摘要
大兴安岭北段额尔古纳地块莫尔道嘎—太平川一带分布有大量的新元古代巨斑状花岗岩,该岩体形成的确切时代及成因尚不清楚。笔者等运用LA-ICP-MS技术进行了锆石U-Pb定年和锆石Hf同位素组成测定。锆石U-Pb年龄结果揭示太平川巨斑状花岗岩形成时代为791.4Ma。锆石Hf同位素研究显示εHf(t)为1.4～6.4,均>0,反映亏损地幔来源新生地壳物质在花岗岩的形成中起主导作用,锆石Hf单阶段的模式年龄tDM为1.09～1.28Ga,与岩石的形成时间791.4Ma有较长的时间间隔,表明该区花岗岩的母岩来自具有较长地壳滞留时间的地壳物质的部分熔融。结合额尔古纳已有的花岗岩锆石Hf同位素资料,认为额尔古纳地块在中、新元古代曾发生过地壳增生事件,存在1.09～1.28Ga的中元古代晚期增生地壳。
Taipingchuan large porphyritic granite pluton was developed in the Erguna Massif in the northern Great Xing＇an Range, NE China. The precise age of the formation and genesis of this pluton are unclear. The authors have carried out zircon U-Pb dating and Hf isotope studies by means of LA-ICP-MS. Zircon U-Pb dating results revealed that the age of Taipingchuan granite is 791.4 Ma. Zircon Hf isotope characteristics indicate that the zircon enf （t）values of the granite range from 1.4 to 6. 4, implying that the depleted-mantle- derived juvenile crustal material played an important role in the formation of the granite magma. The 2-stage model ages t~,~of 1.09 - 1.28 Ca, as revealed by Hf composition in zircon, showed rather large interval with the formation age 791.4 Ma of the granite. It indicates that the parental magma of the granitic rock in this region was derived from the partial melting of the crustal material which had a long resident time within the crust. Combined with the previous zircon Hf isotope data obtained from Erguna Massif, the authors hold that there had been crustal accretion event in Erguna Massif in the late Mesoproterozoic time and the 1.09 - 1.28 Ga late Mesoproterozoie accretional crust had existed.
出处
《地学前缘》
EI
CAS
CSCD
北大核心
2012年第5期114-122,共9页
Earth Science Frontiers
基金
中国地质调查局基础地质研究项目"兴蒙造山带中古老陆块性质与成矿背景综合研究"(1212011085478)
