Abstract

The bulk chemical composition of synrift sandstones and associated mudstones is analyzed. Distribution of their fields in the discriminant paleogeodynamic diagrams SiO₂–K₂O/Na₂O (Roser and Korsch, 1986) and DF1–DF2 (Verma and Armstrong-Altrin, 2013) is examined. In terms of the bulk chemical composition, the sandstones correspond mainly to graywackes, litites, arkoses, and subarkoses. The samples also include sublitites and quartz arenites, as well as a significant part of psammites (with log(Na₂O/K₂O less than –1.0) that are lacking in Pettijohn’s classification diagram. This fact supports our conclusion based on the results of mineralogical-petrographic studies: the sedimentary infill of riftogenic structures combines immature sandstones, clastic framework of which is derived from local provenances represented by diverse igneous and sedimentary rocks. Synrift mudstones, relative to sandstones, are composed of a more mature clastic material. Distribution of data points of mudstones in diagram F1–F2 (Roser and Korsch, 1988) suggests that they were sourced mainly from sedimentary rocks. Contents of the majority of main rock-forming oxides in synrift sandstones are almost similar to those in silty–sandy rocks of the Upper Precambrian–Phanerozoic sedimentary megacomplex in the Russian Plate, but differ from contents in the average Proterozoic and Phanerozoic cratonic sandstones, as well as the average composition in the upper continental crust. It is shown that the distribution of synrift sandstones and mudstones in diagram SiO₂–K₂O/Na₂O lacks any prominent features, and their data points cluster in the fields of terrigenous rocks of passive and active continental margins. In diagram DF1–DF2, fields of the studied psammites and mudstones occur in zones of the riftogenic and collisional settings. We believe that the boundary between these zones in the diagram occupies a different position, and this suggestion needs further examination.

中文翻译：

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同质砂岩和泥岩：某些判别古地动力图中的大块化学成分和位置

摘要

分析了同化砂岩和相关泥岩的整体化学成分。研究了判别古动力学图SiO ₂ -K ₂ O / Na ₂ O（Roser和Korsch，1986）和DF1-DF2（Verma和Armstrong-Altrin，2013）中它们的场分布。就大体化学组成而言，砂岩主要对应于灰泥岩，轻石，石棉和次石棉。样品还包括亚沸石和石英砂，以及很大一部分的滑石（log（Na ₂ O / K ₂Pettijohn的分类图中缺少的O小于–1.0）。这一事实支持我们基于矿物岩石学研究结果得出的结论：裂谷构造的沉积填充物结合了未成熟的砂岩，其碎屑骨架来源于以不同火成岩和沉积岩为代表的当地物源。相对于砂岩而言，同化过的泥岩由更为成熟的碎屑物质组成。图F1-F2中泥岩数据点的分布（Roser和Korsch，1988年）表明，它们主要来自沉积岩。合成砂岩中大多数主要成岩氧化物的含量几乎与俄罗斯板块上前寒武纪-生代沉积巨型复合体的粉质砂质岩中的含量相似，但是与平均元古生代和多生代克拉通砂岩的含量以及上陆壳的平均组成不同。在图SiO中显示了同化砂岩和泥岩的分布₂ -K ₂ O / Na ₂ O没有任何显着特征，它们的数据点聚集在被动和主动大陆边缘的陆源岩石领域。在图DF1-DF2中，研究的滑石和泥岩的田地发生在造山带和碰撞环境的区域。我们认为，图中这些区域之间的边界占据了不同的位置，这一建议需要进一步研究。