L'evolution geodynamique devono-carbonifere de l'extremite occidentale de la chaine hercynienne d'Europe sur le transect Armorique-Cornwall

Rolet, J.; Gall, Bernard Le; Darboux, Jean-René; Thonon, Pierre; Gravelle, M.

doi:10.2113/gssgfbull.ii.1.43

Cited by 35 publications

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“…This result indicates that the micaschists likely correspond to Visean sedimentary units deposited in a basin formed during the Variscan collision and prograde metamorphism of the Léon units (Caroff et al, ; Schulz, ; Figure c and Table ). Visean sedimentary basins with a similar magmatic relation are known at the periphery of the Léon dome, for example, in the Central Armorican Domain (Chateaulin, Morlaix, Laval, Ancenis, and Saint‐Julien‐de‐Vouvantes in Figure b; Darboux & Le Gall, ; Gumiaux et al, ; Le Hérissé & Plaine, ; Le Gall et al, ; Rolet et al, ). Various models have been proposed for the initiation and development of these Visean basins, either in a pull‐apart context (Pelhate, ; Rolet, ) or in response to bending along transpressive faults (Gumiaux et al, ).…”

Section: Geodynamic Settingmentioning

confidence: 87%

“…The dome shows roughly concentric foliation map patterns in its gneissic‐migmatitic core (Paquette et al, ). The dome is cored by low‐grade (Upper unit) to high‐grade (Lower unit) metamorphic rocks intruded by 335‐ to 270‐Ma granitoids and surrounded to the south and east by low‐to‐moderate grade Paleozoic sedimentary series of the Central Armorican domain (Faure et al, ; Le Corre et al, ; Marcoux et al, ; Rolet et al, , ; Figures b and c and Table ). The two metamorphic units are not separated by any major tectonic contact or metamorphic discontinuity (Le Gall et al, ; Schulz et al, ).…”

Section: Geodynamic Settingmentioning

confidence: 99%

“…Prograde metamorphism is associated with top‐to‐the‐NE transpressional sinistral ductile shearing (Balé & Brun, ; Faure et al, ; Le Gall et al, ; Rolet et al, ). Rolet et al (, 1994) proposed that this shearing underthrusts the Léon units relatively toward the southwest beneath the Central Armorican domain during the Variscan collision. Eclogitic rocks of Plounévez Lochrist located at core of the dome were dated by U/Pb on zircon (Paquette et al, ) and gave an age of 439 ± 12 Ma (Figure c and Table ).…”

Section: Geodynamic Settingmentioning

confidence: 99%

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Wrench‐Related Dome Formation and Subsequent Orogenic Syntax Bending in a Hot Orogen (Variscan Ibero‐Armorican Arc, the Ouessant Island, France)

et al. 2019

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During the Carboniferous collision stage, the West European Variscan orogen was affected by oblique convergence, wrenching, plate-scale oroclinal bending, and widespread exhumation of the deep crust. One of these exhumed units forms the Léon dome located on the northern flank of the Ibero-Armorican Arc in the western part of the Armorican massif. Structural field data from the Ouessant Island reveal kinematic changes between 330 and 300 Ma that affected the northwestern margin of the Léon dome. This margin underwent two ductile deformation phases with opposite strike-slip shear senses. Dextral strike-slip wrenching combined with orogen-normal shortening, orogen-parallel stretching, and local top-to-the-NE shearing occurred during the Léon dome formation and exhumation of its gneissic core at 330-310 Ma. During tightening of the Ibero-Armorican Arc at~300 Ma, more localized sinistral wrenching reactivated the northwestern boundary of the Léon dome. The resulting N70°E trending sinistral Porspoder-Ouessant shear zone together with its conjugate dextral South Armorican shear zone controlled the lateral escape of the Léon-North-Central Armorican rigid tectonic wedge triggered by indentation of the Cantabrian orocline at the core of the Ibero-Armorican Arc.

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Section: Geodynamic Settingmentioning

confidence: 87%

Section: Geodynamic Settingmentioning

confidence: 99%

Section: Geodynamic Settingmentioning

confidence: 99%

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Wrench‐Related Dome Formation and Subsequent Orogenic Syntax Bending in a Hot Orogen (Variscan Ibero‐Armorican Arc, the Ouessant Island, France)

et al. 2019

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“…5d). They have a NS direction, consistent with a submeridian compression (Rolet et al, 1986). Their emplacement predates the end of crystallization of their monzo-/syenogranitic host-rocks, as evidenced by the presence of mingling structures along the contact.…”

mentioning

confidence: 78%

Petrogenesis of late-Variscan high-K alkali-calcic granitoids and calc-alkalic lamprophyres: The Aber-Ildut/North-Ouessant complex, Armorican Massif, France

Caroff

Gall

Authémayou

et al. 2015

Lithos

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The Aber-Ildut/North-Ouessant Variscan granitoid complex in the Armorican Massif is an example of high-K alkali-calcic zoned pluton, c. 304 Ma in age. A first magmatic batch intruded through a northern EW-trending sinistral transcurrent shear zone, before injecting southwards as a huge horizontal zoned sill, with moderately peraluminous muscovite-free granitoids in the north and strongly peraluminous muscovite-bearing leucogranites to the south. The second magmatic stage resulted in the intrusion of a large two-mica leucogranitic body from a root zone along the same shear zone, prior to the end of crystallization of the first injection. Finally, ultrapotassic dykes, including calc-alkalic lamprophyres (leucominettes), intrude the complex. The strongly peraluminous granites are interpreted as pure melting products of crustal clay-rich pelitic material. All the other petrographic types, including leucominettes, are thought to result from mixing of crustal melts and mantle-derived mafic liquids. Highly silicic tourmaline-bearing leucogranites are significantly affected by a tetrad effect, in relation with REE complexing behavior. Aber-Ildut/North-Ouessant granitoids probably formed during the Variscan late-orogenic stage associated with exhumation and lithospheric thinning, at low pressure and by advective heating of a ≤ 50 km-thick crust from hot metasomatized asthenosphere.

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“…In the studied area, this formation is overlain by the Cosquer Formation, dated as Hirnantian (Bourahrouh, 2002), and interpreted as glacio-marine deposits (Hamoumi et al, 5 1981). The Postolonnec, Kermeur and Cosquer formations were deposited under stable platform conditions and were affected by weak deformation (Rolet et al, 1986;Darboux, 1991) and low-grade metamorphism (Paradis, 1981) during the Late Devonian-Early…”

Section: Geological Contextmentioning

confidence: 99%

A Palaeozoic open shelf benthic assemblage in a protected marine environment

Vidal¹,

Loi²,

Dabard³

et al. 2011

Palaeogeography, Palaeoclimatology, Palaeoecology

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A Late Ordovician benthic assemblage containing trilobites (Colpocoryphe, Onnia) and diploporid echinoderms (Aristocystites) taxa that are usually typical of open shelf environments is preserved in protected marine settings in the lower part of the Kermeur Formation (Armorican Massif, NW France). A fades analysis carried out on the Veryac'h section (Crozon Peninsula) allows identification of four sedimentary fades (SF), ranging from the bay/lagoon domain (SF1 and SF2) to the back-barrier (SF3) and barrier (SF4) domains. A benthic fauna comprising of trilobites, brachiopods and diploporids is found in the SF1 and SF2. In SF1, fossils are randomly scattered in sediments (taphofacies 1, TF1) showing two different preservation stages: TF1a with complete articulated skeletons and TF1b with disarticulated shells. These two preservation stages can be related either to the different modes of life of the taxa (i.e., recumbent, burrowing or nektobenthic) or to a composite assemblage with both autochthonous and allochthonous taxa. In this benthic assemblage, some trilobites and echinoderms taxa are mostly preserved either as complete exoskeletons and exuviae (Colpocoryphe grandis) or complete thecae (Aristocystites sp.), indicating an autochthonous origin. These taxa are usually found in low-energy open shelf settings. Their occurrence in a protected environment results from the combination of both allocyclic factors (i.e., change in sea level) and local conditions (i.e., shelf morphology, environmental conditions). Indeed, the lower part of the Kermeur Formation was deposited during a transgressive phase following a significant sea-level fall (Sandbian-Katian boundary). During the transgressive phase, barrier-lagoon systems were formed on the flat surface inherited from the sandbian shelf. Under non-restricted ecological conditions (i.e., normal oxygenation and salinity) in the protected settings, the new ecological niches were suitable for benthic organisms accustomed to open shelf environments. The settlement of these open shelf benthic species in coastal and protected environments may represent an offshore-onshore expansion, contrary to that described in the onshore-offshore diversification model of Phanerozoic shelf communities (Jablonski et al., 1983; Sepkoski, 1991). (C) 2011 Elsevier B.V. All rights reserved

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L'evolution geodynamique devono-carbonifere de l'extremite occidentale de la chaine hercynienne d'Europe sur le transect Armorique-Cornwall

Cited by 35 publications

References 0 publications

Wrench‐Related Dome Formation and Subsequent Orogenic Syntax Bending in a Hot Orogen (Variscan Ibero‐Armorican Arc, the Ouessant Island, France)

Wrench‐Related Dome Formation and Subsequent Orogenic Syntax Bending in a Hot Orogen (Variscan Ibero‐Armorican Arc, the Ouessant Island, France)

Petrogenesis of late-Variscan high-K alkali-calcic granitoids and calc-alkalic lamprophyres: The Aber-Ildut/North-Ouessant complex, Armorican Massif, France

A Palaeozoic open shelf benthic assemblage in a protected marine environment

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