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apatite fission-tracks; thermotectonic history; Barrandian; Bohemian Massif; variscides
Abstract:
A fission-track (FT) study was carried out on apatite from Upper Proterozoic to Upper Carboniferous sedimentary and volcanic rocks in the Barrandian, Czech Republic. Apatite FT- ages vary between 324 +/- 8 Ma (Lower Carboniferous) and 196 +/- 14 Ma (Lower Jurassic). Mean confined track lengths range from 11.68 +/- 1.76 to 13.30 +/- 1.41 mum. The temperature-time path of selected samples was simulated by applying the Laslett- annealing model and independent geological constraints from the Barrandian. The first stage of increased temperature that is recorded in nearly all samples occurred at the Upper Devonian/Lower Carboniferous boundary. The change in temperature is due to the thickening of the crust by increased sediment load and stacking of sedimentary rocks along thrusts. FT-data indicate a limitation of the extension of thrust sheets towards the West. Cooling during the Carboniferous is attributed to exhumation of parts of the Barrandian. Deposition of Upper Carboniferous to Lower Permian sediments caused a second increase in temperature in Lower Permian time. Variation in maximum temperature indicates variable thickness of the sedimentary cover. The second cooling during the Mesozoic is linked to the long-term slow to medium exhumation process of the Central Variscan belt. (C) 2002 Elsevier Science B.V. All rights reserved.
