International audienceThis paper provides a synthesis of current data and interpretations on the crustal structure of the Pyrenean-Cantabrian orogenic belt, and presents new tectonic models for representative transects. The Pyrenean orogeny lasted from Santonian (~84 Ma) to early Miocene times (~20 Ma), and consisted of a spatial and temporal succession of oceanic crust/exhumed mantle subduction, rift inversion and continental collision processes at the Iberia-Eurasia plate boundary. A good coverage by active-source (vertical-incidence and wide-angle reflection) and passive-source (receiver functions) seismic studies, coupled with surface data have led to a reasonable knowledge of the present-day crustal architecture of the Pyrenean-Cantabrian belt, although questions remain. Seismic imaging reveals a persistent structure, from the central Pyrenees to the central Cantabrian Mountains, consisting of a wedge of Eurasian lithosphere indented into the thicker Iberian plate, whose lower crust is detached and plunges northwards into the mantle. For the Pyrenees, a new scheme of relationships between the southern upper crustal thrust sheets and the Axial Zone is here proposed. For the Cantabrian belt, the depth reached by the N-dipping Iberian crust and the structure of the margin are also revised.The common occurrence of lherzolite bodies in the northern Pyrenees and the seismic velocity and potential field record of the Bay of Biscay indicate that the precursor of the Pyrenees was a hyperextended and strongly segmented rift system, where narrow domains of exhumed mantle separated the thinned Iberian and Eurasian continental margins since the Albian-Cenomanian. The exhumed mantle in the Pyrenean rift was largely covered by a Mesozoic sedimentary lid that had locally glided along detachments in Triassic evaporites. Continental margin collision in the Pyrenees was preceded by subduction of the exhumed mantle, accompanied by the pop-up thrust expulsion of the off-scraped sedimentary lid above. To the west, oceanic subduction of the Bay of Biscay under the North Iberian margin is supported by an upper plate thrust wedge, gravity and magnetic anomalies, and 3D inclined sub-crustal reflections. However, discrepancies remain for the location of continent-ocean transitions in the Bay of Biscay and for the extent of oceanic subduction. The plate-kinematic evolution during the Mesozoic, which involves issues as the timing and total amount of opening, as well as the role of strike-slip drift, is also under debate, discrepancies arising from first-order interpretations of the adjacent oceanic magnetic anomaly record

We present lithospheric-scale analog models,\ud investigating how the absolute plates’ motion and\ud subduction of buoyant oceanic plateaus can affect both\ud the kinematics and the geometry of subduction,\ud possibly resulting in the appearance of flat slab\ud segments, and how it changes the overriding plate\ud tectonic regime. Experiments suggest that flat\ud subductions only occur if a large amount of a\ud buoyant slab segment is forced into subduction by\ud kinematic boundary conditions, part of the buoyant\ud plateau being incorporated in the steep part of the slab\ud to balance the negative buoyancy of the dense oceanic\ud slab. Slab flattening is a long-term process (10 Ma),\ud which requires the subduction of hundreds of\ud kilometers of buoyant plateau. The overriding plate\ud shortening rate increases if the oceanic plateau is large\ud enough to decrease the slab pull effect. Slab flattening\ud increases the interplate friction force and results in\ud migration of the shortening zone within the interior of\ud the overriding plate. The increase of the overriding\ud plate topography close to the trench results from (1) the\ud buoyancy of the plate subducting at trench and (2) the\ud overriding plate shortening. Experiments are\ud compared to the South American active margin,\ud where two major horizontal slab segments had\ud formed since the Pliocene. Along the South\ud American subduction zone, flat slab segments below\ud Peru and central Chile/NW Argentina appeared at\ud 7 Ma following the beginning of buoyant slab\ud segments’ subduction. In northern Ecuador and\ud northern Chile, the process of slab flattening\ud resulting from the Carnegie and Iquique ridges’\ud subductions, respectively, seems to be active but not\ud completed. The formation of flat slab segments below\ud South America from the Pliocene may explain the\ud deceleration of the Nazca plate trenchward velocity