Kinematics of the Cretaceous Rifting in the Chainons Béarnais and Bigorre Basin (North Pyrenean Zone): Insights From Magnetic Fabrics and Mineral Anisotropy

Abstract The North Pyrenean Zone results from the Late Cretaceous‐Cenozoic inversion of the Mesozoic rift system extending along the Iberia‐Europe plate boundary. The western part of this inverted rift (from the Tardets‐Mauléon basin in the West to the Bigorre basin in the East) is strongly decoupled from the basement along Upper Triassic evaporites and slightly, internally overprinted by orogenic processes. These conditions make the area an ideal candidate for the study of rift‐related structures and mineral fabrics registering the kinematics of the rifting process. This work focuses on the study of meso and micro‐scale rift inheritance through a combination of structural analysis, anisotropy of magnetic susceptibility (AMS) and mineral shape fabrics extracted from X‐Ray microtomography analysis. Previous AMS results (Mauléon basin) are integrated with data from 64 new AMS sites, acquired across both the Mesozoic, syn‐rift cover and the Paleozoic basement. In syn‐rift units, magnetic and mineral fabrics are in agreement and at a great extent inherited from syn‐ and post‐rift stages. The compressional overprint of the Late‐Cretaceous‐Cenozoic inversion is limited and localizes along the south‐western margin of the inverted basin. In the Paleozoic, a partial overprint of Mesozoic extension on AMS occurs in areas where rift‐related peak temperatures exceeded ∼350°C. Rift‐related mineral and magnetic lineations reveal a regional and constant through time NNW‐SSE to NE‐SW extension that attests this ample domain of the Pyrenean rift opened under a roughly orthogonal or slightly oblique rifting. Its easternmost part registered a partitioning between N‐S and NW‐SE extension directions, likely controlled by pre‐rift faulting.