Abstract

The paper presents data on the lithochemistry of Upper Riphean and Vendian metapelites in the Bodaibo structural–facies zone of the Baikal–Patom foldbelt. The typical K₂O/Na₂O and SiO₂/Al₂O₃ ratios of the metapelites indicate that they have not been affected by potassium metasomatism and silicification processes. The ratios in the metapelites of the TM and FM and of the NAM and HM modules of the rocks suggest that their protoliths consisted mostly of the material of the first sedimentation cycle. Its sources were most likely igneous rocks of intermediate and mafic composition. The composition of the protoliths is comparable to kaolinite, kaolinite–illite–smectite, and chlorite–smectite–illite clays, i.e., it did not principally differ from the composition of most “ordinary” clay rocks. The average values of the chemical index of alteration (CIA_correct) exceed its threshold value that distinguishes between rocks formed in cold/arid and warm/humid climates, only for metapelites of the Kharlukhtakh, Khaiverga, Aunakit, and Vacha formations. The metapelites of the other levels of the Upper Riphean and Vendian of the Bodaibo zone are composed of thin-grained aluminosilicate clastic material relatively weakly altered by chemical weathering in the paleocatchment areas. The average values of the phosphorus enrichment coefficient in the formations give reason to believe that the paleoproductivity of the sedimentation areas of the Upper Riphean and Vendian was insignificant, despite the locally rather high content of TOC in the metapelites. The metapelites also show no evidence of the presence of “camouflaged” pyroclastics or products of underwater exhalations.

中文翻译：

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贝加尔—帕托姆褶皱带博戴波带上里弗统和文甸变泥岩原岩形成条件

摘要

本文介绍了贝加尔-帕托姆褶皱带博戴波构造相带上里弗阶和文迪阶变泥质岩的岩石化学数据。典型的 K ₂ O/Na ₂ O 和 SiO ₂ /Al ₂ O ₃变泥岩的比例表明它们没有受到钾交代作用和硅化过程的影响。岩石的 TM 和 FM 以及 NAM 和 HM 模块的变泥岩中的比率表明它们的原岩主要由第一次沉积循环的物质组成。它的来源很可能是中间和镁铁质成分的火成岩。原岩的成分与高岭石、高岭石-伊利石-蒙脱石和绿泥石-蒙脱石-伊利石粘土相当，即它与大多数“普通”粘土岩石的成分没有主要区别。化学变化指数的平均值（CIA_正确) 超过了区分在寒冷/干旱和温暖/潮湿气候中形成的岩石的阈值，仅适用于 Kharlukhtakh、Khaiverga、Aunakit 和 Vacha 地层的变质岩。博戴波带上里弗和文甸其他层次的变泥质岩由古汇合区化学风化作用相对较弱的细粒硅铝酸盐碎屑岩组成。地层中磷富集系数的平均值使我们有理由相信，尽管变泥岩中 TOC 含量局部较高，但上 Riphean 和 Vendian 沉积区的古生产力并不显着。这些变泥岩也没有显示出存在“伪装”的火山碎屑或水下呼气产物的证据。