The Iberia-Eurasia plate boundary east of the Pyrenees

In this work we provide a reappraisal of the mid-Cretaceous extensional basins located to the east of the Pyrenean mountain ranges, from the easternmost portion of Iberia to the Briançonnais Domain of the Western Alps fold-and-thrust belt. These features are reviewed and compared with those of the Bay of Biscay-Pyrenean rift, with the aim of defining geometry, kinematics, timing and lateral extent of the eastern termination of the Mesozoic Iberia-Eurasia plate boundary. Timing and direction of extension, as well as the style of structural segmentation in the Bay of Biscay - Pyrenean rift, are similar to those of basins exposed to the east of the Pyrenean mountain ranges. In both areas, the divergent movement between Iberia and Eurasia caused NNE-SSW oriented extension recorded in WNW-ESE elongated Late Jurassic to mid-Cretaceous basins, segmented by NNESSW trending transfer zones. In this work we also individuate and introduce the eastern termination of the Iberia-Eurasia plate boundary. This is the Marguareis extensional system of the Briançonnais Domain of the SW Alps. The crustal-scale Marguareis extensional system involves Paleozoic and Mesozoic rocks and includes a tens of km long transfer fault flanking an extensional domino array that accounted for ca. 2 km of extension along 6 km long sections. When post-Cretaceous alpine rotation is removed, the mid-Cretaceous transfer fault and the extension direction of the Marguareis extensional system become oriented parallel to those of the other portions of the plate boundary, indicating its pertinence to the Bay of Biscay-Pyrenean rift system. Reviewed and newly presented data about the mid-Cretaceous tectonics spanning from the easternmost portion of Iberia to the Western Alps indicate that: (i) the Marguareis extensional system and the extensional structures of south France constituted the easternmost portion of the segmented and laterally terminating Bay of Biscay-Pyrenean rift system; (ii) this easternmost portion of the Iberia-Eurasia plate boundary was characterised by a purely divergent Early to mid-Cretaceous movement.