International audienceEstimating shortening in collision belts is critical to reconstruct past plate motions. Balanced cross-section techniques are efficient in external domains but lack resolution in the hinterland. The role and the original extent of the continental margins during the earliest stages of continental convergence are debated. Here we combine existing and new sequentially restored cross sections in the central Pyrenees, with Iberia/Europe (IB/EU) plate kinematic reconstructions and new apatite fission track, zircon (U-Th)/He, and U/Pb ages to discuss higher and lower bounds of crustal shortening and determine the amount of distal margin sutured during collision. We show that after extension in the Albian (~110 Ma), a 50 km wide extremely thinned crustal domain underwent subduction at 83 Ma. Low-temperature data and thermal modeling show that synorogenic cooling started at 75–70 Ma. This date marks the transition from suturing of the highly extended margin to collision of the more proximal margin and orogenic growth. We infer a relatively low crustal shortening of 90 km (30%) that reflects the dominant thick-skinned tectonic style of shortening in the Pyrenees, as expected for young (Mesozoic) and weak lithospheres. Our proposed reconstruction agrees with IB/EU kinematic models that consider initially rapid convergence of Iberia, reducing from circa 70 Ma onward. This study suggests that plate reconstructions are consistent with balanced cross sections if shortening predicted by age-dependent properties of the continental lithosphere is taken into account

In natural doubly vergent orogens, the relationship between the pro‐ and retro‐wedges is, as yet, poorly constrained. We present a detailed tectonostratigraphic study of the retro‐wedge of the Eastern Pyrenees (Europe) and link its evolution to that of the pro‐wedge (Iberia) in order to derive insight into the crustal‐scale dynamics of doubly vergent orogens. Based on cross‐section restoration and subsidence analyses, we divide the East Pyrenean evolution into four phases. The first phase (Late Cretaceous) is characterized by closure of an exhumed mantle domain between the Iberian and European plates and inversion of a salt‐rich, thermally unequilibrated rift system. Overall shortening (~1 mm/yr) was distributed roughly equally between both margins over some 20 Myr. A quiescent phase (Paleocene) was apparently restricted to the retro‐wedge with slow, continuous deformation in the pro‐wedge (~0.4 mm/yr). This phase occurred between closure of the exhumed mantle domain and onset of main collision. The main collision phase (Eocene) records the highest shortening rate (~3.1 mm/yr), which was predominantly accommodated in the pro‐wedge. During the final phase (Oligocene), the retro‐wedge was apparently inactive, and shortening of the pro‐wedge slowed (~2.2 mm/yr). Minimum total shortening of the Eastern Pyrenees is ~111 km, excluding closure of the exhumed mantle domain. The retro‐wedge accommodated ~20 km of shortening. The shortening distribution between the pro‐ and retro‐wedges evolved from roughly equal during rift inversion to pro‐dominant during main collision. This change in shortening distribution may be intrinsic to all inverted rift systems.

International audienceThe eastern Aquitaine basin and North Pyrenean Zone show many characteristics of retro-wedge models. However,they differ significantly in that slow subsidence and low deformation continued throughout orogenesis so that growth andsteady-state phases cannot be distinguished. We show that the eastern Pyrenees record two clear phases of convergence andprobably never attained steady state. Analysis of the Aquitaine retro-foreland basin along the Ariège ECORS deep seismic line,eastern French Pyrenees, integrates a new litho- and chronostratigraphy, subsidence analysis, low-temperature thermochronologydata, new interpretations of seismic lines and a balanced cross-section. Within an overall regression, twoshallowing-up cycles (Latest Santonian–Danian, Thanetian–Oligocene) record slow tectonic subsidence of the easternAquitaine basin separated by a quiet period. Continuing thick-skinned shortening was low to moderate. The early marine basin,generated by loading of the weak, extended margin, was supplied axially from an unknown eastern edifice while the youngPyrenean orogeny to the south remained submerged. During the quiet period of ultra-slow subsidence, no basin migration andnegligible sediment supply, continental conditions characterized the eastern orogen. The second marine transgression wasquickly followed by continental conditions. The basin was supplied by the now emerging Pyrenean orogen and continued tosubside until Miocene time

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