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A V Maslov - One of the best experts on this subject based on the ideXlab platform.
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Geochemical Proxies of Endo- and Exospheric Processes in Sedimentary Sequences and the Upper Precambrian Section in the South Urals
Lithology and Mineral Resources, 2020Co-Authors: A V MaslovAbstract:The article characterizes some geochemical proxies of endo- and exospheric processes in sedimentary sequences and analyzes their average values in Upper Precambrian clayey rocks in the South Urals. It is shown that a gradual decrease of the Th/Scaver value in Lower Riphean (Mesoproterozoic) ~1750–1300 Ma ago rocks correlates to a certain extent with the assembly and disintegration of the Columbia/Nuna supercontinent. The assembly of Rodinia corresponds to two peaks (Biryan Member and Min’yar Formation) of relatively high Th/Scaver values. However, they are separated by rocks with Th/Scaver values comparable with those typical of the fine-grained clastic rocks of the Mashak plume episode (~1380 Ma). Variations of Th/Craver in the Lower–Middle Riphean clayey rocks also correlate quite well with the assembly of Columbia/Nuna, whereas the Upper Riphean–Vendian (Neoproterozoic) interval does not show any significant variation in Th/Craver values. Hence, the assembly and disintegration of Rodinia and the associated changes in rock composition in the provenance did not have any notable effect on the fine-grained aluminosilicate rocks of the Riphean stratotype. The Middle–Upper Riphean sequences were also formed at relatively constant values of TDM and eNd(T). Hence, the Grenvillian events did not make significant contribution to the formation of rocks of the Yurmatau and Karatau groups. Average values of indicators of the redox parameters of water in the Late Precambrian basins, which existed in the eastern part (in modern coordinates) of the East European Platform, indicate that their sedimentary infilling was deposited predominantly under oxidizing or similar conditions. This conclusion contrasts markedly with the notion of the prevalence of ferruginous and euxinic environments in the World Ocean during the Late Precambrian. Comparison of variations in the mean EFNi and EFZn values in clayey rocks of the South Urals, as well as other paleoproductivity proxies, does not reveal any definite relationship of their excursions with the Late Precambrian global and subglobal, endo- and exospheric events. In the Early–Middle Riphean succession, the P2O5 values, slightly higher than in PAAS, correspond approximately to the period of Columbia/Nuna supercontinent existence. Lower values are typical for the clayey rocks formed during its disintegration, although the volume of mafic igneous rocks (main sources of phosphorus) in the provenances at that time should be larger. During the existence of Rodinia, the Upper Riphean clayey rocks were characterized by P2O5aver values both higher and lower than the PAAS. The same is true for its disintegration period. These facts suggest that the global and subglobal, endo- and exospheric processes did not significantly affect the formation of the Riphean–Vendian sedimentary sequences in the South Urals. More important here is the role of local factors.
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Geochemical Proxies of Endo- and Exospheric Processes in Sedimentary Sequences and the Upper Precambrian Section in the South Urals
Lithology and Mineral Resources, 2020Co-Authors: A V MaslovAbstract:The article characterizes some geochemical proxies of endo- and exospheric processes in sedimentary sequences and analyzes their average values in Upper Precambrian clayey rocks in the South Urals. It is shown that a gradual decrease of the Th/Sc_aver value in Lower Riphean (Mesoproterozoic) ~1750–1300 Ma ago rocks correlates to a certain extent with the assembly and disintegration of the Columbia/Nuna supercontinent. The assembly of Rodinia corresponds to two peaks (Biryan Member and Min’yar Formation) of relatively high Th/Sc_aver values. However, they are separated by rocks with Th/Sc_aver values comparable with those typical of the fine-grained clastic rocks of the Mashak plume episode (~1380 Ma). Variations of Th/Cr_aver in the Lower–Middle Riphean clayey rocks also correlate quite well with the assembly of Columbia/Nuna, whereas the Upper Riphean–Vendian (Neoproterozoic) interval does not show any significant variation in Th/Cr_aver values. Hence, the assembly and disintegration of Rodinia and the associated changes in rock composition in the provenance did not have any notable effect on the fine-grained aluminosilicate rocks of the Riphean stratotype. The Middle–Upper Riphean sequences were also formed at relatively constant values of T_DM and ε _Nd(T). Hence, the Grenvillian events did not make significant contribution to the formation of rocks of the Yurmatau and Karatau groups. Average values of indicators of the redox parameters of water in the Late Precambrian basins, which existed in the eastern part (in modern coordinates) of the East European Platform, indicate that their sedimentary infilling was deposited predominantly under oxidizing or similar conditions. This conclusion contrasts markedly with the notion of the prevalence of ferruginous and euxinic environments in the World Ocean during the Late Precambrian. Comparison of variations in the mean EF_Ni and EF_Zn values in clayey rocks of the South Urals, as well as other paleoproductivity proxies, does not reveal any definite relationship of their excursions with the Late Precambrian global and subglobal, endo- and exospheric events. In the Early–Middle Riphean succession, the P_2O_5 values, slightly higher than in PAAS, correspond approximately to the period of Columbia/Nuna supercontinent existence. Lower values are typical for the clayey rocks formed during its disintegration, although the volume of mafic igneous rocks (main sources of phosphorus) in the provenances at that time should be larger. During the existence of Rodinia, the Upper Riphean clayey rocks were characterized by P_2O_5aver values both higher and lower than the PAAS. The same is true for its disintegration period. These facts suggest that the global and subglobal, endo- and exospheric processes did not significantly affect the formation of the Riphean–Vendian sedimentary sequences in the South Urals. More important here is the role of local factors.
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To reconstruction of the river’s categories which formed sedimentary basins of Riphean basins in the region of the Eastern European platform and modern south Urals juncture
Proceedings of higher educational establishments. Geology and Exploration, 2019Co-Authors: A V MaslovAbstract:Information on the distribution of trace and rare-earth elements in the bottom sediments of estuarine zones of various river categories (large rivers, rivers draining water collections, composed of sedimentary or magmatic and metamorphic rocks, etc.) of silt and pelitic dimensions can be considered as the data, reflecting characteristic features of the suspention, transported to marine basins from various catchment provinces. In certain situations, the composition of the surface bottom sediments of the marine basin is determined by the suspension composition of any large river flowing into it (the Caspian Sea and the Volga River, the Laptev Sea and the Lena River, etc.). The similarity and difference in the rare-earth elements (REE) systematics of bottom sediments of estuarine zones and suspended particulate matter of rivers of various categories is quite well expressed in the pair diagrams (La/ Yb)N–(Eu/Sm)N, (La/Yb)N–Th, etc. A comparison of the features of the distribution of REE and Th in the Riphean clay rocks of the Southern Urals and in bottom sediments of the estuaries of various categories of recent rivers has been performed. It has been concluded that clay rocks forming a typical Riphean section are formed due to the erosion of mainly or predominantly sedimentary and/or metasedimentary complexes that existed during the PreRiphean or the Riphean in the east part of the East European platform and have not survived to date.
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First Results of U–Pb LA–ICP–MS Isotope Dating of Detrital Zircons from Arkose Sandstone of the Biryan Subformation of Zilmerdak Formation (Upper Riphean, South Urals)
Doklady Earth Sciences, 2018Co-Authors: A V Maslov, Yu. L. Ronkin, Yu. V. Erokhin, Axel Gerdes, K. S. IvanovAbstract:Detrital zircons (DZs) from arkose sandstones of the Upper Riphean Zilmerdak Formation (Southern Urals) yielded ages in the range of 3039–964 Ma. Grains with Late Karelian and Early and Middle Riphean ages compose 35, 34, and 26% of the total number of the analyzed zircons, respectively. This is similar to the age spectra of the Vendian sandstones (Asha Group), but it differs significantly from the age distribution typical of the Riphean stratotype sandstones.
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first results of u pb la icp ms isotope dating of detrital zircons from arkose sandstone of the biryan subformation of zilmerdak formation upper Riphean south urals
Doklady Earth Sciences, 2018Co-Authors: A V Maslov, Yu. L. Ronkin, Yu. V. Erokhin, Axel Gerdes, K. S. IvanovAbstract:Detrital zircons (DZs) from arkose sandstones of the Upper Riphean Zilmerdak Formation (Southern Urals) yielded ages in the range of 3039–964 Ma. Grains with Late Karelian and Early and Middle Riphean ages compose 35, 34, and 26% of the total number of the analyzed zircons, respectively. This is similar to the age spectra of the Vendian sandstones (Asha Group), but it differs significantly from the age distribution typical of the Riphean stratotype sandstones.
M.t. Krupenin - One of the best experts on this subject based on the ideXlab platform.
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First Data on LAICPMS U/Pb Zircon Geochronology of Upper Riphean Sandstones of the Bashkir Anticlinorium
2013Co-Authors: T V Romanyuk, A V Maslov, M.t. Krupenin, V. M. Gorozhanin, N B Kuznetsov, E. A. Belousova, L. Ronkin, E. N. Gorozhanina, E. S. SereginaAbstract:With respect to their petrography and petro� geochemistry, Riphean sedimentary rocks of the stra� totype locality (Bashkir Anticlinorium, western South Urals) are well studied [7]. At the same time, no sys� temic geochronological investigations of their detrital zircons (dZr) have been carried out, although they offer the opportunity (in availability of the statistically significant selection) to derive substantiated infer� ences on the age of eroded rock, the relationships between local and remote sediment sources, the evo� lution of provenances during deposition, and other aspects. In this communication, we present the first such data on zircons from the Lemeza Subformation of the Karatavian Zil’merdak Formation, which rep� resents a standard Upper Riphean unit of northern Eurasia.
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Lithogeochemical features of Riphean fine-grained terrigenous rocks in the Kama-Belaya aulacogen and their formation conditions
Lithology and Mineral Resources, 2010Co-Authors: A V Maslov, M.t. Krupenin, M. V. Isherskaya, V. G. Petrishcheva, T. Ya. Gulyaeva, N. P. GorbunovaAbstract:Lithogeochemical features of Riphean fine-grained terrigenous rocks of the Kama-Belaya aulacogen are discussed. It is shown that aluminosiliciclastic material delivered to the aulacogen during the Riphean was characterized by a low maturity degree. The successively increasing K_2O/Al_2O_3 values in the Riphean summary section correlate negatively with the CIA index values, indicating a gradually strengthening tendency for climate aridization in erosion zones. Data on some indicator ratios of trace elements and REE systematics in Riphean silty mudstones and shales of the Kama-Belaya aulacogen imply the involvement of mafic and ultramafic rocks, in addition to acid igneous and metamorphic varieties, in erosion during accumulation of the Nadezhdino, Tukaevo, Ol’khovka, Usinsk, and Priyutovo formations. Comparison of data on the composition of rocks in provenances based on the mineralogical-petrographic study of sandstones and investigation of geochemical features of silty mudstones and shales revealed their sufficiently high similarity. The geochemical data made it possible to specify the composition of rocks in provenances. Low Ce/Cr values in the fine-grained terrigenous rocks of the Lower Riphean Kyrpy Group suggest their formation with a significant contribution of erosion products of the Archean substrate, which is atypical for higher levels of the section. Thus, the Early-Middle Riphean transition period was likely marked by substantial changes in the mineral composition of material delivered to the Kama-Belaya aulacogen. The lack of exhalative components in the examined specimens of silty mudstones and shales points to a relatively low permeability of the Earth’s crust in the eastern East European Platform through the entire Riphean.
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Geochemical Features of the Riphean Fine-Grained Terrigenous Rocks of the Southern Urals, Uchur-Maya Region, and Yenisei Range: Estimation of the Maturity of the Pre-Riphean Continental Crust and Its Evolution within 1.65-0.6 Ga
Geochemistry International, 2009Co-Authors: A V Maslov, E. Z. Gareev, Yu. L. Ronkin, Victor N. Podkovyrov, M.t. Krupenin, A. D. Nozhkin, O. M. Turkina, E. F. Letnikova, N. V. Dmitrieva, O. P. LepekhinaAbstract:The geochemical features of basal fine-grained terrigenous rocks from the Riphean sedimentary megasequences of the Southern Urals, Uchur-Maya region, and Yenisei Range were compared in order to estimate the maturity of the continental crust that was formed by the beginning of the Riphean. It was shown that initial shales from the base of the Riphean sequence of the Yenisei Range and fine-grained aluminosiliciclastic rocks from the base of the Riphean sections of the Southern Urals were formed by the erosion of a rather mature continental crust. In contrast, fine-grained terrigenous rocks from the base of the Riphean of the Uchur-Maya region were derived from immature Late Archean protoliths or their Early Proterozoic analogs. The fine-grained terrigenous rocks of the three sedimentary megasequences show different variations in the (La/Yb)N ratio. In the Southern Urals, this ratio is high (12–15) in the Burzyan Group and decreases upsection to 6–10. In the shales of the Uchur-Maya region, the (La/Yb)N ratio decreases upsection, and the La/Sc ratio shows a sympathetic behavior. This is due to a decrease in the proportion of “primitive” tonalite-trondhjemite associations of the Archean granite-greenstone terranes in the provenance area with time and the appearance of intra-plate (riftogenic?) granitoids and significant amounts of basic and ultrabasic rocks. The latter marks the onset of large rift-forming events in the Uchur-Maya region at the beginning of the Late Riphean. The (La/Yb)N of the studied rocks from the Yenisei Range are mostly similar to the PAAS ratio, but higher values were found in the Upper Vorogovka and Chingasan groups, which was related to the contribution of strongly LREE-enriched granitoids and rift felsic and alkali basaltic volcanic associations to the formation of the terrigenous material. A comparison of Rb, Sr, Y, Zr, Ba, Hf, Th, U, Cr, and Ni contents and Zr/Y, (La/Yb)N, Ni/Co, Cr/Th, Cr/Sc, and La/Th ratios in the fine-grained terrigenous rocks of the Riphean megasequences of the Southern Urals, Uchur-Maya region, and the Yenisei Range with those in the model geochemical objects (PAAS, UCPR1, UCAR2, and others) showed that, in terms of most of the parameters, the Riphean fine-grained terrigenous rocks from the three regions are similar to each other, PAAS, and Proterozoic cratonic shales. This indicates a fairly high general maturity of the protoliths that were eroded during the Riphean in the eastern East European craton and in the southeastern and southwestern parts of the Siberian craton.
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Geochemistry of Riphean terrigenous rocks in the Southern Urals and Siberia and variations of the continental-crust maturity
Russian Geology and Geophysics, 2009Co-Authors: A. D. Nozhkin, E. Z. Gareev, Yu. L. Ronkin, Victor N. Podkovyrov, A V Maslov, M.t. Krupenin, O. M. Turkina, E. F. Letnikova, N. V. Dmitrieva, O. P. LepikhinaAbstract:Abstract We consider the general and specific features of the evolution of the composition of fine-grained terrigenous rocks in the Riphean sedimentary megasequences of the Southern Urals, Uchur-Maya region, and Yenisei Ridge. It has been established that the crust on the southwestern (in the modern frame of references) periphery of the Siberian craton was geochemically the most mature segment of the Riphean continental crust. For example, the fine-grained clastic rocks and metapelites of all Riphean lithostratigraphic units of the Yenisei Ridge have higher median contents of Th than the most mature Paleoproterozoic crust, and in median contents of Y and Cr/Th values they are the most similar to it. In the Southern Urals and Uchur-Maya region, some units of the Riphean sedimentary sequences show median contents of Y and Th and Cr/Th values close to those of primitive Archean crust. Analysis of Cr/Th variations in the fine-grained terrigenous rocks of all three megasequences shows that the minimum Cr/Th values, evidencing a predominance or the abundance of felsic rocks in provenances, are typical of the Riphean argillaceous shales and metapelites of the Yenisei Ridge. The distinct Cr/Th and Cr/Sc increase in the fine-grained clastic rocks of the Chingasan Group of the ridge reflects the large-scale destruction of continental crust during the formation of rift troughs as a result of the Rodinia breakup in the second half of the Late Riphean. The Cr/Th variations in the Lower and Middle Riphean argillaceous shales and mudstones of the Bashkirian mega-anticlinorium and Uchur-Maya region are in agreement, which evidences the subglobal occurrence of rifting in the early Middle Riphean (so-called “Mashak rifting”).
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Secular variations of the upper crust composition: Implication of geochemical data on the Upper Precambrian shales from the Southern Urals western flank and Uchur-Maya region
Stratigraphy and Geological Correlation, 2006Co-Authors: A V Maslov, E. Z. Gareev, Yu. L. Ronkin, Victor N. Podkovyrov, M.t. Krupenin, V. M. GorozhaninAbstract:In the mid-1980s, it was concluded based on geochemical study that Th, Sc, La concentrations and ratios Th/Sc, La/Sc and Eu/Eu* did not wary significantly in the post-Archean time. It was impossible to judge about compositional variations of upper crust during the Riphean and Vendian, because data of that time characterized a limited number of samples from the post-Archean basins of Australia, New Zealand, and Antarctic. Considered in this work are variations of Eu/Eu*, LREE/HREE, Th/Sc, and La/Sc ratios in Upper Precambrian fine-grained siliciclastic rock of the Southern Urals western flank (Bashkirian meganticlinorium) and Uchur-Maya region (Uchur-Maya plate and Yudoma-Maya belt). As is established, only the Eu anomaly in the studied siliciclastic rocks is practically identical to this parameter of the average post-Archean shale. Three other parameters plot on the Riphean-Vendian variation curves with positive and negative excursions of diverse magnitude, which do not coincide always in time. It is assumed that these excursions likely mark stages of local geodynamic activity, destruction of pre-Riphean cratons, and progressing recycling of sedimentary material during the Riphean.
Yu. L. Ronkin - One of the best experts on this subject based on the ideXlab platform.
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First Results of U–Pb LA–ICP–MS Isotope Dating of Detrital Zircons from Arkose Sandstone of the Biryan Subformation of Zilmerdak Formation (Upper Riphean, South Urals)
Doklady Earth Sciences, 2018Co-Authors: A V Maslov, Yu. L. Ronkin, Yu. V. Erokhin, Axel Gerdes, K. S. IvanovAbstract:Detrital zircons (DZs) from arkose sandstones of the Upper Riphean Zilmerdak Formation (Southern Urals) yielded ages in the range of 3039–964 Ma. Grains with Late Karelian and Early and Middle Riphean ages compose 35, 34, and 26% of the total number of the analyzed zircons, respectively. This is similar to the age spectra of the Vendian sandstones (Asha Group), but it differs significantly from the age distribution typical of the Riphean stratotype sandstones.
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first results of u pb la icp ms isotope dating of detrital zircons from arkose sandstone of the biryan subformation of zilmerdak formation upper Riphean south urals
Doklady Earth Sciences, 2018Co-Authors: A V Maslov, Yu. L. Ronkin, Yu. V. Erokhin, Axel Gerdes, K. S. IvanovAbstract:Detrital zircons (DZs) from arkose sandstones of the Upper Riphean Zilmerdak Formation (Southern Urals) yielded ages in the range of 3039–964 Ma. Grains with Late Karelian and Early and Middle Riphean ages compose 35, 34, and 26% of the total number of the analyzed zircons, respectively. This is similar to the age spectra of the Vendian sandstones (Asha Group), but it differs significantly from the age distribution typical of the Riphean stratotype sandstones.
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Reconstruction of Source-Rock Composition of the Middle and Upper Riphean Rocks of the Isherim and Bashkir Anticlinoria, Urals
Geochemistry International, 2018Co-Authors: A V Maslov, G. A. Petrov, Yu. L. RonkinAbstract:It is shown that the Riphean sediments of the Bashkir and Isherim anticlinoria of the Ural mobile belt were formed in different settings. Sediments of the Bashkir Anticlinorium are autochthonous and were formed in the eastern (in present-day coordinates) Baltica from proximal siliciclastics, whereas the complexes of the Isherim Anticlinorium did not belong to it. Geochemical features of the Middle and lower Upper Riphean metapelites of the Isherim Anticlinorium and U–Pb isotope ages of detrital zircons from sandstones suggest that their provenances were the northern and northwestern parts of Baltica. In the Late Riphean (?)–Vendian, the Isherim block migrated along the Timan margin of Baltica into the present-day position.
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The Southern Urals Large Igneous Province with an age of approximately 1380 Ma: Precision U–Pb ID-TIMS constraints
Doklady Earth Sciences, 2016Co-Authors: Yu. L. Ronkin, Marion Tichomirowa, Alekseevich Vladimir MaslovAbstract:The formation of the Large Igneous Province (LIP) approximately 1380 Ma old in the South Urals was related to the Mashak riftogenic event in the Bashkir meganticlinorium, which was synchronous with the emplacement of different magmatic bodies (the Berdyaush pluton of rapakivi granites and associated rocks, the Main dike of the Bakal ore field, and the Medvedev, Guben, and Kusa massifs, among others) localized among sedimentary deposits of the Burzyan and Yurmatin Groups representing Lower and Middle Riphean type units of northern Eurasia. The U–Pb ID-TIMS age of 1379.6 Ma (MSWD = 1.3) obtained with an accuracy of ±2.9 Ma (confidence interval 95%) combined with the available published U–Pb ID-TIMS data constrain the age and duration of the Early–Middle Riphean pulse in the LIP formation in the Southern Urals.
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Contribution of Grenvillian events to the formation of most complete Riphean sedimentary successions in Northern Eurasia
Stratigraphy and Geological Correlation, 2014Co-Authors: A V Maslov, E. Z. Gareev, Victor N. Podkovyrov, Yu. L. RonkinAbstract:The Grenvillian orogeny (∼1250 to 980 Ma) was one of the most significant Riphean events. It determined the formation of many structures observable now in North and South America, northwestern Europe, South Africa, Western Australia, Antarctica, and other regions. Nevertheless, its reflections in the most complete and relatively well investigated Upper Precambrian sedimentary sections of northern Eurasia such as the Riphean stratotype (Bashkir meganticlinorium) and hypostratotype (Uchur-Maya region) still remain unknown. This is primarily true of the petrographic and chemical compositions of terrigenous rocks. This work is dedicated to the analysis of peculiar features in variations of the whole-rock chemical composition of sandstones and fine-grained clastic rocks (shales, mudstones, fine-grained clayey siltstones) that constitute Middle-Upper Riphean boundary layers of the Bashkir meganticlinorium, Kama-Belaya aulacogen, and Uchur-Maya region. The analysis reveals no tendency for the decrease in the degree of the chemical and, consequently, mineralogical maturity in the upward direction through the Middle-Upper Riphean sections in the above-mentioned regions. The whole-rock compositions of fine-grained clastic rocks associated with sandstones correspond mostly to that of “common” Upper Precambrian clayey rocks. The formation of practically the entire Yurmatinian-Karatavian succession in the Bashkir meganticlinorium proceeded under relatively stable T_DM and ɛ_Nd(T) values. The period of 1250 to 980 Ma in the central and eastern parts of the Siberian Platform was marked by repeated rifting episodes alternating with accumulation of mature platformal sediments, although repercussions of Grenvillian collisional processes are missing from this region as well. The performed analysis provides grounds for the conclusion that contribution of the Grenvillian events to the formation of most complete Riphean successions in northern Eurasia was insignificant.
Victor N. Podkovyrov - One of the best experts on this subject based on the ideXlab platform.
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U–Pb LA–ICP–MS Age of Detrital Zircons from the Lower Riphean and Upper Vendian Deposits of the Luga–Ladoga Monocline
Doklady Earth Sciences, 2018Co-Authors: A. S. Ivleva, V. B. Khubanov, S. N. Sychev, N. I. Vdovina, Victoria B Ershova, Andrey K. Khudoley, Victor N. Podkovyrov, A V MaslovAbstract:The results of LA–ICP–MS U–Pb analyses of detrital zircons from the Precambrian deposits of Luga–Ladoga monocline are discussed. The age spectra of the zircons separated from the Riphean to Upper Vendian sandstones from the Shotkusa-1 well demonstrate dominance of the Paleo- and Mesoproterozoic grains while the Archaean zircons are subordinate. The Riphean debris sources were local swells of the Northern Ladoga basement. The sequence interval presumably corresponding to the Vasilieostrov Formation (Upper Vendian) has yielded not only Paleo- and Mesoproterozoic zircon ages, but Neoproterozoic as well, implying a Timanide provenance: these zircons (527 ± 9 and 516 ± 13 Ma) allow deposition of a significant part of the Shotkusa-1 sequence at the very beginning of the Cambrian.
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u pb la icp ms age of detrital zircons from the lower Riphean and upper vendian deposits of the luga ladoga monocline
Doklady Earth Sciences, 2018Co-Authors: A. S. Ivleva, V. B. Khubanov, S. N. Sychev, N. I. Vdovina, Victoria B Ershova, Andrey K. Khudoley, Victor N. Podkovyrov, A V MaslovAbstract:The results of LA–ICP–MS U–Pb analyses of detrital zircons from the Precambrian deposits of Luga–Ladoga monocline are discussed. The age spectra of the zircons separated from the Riphean to Upper Vendian sandstones from the Shotkusa-1 well demonstrate dominance of the Paleo- and Mesoproterozoic grains while the Archaean zircons are subordinate. The Riphean debris sources were local swells of the Northern Ladoga basement. The sequence interval presumably corresponding to the Vasilieostrov Formation (Upper Vendian) has yielded not only Paleo- and Mesoproterozoic zircon ages, but Neoproterozoic as well, implying a Timanide provenance: these zircons (527 ± 9 and 516 ± 13 Ma) allow deposition of a significant part of the Shotkusa-1 sequence at the very beginning of the Cambrian.
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Contribution of Grenvillian events to the formation of most complete Riphean sedimentary successions in Northern Eurasia
Stratigraphy and Geological Correlation, 2014Co-Authors: A V Maslov, E. Z. Gareev, Victor N. Podkovyrov, Yu. L. RonkinAbstract:The Grenvillian orogeny (∼1250 to 980 Ma) was one of the most significant Riphean events. It determined the formation of many structures observable now in North and South America, northwestern Europe, South Africa, Western Australia, Antarctica, and other regions. Nevertheless, its reflections in the most complete and relatively well investigated Upper Precambrian sedimentary sections of northern Eurasia such as the Riphean stratotype (Bashkir meganticlinorium) and hypostratotype (Uchur-Maya region) still remain unknown. This is primarily true of the petrographic and chemical compositions of terrigenous rocks. This work is dedicated to the analysis of peculiar features in variations of the whole-rock chemical composition of sandstones and fine-grained clastic rocks (shales, mudstones, fine-grained clayey siltstones) that constitute Middle-Upper Riphean boundary layers of the Bashkir meganticlinorium, Kama-Belaya aulacogen, and Uchur-Maya region. The analysis reveals no tendency for the decrease in the degree of the chemical and, consequently, mineralogical maturity in the upward direction through the Middle-Upper Riphean sections in the above-mentioned regions. The whole-rock compositions of fine-grained clastic rocks associated with sandstones correspond mostly to that of “common” Upper Precambrian clayey rocks. The formation of practically the entire Yurmatinian-Karatavian succession in the Bashkir meganticlinorium proceeded under relatively stable T_DM and ɛ_Nd(T) values. The period of 1250 to 980 Ma in the central and eastern parts of the Siberian Platform was marked by repeated rifting episodes alternating with accumulation of mature platformal sediments, although repercussions of Grenvillian collisional processes are missing from this region as well. The performed analysis provides grounds for the conclusion that contribution of the Grenvillian events to the formation of most complete Riphean successions in northern Eurasia was insignificant.
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Clarkes of concentrations of trace elements in the Riphean fine-grained terrigenous rocks of the Uchur-Maya region and the Yenisei Range
Russian Journal of Pacific Geology, 2010Co-Authors: A V Maslov, Victor N. Podkovyrov, A. D. Nozhkin, E. F. Letnikova, N. V. Dmitrieva, Yu. L. RonkinAbstract:The clarkes of concentrations (Kc) of a wide range of trace elements (Li, Be, B, Sc, V, Cr, Co, Ni, Cu, Zn, Ga, Ge, As, Rb, Sr, Y, Zr, Nb, Mo, Ag, Cd, In, Sb, Cs, Ba, REE, Hf, Ta, Hg, Tl, Pb, Bi, Th, and U) were analyzed for fine-gained terrigenous rocks (mudstones, metapelites) from the reference Riphean sections of the Uchur-Maya region and the Yenisei Range. It was established that the shales and mudstones of the Uchur and Aimchan groups in the Riphean hypostratotype section are characterized by moderate (2.5 5) geochemical specialization for Li, B, and Zn. At the same time, the similar rocks of the Lakhanda and Ui groups do not exhibit any distinct geochemical specialization, although they are notably enriched in HREE. The metapelites from the basal formations of the Riphean sedimentary successions in the Yenisei Range are distinctly specialized for B and slightly for Li, Rb, Be, Nb, Ta, Th, Ge, and Cd. In addition, moderate specialization for Cu is characteristic of the metapelites from the Korda and Lopatino formations; for Bi, Sb, Hg, and V, for their analogs from the Potoskui Formation; and, for Hg and Cs, for the similar rocks from the Lopatino Formation. The metapelites of the Lower Riphean Korda Formation from the central zone of the Yenisei Range have elevated contents of significantly more elements (Li, Be, Sc, V, Cr, Co, Ni, Zn, As, Rb, Y, Zr, Nb, Sb, Ag, In, Hf, Hg, and others) than their counterparts from its eastern near-platform part. The mudstones of the ore-bearing (Pb, Zn) Gorevo Formation are characterized by elevated concentrations of several ore elements such as Pb, Cd, As, Sb, and Bi. The elevated Kc values of the rare lithophile and of several ore elements in the metapelites of the Yenisei Range are determined by the high geochemical differentiation of the Early Precambrian blocks constituting the western margin of the Siberian Craton, which were eroded in the Riphean, and the syn-sedimentary riftogenic and intraplate magmatism. On the contrary, the fine-grained and terrigenous rocks from the basal part of the Riphean section in the Uchur-Maya region are compositionally closer to the immature Late Archean substrates or their Early Proterozoic analogs.
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Upper Riphean and Vendian sandstones of the Bashkirian anticlinorium
Lithology and Mineral Resources, 2010Co-Authors: A V Maslov, E. Z. Gareev, Victor N. PodkovyrovAbstract:The analysis of lithogeochemical data on the Upper Riphean and Vendian sandstones from the Bashkirian anticlinorium showed that sandstone associations formed in a passive sluggish tectonic regime in the middle Late Vendian were replaced by associations accumulated in the more active tectonic settings. This is well seen in the SiO2-K2O/Na2O and (Fe2 + MgO)-TiO2 diagrams reflecting the particular and median compositions of psammites. The lithochemical characteristics of sandstones were examined to deter� mine the compositional variation of rock complexes eroded on paleodrainage areas. Quartzrich sedimentary, metasedimentary, and metamorphic rocks, as well as felsic igneous rocks prevailed in the paleodrainage areas throughout the entire Late Riphean and Early Vendian, while the main sources of clastic material in the Late Vendian were igneous intermediate and basic rocks. With allowance made for the previous comparativelitho� logical data and some other materials, significant similarity in the position and orientation of compositional fields of psammites from the middle and upper levels of the Asha Group (Bashkirian anticlinorium) with fields of psammites from different syncollisional (flysch and molasse) basins in the SiO2-K2O/Na2O, K2 O/Na 2 O-SiO 2 /Al 2 O 3 , F1-F2 and other diagrams suggests that the middle Late Vendian (beginning from the Basa level) was marked by a variation in tectonic/geodynamic settings of sandstone accumulation and in composition of the eroded paleodrainage systems. The revealed trend agrees well with concept of the exist� ence of the Late Riphean-Vendian Pechora paleocean.
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typology and single grain u pb ages of detrital zircons from proterozoic sandstones in the sw urals russia early time marks at the eastern margin of baltica
Precambrian Research, 2003Co-Authors: Arne P Willner, Sven Sindern, R Metzger, Tatiana Ermolaeva, U Kramm, V Puchkov, Andreas KronzAbstract:Abstract In the SW Urals a change of tectonic conditions occurred at around 620 Ma leading to a detrital input from contrasting provenance areas. Fifty-seven detrital zircons were separated from Proterozoic sandstones of this setting to study their typologies and pattern of U–Pb systematics. Detritus from Riphean sandstones (1.63–0.65 Ga) contains three populations of zircon: (1) completely rounded fragmental grains with complicated, but weak internal fabrics derived from high grade metamorphic areas with multistage reworking; (2) long-prismatic zircon grains with rounded edges and weakly preserved growth zoning from S-type granites; (3) types 1 and 2, but cloudy due to intense alteration (hydration of metamict areas). Zircons from Upper Vendian sandstones (0.62–0.54 Ga) comprise two groups: (1) zircons similar to those of Riphean populations 1, 2 and 3; (2) perfectly euhedral zircons with preserved magmatic growth zoning from potassic alkaline as well as acid magmas. Age signatures of polycyclic zircons from both Riphean and Upper Vendian detritus are compatible with crystallization in the interval of 1.8–2.3 Ga. This appears to be the significant age signature for the largely covered basement of the East European Platform, the presumed source region in the W. The pattern of U–Pb systems shows evidence of at least two events leading to lead loss. Data clusters in the concordia diagram confined to single samples show a remarkably strong influence of local sources. Alteration during diagenesis was an important factor of lead loss. Upper Vendian detrital zircons have two sources: (1) The majority of the polycyclic rounded zircons also has a Paleoproterozoic crystallization age consistent with that of the Riphean detrital zircons. However, a few zircon grains point to a later anorogenic event which does not match with known events in the Riphean basin and hence underline an allochthonous character of the source area. (2) The data of the euhedral zircon would reflect a source age between 643 and 512 Ma. The latter age signature is compatible with a local magmatic event concomitant with exhumation and emplacement of the allochthonous Beloretzk Terrane after 620 Ma. This eastern source area for the Upper Vendian detritus had partly been affected by high-pressure/low temperature metamorphism. The change of tectonic conditions reflected by the detritus composition represents a change from a passive continental margin along the Rodinia supercontinent persisting during the Riphean to a convergent continental margin during the Upper Vendian within a transpressional setting.
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contrasting provenance signals in Riphean and vendian sandstones in the sw urals russia constraints for a change from passive to active continental margin conditions in the neoproterozoic
Precambrian Research, 2001Co-Authors: Arne P WillnerAbstract:Abstract Two contrasting provenance areas for Neoproterozoic sandstones can be distinguished in the southwestern Urals by light and heavy mineral analyses as well as by mineral chemistry. These reflect a dramatic change of geotectonic conditions at the eastern border of the Baltica protocontinent at around 610–620 Ma. Detritus from Riphean and Lower Vendian sandstones representing about 1 Ga of continuous sedimentation is characterised by a ‘continental platform provenance’ reflecting its derivation from the Proterozoic basement of the East European platform. Source rocks include mainly minerals and few lithic clasts from granitoids and high-grade metamorphic rocks as well as reworked clastic sediments and silicic volcanic rocks. The provenance signal changes abruptly with Upper Vendian detritus representing a ‘recycled orogenic provenance’. This includes mineral and lithic clasts of low-grade siliciclastic metasediments and mylonites containing phengites with a high-pressure signature as well as clasts of bimodal volcanic rocks and reworked siliciclastic sediments. The composition of phengites contrasts strongly with those of detrital white mica in the Riphean rocks. Also, the composition of tourmalines derived from a metapsammopelitic source indicates a mainly Al-poor metasediment provenance, whereas Riphean tourmalines were derived from mainly Al-rich metapsammopelites. Zircon morphology, tourmaline zoning and a reduced heavy mineral spectrum provide evidence for polycyclic sedimentation during Riphean and Vendian. Upper Vendian sedimentary rocks were deposited in a foreland basin derived from a proximal uplift to the east. Provenance characteristics of the Upper Vendian detritus are consistent with areas affected by a high-pressure/low-temperature metamorphism during a pre-Uralian orogenic event, most likely from the metamorphic complex of Beloretsk, which was emplaced and exhumed during the Upper Vendian. The change of geotectonic conditions in the Upper Vendian reflects a change from a passive continental margin in the South Urals throughout the entire Riphean since at least 1350 Ma to a convergent continental margin within a presumed transpressional setting.
