Crystal Chemical, Mineralogical, and Geochemical Features of Dolomites of the Middle Riphean Avzyan Formation (Southern Urals)

IF 0.7 4区 地球科学 Q4 GEOCHEMISTRY & GEOPHYSICS
R. R. Akhmedova, S. V. Michurin, E. O. Shiyanova, N. D. Sergeeva, A. A. Sharipova
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Abstract

The crystal chemical characteristics and causes of their variations in the weakly and strongly modified by epigenetic processes dolomites of the Middle Riphean Avzyan Formation in the Bashkir meganticlinorium have been determined. The studies were accomplished by the X-ray diffraction, X-ray fluorescence, and SEM/EDS analysis methods. The Avzyan dolomites are marked by increased parameters of the crystal lattice (aav = 4.8105 Å, cav = 16.0211 Å) and reduced values of the substructural reflection (Kav = 0.66) in comparison with stoichiometric dolomites. The average content of elements is as follows: Fe(II) 4545 ppm, Mn 423 ppm, and Sr 124 ppm. Increase in parameters of the crystal lattice of the Avzyan dolomites shows direct correlation with increase in the contents of Fe and Mn, whereas values of the substructural reflection have an inverse correlation. Rocks of all studied sections include two generations of dolomite and calcite. The calcite–dolomite veinlets were formed at 260–530°C and 0.3–2.3 kbar. In dolomites of different subformations, the average value of parameters of the crystal lattice a and c decreases from the early (Kataskin subformation) to the late Avzyan (Tyul’men subformation). In the same direction, average values of the coefficient K of the dolomite structure ordering increase. Dolomites of different stratigraphic levels of the Avzyan Formation underwent intense epigenetic transformations caused by the impact of medium- and high-temperature Fe- and Mn-containing fluids on rocks. Change in the crystal chemical characteristics of the Avzyan dolomites is associated not so much with the process of regional metamorphism, as with the activity of postmagmatic (sections near the Veselovka Settlement and on the Tyul’men River) and catagenetic (sections near the Islambaevo Settlement and on the Bol’shoi Avzyan River) of fluids, which percolated along the fracture zones.

Abstract Image

中里皮安阿夫齐安岩层(乌拉尔南部)白云岩的晶体化学、矿物学和地球化学特征
该研究确定了巴什基尔巨岩层中里弗安-阿夫赞组(Middle Riphean Avzyan Formation)弱表生过程和强表生过程白云岩的晶体化学特征及其变化原因。研究是通过 X 射线衍射、X 射线荧光和扫描电镜/电子显微镜分析方法完成的。与化学白云石相比,阿夫齐安白云石的特点是晶格参数增加(aav = 4.8105 Å,cav = 16.0211 Å),亚结构反射值降低(Kav = 0.66)。元素的平均含量如下Fe(II) 4545 ppm,Mn 423 ppm,Sr 124 ppm。阿夫齐安白云岩晶格参数的增加与铁和锰含量的增加直接相关,而亚结构反射值则呈反向相关。所有研究地段的岩石都包含两代白云石和方解石。方解石-白云石细脉是在 260-530°C 和 0.3-2.3 千巴条件下形成的。在不同亚形态的白云石中,晶格参数 a 和 c 的平均值从早期(卡塔斯金亚形态)向晚期阿夫齐安(秋门亚形态)递减。同样,白云石结构有序性系数 K 的平均值也在增加。由于含铁和锰的中温和高温流体对岩石的影响,阿夫齐安岩层不同地层的白云岩经历了强烈的表生变化。阿夫齐安白云岩晶体化学特征的变化与其说是与区域变质过程有关,不如说是与沿断裂带渗流的后岩浆流(Veselovka 聚居区附近和 Tyul'men 河上的地段)和成岩流(Islambaevo 聚居区附近和 Bol'shoi Avzyan 河上的地段)的活动有关。
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来源期刊
Lithology and Mineral Resources
Lithology and Mineral Resources 地学-地球化学与地球物理
CiteScore
1.30
自引率
37.50%
发文量
29
审稿时长
>12 weeks
期刊介绍: Lithology and Mineral Resources is an international peer reviewed journal that publishes articles on a wide range of problems related to the formation of sedimentary rocks and ores. Special attention is given to comparison of ancient sedimentary rock and ore formation with present-day processes. The major part of the journal is devoted to comparative analysis of sedimentary processes on the continents and in oceans, as well as the genetic aspects of the formation of sedimentary and hydrothermal–sedimentary mineral resources. The journal welcomes manuscripts from all countries in the English or Russian language.
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