Abstract
The Intra-Sudetic Basin, a ~ 12 km deep Variscan intramontane basin, has the best preserved post-orogenic sedimentary record available at the NE margin of the Bohemian Massif. Apatite fission track (AFT) analyses have been performed on 16 sedimentary and volcanic samples of Carboniferous to Cretaceous age from the Intra-Sudetic Basin to improve understanding of the post-Variscan thermal evolution. AFT central ages range from 50.1 ± 8.8 to 89.1 ± 7.1 Ma (Early Eocene to Coniacian), with 13 of them being Late Cretaceous. The mean track length values range from 12.5 ± 0.4 to 13.8 ± 0.5 (except for one sample 14.4 ± 0.2) µm. This relatively short mean track length together with the unimodal track length distributions and rather low standard deviation (0.8 to 1.7 µm) in most samples indicate a long stay in the partial annealing zone during slow cooling. However, in the northern part of the Intra-Sudetic Basin, samples show a wider track length distribution (standard deviation of 1.8 to 2.1 µm) that could indicate a more complex thermal evolution possibly related to Mesozoic reheating. Vitrinite reflectance data combined with thermal models based on the AFT results indicate that the Carboniferous strata reached maximum palaeotemperatures in the latest Carboniferous to Early Permian time, corresponding to a major coalification event. The second phase of temperature rise occurred due to Late Mesozoic sedimentary burial, but it had no influence on maturation of the Carboniferous organic matter. Final cooling phase in the Late Cretaceous–Paleogene was related to tectonic inversion of the Intra-Sudetic Basin, which occurred after deposition of a significant thickness of Cenomanian–Turonian sediments. Thermal modelling demonstrates that ~ 4 km thick cover of Upper Cretaceous sediments is required to obtain a good match between our AFT data and modelled time–temperature paths. This outcome supports a significant amount of Late Cretaceous–Paleogene inversion within the Variscan belt of Central Europe.
Highlights
The low-temperature post-Variscan history of the Sudetes, NE Bohemian Massif (Fig. 1), is still a matter of debate, due to the sparsely preserved post-Variscan geological record (e.g. Maluski et al 1995; Migoń and Danišík 2012; Danišík et al 2012; Sobczyk et al 2015; Botor et al 2017a, b)
Previous low-temperature thermochronological studies, mostly based on apatite fission track (AFT) data, suggest that the Bohemian Massif experienced a complex post-orogenic thermal evolution that may have been influenced by burial under Mesozoic sediments, Late Cretaceous inversion-related exhumation and inception of the European Cenozoic Rift System
Apatite fission track (AFT) central ages of Carboniferous to Turonian samples from the Intra-Sudetic Basin (ISB) range from 89.1 ± 7.1 to 50.1 ± 8.8 Ma (Coniacian to Early Eocene), but most of them are Late Cretaceous. These results indicate that studied rocks were heated to temperatures above ~ 120 °C, which is sufficient to totally anneal apatite fission tracks
Summary
The low-temperature post-Variscan history of the Sudetes, NE Bohemian Massif (Fig. 1), is still a matter of debate, due to the sparsely preserved post-Variscan geological record (e.g. Maluski et al 1995; Migoń and Danišík 2012; Danišík et al 2012; Sobczyk et al 2015; Botor et al 2017a, b). Previous low-temperature thermochronological studies, mostly based on apatite fission track (AFT) data, suggest that the Bohemian Massif experienced a complex post-orogenic thermal evolution that may have been influenced by burial under Mesozoic sediments, Late Cretaceous inversion-related exhumation and inception of the European Cenozoic Rift System
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