The Basque-Cantabrian junction corresponds to an inverted rift accommodation zone at the limit between the former hyperextended Pyrenean and Cantabrian rift segments. The recognition of an inherited rift segment boundary allows to investigate the reactivation associated with large-scale rift segmentation in an orogenic system. We use criteria from published field observations and seismic data to propose a new map of rift domains for the Basque-Cantabrian junction. We also provide balanced cross-sections that allow to define the along-strike architecture associated with segmentation during rifting and subsequent Alpine reactivation. Based on these results, this study aims to characterize and identify reactivated and newly formed structures during inversion of two rift segments and its intermitted segment boundary. It also aims to describe the timing of thin-skinned and thick-skinned deformation associated with the inversion of segmented rift systems. During convergence, two phases have been recognized within the rift segment (eastern Mauléon basin). The Late Cretaceous to Paleocene underthrusting/subduction phase was mostly governed by thin-skinned deformation that reactivated the former hyperextended domains and the supra-salt sedimentary cover. The Eocene to Miocene collisional phase, controlled by thick-skinned deformation that took place once necking domains collided and formed an orogenic wedge. At the rift segment boundary, the underthrusting/subduction phase was already controlled by thick-skinned deformation due to the formation of shortcutting thrust faults at the termination of overlapping V-shaped rift segments. This led to the formation of a proto-wedge composed of the Basque massifs. We suggest that this proto-wedge is responsible for the preservation of pre-Alpine structures in the Basque massifs and for the emplacement of subcontinental mantle rocks at a crustal level beneath the western Mauléon basin. These results argue for a first order cylindrical orogenic architecture from the Central Pyrenean segment to the Cantabrian segment (up to the Santander transfer zone) despite rift segmentation. They also highlight the control of 3D rift-inheritance for the initial phase of orogenic evolution and for the local architecture of mountain belts.

The aim of this paper is to provide a conceptual framework that integrates the role of inheritance in the study of rifts, rifted margins and collisional orogens based on the work done in the OROGEN project, which focuses on the Biscay-Pyrenean system. The Biscay-Pyrenean rift system resulted from a complex multistage rift evolution that developed over a complex lithosphere pre-structured by the Variscan orogenic cycle. There is a general agreement that the Pyrenean-Cantabrian orogen resulted from the reactivation of an increasingly mature rift system along-strike, ranging from a mature rifted margin in the west to an immature and segmented hyperextended rift in the east. However, different models have been proposed to explain the preceding syn-rift evolution and its influence on the subsequent reactivation. Results from the OROGEN project show a sequential reactivation of rift inherited decoupling horizons and identify the specific role of exhumed mantle, hyperextended and necking domains during reactivation. They also highlight the contrasting fate of segment centres vs. segment boundaries during convergence, explaining the non-cylindricity of internal parts of collisional orogens. Results from the OROGEN project also suggest that the role of inheritance is more important during the initial stages of subduction and collision, which may explain the complexity of internal parts of orogenic systems. In contrast, once tectonic systems get more mature, orogenic evolution becomes mostly controlled by first-order physical processes as described in the Coulomb Wedge theory for instance. This may account for the simpler and more continuous architecture of external parts of collisional orogens. It may also explain why most numerical models can reproduce mature orogenic and rift architectures with better accuracy compared to the initial stages of such systems. Thus, while inheritance may not explain steady-state processes, it is a prerequisite for comprehending the initial stages of tectonic systems. The new concepts developed from the OROGEN research are now ready to be tested at other orogenic systems that result from the reactivation of rifted margins, such as the Alps, the Colombian cordilleras and the Caribbean, Taiwan, Oman, Zagros or Timor.

We investigate the thermal and structural evolution of asymmetric rifted margin using numerical modeling and geological observations derived from the Western Pyrenees. Our numerical model provides a self-consistent physical evolution of the top basement heat flow during asymmetric rifting. The model shows a pronounced thermal asymmetry that is caused by migration of the rift center toward the upper plate. The same process creates a diachronism for the record of maximum heat flow and maximum temperatures (T max ) in basal rift sequences. The Mauléon-Arzacq basin (W-Pyrenees) corresponds to a former mid-Cretaceous asymmetric hyperextended rift basin. New vitrinite reflectance data in addition to existing data sets from this basin reveal an asymmetry in the distribution of peak heat (T max ) with respect to the rift shoulders, where highest values are located at the former upper-to lower-plate transition. This data set from the Arzacq-Mauléon field study confirms for the first time the thermal asymmetry predicted by numerical models. Numerical modeling results also suggest that complexities in synrift thermal architecture could arise when hanging-wall-derived extensional allochthons and related T max become part of the lower plate and are transported away from the upper-to lower-plate transition. This study emphasizes the limitations of the common approach to integrate punctual thermal data from pre-rift to synrift sedimentary sequences in order to describe the rift-related thermal evolution and paleothermal gradients at the scale of a rift basin or a rifted margin.

The Pyrenean-Cantabrian orogenic system (Figure 1a) resulted from the inversion of a hyperextended rift system that developed during the Late Jurassic-Late Cretaceous all along the Iberian, Ebro, and European plate boundaries (Teixell et al., 2018;Tugend et al., 2014). Before this extensional event, Triassic rifting, Stephano-Permian to late Variscan tectonics involving strike-slip and extensional deformation, and Variscan and pre-Variscan tectono-metamorphic events also affected the Pyrenean-Cantabrian domain (e.g., Burg et al., 1994).The structural style of the Pyrenean-Cantabrian orogen and the related tectono-sedimentary evolution change significantly along-strike. These changes are mainly expressed by differences in width, asymmetry of the double-wedge, thrust kinematics, involvement of basement, and topography. Differences in basement involvement and topography are so strong that different geological and physiographic units formed, receiving distinct names such as Cantabrian and Pyrenean Ranges. The main factors controlling the orogenic structural style, and as a result of the along strike differences, are the inversion of the inherited Mesozoic rift template and the distribution of the Triassic salt (Beaumont et al., 2000;Jammes et al., 2014;Teixell et al., 2018). Other factors, such as the weakness of the inherited Variscan crust and the lithospheric thermal state, have also contributed to the structural evolution and the observed longitudinal changes (Clerc & Lagabrielle, 2014;Jammes et al., 2014). These longitudinal changes are so strong that Souquet et al. (1977) proposed to subdivide the Pyrenean-Cantabrian orogenic system into three main segments, bounded by two major crustal-scale transverse structures: the Segre and Pamplona faults. This interpretation was in opposition to the most accepted structural subdivision into strike-parallel zones (