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Conditions of formation of serpentinites in Pyrenees and new constraints on the model of exhumation of mantle peridotites

Abstract : Since the mid-80’s, several models of emplacement of Pyrenean peridotites have been suggested. The most recent one, published by Lagabrielle et al. in 2010, proposed two types of geological setting for the formation of peridotites : i) sedimentary as debris flows deposits or ii) tectonic via detachment exhumation. In order to bring new constraints on this exhumation model and to integrate it in the Pyrenean history, we studied the conditions of serpentinization of peridotites in several massifs of the Pyrenees. A detailed petrological study reveals that lherzolites were heterogeneously affected by serpentinization all over the Pyrenees. Three different stages of serpentinization have be distinguished : i) massive serpentinization with development of a mesh texture, ii) formation of fibrous or crack-seal chrysotile veins and iii) formation of antigorite veins, in locations with important deformation (Sarailhé). In some localities (Urdach, Espechère), a late stage of CO2-rich fluid circulation precipitated abundant carbonates, similarly to ophicalcites. Serpentinites show similar multi-elementary spectra, with positive anomalies in Cs, U, Ta and Pb ; however, differences reside in concentrations (from 3 to 250 times primitive mantle). REE patterns are broadly flat with a slight enrichment in HREE. A negative Ce anomaly is observed for some samples attesting of interaction with seawater. First d18O values measured on serpentinites seem to argue that serpentinization in the western Massifs (Urdach, Saraillé) occurred at lower temperatures (a few tens of degrees) than in other massifs. Combination of all these petrological and geochemical data suggest that Pyrenean peridotites were, at some point of their exhumation history, affected by interaction with seawater.
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Conference papers
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https://hal-insu.archives-ouvertes.fr/insu-01080830
Contributor : Isabelle Dubigeon <>
Submitted on : Thursday, November 6, 2014 - 12:57:14 PM
Last modification on : Thursday, October 15, 2020 - 3:11:45 AM

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  • HAL Id : insu-01080830, version 1

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Nicolas Ferreira, Adélie Delacour, Michel De Saint Blanquat, Philippe Boulvais, Mathieu Benoit, et al.. Conditions of formation of serpentinites in Pyrenees and new constraints on the model of exhumation of mantle peridotites. 24 ème Réunion des sciences de la Terre 2014, Oct 2014, Pau, France. pp.229. ⟨insu-01080830⟩

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