Geochronological study on the Fenghuangzui complex of Dantazi Group at northern Hebei Province
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摘要:
冀北地区基底的研究对理解华北克拉通早前寒武纪的演化具有重要意义。本文通过对冀北地区单塔子群凤凰嘴杂岩的锆石年代学工作探讨早前寒武纪华北克拉通北缘所经历的构造事件。单塔子群凤凰嘴杂岩主要由糜棱岩化的花岗质片麻岩和侵入其中的变质的基性岩墙组成。其中花岗质片麻岩的锆石呈明显的核边结构, 岩浆核的谐和年龄为2.45Ga, 变质边的年龄为1.95Ga。变质岩墙中的锆石未见明显的核边结构, 阴极发光照片显示为变质锆石的特征, 得到的年龄为1.9Ga。此年龄与花岗质片麻岩锆石的变质年龄相似, 说明二者共同经历了古元古代的造山事件。此外, 尽管没有得到岩墙的确切形成时代, 但单塔子群内普遍发育的大规模岩墙说明在2.54~1.9Ga之间, 该区经历了一次规模较大的伸展事件。
Abstract:The study of the basement of the northern Heibei Province plays an important role in understanding the Early Precambrian evolution of the North China Craton. In this paper, detailed geochronological study on Fenghuangzui complex of the Dantazi Group was reported, which indicate at least two tectonic events between Late Archean and Early Proterozoic. The Fenghuangzui complex of Dantazi Group, occupies the northern Hebei Province, is mainly composed of granitic mylonite gneiss and is intruded by metamorphic dyke. Zircons from the granitic mylonite gneiss show typical core-rim structure, and the age of magmatic core is 2.45Ga and the metamorphic rim 1.95Ga.However, zircons from the metamorphic dyke occur as only single grains and cathodoluminescence images constrain their metamorphic origin. Their concordant age of 1.9Ga, similar to metamorphic age of the granitic mylonite gneiss, indicate the granitic gneiss and the dyke underwent Paleoproterozoic orognic event together. Though the original age of the dyke is unknown, prominent Paleoproterozoic extension in the study area, occurred between 2.45~1.9Ga, can be deduced by existence of large-scale massive dykes.
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Key words:
- Zircon geochronology /
- Fenghuangzui /
- Dantazi /
- Northern Hebei Province
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图 1
冀北地区前寒武纪变质杂岩地质简图(据刘树文等, 2007a修改)
Figure 1.
Geological map of the Precambrian metamorphic complexes in northern Hebei (after Liu et al., 2007a)
图 2
承德地区单塔子群地质简图
Figure 2.
Geological map of distribution of the Dantazi Group in Chengde
图 5
变基性岩样品TD89-5 CL图像及部分定年结果
Figure 5.
Representative cathodoluminescence (CL) images of zircon from the sample TD89-5
图 7
样品TD89-4 CL图像及部分定年结果
Figure 7.
Representative cathodoluminescence (CL) images of zircon from the sample TD89-4
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