Permo‐Silesian movements between Baltica and Western Europe: tectonics and ‘basin families’

The Plechý pluton, southwestern Bohemian Massif, represents a late-Variscan, complexly zoned intrusive center emplaced near the crustal-scale Pfahl shear zone; the pluton thus provides an opportunity to examine the interplay among successive emplacement of large magma batches, magmatic fabric acquisition, and the late-Variscan stress field associated with strike-slip shearing. The magmatic history of the pluton started with the emplacement of the porphyritic Plechý and Haidmühler granites. Based on gravity and structural data, we interpret that the Plechý and Haidmühler granites were emplaced as a deeply rooted, *NE-SW elongated body; its gross shape and internal fabric (steep *NE-SW magmatic foliation) may have been controlled by the late-Variscan stress field. The steep magmatic foliation changes into flat-lying foliation (particularly recorded by AMS) presumably as a result of divergent flow. Magnetic lineations correspond to a sub-horizontal *NE-SW finite stretch associated with the divergent flow. Subsequently, the Třístoličník granite, characterized by steep margin-parallel magmatic foliation, was emplaced as a crescent-shaped body in the central part of the pluton. The otherwise inward-younging intrusive sequence was completed by the emplacement of the outermost and the most evolved garnet-bearing granite (the Marginal granite) along the southeastern margin of the pluton.

Section: The Pfahl Shear Zonementioning

confidence: 99%

Magmatic history and geophysical signature of a post-collisional intrusive center emplaced near a crustal-scale shear zone: the Plechý granite pluton (Moldanubian batholith, Bohemian Massif)

Verner

Žák

Pertoldová

et al. 2007

“…1), a major shear zone within the southwestern part of the Bohemian Massif (Hofmann 1962;Brandmayr et al 1995;Mattern 2001). The Pfahl zone represents a tectonic zone of persistent crustal weakness and, as such, provides a window into processes that control crustal reactivation.…”

Section: Geological Settingmentioning

confidence: 99%

Geochronology and geochemistry of a dyke?host rock association and implications for the formation of the Bavarian Pfahl shear zone, Bohemian Massif

Siebel

Blaha

Chen

et al. 2004

To place constraints on the formation and deformation history of the major Variscan shear zone in the Bavarian Forest, Bavarian Pfahl zone, SW Bohemian Massif, granitic dykes and their feldspar-phyric massive host rock (so-called ''palite''), zircons were dated by the U-Pb isotope dilution and Pb-evaporation methods. The dated samples comprise two host rocks and four dykes from a K-rich calc-alkaline complex adjoining the SW part of the Bavarian Pfahl shear zone. The palites, which appear to be the oldest magmatic rocks emplaced in the shear zone, yield ages of 334±3, 334.5±1.1 Ma (average 207 Pb/ 206 Pb-evaporation zircon ages) and 327-342 Ma (range of U/Pb zircon ages) suggesting a Lower Carboniferous age for the initiation of the Pfahl zone. Absence of inherited older cores in all investigated zircons indicates that incorporation of crustal zircon material has played virtually no role or that the melting temperature was very high. Determination of the dyke emplacement age is complicated by partial Pb-loss in most of the fractions analysed. This Pb-loss can be ascribed to higher U content of the dyke zircons compared to those from host rock. Upper discordia intercept ages of the different dykes range from 322±5 to 331±9 Ma. The dykes are pre-to synkinematic with respect to penetrative regional mylonitisation along the Pfahl zone, and the upper intercept ages provide a maximum age for this tectonic event.

“…1a). Within the Bohemian Massif, a major intraplate system of NW-SE and NE-SW trending faults developed in response to reorganization of tectonic style and stress transfer between Western Europe and the East European platform (Mattern 2001). The Danube Fault together with its sister fault, the Bavarian Pfahl with its well-known quartz-lode (e.g.…”

Section: Geological Backgroundmentioning

confidence: 99%

“…Major shear zones in the Bohemian Massif have been initiated during late-Palaeozoic strike slip faulting of the Variscan basement (Mattern 1995(Mattern , 2001). The Danube Fault zone, which cuts granite, underwent ductile and brittle deformation followed by hydrous argillic alteration.…”

Section: Summary Of Fault Chronologymentioning

confidence: 99%

Age constraints on faulting and fault reactivation: a multi-chronological approach

Siebel¹,

Hann²,

Danišík

et al. 2009

Movement within the Earth's upper crust is commonly accommodated by faults or shear zones, ranging in scale from micro-displacements to regional tectonic lineaments. Since faults are active on different time scales and can be repeatedly reactivated, their displacement chronology is difficult to reconstruct. This study represents a multi-geochronological approach to unravel the evolution of an intracontinental fault zone locality along the Danube Fault, central Europe. At the investigated fault locality, ancient motion has produced a cataclastic deformation zone in which the cataclastic material was subjected to hydrothermal alteration and K-feldspar was almost completely replaced by illite and other phyllosilicates. Five different geochronological techniques (zircon Pb-evaporation, K-Ar and Rb-Sr illite, apatite fission track and fluorite (U-Th)/He) have been applied to explore the temporal fault activity. The upper time limit for initiation of faulting is constrained by the crystallization age of the primary rock type (known as ''Kristallgranit'') at 325 ± 7 Ma, whereas the K-Ar and Rb-Sr ages of two illite fractions \2 lm (266-255 Ma) are interpreted to date fluid infiltration events during the final stage of the cataclastic deformation period. During this time, the ''Kristallgranit'' was already at or near the Earth's surface as indicated by the sedimentary record and thermal modelling results of apatite fission track data. (U-Th)/He thermochronology of two single fluorite grains from a fluorite-quartz vein within the fault zone yield Cretaceous ages that clearly postdate their Late-Variscan mineralization age. We propose that later reactivation of the fault caused loss of helium in the fluorites. This assertion is supported by geological evidence, i.e. offsets of Jurassic and Cretaceous sediments along the fault and apatite fission track thermal modelling results are consistent with the prevalence of elevated temperatures (50-80°C) in the fault zone during the Cretaceous.