The Mesozoic Iberia-Eurasia diffuse plate boundary: A wide domain of distributed transtensional deformation progressively focusing along the North Pyrenean Zone

Abstract

Plate kinematic reconstructions available for the Late Jurassic-Early Cretaceous eastward drift and counterclockwise rotation of the Iberian plate imply a major left-lateral motion of Iberia with respect to Eurasia. According to most authors, this displacement has been accommodated along the transform North Pyrenean Zone. However, no relevant field evidence exists for the proposed >400 km of horizontal displacement along the North Pyrenean Fault. Several Permian-Mesozoic basins are distributed around the Iberia/Eurasia plate boundary and have been more or less inverted during the Cenozoic Pyrenean Orogeny (i.e. Iberian Chain basins, North and South Pyrenean basins, Basque-Cantabrian Basin, Parentis Basin, Bay of Biscay/Asturian margins). All of these basins experienced a complex kinematic history and shared the same tectono-stratigraphic evolution, with two successive rifting stages: (i) Permian-Triassic rifting following the dismantling of the Variscan belt and recording the early breakup of Pangea and (ii) Late Jurassic-Early Cretaceous rifting developing after a Jurassic post-rift thermal cooling stage. Depending on the different techniques of investigation and on the interpretation of controversial datasets, authors proposed either opening by orthogonal rifting or by transtensional/pull-apart tectonics for these basins.In this work, we propose a reappraisal of the processes responsible for the Mesozoic Iberia/Eurasia plate boundary compartmentalization by reviewing the tectono-sedimentary history and the kinematic evolution of the sedimentary basins involved in this domain. We shed light on the fact that the Cretaceous left-lateral movement within the plate boundary was not accommodated by localized deformation along the single North Pyrenean Fault wrench structure, but rather by a distributed zone of deformation in which the transtensional regime was recorded by the sedimentary basins therein. We also suggest that other Permian-Mesozoic depocenters located below the Cenozoic foreland basins of the Pyrenean belt (i.e. the Ebro and Aquitaine basins) may have been active segments of this rift system. We then propose that the real extent of the Mesozoic plate boundary is roughly defined by two NW-SE trending lineaments corresponding to the southwestern margin of the Iberian Chain, on the Iberian side, and to the southern Armorican margin and the southwestern border of the French Central Massif, on the Eurasian side. The complex pre-Cretaceous tectono-sedimentary history of this region determined its peculiar pre-rift structure. Such structural inheritance may have favored a distributed rather than a localized mode of deformation at the Iberia/Eurasia diffuse plate boundary during the Late Jurassic-Early Cretaceous, whilst mechanisms related to the eastward propagation of the Bay of Biscay system might have been responsible for the final localization of the plate boundary along the Basque-Cantabrian/North Pyrenean corridor.