Age and Evolution of the Early Precambrian Continental Crust of the Ukrainian Shield

Shcherbak, N. P.; Bartnitsky, E. N.; Bibikova, Elena; Boiko, V. L.

doi:10.1007/978-3-642-70001-9_12

Cited by 12 publications

(15 citation statements)

References 3 publications

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“…In such a case, the data points of errorchrons strongly deviate from the ideal isochron, with a wide range of possible depositional ages. However, the published metamorphic U-Pb age for granitoid emplacement and regional metamorphism is 2.0 Ga ± 100 Ma (Shcherbak et al, 1984), which is considerably younger than the age suggested by our errorchron, which in turn is similar to the published formation age within the 2 error range. (ii) The BIF samples were affected by different amounts of detrital contamination which strongly affects their specific isotopic compositions.…”

Section: Samarium-neodymium Isotope Geochronologysupporting

confidence: 73%

“…The Fe content of the lower sequences is less than 40%, while upper Saxagan Group BIF horizons may contain up to 65% Fe (Mboudou et al, 2012), probably triggered by post-depositional supergene Fe-ore upgrade. Mboudou et al (2012) and Belevtsev and Belyaev (1989) report greenschist facies metamorphic conditions in the lower part of the Saxagan BIF stratigraphy which increase to amphibolite facies in the upper part of the sequence and are probably related to a Kulik and Korzhnev, 1997). regional granitoid emplacement at 2000 ± 100 Ma (Shcherbak et al, 1984). However, all BIF samples we studied are mainly composed of magnetite and quartz with minor siderite, hematite and low-grade metamorphic trace minerals such as riebeckite, cummingtonite, stilpnomelane and chlorite minerals.…”

Section: Geological Overviewmentioning

confidence: 70%

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Geochemistry of the Krivoy Rog Banded Iron Formation, Ukraine, and the impact of peak episodes of increased global magmatic activity on the trace element composition of Precambrian seawater

Viehmann

Bau

Hoffmann

et al. 2015

Precambrian Research

100

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Section: Samarium-neodymium Isotope Geochronologysupporting

confidence: 73%

Section: Geological Overviewmentioning

confidence: 70%

Geochemistry of the Krivoy Rog Banded Iron Formation, Ukraine, and the impact of peak episodes of increased global magmatic activity on the trace element composition of Precambrian seawater

Viehmann

Bau

Hoffmann

et al. 2015

Precambrian Research

100

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“…The obtained results (695 ± 20 °C, 5 kbar) correspond to the data of Savko (1999a) for the VCM and also characterize one of the retrograde metamorphic events. Absolute age data for the Azov Block (Shcherbak et al. , 1984, 1993) have identified three tectono‐thermal (metamorphic) events with the ages of 3.45, 2.9–2.8 and 2.3–2.2 Ga, which agrees with the multistage character of metamorphism of the VCM BIF.…”

Section: Discussionsupporting

confidence: 60%

Exsolution textures of orthopyroxene and clinopyroxene in high‐grade BIF of the Voronezh Crystalline Massif: evidence of ultrahigh‐temperature metamorphism

Fonarev

Pilugin

Савко

et al. 2006

Journal Metamorphic Geology

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Archaean banded iron formation (BIF) of the Voronezh Crystalline Massif (VCM) contains coexisting clino-and orthopyroxenes with exsolution textures. The pyroxene in the VCM BIF is found in two generations, with only the first generation containing such textures. Clinopyroxene contains large (up to 5-10 lm) (0 0 1) orthopyroxene (Opx1L) lamellae in a host clinopyroxene (Cpx1H). This host Cpx, in turn, exsolves into thin (1 lm) (1 0 0) lamellae of orthopyroxene (Opx2L) and clinopyroxene (Cpx2H). Orthopyroxene exhibits similar exsolution textures with large (up to 50 lm) (0 0 1) clinopyroxene (Cpx1L) lamellae developed in a host orthopyroxene (Opx1H). This clinopyroxene Cpx1L shows further exsolution of thin (1 0 0) Opx2LL lamellae and clinopyroxene (Cpx2LH). Point microprobe analysis, raster-mode microprobe analysis, and microprobe element mapping of mineral grains with a large number of point analysis were used to determine the composition of the exsolution products and the primary chemistry of the coexisting clinopyroxene (CaO ¼ 14.86-17.26 wt%) and pigeonite (CaO ¼ 4.45-6.23 wt%). These pyroxenes crystallized during the peak of metamorphism, and application of the Lindsley geothermometer suggested that they formed at extremely high temperatures of about 1000°C. Primary very dense CO 2 -rich fluid inclusions (q ¼ 1.152 g cm )3 , T h ¼ )49.2°C) were discovered for the first time in these BIF. With these data, the metamorphic pressure was estimated as 10-11 kbar (depth 36-40 km). Such ultrahigh temperature-high pressure (UHT-HP) conditions for the regional metamorphism of the Precambrian BIF have previously been reported only for Archaean metaironstone from the Napier Complex (Enderby Land, Antarctica). They give an insight into the peak metamorphic conditions of the BIF of the VCM, their burial under thickened continental crust during this period of Earth evolution and suggest a more complicated multistage metamorphic and tectonothermal history for the region than has previously been postulated.

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“…Fe-rich and Si-rich banded chemical sediments alternate with clastic sedimentary units that were deposited during cycles of transgression and regression periods of the Krivoy Rog sea (Kulik et al, 1991). The depositional age of the chemo-clastic Krivoy Rog Supergroup was bracketed between 2.7 and 2.0 Ga (Shcherbak et al, 1984;1989)…”

Section: Geological Overview Of the Neoarchean Krivoy Rog Bifmentioning

confidence: 99%

Decoupled Hf and Nd isotopes in suspended particles and in the dissolved load of Late Archean seawater

et al. 2018

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It is generally agreed that decoupling of the Hf and Nd isotope systems in modern aqueous systems is a result of incongruent release of Hf during terrestrial weathering of the continental crust, although the mechanism(s) behind this process are not yet fully understood. We here present Hf-Nd isotope data for the Neoarchean Krivoy Rog Banded Iron Formation (BIFs), Ukraine, and combine observations on modern aqueous environments with those of the early Earth to further evaluate the mechanism(s) behind Hf-Nd isotope decoupling in aqueous systems.The pure Late Archean Krivoy Rog chemical sediment endmember, representing the dissolved pool of ancient seawater, shows decoupled εNd2.60Ga-εHf2.60Ga values of -2.3 and +9.48, respectively, and suggests that decoupled Hf-Nd isotopes had been a global rather than a local phenomenon in Neoarchean seawater. This further reveals that incongruent Hf release via terrestrial weathering and erosion of emerged and evolved continental landmasses were widespread geological processes by Late Archean time.Impure Krivoy Rog BIF samples, composed of a mixture of seawater-derived and detrital Nd and Hf, show systematically more positive εNd2.60Ga values, but still reveal decoupled εNd-εHf values relative to an associated schist that plots slightly below the 'terrestrial array'. This suggests that mineral sorting between a zircon-bearing sand-sized fraction and fine-grained sediment particles occurred on/in Late Archean continents, rivers and oceans, and had significant impact on the chemical compositions of the suspended and dissolved element loads of Late Archean seawater. Less radiogenic Hf isotope compositions in the Krivoy Rog seawater relative to detritus-contaminated BIFs further suggest a pathway for high-temperature hydrothermal Hf into anoxic Archean seawater, that diluted the even more radiogenic Hf isotopic composition of continental run-off, created by the mineralogical composition of the continental hinterland and the 'zircon effect'. Alternatively, the less pronounced decoupling of εHf-εNd in Late Archean seawater may be related to a shorter residence time of Hf relative to Nd. Furthermore, systematically more positive initial εNd values in detritus-contaminated Archean BIFs relative to respective dissolved seawater loads suggest that weathered and eroded material of (ultra)mafic rock suites had significant impact on the suspended and dissolved fractions in Archean seawater.

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Age and Evolution of the Early Precambrian Continental Crust of the Ukrainian Shield

Cited by 12 publications

References 3 publications

Geochemistry of the Krivoy Rog Banded Iron Formation, Ukraine, and the impact of peak episodes of increased global magmatic activity on the trace element composition of Precambrian seawater

Geochemistry of the Krivoy Rog Banded Iron Formation, Ukraine, and the impact of peak episodes of increased global magmatic activity on the trace element composition of Precambrian seawater

Exsolution textures of orthopyroxene and clinopyroxene in high‐grade BIF of the Voronezh Crystalline Massif: evidence of ultrahigh‐temperature metamorphism

Decoupled Hf and Nd isotopes in suspended particles and in the dissolved load of Late Archean seawater

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