Fission-track dating of the western border of the Bohemian massif: thermochronology and tectonic implications

Abstract

Since 1985, apatite fission-track analysis was applied to more than 70 samples from surface outcrops and shallow boreholes at the western margin of the Bohemian massif. Apatite ages were determined by the grain-population method. Additional information from the frequency distributions of fully confined spontaneous tracks was used for modelling of t-T paths in the low-temperature range ((120°C). Seven zircon samples were dated by the external detector method. Zircon ages between 283 and 215 Ma indicate unroofing during the Permian molasse stage and the Triassic. Tectonic quiescence and slow subsidence prevailed from the Jurassic until the middle Cretaceous. In the basement area south of Weiden, a Mesozoic partial annealing zone (for apatite fission tracks) is now exposed at the surface. Farther north, the basement was affected by stronger Cretaceous and Palaeogene erosion, which yielded cooling ages between 110 and 49 Ma. This second period of post-Variscan denudation was correlated to reverse faulting along the Franconian Line.

Long-term landscape evolution of the northeastern margin of the Bohemian Massif: apatite fission-track data from the Erzgebirge (Germany)

“…Jurassic and Cretaceous AFT ages have also been reported in fission-track studies from the Ruhla Crystalline Complex (Thomson and Zeh 2000), the Harz Mountains and Thuringer Wald (Thomson 2001), the Fichtelgebirge (Hejl et al 1997), and along the Franconian Line (Wagner et al 1989;Bischoff et al 1993;Coyle et al 1997;Hejl et al 1997). The majority of these data shows Late Cretaceous AFT ages that have been interpreted in terms of Late Cretaceous denudation.…”

“…Similar to the igneous activity, the amount of denudation varies significantly along the graben, with <2-~4 km (referring to modeling results in Hejl et al 1997) in its western segment and 2.5-5.6 km in the Erzgebirge.…”

“…Recent apatite fission-track (AFT) studies reveal that large portions of the European Variscides such as the Brabant Massif (Vercoutere and Van den haute 1993), the Caledonian backbone of Britain (Carter et al 1995), or the Massif Central (e.g., Barbarand et al 2001), were partly or entirely covered by Cretaceous transgressive sediments, and later exhumed. Considerable amounts of post-Cretaceous denudation were also reported from the western margin of the Bohemian Massif (Wagner et al 1989;Bischoff et al 1993;Coyle et al 1997;Hejl et al 1997; Thomson and Zeh 2000;Thomson 2001).…”

“…Thus, exhumation may be explained by initial thermal uplift with associated extensional faulting and the development of rapidly eroding fault topography with high local relief. Denudation and uplift of the graben shoulders are also manifest in a clear trend of AFT ages from the Fichtelgebirge that systematically decrease from >100 to 50-60 Ma towards the Eger Graben (Hejl et al 1997). The rather low amount of denudation is probably related to the relatively thick lithosphere of 90-100 km (e.g., Suk et al 1984;Malkovsky 1987;Babuska et al 1987) that limits isostatic and flexural response of the crust.…”

The KTB apatite fission-track profiles: Building on a firm foundation?

“…The pilot hole is 4000 m deep, of which 3276 m were cored. The main hole reaches 9101 m. The KTB has long been a test site for low-temperature geothermochronometers, e.g., Wagner et al (1997), Hejl et al (1997), Coyle et al (1997), Warnock and Zeitler (1998), Stockli and Farley (2004) and Stockli (2008, 2010).…”