伊春花岗质片麻岩锆石 U-Pb 年代学特征

通过1∶5万朱拉比拉河等图幅区域地质调查工作，在伊春地区发现了新元古代花岗质片麻岩。应用锆石 U-Pb 测龄方法对花岗质片麻岩进行了年代学研究，23个点的206 Pb／238 U表面谐和年龄均在850 Ma 左右，加权平均为850．2±2．1 Ma。该年龄代表花岗质片麻岩体的侵位时间为新元古代；而较新的499 Ma 年龄可能是后期构造事件改造的新生锆石，反映后期构造热事件的年龄；1518 Ma 的年龄应是本次岩浆作用过程中捕获的早期锆石的年龄，该锆石年龄可能代表本区花岗岩的继承性锆石年龄。伊春花岗质片麻岩所在的地区存在前寒武纪的古老微陆块。

Zircon U-Pb dating of granitic gneiss in Yichun,Heilongjiang, China and its geological significance

The Neoproterozoic granitic gneiss is reported for the first time in Yichun based on the regional geological survey in the Zhulabila river and its adjacent areas at 1∶50 000 scale.Zircon U-Pb dating yields 206 Pb/238 U concordant ages of ~850 Ma and the weighted mean age of 850.2 ±2.1 Ma, which are defined by 23 grains.This age indicates that the emplacement time of the granitic gneisses is Neoproterozoic.Meanwhile,the dating also yields the age of 499 Ma that probably suggests the newly generated zircon reformed by the later tectonic event,representing the time of the later tectono-thermal event.The age of 1518 Ma should be the age of the zircon captured during the Neoproterozic magmatic event,which suggests that an ancient massif exists in Yichun.The discovery of the Neoproterozoic granitic gneiss provides a new evidence for the tectonic and magmatic evolution in Yichun.