Résumé
Based on fieldwork and modern analytical technics, this work presents an overview of the Mid-Cretaceous hyper-extended rift system exposed in the northern part of the Pyrenean mountain range. Its inversion during the Pyrenean orogeny allows for precious observations of the deep-seated processes occurring at the foot of distal margins. Some peculiar aspects characterizing the pre-Alpine hyper-extended domain are examined throughout the 400km long suture that is fossilized in the North Pyrenean Zone (NPZ). The High Temperature/Low Pressure (HT/LP) thermal imprint of the extensional event is studied thanks to a dataset of more than hundred peak temperature measurement by Raman spectroscopy of the carbonaceous material (RSCM). The pre- and syn-rift metasediments are characterized by an intense ductile deformation. Field and EBSD investigations of the mechanisms of deformation reveal ductile and syn-metamorphic processes. The emplacement conditions of the peridotite into crustal levels and localized exhumation is examined in the key-localities of Urdach, Saraillé-Tos de la Coustette, Moncaup, Lherz, Caussou-Bestiac and Salvezines, The results indicate an early boudinage of the crust during the rifting process, resulting in the direct superposition of pre-rift sediments on top of mantle peridotites. Field, textural and isotopic characterization of the various ophicalcite and breccias found in the vicinity of the peridotite outcrops allow to decipher their exhumation history. New Ar-Ar geochronological results allow to precise the temporal evolution of the NPZ.