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G. V. Ovchinnikova A. B. Kuznetsov I. M. Vasil’eva I. M. Gorokhov M. T. Krupenin B. M. Gorokhovskii A. V. Maslov 《Doklady Earth Sciences》2013,451(2):798-802
The Pb-Pb age of phosphorite concretions of the Zigaza-Komarovo Formation, which composes the intermediate horizons of the Riphean stratotype of the South Urals, was determined in fractions resulting from the stepwise dissolution of concretions in 0.1 N, 0.5 N, and 1 N HCl. The determination of the Sr isotopic composition in phosphate fractions was favorable for rejection the fractions polluted with extraneous material. On the 207Pb/204Pb-206Pb/204Pb diagram, the isochron based on 31 points corresponds to 1330 ± 20 Ma (MSWD = 1.12), which is in agreement with the stratigraphic position of the Zigaza-Komarovo Formation. The decreased μ2 value of 9.57 for the phosphorite concretions relative to that of the average earthly lead based on the Stacey-Kramers model (9.74) is related to the rocks with an admixture of mantle lead, which occur in the run-off area of the Zigaza-Komarovo sediments. 相似文献
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M. T. Krupenin A. V. Maslov I. D. Tsybulenko R. A. Nafikov V. G. Petrishcheva 《Lithology and Mineral Resources》2000,35(3):267-277
A property of swelling on heating to yield firm lightweight granules has first been revealed for lowcarbonaceous shales (LCS)
from the Riphean stratotype in the Bashkirian Megaanticlinorium, Southern Urals. These granules possess all technological
properties of “keramzite” or claydite (an artificial, expanded clayey material) and can successfully substitute this material.
Moreover, the procedure of their manufacture, analogous to the manufacture of “shungizite” (an artificial carbonaceous-clayey
material) from Lower Proterozoic clayey rocks of Karelia, is more economical than that for keramzit. Productive beds of the
homogeneous LCS make up extended bodies tens of meters thick. At the present time, they can be used as cover rocks during
the exploitation of the Bakal siderite deposits. The LCS represent fine-grained quartz-chlorite-sericite aggregates (with
variable relationships between the major components), bearing fine-dispersed shungite in amounts of 0.5–1.0%. High-quality
raw material of this kind is characterized by a fine-dispersed admixture of a mixed-layer clayey material bearing montmorillonite
and vermiculite. Geological, lithological, mineralogical, and chemical prognostic criteria have been developed for the shungizite
raw material. It has been concluded that this construction material, new for the Urals, is promising for industrial use 相似文献
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G. V. Ovchinnikova A. B. Kuznetsov I. M. Vasil’eva I. M. Gorokhov M. T. Krupenin A. V. Maslov T. L. Turchenko 《Stratigraphy and Geological Correlation》2008,16(2):138-142
The mineral composition and U-Pb and Rb-Sr systematics of phosphorites from the Satka Formation of Lower Riphean carbonates, the Burzyan Group of Southern Urals, are studied. Phosphorites occurring as small lenses between stromatolite layers are composed largely of fluorapatite with admixture of detrital quartz, feldspars, illite, and chlorite. Phosphorite samples have been subjected to stepwise dissolution in 1 N (fraction L-1) and 2 N (fraction L-2) HCl. As is established, the maximum apatite content is characteristic of fraction L-1, while fraction L-2 is enriched in products of dolomite and sulfide dissolution and in elements leached from siliciclastic components. The Sr content in the Satka apatites (280–560 ppm) is substantially lower as compared with that in unaltered marine apatite. The 87Sr/86Sr “initial ratio in the phosphorites studied (0.71705–0.72484) and host dolomites from the lower part of the Satka Formation is significantly higher than in the Early Riphean seawater that indicates a reset of the Rb-Sr original systems in sediments. The Pb-Pb age of 1340 ± 30 Ma (MSWD = 6.4) estimated based on 7 data points characterizing fractions L-1 and L-2 is younger than the formation time of overlying Burzyan sediments, being consistent, within the error range, with date of the Mashak rifting event recorded at the Early-Middle Riphean boundary. The comparative U-Pb characteristics of two soluble fractions (L-1 and L-2) and silicate residue of phosphorites show that epigenetic redistribution of Pb and U was characteristic of the phosphorite horizon only. The initial Pb isotope composition and μ (238U/204Pb) estimated according to model by Stacey and Kramers for the early diagenetic fluids in carbonate and phosphate sediments of the Satka Formation suggest that they were in isotopic equilibrium with erosion products of the Taratash crystalline complex. 相似文献
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A. V. Maslov G. M. Vovna V. I. Kiselev M. T. Krupenin Yu. L. Ronkin 《Doklady Earth Sciences》2011,439(1):933-938
The results of application of the LA-ICP-MS method for analysis of U-Pb ages of detrital zircons from Serebryanka Group (Middle
Urals) has been presented for the first time. It has been found that the detrital zircon population in tillite-like conglomerates
of the Tany Formation is represented nearly in equal shares by grains with Neoarchean and Paleoproterozoic U-Pb ages. This
allows the basement crystalline rocks from the eastern part of the East European Craton to be considered as the principal
source of aluminosilicate clastic material in the beginning of the Serebryanka. The population of detrival zircons in sandstones
from the Kernos Formation consists of Meso- and Neoarchean (approximately 15%), Paleoproterozoic (∼60%), and Mesoproterozoic
(∼26%) zircon grains. Comparison of the obtained data with the materials on detrital zircons from Tonian and Ediacarian sandstones
in the southern Urals has shown that the principal role in formation of Tonian and Ediacaran sedimentary sequences was played
by the products of Mid- and Late Paleoproterozoic crystalline rock erosion in the craton socle. In addition to this, accumulation
of the Serebryanka Group took place with visible participation of more ancient—Early Paleoproterozoic, Neo- and Mesoarchean—rock
associations on the paleo-water catchment areas. The end of the Serebryanka period differed from its beginning by the additional
appearance of Mesoproterozoic complexes in alimentation zones; for comparison, the role played by these complexes in formation
of Ectasian-Ediacarian deposits of the adjacent southern Urals segment is insufficient, judging by the currently available
data. All these facts may indicate that there are significant differences in the spatiotemporal distribution of clastic material
sources for Upper Precambrian deposits in the West Megazone of the southern and middle Urals. 相似文献
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A.?V.?MaslovEmail author G.?M.?Vovna V.?I.?Kiselev Yu.?L.?Ronkin M.?T.?Krupenin 《Lithology and Mineral Resources》2012,47(2):160-176
Based on the LA-ICP-MS data, detrital zircons from the tillite-type conglomerates of the Tanin Formation (Serebryanka Group)
on the western slope of the Central Urals include approximately equal proportions of crystals with Neoarchean and Paleoproterozoic
U-Pb ages. Therefore, we can assume that crystalline rocks of the basement beneath the eastern part of the East European Craton
served as a provenance for aluminosilicate clastics in the initial Serebryanka period. Detrital zircons from sandstones of
the Kernos Formation have the Meso-Neoarchean (∼15%), Paleoproterozoic (∼60%), and Mesoproterozoic (∼26%) age. Comparison
of the obtained data with the results of the study of detrital zircons from Riphean and Vendian sandstones of the Southern
Urals shows that the Riphean and Lower Vendian rocks are mainly represented by erosional products of Middle and Upper Paleoproterozoic
crystalline rocks that constitute the basement of the East European Craton. In addition, a notable role belonged to older
(Lower Proterozoic, Neoarchean and Mesoarchean) rock associations during the formation of the Serebryanka Group. The terminal
Serebryanka time (Kernos Age) differed from its initial stage (Tanin Age) by the appearance of Mesoproterozoic complexes in
provenances. According to available data, these complexes played an insignificant role in the formation of Riphean-Vendian
rocks in the neighboring South Uralian segment. This implies a spatiotemporal diversity of clastic material sources for Upper
Precambrian rocks in the western megazone of the Southern and Central Urals. 相似文献
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A. B. Kuznetsov G. V. Ovchinnikova M. A. Semikhatov I. M. Gorokhov O. K. Kaurova M. T. Krupenin I. M. Vasil’eva B. M. Gorokhovskii A. V. Maslov 《Stratigraphy and Geological Correlation》2008,16(2):120-137
The Rb-Sr and U-Pb systematics are studied in carbonate deposits of the Satka and Suran formations corresponding to middle horizons of the Lower Riphean Burzyan Group in the Taratash and Yamantau anticlinoria, respectively, the southern Urals. The least altered rock samples retaining the 87Sr/86Sr ratio of sedimentation basin have been selected for analysis using the original method of leaching the secondary carbonate phases and based on strict geochemical criteria of the retentivity (Mn/Sr < 0.2, Fe/Sr < 5 and Mg/Ca < 0.024). The stepwise dissolution in 0.5 N HBr has been used to enrich samples in the primary carbonate phase before the Pb-Pb dating. Three (L-4 to L-6) of seven consecutive carbonate fractions obtained by the step-wise leaching are most enriched in the primary carbonate (in terms of the U-Pb systematics). In the 206Pb/204Pb-207Pb/204Pb diagram, data points of these fractions plot along an isochron determining age of 1550 ± 30 Ma (MSWD = 0.7) for the upper member of the Satka Formation. The initial 87Sr/86Sr ratio in the least altered limestones of this formation is within the range of 0.70460–0.70480. Generalization of the Sr isotopic data published for the Riphean carbonates from different continents showed that 1650–1350 Ma ago the 87Sr/86Sr ratio in the world ocean was low, slightly ranging from 0.70456 to 0.70494 and suggesting the prevalent impact of mantle flux. 相似文献