Cretaceous mantle exhumation in the central Pyrenees: New constraints from the peridotites in eastern Ariè ge (North Pyrenean zone, France)

Michel de Saint Blanquat (1) , Flora Bajolet (2) , Alexis Grand 'Homme (3) , Arnaud Proietti (4) , Matthieu Zanti (5) , Alexandre Boutin (1) , Camille Clerc (6, 7) , Yves Lagabrielle (8, 9) , Pierre Labaume (2, 9)

1 GET - Géosciences Environnement Toulouse
2 Géosciences Montpellier
3 ISTerre - Institut des Sciences de la Terre
4 IRAP - Institut de recherche en astrophysique et planétologie
5 GEOAZUR 7329 - Géoazur
6 ISTO - Institut des Sciences de la Terre d'Orléans - UMR7327
7 Géodynamique - UMR7327
8 GR - Géosciences Rennes
9 LIVE - Laboratoire Insulaire du Vivant et de l'Environnement

We provide new constraints on the modes of mantle exhumation and denudation in the pre-orogenic Pyrenees by investigating the poorly known peridotites located east of the Lherz body, in eastern Ariè ge (Vicdessos, Urs, Bestiac, Caussou and Prades main peridotitic bodies). We show that: (1) numerous peridotite bodies, not described so far, are constituted by decametric to sub-metric outcrops scattered between and around the main outcrops identified by Monchoux (1970); (2) most of the peridotites form blocks and lenses of various sizes, from millimetric monocrystalline grains to hectometric olistoliths, embedded in debris flows involving mainly Mesozoic metasediments; these peridotites can therefore be linked to the S-type peridotites of Lagabrielle et al. (2010), and share similarities with the peridotites of Lherz region (Clerc et al., 2012). All originated from tectono-sedimentary processes associated with mantle exhumation in relation with extreme thinning and breakoff of the continental basement; (3) the various petrographic characters of these peridotites and their heterogeneity in serpentinisation degree imply a peculiar mode of exhumation, which merges mantle fragments inherited from different structural levels; (4) the lack of tectonic structures such as faults and shear planes associated with the ultramafic-rich breccia formation and the presence of neoformation of metamorphic minerals within the matrix preclude their origin as cataclasites related to the Latest Cretaceous and Tertiary Pyrenean contractional deformation. The peridotites of eastern Ariè ge are indisputable witnesses of the presence of an inverted hyper-extended Cretaceous passive margin forming the current North Pyrenean zone. The geometry of the extensional system was complex and probably associated with strike-slip faults and transcurrent motion. ß 2016 The Authors. Published by Elsevier Masson SAS on behalf of Acadé mie des sciences. This is an open access article under the CC BY-NC-ND license (http://creativecommons. org/licenses/by-nc-nd/4.0/).

Mots clés: Breccia; Hyper-extended passive margins; Orogenic peridotite; Lherzolite; Pyrenees

Domaines: Planète et Univers [physics]; Sciences de la Terre; Tectonique

Michel de Saint Blanquat, Flora Bajolet, Alexis Grand 'Homme, Arnaud Proietti, Matthieu Zanti, et al.. Cretaceous mantle exhumation in the central Pyrenees: New constraints from the peridotites in eastern Ariè ge (North Pyrenean zone, France). Comptes Rendus Géoscience, 2016, From rifting to mountain building: the Pyrenean Belt, 348 (2-4), pp.268-278. ⟨10.1016/j.crte.2015.12.003⟩. ⟨insu-01280502⟩