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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. [ABSTRACT FROM AUTHOR]

In order to resolve the age of Navysh volcanics (NV), which is usually attributed to the Lower Riphean of the Ai Formation, we have used geochronological, petrologic, and mineralogical methods of zirconology, apart from the SHRIMP isotopic data of single zircon grains. Moreover, TIMS isotope age analyses have been conducted, the results of which can be regarded as both controlling and providing the most correct information. The TIMS and SHRIMP data make it possible to suggest a polychronous character of the NV, which include not only Riphean, but also Paleozoic groups of volcanics. In this situation, an assessment of the scales of such polychroneity of NV and, correspondingly, of the Ai Formation as a whole becomes urgent. [ABSTRACT FROM AUTHOR]

Zircons in serpentinites from Nyashevo massif of the Ilmenogorskii complex were dated for the first time by means of the SHRIMP technique. The maximum date of 1892 ± 23 Ma for the zircons accounts for the minimum age of their mantle substrate probably constituting the restite residue. The date is comparable to those for metamorphic rocks of the Selyankino group, as well as of fenite-sand amphibolites of the Ilmenogorskii complex. The Upper Ordovician age limit of 443 ± 12 Ma is adequate for formation of the massif and conforms to the age of the Buldym massif and miaskites. The Early Permian dates of zircons (275.8 ± 2.1 Ma) represent late shear processes in the Ilmenogorskii complex. [ABSTRACT FROM AUTHOR]

The first results of U-Pb dating of detrital zircons from Upper Ordovician sandstones of the Bashkir uplift in the Southern Urals and U-Pb isotopic ages available for detrital zircons from six stratigraphic levels of the Riphean-Paleozoic section of this region are discussed. It is established that the long (approximately 1.5 Ga) depositional history of sedimentary sequences of the Bashkir uplift includes a peculiar period lasting from the Late Vendian to the Emsian Age of the Early Devonian (0.55-0.41 Ga). This period is characterized by the following features: (1) prevalence of material from eroded Mesoproterozoic and Early Neoproterozoic crystalline complexes among clastics with ages atypical of the Volga-Urals segment of the East European Platform basement; (2) similarity of age spectra obtained for detrital zircons from different rocks of the period: Upper Vendian-Lower Cambrian lithic sandstones and Middle Ordovician substantially quartzose sandstones. [ABSTRACT FROM AUTHOR]

The U-Pb SIMS age dating of zircons from different-age granitoid assemblages varying in composition of the Verkhisetsk batholith shows that it comprises rocks of three age groups, formed at different stages of the Ural Mobile Belt. The first age group is represented by quartz diorites (396 ± 5 Ma) with insignificant distribution in area. Their formation was synchronous to island arc volcanism, manifested in the area of study from the second half of the Emsian to late Givetian-early Frasnian. According to this, we could consider these granitoides as comagmatic to island arc volcanites. The second age group includes tonalites and trondhjemites (367 ± 4 Ma), comprising the western part of the batholith. On the basis of similarity between these rocks and granitoides of modern active continental margins in material composition, it is assumed that they formed throughout the island arc-continental stage of development of the Ural Mobile Belt. Granitoides of the third age group, dominating in the Verkhisetsk batholith, formed as a result of several homodrome rhythms of granodiorite-granite intrusions of moderate-potassium composition during a short period of time (315-300 Ma). Their formation is related to the initial stage of the collision stage of development of the region, lasting from the early Bashkirian to Late Permian in the Middle Urals, which is fixed by deposition of flysch and molasse sediments in the Ural Foredeep. The data obtained change our understanding significantly of the character of evolution of granitoid magmatism and the place of rock assemblages studied in the geological history of the Urals. [ABSTRACT FROM AUTHOR]

The article presents a research related to zirconology of ultramafic rocks from the Vostochnotagilskii massif (Middle Urals). Topics discussed under research include analysis of mineralogical peculiarities of zircons from ultramafic rocks of the massif and Zircons from dunite showing signs of early and late generations. It reveals that zircons showed clear signs of crushing, recrystallization and idiomorphism.