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G. N. Savelieva V. G. Batanova N. A. Berezhnaya S. L. Presnyakov A. V. Sobolev S. G. Skublov I. A. Belousov 《Geotectonics》2013,47(3):167-179
The paper presents new determinations of the U-Pb zircon age of high-Al chromitite from dunite of the mantle section of the Voikar-Synya massif at the Kershor site in the boundary zone with rocks of the dunite-wehrlite-clinopyroxenite complex. The high-Cr chromitite from dunite in the central part of the same massif contains zircon dated at ca. 0.6 Ga [10]. It is suggested that Paleoproterozoic (2.0?1.9 Ga) zircons from chromitites of the mantle section near the petrological Moho boundary were formed in the course of partial melting of peridotites and/or their interaction with migrating MORB-type melts. The occurrence of Vendian and Paleoproterozoic zircons in chromitites from different parts of the mantle section, as well as previously published petrological, geochemical, and geological data [2, 11, 22] allow us to suggest a complex multistage evolution of the mantle section in ophiolites. The arguments stated below show that chromitites and host dunites could have been formed at different times and were probably related to different processes. Thus, not only various complexes of the pre-Paleozoic oceanic crust reworked in the suprasubduction setting differ in age, but also the mantle rock of similar petrography, vary in the time of their formation. 相似文献
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T. A. Myskova N. M. Ivanov M. A. Korsakova R. I. Mil’kevich N. G. Berezhnaya S. L. Presnyakov 《Stratigraphy and Geological Correlation》2013,21(4):337-358
The geological, geochemical, and isotopic-geochronological data obtained for Sumian moderate-basic metavolcanites of Shombozero and Lekhta structures of the Panayarvi-Vygozero belt shows that the Tunguda Formation is confined to the Paleoproterozoic structural and material complex. This formation is represented by the complex of weakly differentiated andesitobasalts and andesites of calc-alkaline series with higher contents of MgO and moderate contents of Al2O3 and rare earth elements. The rocks of the Tunguda Formation are different from the Late Archean basic rocks of the Hiziyarvi Formation represented mainly by tholeiitic basalts with low REE contents and undifferentiated spectrum of REE distribution. The age of volcanites of the Tunguda Formation was determined to be 2439 ± 21 Ma. The xenogenic zircons from metaandesites of the Tunguda Formation have Neoarchean age according to the 207Pb/206Pb ratio (from 2536 ± 4 to 2825 ± 7 Ma). The Neoarchean zircons, a negative value of ?Nd (?3.8), and indicative geochemical parameters are evidence that the crustal component took part in formation of the protolith of the studied rocks. 相似文献
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O. M. Turkina L. N. Urmantseva N. G. Berezhnaya S. L. Presnyakov 《Stratigraphy and Geological Correlation》2010,18(1):16-30
The Early Precambrian granulite-gneiss complex of the Irkut Block (Sharyzhalgai salient of the Siberian Craton basement) with
the protoliths represented by a wide range of magmatic and sedimentary rocks, has a long-term history including several magmatic
and metamorphic stages. To estimate the age of sedimentation and metamorphism of the terrigenous deposits, the composition
of the garnet-biotite, hyper-sthene-biotite, and cordierite-bearing gneisses has been studied; their isotopic Sm-Nd values
have been revealed; and the U-Pb zircon dating has been performed using the SHRIMP II ion microprobe. The protoliths of the
terrigenous sediments metamorphosed under conditions of the granulite facies correspond to a rock series from siltstones and
graywackes to pelites. The Nd model ages of paragneisses range from 2.4 to 3.1 Ga. Zircons of the cordierite-bearing and hypersthene—biotite
gneisses show the presence of cores and rims. The clastic, smoothed, and irregular shape of the cores indicates their detrital
character and relicts of oscillatory zoning suggest the magmatic origin of zircon. The rim’s metamorphic genesis is indicated
by the lack of zoning and by the lower Th/U ratio compared to that of the cores. The age of the detrital cores (≥2.7, ~2.3,
and 1.95—2.0 Ga) and metamorphic rims (1.85–1.86 Ga) defines the time of sedimentation at 1.85–1.95 Ga ago. Potential sources
for the Archean detrital zircons were metamagmatic rocks of the granulite—gneiss complexes in the southwestern margin of the
Siberian Craton. The age of the dominant detrital cores at 1.95–2.0 Ga ago, together with the minimal TNd(DM) values, indicates the contribution of the juvenile Paleoproterozoic crust to the formation of sediments. The juvenile
Paleoproterozoic crust was likely represented by magmatic complexes similar to the volcanic and granitoid associations of
the Aldan shield, which were formed 1.99–2.0 Ga ago and showthe model age of 2.0—2.4 Ga. The isotopic Sm-Nd data show that
the Late Paleoproterozoic metasedimentary rocks occur not only in the Sharyzhalgai salient but in the Aldan and Anabar shields
of the Siberian Craton as well. 相似文献
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G. A. Shatkov N. G. Berezhnaya Ye. N. Lepekhina N. V. Rodionov I. P. Paderin S. A. Sergeyev 《Doklady Earth Sciences》2010,432(1):587-592
The precision dating (U-Pb local by zircons, SHRIMP-II) of volcanic rocks in the unique uranium-bearing structure of Transbaikalia
is performed for the first time. The basic conclusions are as follows. The volcanic activity in the Tulukuev caldera covers
the period of not less than 30–35 mln years, within the period from (not later than) 162 to 128 mln years. Two stages of caldera
evolution are established: the early (trachydacite-basalt) stage up to 154 mln years and the late (trachybasalt-rhyolite)
stage from 142 to 128 mln years, with a 10 mln year break, which caused the deep erosion of the lower layer. Three phases
of rhyolite magmatism are substantiated. The first one, 142 mln years, is the ejection of ignimbrites (microfelsitic rhyolites);
the second one, 137–135 mln years, is the outflow of lavas of sanidine-morion rhyolites and subvolcanic and ring dyke intrusions.
The third phase, 128 mln years, is connected with the occurrence of cesium-bearing perlites in the southwestern part of the
caldera. The age of the granite-porphyries of the Krasnokamensk stock almost coincides with the precision data of the age
of the uranium ores [4]. It is found that zircons from the granite-porphyries within the ore field of the Argunsk deposit
have an anomalously high content of uranium. This fact can additionally testify to the time-and-spatial closeness of magmatism
and processes of ore formation. 相似文献
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