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  • 1
    Electronic Resource
    Electronic Resource
    40Ar/39Ar Thermochronology west of the Main Uralian fault, southern Urals, Russia (1999)
    Springer
    Geologische Rundschau 87 (1999), S. 515-525 
    Details
    ISSN: 0016-7835
    Keywords: Key words40Ar/39Ar Thermochronology ; Southern Urals ; Neoproterozoic event ; Eastern margin of East European platform
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract West of the Main Uralian fault, the main suture in the southern Urals, 40Ar/39Ar apparent ages of amphibole, muscovite and potassium feldspar are interpreted as cooling ages. A fast exhumation of the metamorphic complex of Kurtinsky during Upper Carboniferous time is indicated by the small age difference (15 Ma) between cogenetic amphibole and muscovite. Differentiated movement in the footwall of the Main Uralian fault along strike is indicated by the age difference of 70 Ma between the metamorphic complexes of Kurtinsky (north) and Maksyutov (south). No Upper Paleozoic (Uralian) medium- to high-temperature event is recorded in 40Ar/39Ar data from the metamorphic complex of Beloretzk (MCB). An amphibole age of 718±5 Ma and the occurrence of mafic intrusions might signal the break-up of Rodinia and therefore indicate the rifting period followed by the separate movement of the "Beloretzk terrane". Muscovite ages of approximately 550±5 Ma, the unique pre-Ordovician tectonometamorphic evolution of the MCB and the Late Vendian sedimentary history of the western Bashkirian Megaanticlinorium (BMA) imply the existence of a Neoproterozoic orogeny at the eastern margin of Baltica. This orogeny might have been initiated by the accretion of the "Beloretzk terrane". The metamorphic grade of the overlain Silurian shales and the K/Ar microcline ages from the "Beloretzk terrane" give evidence for a new thermal event at approximately 370 Ma. A microcline age of 530–550 Ma obtained for the Vendian conglomerate in the western BMA suggests that a maximum temperature of approximately 200°C was reached in Cambrian or Vendian times. An orthoclase age (590–630 Ma) of the Vendian Zigan flysch deposits might be inherited from the eastern source area, the Cadomian orogen. An orthoclase age (910–950 Ma) from the Riphean Zilmerdak conglomerate coincides with a documented decrease in the subsidence rate of the Upper Riphean basin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s005310050228
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  • 2
    Electronic Resource
    Electronic Resource
    Incipient metamorphism between Ufa and Beloretzk, western fold-and-thrust belt, southern Urals, Russia (1999)
    Springer
    Geologische Rundschau 87 (1999), S. 545-560 
    Details
    ISSN: 0016-7835
    Keywords: Key words incipient metamorphism ; Southern Urals ; Clay mineral crystallinity ; Vitrinite reflectance ; Conodont color alteration index (CAI)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The low-temperature thermal history of Paleozoic and Precambrian shales and slates was studied in detail along a NW–SE transect between Ufa and Beloretzk in the western fold-and-thrust belt of the southern Urals, Russia. The aim of the investigations was to compare four thermal parameters, namely illite and chlorite crystallinity, vitrinite reflectance, and Conodont color alteration index (CAI), in order to quantify the finite (i.e. maximum) thermal grade. The transect extends from Devonian to Permian sedimentary units of the pre-Uralian foredeep, crossing Precambrian siliciclastic and carbonate units of the Bashkirian megaanticlinorium into the Paleozoic units of the Ural-Tau antiform. In general, the four methods indicate similar metamorphic grades of the samples. The finite thermal grade ranges from lower diagenesis (Ro=0.9%, CIS-FWHMill001ad=0.770 Δ°2Θ, CIS-FWHMchl002ad=0.447 Δ°2Θ, CAI=1.5) in the pre-Uralian foredeep to epizone (CIS-FWHMill001ad=0.243 Δ°2Θ, CIS-FWHMchl002ad=0.252 Δ°2Θ, CAI=6) in the eastern part of the Bashkirian mega-anticlinorium and the Zilair synclinorium. All parameters show a sudden change in value at thrust boundaries and an increase in metamorphic grade with stratigraphic age within structural units. In comparison, the westernmost Precambrian units of the Ala-Tau-anticlinorium are characterized by thermal grades of lower diagenesis. Magmatic dikes cause a wide variation of the thermal grade in the western part of the Bashkirian megaanticlinorium. Also in areas with an intensive cleavage development (Zilair synclinorium) the finite thermal grade shows a stronger relationship towards the deformation than the stratigraphic position.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s005310050230
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