摘要
内蒙古达茂旗南部北口子片麻状花岗闪长岩位于华北克拉通北缘集宁地块,该地区记录了两期(~2.7 Ga和~2.5 Ga)非常重要的新太古代—早古元古代岩浆构造热事件。尽管地质学家对该地区做了大量的工作,但是对~2.5 Ga时期地壳形成机制仍存在较大争议:地壳增生还是地壳再造?为了解决上述争议问题,对北口子地区的片麻状花岗闪长岩进行了年代学以及Hf同位素研究工作。锆石U-Pb测年结果显示,片麻状花岗闪长岩的原岩形成年龄为2572.8 Ma,且经历了2520.6 Ma的变质作用改造。锆石Hf同位素结果显示,大部分ε_(Hf)(t)值位于球粒陨石线之上(-0.4~+3.15,平均值为+1.34),Hf同位素单阶段模式年龄(T_(DM))范围为2752~2885 Ma,Hf同位素二阶段模式年龄(T^(C) _(DM))介于2864~3082 Ma,表明达茂旗南部北口子地区的该期岩浆作用代表着一期地壳再造事件。结合华北克拉通Hf同位素特征,认为华北克拉通~2.5 Ga岩浆作用既有地壳增生作用也有地壳改造作用。
The Beikouzi gneissic granodiorite is located in Jining Block,northern margin of North China Craton.Two important Neoarchean—Early Proterozoic magmatic-tectonic thermal events(~2.7 Ga and~2.5 Ga)are recorded in this area.Although geologists have done a lot of work in this region,there is still controversy about the~2.5 Ga crustal formation mechanism:crustal accretion or crustal reconstruction?In order to solve the controversial issues,this paper carried out Geochronology and Hf isotope research on the gneissic granodiorite in Beikouzi area.Zircon U-Pb dating results show that the protolith formation age of gneissic granodiorite is 2572.8 Ma,and has undergone metamorphism of 2520.6 Ma.Zircon Hf isotope results show that most ofεHf(t)values are above the meteoroid line(-0.4~+3.15,averageεHf(t)values is+1.34),Hf isotope single-stage model ages(TDM)range from 2752 Ma to 2885 Ma,and Hf two-stage model ages(TCDM)range from 2864 Ma to 3082 Ma,suggesting that the~2.5 Ga magmatism in the Beikouzi represents a crustal reconstruction event.Combined with Hf isotope characteristics of North China Craton,it is considered that the~2.5 Ga magmatism of the North China Craton has both crustal accretion and crustal transformation.
作者
张晓伟
张万益
郭磊
欧阳江城
ZHANG Xiao-wei;ZHANG Wan-yi;GUO Lei;OUYANG Jiang-cheng(Chifeng University,Chifeng 024000,China;China Geological Surveys,Beijing 100037,China;Chinese Academy of Geological Sciences,Beijing 100037,China)
出处
《河北地质大学学报》
2022年第3期1-8,共8页
Journal of Hebei Geo University
基金
中国地质调查局地质调查项目(DD20190464)。
