山东半岛荆山群富铝片麻岩锆石U-Pb定年及其地质意义  

U-Pb dating of zircons from Al-rich paragneisses of Jingshan Group in Shandong peninsula and its geological significance

作　　者：刘平华[1] 刘福来[1] 王舫[1] 刘建辉[1] 

机构地区：[1]中国地质科学院地质研究所,北京100037

出　　处：《岩石矿物学杂志》2011年第5期829-843,共15页Acta Petrologica et Mineralogica

基　　金：国家杰出青年基金资助项目(40725007);国家自然科学基金创新群体项目(40921001);中国地质调查局地质大调查资助项目(1212011120150;1212010811065)

摘　　要：荆山群富铝片麻岩广泛分布于山东半岛早前寒武纪变质基底之中。锆石阴极发光图像分析和U-Pb定年结果表明,荆山群富铝片麻岩中锆石成因比较复杂,可划分为3种类型：第一类为继承性（岩浆或碎屑）锆石,U-Pb定年结果显示该类锆石微区记录了~2 650 Ma和~2 100 Ma两组207Pb/206Pb年龄,这不仅表明研究区变质基底在中太古代末期和古元古代早期至少存在两期岩浆-热事件,同时,也说明荆山群原岩形成时代应晚于2 100 Ma;第二类为变质锆石,记录的207Pb/206Pb年龄集中在1 900~1 850 Ma之间,应代表荆山群富铝片麻岩峰期高压麻粒岩相变质时代;第三类亦为变质锆石,记录的207Pb/206Pb年龄集中在1 840~1 820 Ma之间,应代表荆山群富铝片麻岩峰后中低压麻粒岩相退变质时代。该项成果准确地限定了荆山群富铝片麻岩的原岩形成时代、峰期高压麻粒岩相变质时代和峰后中低压麻粒岩相退变质时代的年代学格架,对深入探讨华北克拉通东南缘高压麻粒岩的成因机制及其形成的动力学背景具有重要的科学意义。Al-rich paragneisses in Jingshan Group are extensively distributed in the early Precambrian metamorphic basement of Shandong peninsula,southeast part of the North China Craton.Zircons separated from Al-rich paragneisses are divided into three main types based on cathodoluminescence（CL） and in situ U-Pb dating,i.e.,inherited（magmatic or detrital） zircon,HP metamorphic zircon and retrogressive zircon.The inherited zircon records two group 207Pb/206Pb ages of ~2 650 Ma and ~2 100 Ma,indicating two magmatic-thermal events occurring in Neoarchean and Paleoproterozoic epochs and the existence of Paleoproterozoic protoliths of Al-rich paragneisses.In contrast,the homogeneous HP metamorphic zircon records younger 207Pb/206Pb ages ranging from 1 900 Ma to 1 850 Ma,which represent peak HP granulite-facies metamorphic times of Al-rich paragneisses in Jingshan Group.The retrogressive zircon records the youngest 207Pb/206Pb ages of 1 840~1 820 Ma,which represent late medium-and low-granulites-facies retrograde metamorphic times of Al-rich paragneisses in Jingshan Group.These results indicate that the Paleoproterozoic protoliths of Al-rich paragneisses,together with their TTG rocks and mafic rocks,were subducted to coeval Paleoproterozoic HP metamorphism（1 900~1 850 Ma）,followed by late medium-and low-granulites-facies retrogression（1 840~1 820 Ma）.This new result has very important significance for deep discussion of the genetic mechanism and geodynamic model of the HP granulites distributed in the southeast part of the North China Craton.

关 键 词：富铝片麻岩 锆石 U-PB定年 荆山群 山东半岛 

分 类 号：P588.345[天文地球—岩石学] P597.3[天文地球—地质学]