Synorogenic sedimentation in the Variscan Belt of Europe

Franke, Wolfgang; Engel, Wolfgang

doi:10.2113/gssgfbull.ii.1.25

Cited by 75 publications

(15 citation statements)

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“…A similar situation, with detritals and olistoliths derived from nearby, contemporaneous thrust sheets, has been described in the Montagne Noire (Engel, Feist & Franke, 1982). But other, more external Variscan syn-orogenic deposits contain an important component of recycled passive margin components of the relative autochthon, as for instance, the Rhenish Massif (Engel, Flehmig & Franke, 1983; Franke & Engel, 1986).…”

Section: Age Summary and Geological Interpretationmentioning

confidence: 99%

Relationships between syn-orogenic sedimentation and nappe emplacement in the hinterland of the Variscan belt in NW Iberia deduced from detrital zircons

et al. 2015

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Flysch-type, syn-orogenic deposits of Carboniferous age occur in relation to the emplacement of a large allochthonous nappe stack in the Variscan belt of NW Iberia. New U-Pb age populations of detrital zircons obtained using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) are considered together with others from previously dated samples to establish the relationships between sedimentation and thrusting. The age populations of four syn-orogenic formations are compared with those of the pre-orogenic sequence in the Autochthon and Parautochthon, representing the Gondwanan passive margin, and in the Allochthon, formed by peri-Gondwanan and oceanic terranes. In addition, a new structural study has been carried out to understand the relationships between the syn-orogenic deposits and the development of Variscan structures. The aims are to identify the sources of sediments and to establish the relationship between Variscan structural evolution and syn-orogenic sedimentation. Development of a forebulge outwards from the allochthonous front, deduced from the structural study, suggests the existence of depocentres that hosted the syn-orogenic sediments. Together with the trend shown by the more recent zircons in each formation, that are younger towards the external zones, the data suggest that sedimentation occurred in progressively migrating depocentres formed in front of the allochthonous wedge during its emplacement. The zircon age populations point to the Allochthon as the main source of detritus for the syn-orogenic basins, with perhaps a limited participation of the Parautochthon and Autochthon in the younger formations.

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Section: Age Summary and Geological Interpretationmentioning

confidence: 99%

Relationships between syn-orogenic sedimentation and nappe emplacement in the hinterland of the Variscan belt in NW Iberia deduced from detrital zircons

et al. 2015

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“…Pioneer work correlating data from the eastern (Bohemia) and western (Iberia) terminations of the belt led to (i) the definition of the main geological-tectonic zones, (ii) the identification of the principal Paleozoic tectonic events based on the relationship between structures and Ediacaran to Carboniferous sedimentary deposits in the external zone and along the foreland, and (iii) the recognition of high-grade nappes in the internal zone (Stille, 1924;Kossmat, 1927;Gaertner, 1937;Demay, 1948;Gèze, 1949). The relationship between sedimentation and deformation, best exposed along its external domains, allowed the identification of continental blocks such as Avalonia, Armorica, Saxo-Thuringia, Barrandia and Brunia, all of which preserve Cambrian unconformities more or less affected by Variscan deformation and metamorphism (Matte, 1986(Matte, , 1991Franke and Engel, 1986;Franke, 1989Franke, , 2000Kroner and Romer, 2013). These continental blocks are separated by oceanic sutures marked by ophiolitic assemblages or mélanges.…”

Section: Introductionmentioning

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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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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“…Location of the suture and deformation fronts in the northern part of Norway is after Asher et al (2001) and Mosar (2003), respectively, and the Variscan deformation front in northern Africa is from Frizon de Lamotte et al (2011). The location of the Variscan foreland basin is after Franke and Engel (1988) and Ziegler (1988); the Caledonian foreland is mapped after Larson et al (1999). Palaeozoic magmatic arcs are mapped after Edel et al (2013) and Roberts (2003).…”

Section: Mapping Methodsmentioning

confidence: 99%

Assessing the impact of orogenic inheritance on the architecture, timing and magmatic budget of the North Atlantic rift system: a mapping approach

Chenin

Manatschal

Lavier³

et al. 2015

JGS

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To investigate the impact of orogenic inheritance on the characteristics of the North Atlantic rift system we develop new mapping methods that highlight the first-order architecture and timing of rifts, as well as the distribution of heterogeneities inherited from the Palaeozoic Caledonian and Variscan orogenies. These maps demonstrates major differences in the behaviour of the North Atlantic rift system relative to both orogens, with the Variscan front appearing to be an important boundary. Indeed, the rift cuts through the Caledonian orogen and parallels its structural grain to the north, while it circumvents the core of the Variscides to the south. In addition, rifting is protracted and polyphase with breakup being magma-rich north of the Variscan front, as opposed to the south where a single, apparently continuous extensional event led to magma-poor breakup in less than 50 Myr. Besides, the North Atlantic rift system reactivates sutures corresponding to large (> 2,000 km) former oceans, while sutures of small (< 500-1,000 km) oceanic basins are little affected in both the northern and southern North Atlantic. These observations point to a major influence of orogenic inheritance on the characteristics of rift systems.

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Synorogenic sedimentation in the Variscan Belt of Europe

Cited by 75 publications

References 0 publications

Relationships between syn-orogenic sedimentation and nappe emplacement in the hinterland of the Variscan belt in NW Iberia deduced from detrital zircons

Relationships between syn-orogenic sedimentation and nappe emplacement in the hinterland of the Variscan belt in NW Iberia deduced from detrital zircons

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

Assessing the impact of orogenic inheritance on the architecture, timing and magmatic budget of the North Atlantic rift system: a mapping approach

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