于934 Ma.The Neoproterozoic Yanbian volcanic rocks are extensively exposed in the western Yangtze block,providing an ideal opportunity to study the Precambrian tectonic evolution of the Yangtze block.LA-ICP-MS zircon U-Pb dating of Zhagu Formation,Xiaoping Formation,Yumen Formation and Huangtian Formation yielded zircon U-Pb ages of 934±5 Ma,863±4 Ma,843±7 Ma and 797±9 Ma,respectively.The N-MORB(normal mid-ocean ridge basalts)type basalts from the Huangtian Formation belong to calc-alkaline series,and display light rare earth element depleted patterns,with moderate negative Nb,Ta anomaly and minor negative Ti anomalies.In addition,these rocks have positiveεNd(t)values(+3.8 to+4.9).They are suggested to be derived from 10%-20%partial melting of the MORB-like source in a fore-arc basin setting in the garnet+spinel stability field.Combined with previous studies,the data confirm the existence of an arc-trench system in the western Yangtze block in the Neoproterozoic.It proposes that the western Yangtze block was located in a convergent setting during the Neoproterozoic.The subduction of oceanic lithosphere beneath the western margin of the Yangtze block initiated no later than 934 Ma.

关 键 词：扬子西缘 盐边群 锆石U-PB年龄 地球化学 大地构造背景 

分 类 号：P58[天文地球—岩石学]