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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Geologische Rundschau 86 (1997), S. 178-184 
    ISSN: 0016-7835
    Keywords: Key words Bohemian massif ; SW margin ; Post-Variscan structural record ; Sedimentary record ; Clastic supply ; Source areas
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  The late-Palaeozoic to Cenozoic stratigraphic and structural record of the southwestern margin of the Bohemian massif and its extension beneath the southward adjacent Molasse basin shows that it is controlled by a system of basement-involving faults which came into evidence during Stephanian– Autunian times and which were subsequently repeatedly reactivated. Thick Permo-Carboniferous clastics accumulated in fault-bounded transtensional basins aligned with the southwestern Bohemian border zone (SWBBZ). Following late-Autunian deformation of these basins, the SWBBZ was overstepped by late-Permian to Late Jurassic platform sediments, reflecting tectonic stability. During the Early Cretaceous the SWBBZ was strongly reactivated, causing disruption and erosion of its Mesozoic sedimentary cover. Sedimentation resumed in the area of the SWBBZ during late Early and Late Cretaceous with clastic influx from the Bohemian massif reflecting gradually increasing tectonic activity along the SWBBZ. During the Late Senonian and Paleocene transpressional deformations resulted in upthrusting of major basement blocks. In the Molasse basin such structures are sealed by transgressive Late Eocene marine strata. Mio-Pliocene uplift of the Bohemian massif, involving mild reactivation of the SWBBZ, is related to the development of the volcano-tectonic Eger zone. The structural configuration of the SWBBZ is largely the result of Late Senonian–Paleocene compressional intraplate tectonics which play a major role in the structural framework of the northern Alpine and Carpathian foreland.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0016-7835
    Keywords: Key words Bohemian Massif ; KTB ; K ; Ar and Rb ; Sr mineral dating ; Middle to post-Variscan tectonothermal evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  K–Ar and Rb–Sr age determinations on muscovites and biotites and K–Ar age determinations on amphiboles are presented for leucocratic gneisses, amphibolites and (meta-)igneous rocks from the Zone of Erbendorf Vohenstrauss (ZEV) and the KTB boreholes located in the northeastern ZEV and leucocratic gneisses from the Erbendorf Greenschist zone (EGZ). The investigations were carried out to contribute to the knowledge of the tectonothermal evolution of the area and to the response of the isotope systems to retrograde processes including recent elevated in- situ temperatures in the boreholes. A memory of an early Ordovician igneous event is given by Rb–Sr ages of 480±5–475±5 Ma obtained on very coarse-grained relic igneous muscovites of metapegmatites from the ZEV. This memory is missing in micas from peg matoids of the drill site. Coarse-grained muscovites of gneisses from ZEV and EGZ surface outcrops and of gneisses and pegmatoids from the boreholes yielded maximum K–Ar ages of 377±3–371±3 Ma related to the end of the Devonian regional metamorphism in both units. Consistent K–Ar and Rb–Sr apparent ages of some muscovites from surface outcrops point to a fast cooling of the metamorphic rocks due to rapid tectonic uplift. The lack of a depth-related gradient in model ages of coarse-grained KTB muscovites is explained by post-Variscan stacking processes. For minerals from intermediate to greater depths of the KTB, a strong age dependence on grain size and disturbances of the isotope systems due to various late- to post-Variscan retrograde processes can be demonstrated. A strong decrease in K–Ar model ages with increasing depth as obtained for biotites from the deepest section of the HB borehole probably indicates time-integrated response of the isotope system to elevated in situ temperatures.
    Type of Medium: Electronic Resource
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