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滹沱群是华北最典型的古元古界地层之一,限定其时代对建立早期地层年代格架和探讨华北早前寒武纪地质演化过程意义重大。本文对五台山地区蒋村镇附近的滹沱群地层进行了详细研究,从与蒋村砾岩中石英斑岩砾石相同的基岩中选取了2件石英斑岩样品,并获得其锆石U-Pb年龄结果分别为(2166±17)Ma和(2138±17)Ma。据此,限定蒋村地区碎屑沉积岩时代应小于2138 Ma。结合四集庄组底部发育厚层的砾岩和区域内2.2~2.1 Ga岩浆事件,我们进一步认为滹沱群底界年龄为~2.2 Ga。由于滹沱群豆村亚群和东冶亚群经历了同期褶皱变形作用,而侵入于蒋村四集庄组未变形正长花岗岩脉的锆石U-Pb年龄结果为(1816±18)Ma。因此,本文限定豆村亚群、东冶亚群的时代为2.2~1.82 Ga。石英斑岩中锆石Lu-Hf同位素分析结果为176Lu/177Hf为0.000717~0.002239,176Hf/177Hf为0.281399~0.281563,其176Hf/177Hfi为0.281315~0.281496和εHf(t)为–3.37~4.11,变化范围较大,初步认为其源自于新太古代早期上地壳的部分熔融并有地幔物质添加。
Hutuo Group is one of the most typical Paleoproterozoic strata in North China. Limiting its age is of great significance to the establishment of early stratigraphic chronology and exploration of the geological evolution of North China in the early Precambrian. In this paper, we studied in detail the Hutuo Group strata near Jiangcun Town in Wutaishan. Two samples of quartz porphyry were selected from the same bedrock of quartz porphyry gravel in Jiangcun conglomerate, and their zircon U-Pb ages The results were (2166 ± 17) Ma and (2138 ± 17) Ma, respectively. Accordingly, the age of the clastic sedimentary rocks that bound the Jiangcun area should be less than 2138 Ma. Combining with thick conglomerates in the bottom of the Shijiazhuang Formation and 2.2 ~ 2.1 Ga magmatic events in the area, we further believe that the bottom boundary of the Hutuo Group is ~ 2.2 Ga. The U-Pb zircon age of intrusive granitic veins intruding into the Sijiacun Formation of Jiangcun Formation is (1816 ± 18) Ma, because the Beitou Group Doucun Sub-group and the Dongye Sub-Group experienced the same period of fold-deformation. Therefore, this article defines the village bean subgroup and the Dongye subgroup is from 2.2 to 1.82 Ga. The results of Lu-Hf isotopic analysis of zircons from quartz porphyries show that for 176Lu / 177Hf 0.000717-0.002239 and 176Hf / 177Hf 0.281399-0.281563, 176Hf / 177Hfi 0.281315-0.281496 and εHf (t) -3.37-4.11, Larger, initially believed to have originated from the partial melting of the upper crust in the Early Neo-Archean with the addition of mantle material.