Progressive localization of a diffuse transtensional plate boundary: the example of the Iberia-Eurasia plate boundary during the opening of the Bay of Biscay (Late Jurassic-Early Cretaceous)
Authors: Asti Riccardo , Saspiturry Nicolas , Angrand Paul 
Published: February 2023

Most plate kinematic reconstructions concerning the Iberian plate imply a major (>400 km) left-lateral displacement between Iberia and Eurasia during the opening of the Bay of Biscay (Late Jurassic-Early Cretaceous). In the past, authors identified the North Pyrenean Zone (NPZ) as the domain accommodating this lateral displacement, while more recent works tend to distribute the deformation in two or three transtensional corridors located in the NPZ and in the Iberian Chain basins. Nevertheless, field evidence contrasts with such models, since no structure seems to have accommodated such huge amount of displacement. Moreover, debate exists concerning the timing of the left-lateral displacement between Iberia and Eurasia (Late Jurassic vs Early Cretaceous).We present a review of the tectono-sedimentary and kinematic evolution of rift basins distributed across the wide Iberia-Eurasia plate boundary that recorded the Late Jurassic-Early Cretaceous rifting phase, from the Iberian Chain basins (in the southwest) to the northern part of the Aquitaine domain aligned with the Armorican Margin (to the northeast). To the first order, these basins experienced the same tectonic evolution, with an initial Permian-Triassic rifting phase related to the breakup of Pangea, and a subsequent Late Jurassic-Early Cretaceous rifting phase related to the opening of the Bay of Biscay. For this latter phase, authors have proposed contrasting kinematic models, with opening mechanisms varying between orthogonal rifting and transtensional/pull-apart tectonics. Our review allows to propose a reappraisal of the kinematic evolution of the Iberia-Eurasia diffuse plate boundary during the Late Jurassic-Early Cretaceous rifting, which consists in four phases: (i) a Late Jurassic phase of transtensional deformation localized at the borders of the system (Asturian Basin/Southwesternmost Iberian Chain basins and Armorican Margin), while the rest of the basins underwent orthogonal rifting, contemporaneous with rifting in the Bay of Biscay margins; (ii) a Neocomian phase of generalized marine regression; (iii) a Barremian-Early Albian phase of distributed left-lateral transtension, contemporaneous with crustal breakup in the Bay of Biscay; (iv) an Albian-Cenomanian phase of left-lateral transtension localized in the Basque-Cantabrian/North Pyrenean corridor, contemporaneous with ocean spreading in the Bay of Biscay, while the rest of the rift basins within the plate boundary became tectonically inactive. This evolution highlights a trend of progressive localization of the plate boundary from the Late Jurassic to the Early Cretaceous in response to the different tectonic phases of the Bay of Biscay margins. This work also allows to highlight the role of some rift basins in accommodating part of the deformation between Iberia and Eurasia which have been often disregarded, due to their position below the Cenozoic cover of the Pyrenean foreland basins, such as the Ebro and Aquitaine domains.