| 1. |
- Nosova, A. A., et al.
(författare)
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Early Cambrian Syenite and Monzonite Magmatism in the Southeast of the East European Platform : Petrogenesis and Tectonic Setting
- 2019
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Ingår i: Petrology. - 0869-5911. ; 27:4, s. 329-369
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Tidskriftsartikel (refereegranskat)abstract
- Abstract—The paper reports new geochronological, petrological, and isotope-geochemical data on the syenites and alkali syenites of the Artyushki massif, and the monzonites of the Gusikha massif. These massifs are located along the southwestern and northeastern margins of the Pachelma aulacogen, in the southeastern part of the East European Platform (EEP). They have Early Cambrian ages of 524 ± 3 (Artyushki) and 514 ± 2 Ma (Gusikha) obtained by the U-Pb zircon method and similar ages of amphibole and K-feldspar by the 40Ar/39Ar method. This time period has previously been regarded as amagmatic in the EEP evolution. The Artyushki massif is made up of Amp–Cpx syenite porphyries and Grt–Cpx alkali syenite porphyries and their fenitized varieties. As compared to the Amp–Cpx varieties the Grt–Cpx rocks are more peralkaline (A/NK > 0.9) and have higher LREE and HFSE, and fractionated HREE patterns. The metasomatized (fenitized) varieties are more potassic and bear geochemical evidence of fluid reworking (high Y/Ho ratios, significant Zn variations, and etc.). Bulk samples have weakly radiogenic Sr isotopic compositions: (87Sr/86Sr)520 are within 0.703066–0.703615. The values of εNd(520) vary from –0.69 to +1.64. The Grt–Cpx syenite porphyries have the positive εNd(520), while the Amp–Cpx and fenitized syenite porphyries feature negative εNd. The Gusikha massif consists of biotite–amphibole and biotite monzonites. Similar to the Artyushki syenites in SiO2 contents, the Gusikha monzonites have higher Mg# (0.22–0.54 and 0.34–0.71 for the Artyushki and Gusikha massifs, respectively). They are also characterized by a negative Nb–Ta anomaly (Nb/Nb* = 0.5), high Ва/Sr ratio, and highly radiogenic (87Sr/86Sr)520 = 0.705204 and 0.705320. Their Nd-isotopic compositions correspond to εNd(520) = –6.7 and ‒7.0. Two melts contributed to the formation of the Artyushki massif. One was a strongly contaminated melt (Amp–Cpx syenite porphyries, the other was weakly contaminated (Grt–Cpx syenite porphyries). The main contribution was phonolitic melt derived from the melting of a moderately metasomatized (carbonate- and amphibole-bearing) shallow lithospheric mantle. The earliest and deepest melt portions were carbonate–silicate in composition. The geochemical, as well as the Sr and Nd isotopic compositions of the Gusikha monzonites indicate a predominant crustal contribution and pervasive reworking of the lithospheric mantle beneath southeastern Volgo–Uralia of the EEP in the Mesoproterozoic. Both massifs feature the geochemistry of within-plate and supra-subduction derivatives, which suggests a postorogenic tectonic setting of the magmatism. The presence of the Early Cambrian postorogenic magmatism within the East European Platform/Baltica is direct evidence for the involvement of Baltica in the collisional and/or accretionary events during the terminal Neoproterozoic–the beginning of the Paleozoic. This suggests reworking of the lithospheric mantle of Baltica during its collision with Timanian and East Avalonian/Cadomian terranes, including Scythia.
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| 2. |
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| 3. |
- Bibikova, E. V., et al.
(författare)
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Sarmatia-Volgo-Uralia junction zone: Isotopic-geochronologic characteristic of supracrustal rocks and granitoids
- 2009
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Ingår i: Stratigraphy and Geological Correlation. - 0869-5938. ; 17:6, s. 561-573
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Tidskriftsartikel (refereegranskat)abstract
- The geochronologic (U-Pb isotopic system of zircons) and isotopic-geochemical (Sm-Nd isotopic system of the bulk rock) studies were performed along the profile extending from the eastern Sarmatia (in the west) to the Middle Volga megablock of Volgo-Uralia (in the east), i.e., across the entire junction zone for dating the integration of Sarmatia and Volgo-Uralia, representing two segments of the East European Craton. It is established that the examined rocks are characterized by the Paleoproterozoic Nd isotopic model age, which varies from 2.1 and 2.4 Ga, except for some samples indicating a similar age of the crust through the entire Sarmatia-Volgo-Uralia junction zone. The highly metamorphosed complexes of the granulite and amphibolite facies constituting the southwestern margin of Volgo-Uralia are Paleoproterozoic, not Archean, in age, contrary to previous views. Two Early Paleoproterozoic lithotectonic complexes are defined in Volgo-Uralia: South Volga metasedimentary and Tersa metasedimentary-volcanogenic. The obtained data confirm the asynchronous integration of individual segments into the East European Craton: the integration of Sarmatia and Volgo-Uralia approximately 2100-2000 Ma ago was followed by the conjunction of this newly-formed continent with Fennoscandia ca. 1800 Ma ago.
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| 4. |
- Bibikova, E. V., et al.
(författare)
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The early crust of the Volgo-Uralian segment of the East European Craton: Isotope-geochronological zirconology of metasedimentary rocks of the Bolshecheremshanskaya Formation and their Sm-Nd model ages
- 2015
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Ingår i: Stratigraphy and Geological Correlation. - 0869-5938. ; 23:1, s. 1-23
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Tidskriftsartikel (refereegranskat)abstract
- We present the results of isotope-geochronological study of metasedimentary rocks of the Bolshecheremshanskaya Formation of the Volgo-Uralian segment of the East European Craton carried out to identify their protoliths. 16 samples of high-alumina gneisses from well cores were studied using the Sm-Nd isotope method and T-Nd(DM) model ages. Accessory zircons were selected from rocks with the most ancient model ages (more 3.2 Ga) in three wells: Minnibaevskaya 20000, Novo-Elkhovskaya 20009, and Zai-Karatayskaya 12930 in South Tatarstan. The isotope U-Pb dating of 200 zircon grains was performed on a Cameca 1280 NORDSIM secondary ion mass spectrometer at the Natural History Museum (Stockholm, Sweden). The most applicable sites for analysis of zircon crystals were pre-selected based on cathodoluminescence images. The analytical results demonstrate the diversity of zircon groups in age from 3.8 to 2.6 Ga and together with geochemical features of metasedimentary rocks of the Bolshecheremshanskaya Formation suggest the heterogeneous composition and age of provenance areas under denudation. Occurrence of Eoarchean and Paleoarchean zircons in the clastic material of the protolith of the Bolshecheremshanskaya gneisses indicates the existence of Early Archean crustal terrains in Volgo-Uralia.
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| 5. |
- Fedotova, A. A., et al.
(författare)
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New Data on the Paleoproterozoic Age of Metamorphism in the Yelabuga Deformation Zone of Volgo-Uralia, East European Craton
- 2019
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Ingår i: Doklady Earth Sciences. - 1028-334X. ; 488:1, s. 1123-1127
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Tidskriftsartikel (refereegranskat)abstract
- Abstract: This data on the age of metamorphism of rocks of the Yelabuga zone and the geochronological data on detrital zircon from paragneisses of the same zone are presented, and their correlation with the ages of rocks from the Middle Volga megablock is made. The rocks of the Yelabuga zone and Middle Volga megablock have similar geochemical characteristics and degrees of metamorphism, but demonstrate the following differences: Paleoproterozoic metamorphism was clearly expressed in the studied rocks of the Yelabuga zone, which contrasts to rocks of the Middle Volga megablock, where no metamorphism of this age is manifested. The study of the U–Pb isotopic system in external zones of zircon crystals from the Yelabuga deformation zone suggests that rocks underwent two stages of metamorphism, 1.99 and 1.95 Ga ago.
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| 6. |
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| 7. |
- Bogdanova, Svetlana, et al.
(författare)
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Volgo-Uralia: The First U-Pb, Lu-Hf and Sm-Nd Isotopic Evidence of Preserved Paleoarchean Crust
- 2010
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Ingår i: American Journal of Science. - : American Journal of Science (AJS). - 0002-9599. ; 310:10, s. 1345-1383
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Tidskriftsartikel (refereegranskat)abstract
- The crustal segment Volgo-Uralia is the least known part of the East European Craton. Its crystalline crust is hidden beneath a thick Neoproterozoic to Phanerozoic cover but disclosed by thousands of drill holes. In conjunction with the recent "Tatseis" reflection seismic profile, we conducted the first isotopic study of the Bakaly granitoid block in eastern Volgo-Uralia, which represents a subsurface section of the layered upper-middle crust. The study included whole-rock Sm-Nd and ion-probe zircon U-Th-Pb (SIMS) and Lu-Hf (LA-ICPMS) analyses of granitoids from seven drill cores. The Bakaly block was also targeted because its rocks have never been subjected to granulite facies metamorphism, making it possible to date pristine, pre-metamorphic zircon. Our study showed that the four principal suites of granitoids in the Bakaly block are different in age, each corresponding to a particular stage of Archean crustal evolution between 3.3 and 2.6 Ga. The Tashliar monzonitic suite, belonging to an alkaline series yielded zircon ages of 3.3 and 3.2 Ga, which are the oldest ages yet found in Volgo-Urafia. The epsilon(Hf)(T) values of the dated zircon and the epsilon(Nd)(T) values of their host rocks indicate that a Paleo- to Eoarchean protolith with model T-DM ages up to 3.8 Ga had been involved in the formation of the Tashliar melts. Three Neoarchean rock suites, one comprising quartz dioritic and tonalitic gneisses (the Bak 1), another K-rich granodiorites, granites and migmatites (the Bak 2), and the third monzonitic granitoids (the Aktanysh suite) were formed sequentially between 2.72 and 2.60 Ga. The 2.72 Ga Bak 1 suite is chemically diverse. It includes granitoids of the TTG type related to slab/subduction melts as well as rocks formed by the re-melting of older crust with whole-rock Nd T-DM and Hf T-DM model ages of 3.4 to 3.2 Ga. The 2.69 to 2.65 Ga Bak 2 suite was probably associated with a major collisional event, which defined the stacked structure of the Archean crust in Volgo-Uralia and its seismic layering. Our data suggest that the Bak 2 melts originated partly from juvenile sources with epsilon(Hf)(T) zircon values up to +4.8, as well as mixed crustal and juvenile mantle materials. Some crustal contamination of the melts appears to have occurred as evidenced by incorporated xenocrystic zircon. The chemical compositions of Bak 2 granitoids from the different plutons, their zircon epsilon(Hf) values, and the Hf- and Nd T-DM ages all mirror a heterogeneous, collisional, crustal structure. During post-collisional extension at 2.6 Ga, the intrusion of Aktanysh monzonitic granitoids took place. These rocks also bear evidence of a long crustal pre-history with Nd and Hf T-DM model ages of 3.3 to 3.5 Ga. The Aktanysh rocks are coeval with the Tuymazy gabbro-norite-anorthosite intrusions, which are widely distributed along post-collisional shear zones in the Bakaly block. They could have provided the heat necessary to melt the crust at this stage. Altogether, the isotopic evidence suggests several episodes of crustal growth and recycling possibly reaching back to 3.6 and 3.8 Ga. Metamorphic zircon rims show that the Archean crust in the Bakaly block were subjected to several tectonothermal overprints in the Paleoproterozoic between 2.4 and 1.9 Ga ago.
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| 8. |
- Chioncel, L., et al.
(författare)
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Transmission through correlated CunCoCun heterostructures
- 2015
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 92:5
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Tidskriftsartikel (refereegranskat)abstract
- We propose a method to compute the transmission through correlated heterostructures by combining density functional and many-body dynamical mean field theories. The heart of this combination consists in porting the many-body self-energy from an all electron basis into a pseudopotential localized atomic basis set. Using this combination we study the effects of local electronic interactions and finite temperatures on the transmission across the Cu4CoCu4 metallic heterostructure. It is shown that as the electronic correlations are taken into account via a local but dynamic self-energy, the total transmission at the Fermi level gets reduced (predominantly in the minority-spin channel), whereby the spin polarization of the transmission increases. The latter is due to a more significant d-electron contribution, as compared to the noncorrelated case in which the transport is dominated by s and p electrons.
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| 9. |
- Kosyak, Volodymyr, et al.
(författare)
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Calculation of point defect concentration in Cu2ZnSnS4 : Insights into the high-temperature equilibrium and quenching
- 2017
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Ingår i: Journal of Applied Physics. - : AMER INST PHYSICS. - 0021-8979 .- 1089-7550. ; 122:3
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Tidskriftsartikel (refereegranskat)abstract
- Herein, we study the native point defect equilibrium in Cu2ZnSnS4 (CZTS) by applying a statistical thermodynamic model. The stable chemical- potential space (SCPS) of CZTS at an elevated temperature was estimated directly, on the basis of deviations from stoichiometry calculated for the different combinations of chemical potential of the components. We show that the SCPS is narrow due to high concentration of (V-Cu(-) Zn-Cu(+)) complex which is dominant over other complexes and isolated defects. The CZTS was found to have p-type conductivity for both stoichiometric and Cu-poor/Zn-rich composition. It is established that the reason for this is that the majority of donor-like Zn-Cu(+) antisites are involved in the formation of (V-Cu(-) Zn-Cu(+)) complex making Cu-Zn dominant and providing p- type conductivity even for Cu-poor/Zn-rich composition. However, our calculation reveals that the hole concentration is almost insensitive to the variation of the chemical composition within the composition region of the single-phase CZTS due to nearly constant concentration of dominant charged defects. The calculations for the full equilibrium and quenching indicate that hole concentration is strongly dependent on the annealing temperature and decreases substantially after the drastic cooling. This means that the precise control of annealing temperature and post-annealing cooling rate are critical for tuning the electrical properties of CZTS.
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| 10. |
- Puchkov, Victor N., et al.
(författare)
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The ca. 1380 Ma Mashak igneous event of the Southern Urals
- 2013
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Ingår i: Lithos. - : Elsevier BV. - 0024-4937. ; 174, s. 109-124
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Tidskriftsartikel (refereegranskat)abstract
- A review of the geochronology, geochemistry and distribution of the 1380 Ma Mashak Large Igneous Province (LIP) of the eastern margin of the East European craton indicates a potential link to a major breakup stage of the Mesoproterozoic supercontinent Columbia (Nuna), link to a major stratigraphic boundary (Lower-Middle Riphean), and economic significance for hydrocarbons and metallogeny. Specifically, the Mashak event likely has much greater extent than previously realized. Two U-Pb baddeleyite (ID TIMS) age determinations on dolerite sills obtained from borehole (Menzelinsk-Aktanysh-183) confirm the western extent of the Mashak event into the crystalline basement of the East European Craton (1382 +/- 2 Ma) and into the overlying Lower Riphean sediments (1391 +/- 2 Ma), and the imprecise ages reported elsewhere indicate the possible extension into the Timan region, with an overall areal extent of more than 500,000 km(2) (LIP scale). It has tholeiitic compositions and is associated with breakup on the eastern margin of the craton - in addition, precise SHRIMP zircon ages of 1386 +/- 5 Ma and 1386 +/- 6 Ma (this paper) provide confirmation of previous approximate 1380-1383 Ma zircon age determination of the same formation, and suggest an age of ca. 1.4 Ga for the Lower/Middle Riphean boundary which was formerly considered to be 1350 +/- 10 Ma. Contemporaneous magmatic rocks in the northeastern Greenland part of Laurentia (Zig-Zag Dal and Midsommerso formations) and Siberia (Chieress dykes and other dolerites) together with the Mashak event are suggested to be fragments of a single huge LIP and to correspond to breakup stage of the Columbia (Nuna) supercontinent. The Mashak LIP also has some significance, at least in Volgo-Uralia, for hydrocarbons and metallogeny. (C) 2012 Elsevier B.V. All rights reserved.
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