Variscan potassic dyke magmatism of durbachitic affinity at the southern end of the Bohemian Massif (Lower Austria)

Zeitlhofer, Helga; Grasemann, Bernhard; Petrakakis, Konstantin

doi:10.1007/s00531-015-1238-3

Cited by 9 publications

(4 citation statements)

References 37 publications

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“…In the southern region, dykes of kersantites and spessartites intruded the South Bohemian Batholith. They are dated from 334 to 318 Ma by Rb-Sr method (Neubauer et al 2003;Zeitlhofer et al 2016). Representative chemical analyses are given by Krmíček et al (2014) and by Zeitlhofer et al (2016).…”

Section: Bohemian Massifmentioning

confidence: 99%

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Variscan lamprophyres of the South Armorican Domain and comparison with lamprophyres of the Western European Variscan belt

2022

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Late to post-orogenic lamprophyres of the European Variscides attest variable compositions of the mantle beneath the structural zones of the belt. These compositions resulted from different contributions of mantle components involving geotectonic processes during the orogeny, such as oceanic subduction of mafic crust and sediments, continental subduction, collision with mantle input, and delamination of overriding plates. For documenting these processes, we have surveyed three sites of lamprophyre intrusions in the Vendean part of the South Armorican tectonic Zone with spessartite sills and minette dykes, and a fourth site in the West-Armorican kersantite swarm. The age of spessartite is estimated between 320 and 315 Ma on the base of structural relationships with the dated neighbouring granite. Dykes of minette share similar intrusive setting along the post-orogenic NW-SE dextral shear zones. One dyke is dated at 286.2 +/-6.6 Ma (Early Permian) by K/Ar method. The Western Brittany kersantite swarm is Middle to Late Carboniferous in age. All these rocks display common mineral and chemical compositions of lamprophyres. A review of the Variscan European lamprophyres is conducted in order to document their geochemical fingerprints compared with those of the studied samples.

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Section: Bohemian Massifmentioning

confidence: 99%

“…They are dated from 334 to 318 Ma by Rb-Sr method (Neubauer et al 2003;Zeitlhofer et al 2016). Representative chemical analyses are given by Krmíček et al (2014) and by Zeitlhofer et al (2016).…”

Section: Bohemian Massifmentioning

confidence: 99%

Variscan lamprophyres of the South Armorican Domain and comparison with lamprophyres of the Western European Variscan belt

2022

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“…The first generation is "weakly-metamorphosed", trends westnorthwest-eastsoutheast and yields 40 Ar/ 39 Ar biotite plateau ages around 323 Ma, whereas a second unmetamorphosed group is northnortheast-southsouthwest-trending and yields 40 Ar/ 39 Ar plateau ages of 315-306 Ma (Neubauer et al, 2003). Additionally, Rb-Sr biotite cooling ages yielding c. 322-311 Ma on "partly-deformed" lamprophyric and porphyric dikes are described in the Strudengau area (Zeitlhofer et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

Polyphase deformation along the South Bohemian Batholith-Moldanubian nappes boundary – The Freyenstein Fault System (Bohemian Massif/Austria)

Griesmeier

Iglseder

Schuster

et al. 2020

Austrian Journal of Earth Sciences

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This work describes the Freyenstein Fault System, which extends over 45 km in the southeastern part of the Bohemian Massif (Lower Austria). It represents a ductile shear zone overprinted by a brittle fault located at the eastern edge of the South Bohemian Batholith towards the Moldanubian nappes. It affects Weinsberg- and a more “fine-grained” granite, interlayered aplitic granite and pegmatite dikes as well as paragneiss of the Ostrong Nappe System. The ductile shear zone is represented by approximately 500 m thick greenschist-facies mylonite dipping about 60° to the southeast. Shear-sense criteria like clast geometries, SCC`-type shear band fabrics as well as abundant microstructures show top to the south/ southsouthwest normal shearing with a dextral strike-slip component. Mineral assemblages in mylonitized granitoid consist of pre- to syntectonic muscovite- and biotite-porphyroclasts as well as dynamically recrystallized potassium feldspar, plagioclase and quartz. Dynamic recrystallization of potassium feldspar and the stability of biotite indicate upper green-schist-facies metamorphic conditions during the early phase of deformation. Fluid infiltration at lower greenschist-facies conditions led to local sericitization of feldspar and synmylonitic chloritisation of biotite during a later stage of ductile deformation. Finally, a brittle overprint by a north-south trending, subvertical, sinistral strike-slip fault that shows a normal component is observed. Ductile normal shearing along the Freyenstein Shear Zone is interpreted to have occurred between 320 Ma and c. 300 Ma. This time interval is indicated by literature data on the emplacement of the hostrock and cooling below c. 300°C inferred from two Rb-Sr biotite ages measured on undeformed granites close to the shear zone yielding 309.6 ± 3 Ma and 290.9 ± 2.9 Ma, respectively. Brittle sinistral strike-slip faulting at less than 300°C presumably took place not earlier than 300 Ma. Early ductile shearing along the Freyenstein Fault System may be genetically, but not kinematically linked to the Strudengau Shear Zone, as both acted in an extensional regime during late Variscan orogenic collapse. A relation to other major northeast-southwest trending faults of this part of the Bohemian Massif (e.g. the Vitis-Pribyslav Fault System) is indicated for the phase of brittle sinistral movement.

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“…1) i.e. the French Massif Central (Sabatier, 1980;Montel and Weisbrod, 1986;Michon, 1987;Barbey et al, 2015;Solgadi et al, 2007;Couzinié et al, 2014;Laurent et al, 2017), the Armorican and Cornwall massifs (Exley et al, 1983;Le Gall et al, 1989;Dupuis et al, 2015), the Vosges-Black Forest-Saxothuringian massifs (Gagny, 1978;André, 1981;Hegner et al, 1998;von Seckendorff et al, 2004b;Tabaud et al, 2014;Tabaud et al, 2015;Soder and Romer, 2018), the Bohemian massif (Holub, 1997;Gerdes et al, 2000;Seifert, 2008;Zeitlhofer et al, 2016;Kubínová et al, 2017), the External Crystalline massifs of the Western Alps and Corsica (Banzet, 1987;Bussy et al, 1998;Bonin et al, 1998;Debon et al, 1998;Rossi et al, 2009) and some Variscan massifs from Spain (Scarrow et al, 2008(Scarrow et al, , 2011.…”

Section: Introductionmentioning

confidence: 99%

Zircon age of vaugnerite intrusives from the Central and Southern Vosges crystalline massif (E France): contribution to the geodynamics of the European Variscan belt

Guillot

Averbuch

Dubois

et al. 2020

BSGF - Earth Sci. Bull.

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To provide a better definition of the geodynamical processes active at the Variscan suture zones during the late collisional stage (particularly regarding the evolution of the orogenic system towards HT conditions), we focused here on specific mafic Mg-K magmatic rocks (the vaugnerites), intrusive into the granite-gneiss sequences of the Variscan Vosges crystalline massif. Those rocks, though subordinate in volume, are frequently associated with late collisional granites. In the Central-Southern Vosges, they appear either as (1) pluton margin of the Southern Vosges Ballons granite complex or (2) composite dykes intrusive into migmatite and metamorphic sequences classically referred to as granite-gneiss unit (Central Vosges). Both types correspond to melanocratic rocks with prominent, Mg-rich, biotite and hornblende (20- 40 % vol., 64 < mg# < 78), two-feldspar and quartz. Those Vosges vaugnerites display geochemical signatures characteristic of mafic to intermediate, metaluminous to slightly peraluminous rocks of calc-alkaline affinity. Zircon U-Pb ages were obtained by Laser Ablation Inductively Coupled Plasma Mass Spectrometry. Zircons were extracted from a sillimanite-bearing gneiss from the granite-gneiss unit hosting the Central Vosges vaugnerites. They yielded an age at 451 ± 9 Ma, indicating a pre- Variscan Upper Ordovician protolith for the host sequence. Zircon from the four vaugnerite intrusives display U-Pb ages (± 2s) of 340 ± 2.5 Ma (Ballons), 340 ± 25 Ma, 340 ± 7 Ma and 336 ± 10 Ma (Central Vosges). Synchronous within uncertainty, vaugnerite age data thus give consistent results suggesting a relatively early emplacement of the vaugnerites regarding the Late Variscan collisional history, i.e. during Middle Visean times. These results are in line with previously published ages within the Southern Vosges volcano-sedimentary sequences (Oderen- Markstein) and the nearby Mg-K granite complexes from the Central and Southern Vosges (Ballons, Crêtes) thereby arguing for a Mg-K magmatic event of regional significance. Recent petrological studies on vaugnerites suggest that they derive from partial melting of a metasomatized mantle contaminated to some different degrees by elements of continental crust. We propose here the major Mg-K magmatic pulse at 340-335 Ma to be the marker of a significant evolution into the dynamics of the Rhenohercynian subduction system below the Central-Southern Vosges. In the light of recent thermo-mechanical modelling experiments on mature continental collision, it could traduce the first effects of a syn-collisional lithospheric delamination mechanism involving (1) first, continental subduction evolving towards (2) the underthrusting of the Avalonian continental margin lower crust and (3) the initiation of lithospheric delamination within the supra-subduction retro-wedge (Saxothuringian- Moldanubian continental block). This process would drive the emplacement of an asthenospheric upwelling, initially localized along the Variscan suture zones, and gradually propagating towards the southern front of the belt during the Late Carboniferous, as the delamination front migrated at the base of the crust.

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Variscan potassic dyke magmatism of durbachitic affinity at the southern end of the Bohemian Massif (Lower Austria)

Cited by 9 publications

References 37 publications

Variscan lamprophyres of the South Armorican Domain and comparison with lamprophyres of the Western European Variscan belt

Variscan lamprophyres of the South Armorican Domain and comparison with lamprophyres of the Western European Variscan belt

Polyphase deformation along the South Bohemian Batholith-Moldanubian nappes boundary – The Freyenstein Fault System (Bohemian Massif/Austria)

Zircon age of vaugnerite intrusives from the Central and Southern Vosges crystalline massif (E France): contribution to the geodynamics of the European Variscan belt

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