Ar-40/Ar-39 thermochronology west of the Main Uralian fault, southern Urals, Russia

West of the Main Uralian fault, the main suture in the southern Urals, Ar-4 0/Ar-39 apparent ages of amphibole, muscovite and potassium feldspar are in terpreted as cooling ages. A fast exhumation of the metamorphic complex of Kurtinsky during Upper Carboniferous time is indicated by the small age dif ference (15 Ma) between cogenetic amphibole and muscovite. Differentiated m ovement in the footwall of the Main Uralian fault along strike is indicated by the age difference of 70 Ma between the metamorphic complexes of Kurtin sky (north) and Maksyutov (south). No Upper Paleozoic (Uralian) medium- to high-temperature event is recorded in Ar-40/Ar-39 data from the metamorphic complex of Beloretzk (MCB). An amphibole age of 718+/-5 Ma and the occurre nce of mafic intrusions might signal the break-up of Rodinia and therefore indicate the rifting period followed by the separate movement of the "Belor etzk terrane". Muscovite ages of approximately 550+/-5 Ma, the unique pre-O rdovician tectonometamorphic evolution of the MCB and the Late Vendian sedi mentary history of the western Bashkirian Megaanticlinorium (BMA) imply the existence of a Neoproterozoic orogeny at the eastern margin of Baltica. Th is orogeny might have been initiated by the accretion of the "Beloretzk ter rane". The metamorphic grade of the overlain Silurian shales and the K/Ar m icrocline 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 temper ature of approximately 200 degrees C was reached in Cambrian or Vendian tim es. An orthoclase age (590-630 Ma) of the Vendian Zigan flysch deposits mig ht be inherited from the eastern source area, the Cadomian orogen. An ortho clase age (910-950 Ma) from the Riphean Zilmerdak conglomerate coincides wi th a documented decrease in the subsidence rate of the Upper Riphean basin.