The Lower Riphean Fine-Grained Aluminosilicate Clastic Rocks of the Bashkir Anticlinorium in the Southern Urals: Composition and Evolution of Their Provenance
The Lower Riphean Fine-Grained Aluminosilicate Clastic Rocks of the Bashkir Anticlinorium in the Southern Urals: Composition and Evolution of Their Provenance
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乌拉尔南部巴什基尔背斜层的下里普阶细粒铝硅酸盐碎屑岩：其物源的组成和演化
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发表时间：
2004
期刊：
影响因子：
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通讯作者：
O. P. Lepikhina
中科院分区：
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作者：
A. Maslov;M. Krupenin;E. Z. Gareev;O. P. Lepikhina
利用巴什基尔复向斜布尔津细粒铝硅酸盐碎屑岩的主量和微量元素地球化学资料，研究了1650~1640~1350Ma的物源组成及其演化。所有页岩样品的稀土元素总量均高于200ppm，而艾组上部泥质岩的稀土元素总量则低约3倍。（La/Yb）N和（Gd/Yb）N在该层页岩中也很低。Burzyan页岩的Eu/Eu * 值为0.6 - 0.7，这是大多数后太古代粘土岩的典型值。各岩石地层水平页岩的稀土配分模式十分相似，与PAAS配分模式接近。早期里菲沉积盆地的演化，占据了今天巴什基尔Anticlinorium的领土解释如下。早期里菲期的开始具有以下特征：（1）形成浅沉积盆地，（2）由基性岩脉和其他小侵入体浸渍的长英质岩石组成的成熟陆壳的大块侵蚀，（3）近源的优势。在晚Ai时代，上述地块完全递变，铝硅酸盐碎屑物质的远源变得普遍。源区长英质岩被侵蚀。基性岩在库萨期早期对物源有贡献，但随后直到里菲期早期结束，基性岩才参与侵蚀。在这段时间里，碎屑物质主要是从西部和西北部移走的，从东欧地台的东部来的一个突然的和相对较短的时间内的陆源物质的迁移路径的重新安排，应晚Satka时间，当大量的镁供应到盆地。根据Burzyan剖面页岩的Nd年龄模型，镁的来源具有前里菲时代，位于现今巴什基尔Anticlinorium的北部或东北部。
The major and trace element geochemistry of the Burzyan fine-grained aluminosilicate clastic rocks of the Bashkir Anticlinorium was used to estimate the composition of provenance and its evolution from 1650-1640 to 1350 Ma. Total REE contents are higher than 200 ppm in all the shale samples ana- lyzed, and approximately 3 times lower in the clayey rocks of the upper unit of the Ai Formation. The (La/Yb) N and (Gd/Yb) N in the shales of this level are also much lower. The Eu/Eu* value of Burzyan shales is 0.6-0.7, which is typical of most post-Archean clayey rocks. The REE patterns of shales from all the lithostratigraphic levels analyzed are rather similar and close to the PAAS pattern. The evolution of the Early Riphean sedimentary basin that occupied the territory of the present-day Bashkir Anticlinorium is interpreted as follows. The beginning of the Early Riphean was characterized by (1) the formation of a shallow sedimentary basin, (2) the erosion of large blocks of the mature continental crust composed of felsic rocks impregnated by basic dikes and other minor intrusions, and (3) the predominance of proximal provenances. In late Ai time, the aforementioned blocks were completely graded; and distal sources of alu- minosilicate clastic materials became prevalent. Felsic rocks were eroded in the source areas. Basic rocks contributed to the provenance in early Kusa time, but subsequently they have not been involved in erosion until the end of the Early Riphean. Clastic material was mainly removed during that time period from the west and northwest, i.e., from the eastern parts of the East European Platform. An abrupt and relatively short-term rearrangement of the migration paths of terrigenous material is supposed for late Satka time, when a great amount of magnesium was supplied to the basin. As follows from the model Nd ages of shales throughout the Burzyan section, the source of magnesium had a pre-Riphean age and was situated north or northeast of the present-day Bashkir Anticlinorium.