R. R. Akhmedova, S. V. Michurin, E. O. Shiyanova, N. D. Sergeeva, A. A. Sharipova
{"title":"Crystal Chemical, Mineralogical, and Geochemical Features of Dolomites of the Middle Riphean Avzyan Formation (Southern Urals)","authors":"R. R. Akhmedova, S. V. Michurin, E. O. Shiyanova, N. D. Sergeeva, A. A. Sharipova","doi":"10.1134/S0024490224700706","DOIUrl":null,"url":null,"abstract":"<p>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 (<i>a</i><sub>av</sub> = 4.8105 Å, <i>c</i><sub>av</sub> = 16.0211 Å) and reduced values of the substructural reflection (<i>K</i><sub>av</sub> = 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 <i>a</i> and <i>c</i> decreases from the early (Kataskin subformation) to the late Avzyan (Tyul’men subformation). In the same direction, average values of the coefficient <i>K</i> 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.</p>","PeriodicalId":18150,"journal":{"name":"Lithology and Mineral Resources","volume":"59 6","pages":"691 - 705"},"PeriodicalIF":0.7000,"publicationDate":"2024-11-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Lithology and Mineral Resources","FirstCategoryId":"89","ListUrlMain":"https://link.springer.com/article/10.1134/S0024490224700706","RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q4","JCRName":"GEOCHEMISTRY & GEOPHYSICS","Score":null,"Total":0}
引用次数: 0
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.
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.