华北张家口下花园地区中元古界下马岭组沉积环境与源区构造背景

Sedimentary Environmental Conditions and the Provenance Tectonic Setting of the Middle Proterozoic Xiamaling Formation in the Xiahuayuan Area, Zhangjiakou, North China

华北地区中元古界下马岭组是我国前寒武纪海相富有机质页岩发育的一个重要层段。为揭示华北张家口地区中元古界黑色富有机质页岩的发育条件,对下马岭组黑色页岩进行了黏土矿物、全岩X射线衍射分析以及微量、稀土元素含量和TOC含量分析测试,并据此探讨其沉积环境条件和源区构造背景。结果表明,下马岭组黑色页岩的δCe值为0.72~0.86(平均0.79),Mo/TOC值为0.16~4.51(平均2.49),以及V/(V+Ni)、Ni/Co和U/Th等元素比值均反映出黑色页岩形成于还原滞留环境;Sr/Cu值以及稀土元素配分模式,反映其沉积期为暖湿型气候且沉积速率较低;微量和稀土元素组合图解及比值特征指示张家口地区中元古界黑色页岩的源岩可能为长英质中酸性火山岩,源区构造背景以陆缘弧为主。此外,黑色页岩的TOC与古海洋环境、古生产力、古气候和沉积速率均具有良好的相关性,因此可认为张家口地区下马岭组富有机质页岩的形成是多因素综合作用的结果 。

The Xiamaling Formation of Middle Proterozoic in North China is an important member of Precambrian marine organic-rich shale in China. In order to reveal the development conditions of the Middle Proterozoic black organic-rich shale in the Zhangjiakou area, North China, the X-ray diffraction analysis of clay minerals and whole rock of samples, and the analysis of contents of trace and rare earth elements and the TOC of samples from the Xiamaling Black shale have been carried out, and then the sedimentary environment and the provenance tectonic background of the Xiamaling Black shale have been discussed. The results show that black shales in the Xiamaling Formation have δCe values ranging from 0.72 to 0.86(average 0.79), Mo/TOC ratios ranging from 0.16 to 4.51(average 2.49). These values and ratios of V/(V+Ni), Ni/Co, and U/Th all reflect that the black shales were formed in a reductive retention environment. The Sr/Cu ratios and REE distribution patterns of those black shales indicate that the sedimentation of black shales occurred in a warm and wet climate environment with relatively low deposition rate. The combination diagrams and characteristic ratios of trace and rare earth elements indicate that the middle Proterozoic black shale in the Zhangjiakou area could be sourced from felsic intermediate-acidic volcanic rocks in the tectonic setting of continental marginal arc. According to the good correlations between the TOC and paleo-marine environment, paleo-productivity, paleo-climate and sedimentation rate, it is concluded that the formation of organic-rich shale of the Xiamaling Formation in the Zhangjiakou area was the result of comprehensive influence of multiple factors.