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A. B. Vrevskii 《Doklady Earth Sciences》2009,429(2):1575-1579
This study presents new data on the geochemical and Sm-Nd isotope compositions, as well as the U-Pb age and geodynamic nature,
of the Neoarchean basalt-andesite-dacite (BAD) association from the Kolmozero-Voron’ya greenstone belt. As it was first demonstrated
by the example of the Neoarchean greenstone belt, the formation of BAD associations within a single Neoarchean greenstone
structure may be explained by the long-lasting evolution of separate mantle or crustal sources not related to subduction processes. 相似文献
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V. A. Glebovitsky L. P. Nikitina A. B. Vrevskii Yu. D. Pushkarev M. S. Babushkina A. G. Goncharov 《Geochemistry International》2009,47(9):857-881
The paper reports data on the chemical composition of mantle peridotite xenoliths from kimberlites and alkaline basalts that
represent the continental lithospheric mantle (CLM) beneath Early Precambrian and Late Proterozoic-Cenozoic structures, respectively.
In order to identify compositional trends during the melting of primitive material and propose the most reliable criteria
for constraining the conditions of this process and its degree, we analyzed literature data on the melting of spinel and garnet
peridotites within broad temperature and pressure ranges. It was determined that the degree of melting (F%) of pristine peridotite
of composition close to that of the primitive mantle (PM) can be deduced from the Mg/Si and Al/Si ratios in the residue; an
equation was proposed for evaluating F from the Mg/Si ratio. The Ca/Al ratio of residues at low (1–1.5 GPa) pressures and
degrees of melting from 2–3 to 20–25% increases several times but decreases with increasing F at pressures higher than 3 GPa.
The Na partition coefficient between melt and residue decreases at increasing pressure and approaches one at a pressure close
to 20 GPa. Residues after low-degree melting are strongly depleted in Ti, Zr, Y, and Nb but are enriched in Cr. The application
of these criteria to the composition of xenoliths brought to the surface from the mantle occurring beneath tectonic structures
of various age led us to conclude that compositional heterogeneities of CLM (particularly the variations in the concentrations
of major and certain siderophile elements) are controlled, first of all, by the melting of the mantle source material. These
processes occurred under various thermodynamic conditions (T, P, and $
f_{O_2 }
$
f_{O_2 }
) and differed in their intensity, and this predetermined the compositional diversity of the residual mantle material (its
concentrations of Mg, Al, Si, Ca, Na, K, Ni, Co, V, and Cr). Our results are principally consistent with the hypothesis of
the global magmatic ocean. It is thought that the early phases of its consolidation were variably controlled by the fractionation
of minerals, for example, majorite. Moreover, heterogeneities in the distribution of siderophile elements could be partly
predetermined by changes in the properties of these elements at ultrahigh temperatures and pressures. The processes of partial
melting were the most intense during the early evolution of the mantle (perhaps, in the Early Precambrian), and hence, the
mantle has different chemical composition beneath Archean cratons and Phanerozoic foldbelts. 相似文献
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A. B. Vrevskii 《Petrology》2018,26(2):121-144
The paper reports newly obtained geological and isotopic-geochemical data on the volcano-sedimentary complex of the Uraguba Neoarchean greenstone structure in the Kola–Norwegian province of the Fennoscandian Shield. New U–Th–Pb geochronologic data (SIMS) on the metadacite (2790 ± 9 Ma) from a rock unit of interbedding metadacite, komatiite tuff, and lava breccia and on veins of plagioclase–microcline granite (2697 ± 10 and 2696 ± 9 Ma) that cuts the komatiite constrain the time span when supracrustal complex of the Uraguba structure was produced and underwent tectono-metamorphic transformations to approximately 100 Ma. The metavolcanic rocks of the komatiite–tholeiite association of the Uraguba structure belong to two distinct isotopic-geochemical types, which are spatially separated from one another and were produced by melting different mantle sources. Geological and isotopic-geochemical data indicate that the Uraguba structure is analogous to such unique tectonic structures on cratons as the Neoarchean Belingwe and Bulawayo belts in the Zimbabwe Shield, Kalgoorlie Belt in the Eastern Goldfilds province at the Yilgarn Craton, Kuhmo–Tipasjarvi Belt in the Karelian epi-Archean craton, and the Warawoona Paleoarchean Belt in the Pilbara Craton. 相似文献
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A. B. Vrevskii 《Petrology》2016,24(6):527-542
New data are reported on U-Pb (SHRIMP-II) age (2662 ± 7 Ma), isotope (Sm-Nd) and geochemical compositions of the anorthosites of the Patchemvarek Massif and “ovoidal” anorthosite sills of the Neoarchean Kolmozero-Voron’ya greenstone belt. Mesoarchean (2938 ± 8 Ma) zircons found in the Patchemvarek anorthosite have low Th/U ratio, are overgrown by a thin rim, and may be interpreted as xenogenic crystals assimilated by primary melts of the gabbro-anorthosite massifs from host Mesoarchean tonalites during crystallization in a magmatic chamber. The “ovoidal” anorthosite sills are dated at 2730–2740 Ma on the basis of U-Pb local zircon isotope analysis. The sills of the “ovoidal” anorthosites in the Kolmozero-Voron’ya GSB represent the older (2730–2740 Ma) rock group, which differs from the Patchemvarek anorthosites in strongly depleted Nd isotope composition and some geochemical features. In terms of age and Sm-Nd isotope characteristics, the “ovoidal” anorthosites are close to the komatiites of the lower volcanogenic sequence (εNd(Т) + 3.0–3.2), and metaandesites (2778 ± 5.4 Ma, U-Pb TIMS, εNdТ + 3.5) and metatholeiites of the upper volcanogenic sequence (εNd(Т) + 3.5–3.7) of the supracrustal complex of the Kolmozero-Voron’ya GSB. 相似文献
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A. B. Vrevskii 《Petrology》2018,26(3):246-254
Numerical modeling of the generation and evolution of parental melts of the komatiite–tholeiite association of the Uraguba structure was carried out using previously obtained geochemical and isotope data. It was established that komatiite, komatiite and tholeiite basalts depleted in LREE and having εNd(Т = 2.79) = +2.9…+3.2 were generated by equilibrium partial melting (F > 15%) of a depleted source (garnet-bearing Ol0.63 + Opx0.22 + Cpx0.06 + Grt0.09 mantle peridotite) at 4–8 GPa, while the genesis of primary melts of LREE-enriched komatiites (LaN/SmN ~ 1.2–1.6) with εNd(Т = 2.79) = +2.5…+2.2 was related to the equilibrium partial melting (F > 20%) of an “enriched mantle peridotite” (EM–Ol0.60 + Opx0.20 + Cpx0.08 + Grt0.12) at pressure of 2.5–4 GPa. Coexistence in space and time of two types of melting products of mantle peridotites formed at different depths is explained by melting of different parts of adiabatically ascending mantle plume. 相似文献
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