Flow of the partially molten Variscan orogenic crust from syn-orogenic exhumation of subducted continental crust to gravitational collapse along a convergent plate boundary marked by slab retreat

Abstract : The Variscan belt ofWestern Europe exposed in the French Massif Central is a perfect example of a collision zone characterized by protracted syntectonic magmatism and partial melting (from 380 to 280 Ma) with a wide range of petrologic and geochemical signatures (calc-alkaline, high-K, Mg-K, peraluminous) that have been inferred to fingerprint lithospheric subduction, mantle upwelling and/or partial melting of the orogenic wedge. The nappe pile encompasses an upper gneiss unit (UGU) and a lower gneiss unit (LGU) that are separated by an association of maficultramafic rocks designated as the Leptynite-Amphibolite Group (LAG) and has been interpreted as representing remnants of former small immature oceanic basins. Both the UGU and the LGU are made of migmatites but are distinguished on the basis of their structural position with respect to the LAG and of their metamorphic record. The UGU has preserved relics of high-pressure metamorphism whereas the LGU has only recorded a high-temperature metamorphism. We present a synthesis of structural, petrologic, geochemical and geochronological data from the various lithologic-tectonic units exposed along a transect across the Variscan belt of Western Europe from the French Massif Central to the Pyrenees. In particular, the new geochronological and geochemical dataset presented by Couzinié et al. (this conference) suggests the contribution of mantle and crustal derived magmas with a southward younging of syntectonic emplacement. These data provide a basis to elaborate a model for the structure of the Laurussia- Gondwana plate boundary at the onset of convergence and for the generation and flow of migmatites during orogenic evolution from the early stage of subduction of the continental crust to gravitational collapse of the orogenic belt in a context of a convergent plate boundary marked by southward slab retreat.
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Submitted on : Tuesday, March 22, 2016 - 10:11:54 AM
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  • HAL Id : insu-01291783, version 1

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Olivier Vanderhaeghe, Véronique Gardien, Jean-François Moyen, Oscar Laurent, Simon Couzinié, et al.. Flow of the partially molten Variscan orogenic crust from syn-orogenic exhumation of subducted continental crust to gravitational collapse along a convergent plate boundary marked by slab retreat. 24ème Réunion des Sciences de la Terre, Oct 2014, Pau, France. ⟨insu-01291783⟩

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