The Variscan French Massif Central—a new addition to the ultra-high pressure metamorphic ‘club’: exhumation processes and geodynamic consequences

Lardeaux, Jean‐Marc; Ledru, Patrick; Daniel, Isabelle; Duchêne, Stéphanie

doi:10.1016/s0040-1951(00)00253-5

Cited by 171 publications

(120 citation statements)

References 86 publications

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“…The slab breakoff is a traditional model, in which subducting continental slab becomes wholly exhumed due to breakoff at the transition to the oceanic slab that is pulling the continental deep subduction [32,33]. The model of continental subduction channel has been used to explain exhumation of HP and UHP metamorphic rocks [34][35][36]. In terms of the continental subduction channel model [7], the subducting continental lithosphere is detached at different depths as crustal slices into the subduction channel that are sequentially exhumed toward the surface (Figure 3(a)).…”

Section: Subduction Channel Processesmentioning

confidence: 99%

Continental subduction channel processes: Plate interface interaction during continental collision

2013

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The study of subduction-zone processes is a key to development of the plate tectonic theory. Plate interface interaction is a basic mechanism for the mass and energy exchange between Earth's surface and interior. By developing the subduction channel model into continental collision orogens, insights are provided into tectonic processes during continental subduction and its products. The continental crust, composed of felsic to mafic rocks, is detached at different depths from subducting continental lithosphere and then migrates into continental subduction channel. Part of the subcontinental lithospheric mantle wedge, composed of peridotite, is offscrapped from its bottom. The crustal and mantle fragments of different sizes are transported downwards and upwards inside subduction channels by the corner flow, resulting in varying extents of metamorphism, with heterogeneous deformation and local anatexis. All these metamorphic rocks can be viewed as tectonic melanges due to mechanical mixing of crust-and mantle-derived rocks in the subduction channels, resulting in different types of metamorphic rocks now exposed in the same orogens. The crust-mantle interaction in the continental subduction channel is realized by reaction of the overlying ancient subcontinental lithospheric mantle wedge peridotite with aqueous fluid and hydrous melt derived from partial melting of subducted continental basement granite and cover sediment. The nature of premetamorphic protoliths dictates the type of collisional orogens, the size of ultrahigh-pressure metamorphic terranes and the duration of ultrahigh-pressure metamorphism. In continental collision orogens, exposed ultrahigh-pressure (UHP) metamorphic terranes contain the lithotectonic records of Alpine-type subduction [1]. These records highlight metamorphic P-T conditions and mass transfers, indicating subduction of continental crustal rocks to mantle depths of over 100 km. The UHP terranes are characterized by minor occurrences of mafic eclogites and ultramafic peridotites that are hosted by felsic gneisses. Such UHP eclogite-facies parageneses are absent in Pacific-type subduction zones [2]. These UHP rocks are of crustal and mantle protoliths and now occur together with their lower pressure counterparts in continental collision orogens [3]. It is intriguing how the continental crust is subducted to mantle depths for UHP metamorphism, how UHP slices are exhumed from mantle depths to crustal levels, and how metamorphic rocks of different P-T conditions occur together in the same orogens. The property of plate interface in subduction zones is a key to physical and chemical interactions at interplate boundaries. Physical and chemical transfers at convergent plate margins can occur on various spatial and temporal scales, which is fundamental to subduction-zone processes. Like the plate tectonic theory, the concept of subduction channel was originally developed from the tectonics of oceanic subduction zone [4][5][6]. It was primarily focused on the plate interface interaction in ocean...

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Section: Subduction Channel Processesmentioning

confidence: 99%

Continental subduction channel processes: Plate interface interaction during continental collision

2013

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“…1; Gil Obrien and Vrana, 1995;Lardeaux et al, 2001;Massone, 2001;Arenas and Martínez Catalán, 2002). This type of units contains important information about the tectonothermal evolution of the Variscan or eo-Variscan accretionary complex, mainly because of the extreme metamorphic conditions attained and the superposition of deformational events that they register.…”

Section: Introductionmentioning

confidence: 99%

“…STA: Silesian Terrane Assemblage. High-P and ultra-high-P units involved in the Variscan suture (red stars): 1) High-P and high-T unit of the Sobrado Antiform, Órdenes Complex ; 2) Eclogite facies gneisses and related high-P and high-T rocks of the Cabo Ortegal Complex; 3) Coesite-bearing eclogite in the Monts du Lyonnais Unit, French Massif Central (Lardeaux et al, 2001); 4) High-P and high-T rocks in the Mariánské Lázně Complex, Bohemian Massif (Timmermann et al, 2004); 5) Eclogite facies gneisses bearing Cs + Dia in the Gneiss-Eclogite Unit, Saxonian Erzgebirge, Bohemian Massif (Massone, 2001;Massone, 2003;Massone et al, 2007); 6) High-P and high-T rocks in the Gory Sowie Block, Central Sudetes, Bohemian Massif (Kryza and Pin, 2002). Fig.…”

Section: Introductionmentioning

confidence: 99%

The eclogite facies gneisses of the Cabo Ortegal Complex (NW Iberian Massif): Tectonothermal evolution and exhumation model

Albert

Arenas

Martı́nez

et al. 2013

Journal of Iberian Geology

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The tectonothermal evolution of the eclogite facies gneisses of the Cabo Ortegal Complex has been investigated using new field and petrologic studies. This gneissic unit is included in the high-pressure and high-temperature (HP-HT) upper units of the allochthonous complexes of NW Iberia, a Cambrian arc-derived peri-Gondwanan terrane emplaced above ophiolitic units considered to represent the Rheic Ocean suture. Two detailed cross-sections performed in excellent exposures on the Cantabrian coast allows a clear understanding of the lithological constitution and deformations affecting the unit. The eclogitic gneiss unit is constituted by metasedimentary gneisses with abundant mafic inclusions, felsic rocks and rare ultramafic inclusions. The felsic rocks range from centimetric leucosomes to metric bodies and most of them were generated during extensive partial melting affecting the unit. The first tectonic fabric detected in the unit is a rarely preserved S1 foliation developed during subduction (ca. 400-390 Ma; 22 kbar). A drastic and fast exhumation (ca. 390 Ma; 12-10 kbar) generated a regional mylonitic foliation which represents the most prominent structural feature in the HP-HT upper units. The consecutive generation of extensional detachments, recumbent folds and a basal thrust occurred during the change from continental-type subduction to the underthrusting of ophiolitic units. These consecutive structures are probably related and the consequence of a long and pronounced exhumation of the subducted complex. The tectonothermal evolution of the eclogite facies gneisses of the Cabo Ortegal Complex represents an illustrative example of the intricate history of these deeply subducted units, which are relatively frequent in the suture zone of the Variscan Belt. It is important to remark that the structural, metamorphic and geochronological patterns in the evolution of this gneissic unit follows almost perfectly the ISSN (print): 1698-6180. ISSN (online): 1886-7995

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“…Schertl et al, 1991;Stöckhert et al, 1997;Reinecke, 1998;Groppo et al, 2007;Groppo and Castelli, 2010;Krebs et al, 2011;Angiboust et al, 2012), geochronological results pose narrow time windows for typical timescales of exhumation, asking for displacement rates comparable to plate velocity (e.g. Gebauer et al, 1997;Rubatto and Hermann, 2001;Baldwin et al, 2004;Little et al, 2011). Rapid exhumation with concomitant cooling reconciles neither with uplift and erosion nor with crustal extension (Platt, 1993;Ring and Brandon, 1999).…”

Section: W Friederich Et Al: Seismic Visibility Of a Deep Subductiomentioning

confidence: 99%

“…Moreover, geochronological results suggest that in some cases a large part of exhumation has taken place during ongoing subduction, prior to collision (e.g. Lardeaux et al, 2001;Rubatto et al, 2011). These observations have led to postulation of a deep subduction channel (DSC) with forced return flow as a possible mechanism for exhumation ( Fig.…”

Section: W Friederich Et Al: Seismic Visibility Of a Deep Subductiomentioning

confidence: 99%

Seismic visibility of a deep subduction channel – insights from numerical simulation of high-frequency seismic waves emitted from intermediate depth earthquakes

et al. 2014

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Abstract. Return flow in a deep subduction channel (DSC) has been proposed to explain rapid exhumation of high pressure-low temperature metamorphic rocks, entirely based on the fossil rock record. Supported by thermo-mechanical models, the DSC is envisioned as a thin layer on top of the subducted plate reaching down to minimum depths of about 150 km. We perform numerical simulations of highfrequency seismic wave propagation (1-5 Hz) to explore potential seismological evidence for the in situ existence of a DSC. Motivated by field observations, for modeling purposes we assume a simple block-in-matrix (BIM) structure with eclogitic blocks floating in a serpentinite matrix. Homogenization calculations for BIM structures demonstrate that effective seismic velocities in such composites are lower than in the surrounding oceanic crust and mantle, with nearly constant values along the entire length of the DSC. Synthetic seismograms for receivers at the surface computed for intermediate depth earthquakes in the subducted oceanic crust for models with and without DSC turn out to be markedly influenced by its presence or absence.While for both models P and S waveforms are dominated by delayed high-amplitude guided waves, models with DSC exhibit a very different pattern of seismic arrivals compared to models without DSC. The main reason for the difference is the greater length and width of the low-velocity channel when a DSC is present. Seismic velocity heterogeneity within the DSC or oceanic crust is of minor importance. The characteristic patterns allow for definition of typical signatures by which models with and without DSC may be discriminated.The signatures stably recur in slightly modified form for earthquakes at different depths inside subducted oceanic crust. Available seismological data from intermediate depth earthquakes recorded in the forearc of the Hellenic subduction zone exhibit similar multi-arrival waveforms as observed in the synthetic seismograms for models with DSC. According to our results, observation of intermediate depth earthquakes along a profile across the forearc may allow to test the hypothesis of a DSC and to identify situations where such processes could be active today.

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The Variscan French Massif Central—a new addition to the ultra-high pressure metamorphic ‘club’: exhumation processes and geodynamic consequences

Cited by 171 publications

References 86 publications

Continental subduction channel processes: Plate interface interaction during continental collision

Continental subduction channel processes: Plate interface interaction during continental collision

The eclogite facies gneisses of the Cabo Ortegal Complex (NW Iberian Massif): Tectonothermal evolution and exhumation model

Seismic visibility of a deep subduction channel – insights from numerical simulation of high-frequency seismic waves emitted from intermediate depth earthquakes

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