扬子克拉通崆岭杂岩新太古代花岗片麻岩成因及其构造意义

Neoarchean Granitic Gneisses in the Kongling Complex,Yangtze Craton:Petrogenesis and Tectonic Implications

以崆岭杂岩中新太古代花岗片麻岩为研究对象,系统研究了其锆石U-Pb年代学和全岩地球化学特征,并对其岩石成因和扬子陆核～3.0～2.6Ga构造演化过程进行了初步探讨.锆石LA-ICP-MS U-Pb同位素测年结果表明,花岗片麻岩形成年龄为2 673±39Ma,且遭受了古元古代(2 042±27Ma)的高压麻粒岩相变质作用.地球化学研究表明,该套花岗片麻岩富Si,贫Mg、Cr、Ni,具有Eu、Sr和高场强元素的负异常.花岗片麻岩的εNd(t)值在-1.9～-0.1之间变化,对应两阶段Nd同位素模式年龄为3.15～3.01Ga,锆石饱和温度为789～825℃,显示岩体可能形成于初生长英质地壳物质在后碰撞伸展构造背景高温条件下部分熔融.结合前人已有的研究成果,认为以崆岭杂岩为代表的扬子陆核可能完整记录了～2.9～2.6Ga板块俯冲-碰撞-后碰撞与造山作用相关的完整过程.

This study carries out systematical geochronological and whole-rock geochemical investigations for the Neoarchean granitic gneisses of the Kongling complex,and discusses the petrogenesis and^3.0-2.6 Ga tectonic evolution of the nucleus of the Yangtze craton.The zircon LA-ICP-MS U-Pb dating reveals that the gneisses were crystallized at 2 673±39 Ma,and experienced high-pressure granulite-facies metamorphism at 2 042±27 Ma.The geochemical study illustrates an enrichment of Si and depletions of Mg,Cr and Ni,as well as negative anomalies of high field strength elements,Eu and Sr.TheεNd(t)values of the gneisses vary between-1.9 to-0.1 and the corresponding two-stage Nd isotopic model ages range from 3.15-3.01 Ga,combined with their relatively high calculated zircon saturation temperature(789-825℃),indicating that the Kongling Neoarchean gneisses might have formed by partial melting of juvenile felsic crustal materials under a high-temperature condition in the post-collisional extensional tectonic setting.Combined with the documented work,it is suggested that the nucleus of theYangtze craton,represented by the Kongling complex,may fully record an^2.9-2.6 Ga orogenic-related event including earlier stage of oceanic slab subduction,middle stage of arc(or continent)-continent collision,and later stage of post-collisional extension.