Mineralogical, Crystal-Chemical, and Rb–Sr Isotope Data on Terrigenous Globular Phyllosilicates of the Maastakh Formation (Lower Vendian, Olenek Uplift)

• Published in: Lithology and Mineral Resources 2021-09, Vol.56 (5), p.418-437
• Main Authors: Ivanovskaya, T. A., Zaitseva, T. S., Zviagina, B. B., Sakharov, B. A., Kochnev, B. B., Konstantinova, G. V., Dorzhieva, O. V., Pokrovskaya, E. V.
• Format: Article
• Language: English
• Subjects: Analytical methods; Cations; Computer software; Crystal structure; Data; Diffraction patterns; Earth and Environmental Science; Earth Sciences; Ethylene glycol; Geochronology; Glauconite; Grains; Illite; Illites; Infrared spectroscopy; Iron; Isotopes; Mathematical analysis; Micas; Mineral Resources; Mineralogy; Parameters; Rivers; Rubidium-strontium dating; Sedimentology; Sediments; Short range order; Smectites; Software; Strontium isotopes; Unit cell; Uplift; Vermiculite; Vermiculites; X-ray diffraction
• ISSN: 0024-4902; 1608-3229; 1573-8892
• DOI: 10.1134/S0024490221050035

The mineralogical, structural, crystal-chemical, and isotope-geochronological data were obtained for the first time in two samples of globular phyllosilicates (GPS) of the glauconite–illite series collected from terrigenous rocks in two sections of the lower part of the Lower Vendian Maastakh Formation (Khorbusuonka and Ulakhan-Sololi rivers, northwestern slope of the Olenek Uplift). Simulation of experimental X-ray diffraction patterns for both samples in the air-dried and ethylene glycol-solvated states was used to determine the expandable layer contents (9, 10%), types of expandable layers (smectite- and vermiculite-type), their ratios in a three-component mixed-layer structure, parameter c sinβ (9.98 Å) of mica layers, and the short-range order factor describing the alternation of different layer types ( R = 2, 3). Values of the unit-cell parameter b (9.027, 9.039 Å) correspond to the dioctahedral Al, Fe-bearing micas. The mica components in the studied mixed-layer minerals are shown to be represented by Fe-illites (K Al = VI Al/( VI Fe 3+ + VI Al) = 0.71, 0.82) with the K 2 O content of 7.77 and 8.40%. The Rb–Sr dating of the Maastakh GPS was carried out for the first time in combination with the calculation of theoretical patterns in the cation distribution in the mineral structure and comparison of the calculation results with the Mössbauer and IR spectroscopy data using the Optima software package supplemented with the new Irmes software. The Rb–Sr data obtained for two Fe-illites (Khorbusuonka and Ulakhan-Sololi rivers: 1033, 913 ± 12 Ma, respectively) are “older” relative to the Vendian Maastakh Formation (~640 ± 5), indicating a terrigenous origin of the studied grains. Globular phyllosilicates from the Maastakh Formation are similar in age and composition to the previously studied Lower Khaipakh (Middle Riphean) GPS (1172 ± 18 and 1112 ± 24 Ma, respectively). The age of GPS samples from the Maastakh Formation is younger (1033–913 Ma), probably, due to the initial cationic disordering in the GPS structure and partial loss of radiogenic elements during secondary alterations (rewashing and redeposition of Fe-illite grains in sediments of the Maastakh Formation) and, probably, during their catagenetic changes as well.