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A. A. Krasnobaev P. M. Valizer V. N. Anfilogov S. A. Sergeev A. I. Rusin S. V. Busharina E. V. Medvedeva 《Doklady Earth Sciences》2016,469(1):674-679
Dating of zircon (SHRIMP) from dunite and harzburgite of the Karabash massif was carried out for the first time. Relics of ancient crystals (1940 ± 30 Ma in harzburgite, 1860 ± 16 Ma in dunite) provide evidence for the Paleoproterozoic age of the protolith. The morphological peculiarities of zircon crystals allow us to assume differentiation of the magmatic source 1720 m. y. ago. The major variety of zircons indicates stages of metamorphic evolution in the Neoproterozoic (530–560 Ma) and Early–Late Ordovician (440–480 Ma). 相似文献
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V. N. Puchkov A. A. Krasnobaev N. D. Sergeeva S. V. Busharina S. P. Shokalsky 《Doklady Earth Sciences》2017,477(1):1295-1300
Before our studies, it was considered that the Bagrusha rhyolite–porphyry complex (BC) including veins and thin dykes occurring in the Kusa region among deposits presumably of the Satka and Avzyan Formations of the Lower and Middle Riphean, respectively. Based on the U–Pb SHRIMP and IDTIMS studies of zircons from rhyodacite—porphyry, we established the age of the BC formation of T0 = 1348.6 ± 3.2 Ma for the first time. The age obtained is inconsistent with the idea on the Paleozoic age of the BC and the geological situation shown on geological maps of the region. The age (T0 = 1348.6 ± 3.2 Ma) of rhyodacite–porphyry from the BC provides evidence for acid volcanism controlled by the Mashak (Middle Riphean) magmatic event in the region, and deposits hosting volcanic rocks of the BC cannot be younger than the base of the Middle Riphean, i.e., the Mashak Formation, which was not previously distinguished by researchers in the western part of the Kusa and Bakal–Satka regions. At the same time, it is possible that deposits hosting dykes and veins of the granite–rhyolite formation may have a Bakal (Lower Riphean) age. 相似文献
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A. A. Krasnobaev A. I. Rusin I. A. Rusin S. V. Busharina 《Geochemistry International》2011,49(5):482-497
The paper reports the results of mineralogical and isotope-geochronological study of zircons from the Uzyansky Kraka (UK) Massif, which represents the part of the large (more than 900 km2) lherzolite allochthon thrusted onto the Paleozoic sequences of the East European margin. The massif shows a distinct stratification (from the top downward): spinel lherzolites, garnet pyroxenites, and dunites. The formation of stratified section is considered to be related to the decompression uplift of mantle lherzolite block. Zircons from the massif rocks were dated using SHRIMP-II ion microprobe. The oldest relict datings characterizing endogenous transformations of protolith were established in the zircons from the lherzolites (2037 ± 20 and 1132 ± 6 Ma), garnet pyroxenites (953 ± 11 Ma), and dunites (632 ± 11 Ma). All rock associations contain zircons with ages within 590–550 and 445–390 Ma, which mark the stages of mantle stratification of lherzolite block into complementary series and their emplacement at the upper crustal level. Age values within 299–196 Ma were found only in the dunites and date the influence of the Paleozoic strike-slipping. Our studies led us to conclude that the modern structure of the Ural collision orogen contains the fragments of subcontinental lithosphere, which were previously described only for the massifs of the root zones of the Western and Central Europe. Some general petrogenetic questions of lherzolite massifs from orogenic regions are discussed. 相似文献
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A. A. Krasnobaev P. M. Valizer V. N. Anfilogov E. V. Medvedeva S. V. Busharina 《Doklady Earth Sciences》2018,480(2):741-745
The formation time of 410.5 ± 1.1 Ma (zircon U/Pb SHRIMP) and the duration of rock crystallization (2–2.5 Ma) were determined for gabbro from the Nurali massif. The gabbro zircons showed a complicated polyphase structure. A new polygenous type of zonality including traces of primary growth and of the processes of crushing, dissolution, and substitution was discovered in the zircons. The formations of gabbro and ultramafites (lherzolites) of the massif are separated by a time break of 30–35 Ma determined by the genetic discontinuance. 相似文献
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A. A. Krasnobaev P. M. Valizer V. N. Anfilogov A. B. Nemov S. V. Busharina 《Doklady Earth Sciences》2014,457(2):960-964
Zircons extracted from the nepheline and feldspar crystals of miaskitic and feldspar pegmatites, respectively, are analyzed with the SHRIMP method for the first time. The early (Silurian) zircons coincide in age (432 Ma), composition, and mineralogical peculiarities with early zircons from miaskites. It is concluded that the pegmatite melt is a derivative of the miaskite melt. Permian (240–260 Ma) metamorphic zircons are widespread in pegmatites and miaskites. Zircons from these rocks are characterized by genetic commonality. 相似文献