Ductile deformation and rheology of sub-continental mantle in a hot collisional orogeny: Example from the Bohemian Massif

Kusbach, Vladimír; Ulrich, Stanislav; Schulmann, Karel

doi:10.1016/j.jog.2011.06.004

Cited by 15 publications

(4 citation statements)

References 107 publications

(168 reference statements)

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“…In the Vosges, garnetlherzolite belonging to a subcontinental lithospheric mantle exhumed from more than 150 km are present in the varied gneiss unit dominated by granulite facies migmatitic gneiss (Altherr and Kalt, 1996;Brueckner and Medaris, 2000;O'Brien and Rötzler, 2003). The Bohemian massif also comprises large mafic and ultramafic bodies enclosed in high-grade gneisses (Kusbach et al, 2012). In the French Massif Central, ages interpreted to record eclogite facies peak metamorphism are typically 20 to 30 Ma older to the ones attributed to granulite facies metamorphism and partial melting of their host migmatitic paragneisses and orthogneisses (Duthou et al, 1981(Duthou et al, , 1994Pin and Lancelot, 1982;Chelle-Michou et al, 2017).…”

Section: Late Silurian To Devonian Subduction and Hp Partial Melting mentioning

confidence: 99%

“…Tectonic-geodynamic models attributing the succession of eclogite and granulite facies metamorphism to oceanic subduction followed by continental collision (Matte, 1986;Girardeau et al, 1986;Dubuisson et al, 1989;Ledru et al, 1989;Lardeaux et al, 2001) provide an explanation for the HP metamorphic condition but do not account for the systematic incorporation of the LAC into the migmatitic UGU. Models invoking a vertical extrusion of the mantle into the partially molten granulitic lower crust account for the presence of mafic and ultramafic rocks into the migmatitic continental rocks but do not propose a driving force for such a process (Kusbach et al, 2012). A more appealing proposition is that pieces of suprasubduction mantle might be incorporated into the orogenic belt during relamination of orogenic crust by flow of partially molten crustal units decoupled from the downgoing slab (Lexa et al, 2011;Kusbach et al, 2015).…”

Section: Late Silurian To Devonian Subduction and Hp Partial Melting mentioning

confidence: 99%

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Flow of partially molten crust controlling construction, growth and collapse of the Variscan orogenic belt: the geologic record of the French Massif Central

Vanderhaeghe

Laurent

Gardien

et al. 2020

BSGF - Earth Sci. Bull.

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We present here a tectonic-geodynamic model for the generation and flow of partially molten rocks and magmatism during the Variscan orogenic evolution from the Silurian to the late Carboniferous based on a synthesis of geological data from the French Massif Central. Eclogite facies metamorphism of mafic and ultramafic rocks records the subduction of the Gondwana hyperextended margin. Part of these eclogites are forming boudins-enclaves in felsic HP granulite facies migmatites partly retrogressed into amphibolite facies attesting for continental subduction followed by thermal relaxation and decompression. We propose that HP partial melting has triggered mechanical decoupling of the partially molten continental rocks from the subducting slab. This would have allowed buoyancy-driven exhumation and entrainment of pieces of oceanic lithosphere and subcontinental mantle. Geochronological data of the eclogite-bearing HP migmatites points to diachronous emplacement of distinct nappes from middle to late Devonian. These nappes were thrusted onto metapelites and orthogneisses affected by MP/MT greenschist to amphibolite facies metamorphism reaching partial melting attributed to the late Devonian to early Carboniferous thickening of the crust. The emplacement of laccoliths rooted into strike-slip transcurrent shear zones capped by low-angle detachments from c. 345 to c. 310 Ma is concomitant with the southward propagation of the Variscan deformation front marked by deposition of clastic sediments in foreland basins. These features reflect the horizontal growth of the Variscan belt and the formation of an orogenic plateau by gravity-driven lateral flow of the partially molten orogenic root. The diversity of the magmatic rocks points to various crustal sources with modest, but systematic mantle-derived input. In the eastern French Massif Central, the southward decrease in age of the mantle- and crustal-derived plutonic rocks from c. 345 Ma to c. 310 Ma suggests southward retreat of a northward subducting slab toward the Paleothethys free boundary. Late Carboniferous destruction of the Variscan belt is dominantly achieved by gravitational collapse accommodated by the activation of low-angle detachments and the exhumation-crystallization of the partially molten orogenic root forming crustal-scale LP migmatite domes from c. 305 Ma to c. 295 Ma, coeval with orogen-parallel flow in the external zone. Laccoliths emplaced along low-angle detachments and intrusive dykes with sharp contacts correspond to the segregation of the last melt fraction leaving behind a thick accumulation of refractory LP felsic and mafic granulites in the lower crust. This model points to the primordial role of partial melting and magmatism in the tectonic-geodynamic evolution of the Variscan orogenic belt. In particular, partial melting and magma transfer (i) triggers mechanical decoupling of subducted units from the downgoing slab and their syn-orogenic exhumation; (ii) the development of an orogenic plateau by lateral flow of the low-viscosity partially molten crust; and, (iii) the formation of metamorphic core complexes and domes that correspond to post-orogenic exhumation during gravitational collapse. All these processes contribute to differentiation and stabilisation of the orogenic crust.

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Section: Late Silurian To Devonian Subduction and Hp Partial Melting mentioning

confidence: 99%

Section: Late Silurian To Devonian Subduction and Hp Partial Melting mentioning

confidence: 99%

Flow of partially molten crust controlling construction, growth and collapse of the Variscan orogenic belt: the geologic record of the French Massif Central

Vanderhaeghe

Laurent

Gardien

et al. 2020

BSGF - Earth Sci. Bull.

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“…1;Medaris et al , 2005. The Mohelno type is located in high-pressure felsic granulite, with which it has concordant contacts, and consists predominantly of spinel peridotite, with garnet peridotite occurring only within a few meters of contacts with the surrounding granulite (Kusbach et al 2012). Centimeter-scale spinel pyroxenite layers and lenses occur in spinel peridotite, but neither garnet pyroxenite nor eclogite have been found so far in the Mohelno type of peridotite.…”

Section: Geological Settingmentioning

confidence: 99%

Garnet pyroxenite in the Biskupice peridotite, Bohemian Massif: anatomy of a Variscan high-pressure cumulate

Medaris

Jelínek²,

Beard³

et al. 2013

J. Geosci.

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A strongly layered garnet pyroxenite, consisting of cm-scale layers of garnetite, garnet orthopyroxenite, garnet clinopyroxenite, and websterite, occurs in the Biskupice garnet peridotite, which is located in migmatitic gneiss of the Gföhl Assemblage in the Vysočina District, western Moravia. Major-and trace-element compositions and REE patterns of minerals and layers in the pyroxenite are consistent with origin of the layers by HT-HP crystallization and accumulation of variable proportions of garnet, orthopyroxene, and clinopyroxene. The present compositions of the minerals (pyroperich garnet, low-Al, low-Ca enstatite and low-Al, high-Ca diopside) are the result of extensive subsolidus re-equilibration at ~900 ºC and ~37 kbar, during the Variscan (332 Ma) Orogeny. Neodymium and strontium isotopic values (ε

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“…They left apart the mantlecrust interaction and modeled deformation of crustal layers with contrasting viscosities. The authors presented some reasons for such separate modeling based on a microstructural study of peridotites and granulites occurring in the region (Kusbach et al 2012(Kusbach et al , 2015 and the fact that no ultramafic compositions were found in the cores of the crustal antiforms (Franěk et al 2011a;Chopin et al 2012). The 2-D modeling involved a collision of two crustal blocks comprising three and two layers.…”

Section: Models Of the Moldanubian Crustmentioning

confidence: 99%

Felsic diapirism beneath the high-grade terrains in the eastern Bohemian Massif - refraction tomography evidence

Novotný¹

2018

J. Geosci.

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Unlike standard ray-based tomographies, the Depth-Recursive Tomography on Grid (DRTG) method assesses the travel-time fit at each model grid node using a regular network of refraction rays. This concept allows estimating the lateral resolution achieved in the velocity image that regards the chosen confidence levels and the strength of velocity anomalies. Recently, The DRTG has been applied to the S01 and CEL09 refraction profiles imaging major crustal structures of the Bohemian Massif in enhanced resolution. Now, similar enhanced velocity models are derived along the S04, S02 and S03 profiles mapping the Sudetic and Moldanubian regions. The S02 and S03 and the transverse CEL09 and S04 velocity sections particularly imaged the subsurface of the Moldanubian high-grade belts to the 15-20 km depth. Their common interpretation revealed the signatures of exhumation processes from upper-mantle depths assumed in this region. Particularly, the S02 and S03 sections map large volumes of high-grade metamorphic rocks forming low-velocity (LV) diapirs that are surrounded by 7000-6400 m/s high-velocity (HV) elevations. The S03 section images the coupled HV-LV-HV anomalies beneath the high-grade complexes of the Orlica-Śnieżnik Dome (OSD) and the Góry-Sowie Unit (GSU). The central gradient-free LV (5800-6000 m/s) cores of these triplets apparently correspond to the OSD or GSU felsic granulites/gneisses that ascended to supra-crustal levels. The Bouguer anomaly map suggests that the S02 and S03 profiles intersect the felsic sheets formed along the transverse Sudetic faults. Along the western belt of Moldanubian high-grade rocks, the S02 section revealed an extensive HV body shallowly emplaced beneath the high-grade Gföhl and Ostrong assemblages. Three mid-crustal HV elevations, correlating with local magnetic anomalies, obviously represent the deep sources of this HV mafic body and indicate its autochthonous nature. Finally, the DRTG also detected a shallowly emplaced HV layer beneath the Saxonian Granulite Massif at the S04 section. The mid-crustal HV-LV-HV diapiric triplets and shallowly emplaced HV bodies are likely typical of the high-grade terrains. The observed patterns resulted from contemporaneous intrusion of mafic and, more viscous, felsic magmas during continental collision. The inferred structural features of subduction-exhumation processes are suggested to further constrain their thermo-mechanic modeling.

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Ductile deformation and rheology of sub-continental mantle in a hot collisional orogeny: Example from the Bohemian Massif

Cited by 15 publications

References 107 publications

Flow of partially molten crust controlling construction, growth and collapse of the Variscan orogenic belt: the geologic record of the French Massif Central

Flow of partially molten crust controlling construction, growth and collapse of the Variscan orogenic belt: the geologic record of the French Massif Central

Garnet pyroxenite in the Biskupice peridotite, Bohemian Massif: anatomy of a Variscan high-pressure cumulate

Felsic diapirism beneath the high-grade terrains in the eastern Bohemian Massif - refraction tomography evidence

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