云开地块北缘构造混杂岩的岩石成因探讨  

Petrogenesis of the tectonic mélange on the northern margin of the Yunkai Terrane,South China

作　　者：周岱[1,2] 龙文国[1,2] 柯贤忠[1] 张利国[1,2] 徐德明[1,2] 王晶[1] 

机构地区：[1]中国地质调查局武汉地质调查中心,武汉430205 [2]中国地质调查局花岗岩成岩成矿地质研究中心,武汉430205

出　　处：《岩石学报》2017年第3期810-830,共21页Acta Petrologica Sinica

基　　金：中国地质调查局项目(12120114039201;121201009000150011;121201009000150015)资助

摘　　要：华南云开地块北缘的信宜贵子地区见大量变玄武岩与变沉积岩混杂产出。变玄武岩多以构造岩块或透镜体产出,地球化学以中等Mg#、富钠贫钾为特征,属亚碱性的拉斑玄武岩系列。轻稀土元素中等富集,无Eu异常,微量元素以富Nb、显著的Sr-Nb-Ta弱亏损为特征。143Nd/144Nd变化于0.512513~0.512655之间,对应的εNd(t)值介于2.89~4.90之间。构造环境判别表明,变玄武岩原岩可能为弧后盆地玄武岩。2个变玄武岩样品的锆石U-Pb年龄为1031±28Ma、1025±39Ma。变沉积岩基质以片岩、变砂岩和石英岩为主,表现为陆缘碎屑沉积特征。2个石英岩样品的碎屑锆石U-Pb年龄显示变沉积岩原岩具有~1.0Ga的物源峰,其最年轻锆石为777Ma和571Ma,原岩沉积时间大致为南华纪-震旦纪。本次研究认为,信宜贵子构造混杂岩是Grenville期弧后盆地玄武岩与新元古代晚期陆缘碎屑沉积物构造混杂堆积的结果,构造混杂的时间可能为奥陶纪-志留纪。Xinyi-Guizi area,in where metabasalts and metasedimentary rocks forming tectonic mélange,locates on the northern margin of the Yunkai terrane,South China. Metabasalts which outcrop as tectonite or lentoids,are characterized by moderate Mg#,high Na,low K,and moderately enriched LREE,no Eu anomaly,high Nb,strongly negative Sr-Nb-Ta anomaly.143Nd/144 Nd =0. 512513 - 0. 512655,and εNd（t） = 2. 89 - 4. 90. The tectonic setting identification show that the protolith of metabasalts might erupt in back-arc basin setting. Zircons from two metabasalt samples yield U-Pb age of 1031 ± 28 Ma,1025 ± 39 Ma. The metasedimentary rocks are mainly composed of schist,metasandstone and quartzite,dominated by characters of terrigenous clastic deposit. Detrital zircons from two quartzite samples yield - 1. 0Ga main peak and youngest U-Pb age of 777 Ma,571Ma respectively. It is concluded that the Guizi tectonic mélange is the result of tectonic accumulation mixed by Grenville back-arc basin basalts and Late Neoproterozoic terrigenous clastic sediments,and the formation age of tectonic mélange may be Ordovician-Silurian.

关 键 词：云开群 构造混杂岩 岩石成因 武夷-云开造山带 

分 类 号：P581[天文地球—岩石学] P588.34[天文地球—地质学]