扬子板块新元古代中期的持续俯冲作用:来自南华纪岛弧火山岩年代学和岩石地球化学新证据  

Continued subduction of the Yangtze Plate in the Middle Neoproterozoic:new evidence based on the geochronology and petro-geochemistry of island arc volcanic rocks in the Nanhua Period

作　　者：朱强 施珂 吴礼彬[1] 江来利[1] 胡召齐 徐生发[2] 翁望飞[2] ZHU Qiang;SHI Ke;WU Libin;JIANG Laili;HU Zhaoqi;XU Shengfa;WENG Wangfei(Geological Survey of Anhui Province,Bureau of Geology and Mineral Resources Exploration of Anhui Province,Hefei 230001,China;No.332 Geological Party,Bureau of Geology and Mineral Resources Exploration of Anhui Province,Huangshan 245000,China)

机构地区：[1]安徽省地质矿产勘查局安徽省地质调查院,安徽合肥230001 [2]安徽省地质矿产勘查局332地质队,安徽黄山245000

出　　处：《地学前缘》2020年第4期17-32,共16页Earth Science Frontiers

基　　金：中国地质调查局项目(DD20190379-13);安徽省国土资源公益性项目(2012-g-38);安徽省国土资源科技项目(2014-K-6)。

摘　　要：产于扬子板块东南缘皖南祁门北部地区的铺岭组和扬子板块东北缘皖东张八岭地区的西冷岩组分别发育一套火山岩。前者为陆相火山岩,岩性以玄武安山岩为主;后者为海相火山岩,岩性以细碧-角斑岩系为主。两者之上均角度不整合覆盖着一套砂泥质沉积岩。铺岭组玄武安山岩LA-ICP-MS锆石U-Pb年龄为(765±15) Ma,西冷岩组石英角斑岩LA-ICP-MS锆石U-Pb年龄为(726.8±1.4) Ma,均属南华纪(新元古代中期)。二者主量元素含量差别较大(铺岭组为玄武-安山岩;西冷岩组为石英角斑岩),但它们均属于钙碱性系列,并具有相似的微量元素特征:它们均富集轻稀土元素和Ba、Th、U等大离子亲石元素,高场强元素Nb、Ta、Ti强烈亏损,δEu、Zr、Hf异常不明显。这些特征显示它们与岛弧火山岩类似,可能是受俯冲板片流体影响的亏损地幔楔和新生地壳熔体的混合形成的。这些火山岩系形成于华夏向扬子俯冲形成的沟弧盆体系消失之后。结合前人研究成果,我们认为:扬子板块晋宁期深部的俯冲作用可能一直持续到约700 Ma,新元古代中期可能存在多岛弧拼贴过程,到了南华纪晚期才正式进入板内伸展阶段。The Puling Formation in the northern Qimen area on the southeastern margin of the Yangtze Plate,and the Xileng Formation in the Zhangbaling area on the northeastern margin of the Yangtze Plate,each developed a suite of volcanic rocks.The former is continental volcanic rocks with basalt-andesite series,and the latter is marine volcanic rocks with spilite-keratophyre series.The volcanic rocks are unconformities covered with sand mudstone sedimentary.The LA-ICP-MS zircon U-Pb age of basalt-andesite from the Puling Formation is 765±15 Ma,while quartz keratophyre from the Xileng Formation is 726.8±1.4 Ma,indicating they are formed in the Nanhua Period(Middle Neoproterozoic)after the disappearance of the“trench-arc-basin system”formed by the subduction of the Cathaysian to the Yangtze Plate in the Neoproterozoic.The whole rock geochemical analysis showed that the major elemental contents of the two volcanic rocks were quite different,but they all belonged to calc-alkaline series,and with similar trace elemental characteristics:they were enriched in LREE and large ion lithophile elements(e.g.,Ba,Th,U),strongly depleted in high field strength elements(e.g.,Nb,Ta,Ti),with inconspicuousδEu,Zr and Hf anomalies.These features suggest that they are similar to island arc volcanic rocks and possibly formed by the mixing of the depleted mantle wedges metasomatized by subduction-related fluids and melt of new crust.Combined with previous research results,we consider the deep subduction in the Jinning period might have lasted until ca.700 Ma,affected by a multi-island arc collage process in the Middle Neoproterozoic,and then this area entered an intra-plate extension stage until the late Nanhua Period.

关 键 词：南华纪 岛弧火山岩 俯冲作用 多岛弧 扬子板块 

分 类 号：P588.14[天文地球—岩石学] P597[天文地球—地质学]