华北板块北缘东段石炭纪早期的岩浆事件及其构造意义——锆石U-Pb年龄与岩石组合证据  

Earliest Carboniferous magmatic event in the eastern section of the northern margin of the North China plate and its tectonic implications——Evidence from rock association and zircon U-Pb geochronology

作　　者：王志伟[1] 裴福萍[1] 曹花花[1] 王子进[1] 许文良[1] 

机构地区：[1]吉林大学地球科学学院,吉林长春130061

出　　处：《地质通报》2013年第2期279-286,共8页Geological Bulletin of China

基　　金：中国地质调查局项目<吉黑东部矿化集中区岩浆岩序列与地质成矿事件研究>(编号:1212011085480);<兴蒙造山带基本构造格局综合调查和研究>(编号:1212011085476);国家自然科学基金项目<吉中地区早古生代岩浆作用及其构造意义>(批准号:41172057)

摘　　要：下二台群盘岭组由钠长角闪片岩(原岩为玄武安山岩)、变质流纹岩、云母石英片岩和少量变质粉砂岩组成。钠长角闪片岩和变质流纹岩样品中的锆石均呈自形—半自形晶,发育岩浆振荡生长环带,具有高的Th/U比值(0.77-1.79),显示出岩浆成因的特征。盘岭组钠长角闪片岩中锆石15个测点的206Pb/238U年龄介于337Ma±11Ma～346Ma±13Ma之间,其加权平均年龄为342Ma±6Ma(MSWD=0.053,n=15),盘岭组变质流纹岩16个测点的206Pb/238U年龄介于341Ma±12Ma～351Ma±14Ma之间,206Pb/238U加权平均年龄为347Ma±5Ma(MSWD=0.116,n=16),它们均形成于石炭纪早期,表明下二台群形成于晚古生代而非前人认为的早古生代。研究区石炭纪早期火山岩的岩石组合为玄武质岩石和流纹岩,显示典型的双峰式火山岩组合特征,代表了一种伸展环境。结合区域地质资料,认为石炭纪早期华北板块北缘东段可能处于被动大陆边缘环境。LA-ICP-MS zircon U-Pb daring results and rock association are reported for the metavolcanic rocks from the Panling Formarion in the eastern section of the northern margin of the North China plate, and their tectonic setting has been discussed,with the aim of constraining the tectonic evolution of the eastern section of the northern margin of the North China plate in the Late Paleozoic period. The Panling Formation in the Xia＇ertai Group consists of albite-amphibole schist whose protolith is basaltic andesite, metarhyolite, micaquartz schist, and minor metamorphic siltstone. Zircons from the albite-amphibole schist and metarhyolite in the Panling Formation are euhedral-subhedral in shape and display fine-scale oscillatory growth zoning as well as high Th/U ratios （0.77-1.79）, implying their mag- matic origin. The ^206Pb/^238U ages of 15 spots of zircons from the albite-amphibole schist are between 337Ma±11Ma and 346Ma±13Ma, with a weighted mean ^206Pb/^238U age of 342Ma±6Ma （MSWD=0.053, n=15）, whereas the ^206Pb/^238U ages of 16 spots of zircons from the metarhyolite in the Panling Formation range from 341Ma±12Ma to 351Ma±14Ma, with a weighted mean ^206Pb/^238U age of 347Ma±5Ma （MSWD=0.116, n=16）. The above dating results indicate that these metavolcanic rocks were formed in the earliest Carboniferous, i.e., the Xia＇ertai Group were formed in the Late Paleozoic rather than in the Early Paleozoic as previously thought. The earliest Carboniferous volcanic rocks are composed mainly of basaltic rocks and rhyolites, suggesting a typical bimodal volcanic rock association and implying an extensional environment. Combined with regional geological data, the authors hold that the eastern section of the northern margin of the North China plate might have been in a passive continental-margin setting in the earliest Carboniferous.

关 键 词：华北板块北缘 石炭纪早期 变质火山岩 锆石U-PB年龄 岩石组合 构造意义 

分 类 号：P534.45[天文地球—古生物学与地层学]