Zircon geochronology of the Mashak volcanic rocks and the problem of the age of the lower-middle Riphean boundary (Southern Urals)     

A. A. Krasnobaev  V. I. Kozlov  V. N. Puchkov  S. V. Busharina  N. D. Sergeeva  I. P. Paderin 《Stratigraphy and Geological Correlation》2013,21(5):465-481

In the type sections of the Riphean within the Bashkirian mega-anticlinorium (Southern Urals), the Mashak Formation represents a basal unit of the Middle Riphean erathem. The formation comprises throughout its area of distribution the alternation of volcanic, volcano-sedimentary, and sedimentary sequences and is divided into the lower, middle, and upper subformations. The volcanic rocks containing zircons (four samples, rhyodacite and rhyolite collected at Mashak, Berezyak, and Bolshoi Shatak ranges) are largely confined to the lower subformation. Analyses were performed using a SHRIMP II methodology, with special attention to the mineralogical characteristics of zircons, including their habit, morphology, preservation, and inclusions. All zircons show similarities in their mineral chemistry and geochemistry, which are indicative of the geochemical affinity of the volcanic rocks. At the same time, all zircon grains are characterized by specific typological parameters, which may equally reflect the parameters involved in the development of such volcanic rocks under different conditions. The integrated U-Pb age of zircons (SHRIMP II, VSEGEI, St. Petersbrug) from the four samples is 1383 ± 3 Ma. On the basis of the age of the Berdyaush gabbro-granitoid intrusion (up to 1410 Ma), the most likely age of this boundary is 1400 Ma, which is equated to the Calymmian and Ectasian of the International Stratigraphic Scale.  相似文献   

Thermotectonic evolution of the western fold-and-thrust belt, southern Uralides, Russia, as revealed by apatite fission track data     

U. A. Glasmacher  G. A. Wagner  V. N. Puchkov 《Tectonophysics》2002,354(1-2)

The Uralides, a linear N–S trending Palaeozoic fold belt, reveals an intact, well-preserved orogen with a deep crustal root within a stable continental interior. In the western fold-and-thrust belt of the southern Uralides, Devonian to Carboniferous siliciclastic and carbonate rocks overlay Mesoproterozoic to Neoproterozoic sedimentary rocks. Deformation in the Devonian, Carboniferous and Permian caused thick-skinned tectonic features in the western and central parts of the western fold-and-thrust belt. A stack of several nappes characterizes the deformation in the eastern part. Along the E–W transect AC-TS'96 that crosses the western fold-and-thrust belt, apatite fission track data record various stages of the geodynamic evolution of the Uralide orogeny such as basin evolution during the Palaeozoic, synorogenic movements along major thrusts, synorogenic to postorogenic exhumation and a change in the regional stress field during the Upper Jurassic and Lower Cretaceous. The Palaeozoic sedimentary cover and the Neoproterozoic basement of the Ala-Tau anticlinorium never exceed the upper limit of the PAZ since the Devonian. A temperature gradient similar to the recent one (20 °C/km) would account for the FT data. Reactivation of the Neoproterozoic Zilmerdak thrust was time equivalent to the onset of the Devonian and Carboniferous collision-related deformation in the east. West-directed movement along the Tashli thrust occurred in the Lower Permian. The Devonian and Carboniferous exhumation path of the Neoproterozoic siliciclastic units of the Tirlyan synclinorium mirrors the onset of the Uralian orogeny, the emplacement of the Tirlyan nappe and the continuous west-directed compression. The five main tectonic segments Inzer Synclinorium, Beloretzk Terrane, Ala-Tau anticlinorium, Yamantau anticlinorium and Zilair synclinorium were exhumed one after another to a stable position in the crust between 290 and 230 Ma. Each segment has its own t–T path but the exhumation rate was nearly the same. Final denudation of the western fold-and-thrust belt and exhumation to the present surface probably began in Late Tertiary. In Jurassic and Cretaceous, south-directed movements along W–E trending normal faults indicate a change in the tectonic regime in the southern Uralides.  相似文献   

New data on genesis of the crust in the eastern segment of the Middle Urals: Sr–Nd isotopic constraints     

V. N. Smirnov  Yu. L. Ronkin  V. N. Puchkov  N. G. Soloshenko  M. V. Streletskaya 《Doklady Earth Sciences》2016,467(2):331-336

The analysis of the Sr and Nd isotopic composition in different granitoids of the Verkhisetsk, Shartash, Krasnopolsk, Petrokamensk, and Shabry massifs, which were successively formed in the island arc, continental marginal, and collisional geodynamic settings during the period from the Middle Devonian to the early Permian, revealed that ⁸⁷Sr/⁸⁶Sr₀ values in them vary from 0.70331 to 0.70431 and ε_Nd(t), from +1.9 to +6.2. The two-stage model Nd age of granitoids (938–629 Ma) indicates that their magma originates from material at least Neoproterozoic in age, not younger. The observed variations in the Nd model ages of granitoids and ⁸⁷Sr/⁸⁶Sr₀ values provide grounds for assuming the primary heterogeneity of the source of granitoid melts.  相似文献   

First data on the concentrations and distribution of noble metals in Riphean magmatic complexes of the Bashkir meganticlinorium and eastern margin of the East European Platform     

S. G. Kovalev  V. N. Puchkov  S. I. Vysotsky  S. S. Kovalev 《Doklady Earth Sciences》2016,471(2):1247-1252

The noble metal (PGE and Au) geochemical specialization of igneous rocks of the Bashkir meganticlinorium and adjacent areas of the East European Platform is characterized for the first time. The identical plots of normalized PGE and Au concentrations of igneous rocks in these regions indicate similar conditions and mechanisms of the formation of the noble metal geochemical specialization during the emplacement of magmatic bodies. It is established that a specific feature of noble metal geochemical specialization (the “rhodium anomaly”) in magmatic complexes of the Bashkir meganticlinorium and eastern areas of the East European Platform is determined by the concentrations of noble metals in sulfide minerals (pentlandite); i.e., it is “primary” in origin.  相似文献   

Genesis of Sulfide and Platinum-Metal Mineralization of the Khudolaz Complex (Southern Urals)     

Rakhimov  I. R.  Puchkov  V. N. 《Doklady Earth Sciences》2021,498(1):398-402

Doklady Earth Sciences - Mineralogical and geochemical studies of sulfide–platinum metal assemblages of the Khudolaz complex made it possible for the first time to substantiate their...  相似文献   

Sources of Zircons from Clastic Rocks of the Riphean Sequences of the Urals     

Krasnobaev  A. A.  Puchkov  V. N.  Sergeeva  N. D.  Busharina  S. V. 《Doklady Earth Sciences》2019,488(2):1166-1172

Doklady Earth Sciences - New dates of detrital zircons from sandstones expand the possibilities to interpret their source areas. These interpretations are often constrained by a formal comparison...  相似文献   

Paleomagnetism of Ordovician–Silurian Volcanics on the Western Slope of the Southern Urals     

Golovanova  I. V.  Danukalov  K. N.  Puchkov  V. N.  Sergeeva  N. D.  Sal’manova  R. Yu. 《Doklady Earth Sciences》2019,489(2):1383-1387

Doklady Earth Sciences - This work presents new paleomagnetic data on previously dated Ordovician–Silurian volcanics from four sections in the western framework of the Taratash massif...  相似文献   

First data on Early Carboniferous intrusive magmatism of the eastern margin of the Middle Urals: Geodynamic conditions and U–Pb isotope constraints     

I. I. Kazakov  Yu. L. Ronkin  V. N. Puchkov  V. N. Smirnov  A. Gerdes  A. S. Faust 《Doklady Earth Sciences》2017,476(1):1038-1042

U–Pb LA ICP–MS dating of zircon from rocks of the Nekrasov gabbro–granitoid complex within the eastern margin of the Middle Urals was performed. The average U–Pb age calculated from three concordant measurements (326 ± 8 Ma) shows that their intrusion occurred at the Serpukhov Stage of the Early Carboniferous. According to the ideas on periodization of magmatic processes within the eastern sector of the Middle Urals, the formation of this complex corresponds to the final episodes of the continental marginal (supersubduction) magmatism.  相似文献   

Conditions of formation of igneous rocks in plume magmatism at the example of the western slope of the Southern Urals     

S. G. Kovalev  V. N. Puchkov  S. I. Vysotsky  S. S. Kovalev 《Doklady Earth Sciences》2017,475(1):743-747

This work presents new data on the conditions of formation of igneous rocks on the western slope of the Southern Urals and the adjacent part of the East European Platform. Based on the calculated P–T melting parameters of the mantle substrate, it is shown that plume magmatism leads to the formation of similar rocks (picrites and picrite-dolerites), while the genesis of them is quite different. The first type of rocks is a product of crystallization of the undifferentiated mantle-derived melt in the upper horizons of the crust; the rocks of the second type are formed as a result of magma differentiation in large intracrustal magma chambers.  相似文献   

Structural framework of the Bashkirian anticlinorium, SW Urals     

U. Giese  U. Glasmacher  V. I. Kozlov  I. Matenaar  V. N. Puchkov  L. Stroink  W. Bauer  S. Ladage  R. Walter 《International Journal of Earth Sciences》1999,87(4):526-544

The Bashkirian anticlinorium of the southwestern Urals shows a much more complex structural architecture and tectonic evolution than previously known. Pre-Uralian Proterozoic extensional and compressional structures controlled significantly the Uralian tectonic convergence. A long-lasting Proterozoic rift process created extensional basement structures and a Riphean basin topography which influenced the formation of the western fold-and-thrust-belt with inversion structures during the Uralian deformation. A complete orogenic cycle during Cadomian times, including terrane accretion at the eastern margin of the East European platform, resulted in a high-level Cadomian basement complex, which controlled the onset of Uralian deformation, and resulted in intense imbrication and tectonic stacking in the subjacent footwall of the Main Uralian fault. The Uralian orogenic evolution can be subdivided into three deformation stages with differently oriented stress regimes. Tectonic convergence started in the Late Devonian with ophiolite obduction, tectonic accretion of basin and slope units and early flysch deposits (Zilair flysch). The accretionary complex prograded from the SE to the NW. Continuous NW/SE-directed convergence resulted finally in the formation of an early orogenic wedge thrusting the Cadomian basement complex onto the East European platform. The main tectonic shortening was connected with these two stages and, although not well constrained, appears to be of Late Devonian to Carboniferous age. In the Permian a final stage of E–W compression is observed throughout the SW Urals. In the west the fold-and-thrust-belt prograded to the west with reactivation of former extensional structures and minor shortening. In the east this phase was related to intense back thrusting. The East European platform was subducted beneath the Magnitogorsk magmatic arc during the Late Paleozoic collision. The thick and cold East European platform reacted as a stable rigid block which resulted in a narrow zone of intense crustal shortening, tectonic stacking and high strain at its eastern margin. Whereas the first orogenic wedge is of thick-skinned type with the involvement of crystalline basement, even the later west-directed wedge is not typically thin-skinned as the depth of the basal detachment appears below 15 km and the involvement of Archean basement can be assumed.  相似文献