[1] The Pyrenean peridotites (lherzolites) form numerous small bodies of subcontinental mantle, a few meters to 3 km across, exposed within the narrow north Pyrenean zone (NPZ) of Mesozoic sediments paralleling the north Pyrenean Fault. Recent studies have shown that mantle exhumation occurred along the future NPZ during the formation of the AlbianCenomanian Pyrenean basins in relation with detachment tectonics. This paper reviews the geological setting of the Pyrenean lherzolite bodies and reports new detailed field data from key outcrops in the Béarn region. Only two types of geological settings have to be distinguished among the Pyrenean ultramafic bodies. In the first type (sedimented type or S type), the lherzolites occur as clasts of various sizes, ranging from millimetric grains to hectometric olistoliths, within monogenic or polymictic debris flow deposits of Cretaceous age, reworking Mesozoic sediments in dominant proportions as observed around the Lherz body. In the second type (tectonic type or T type), the mantle rocks form hectometric to kilometric slices associated with crustal tectonic lenses. Both crustal and mantle tectonic lenses are in turn systematically associated with large volumes of strongly deformed Triassic rocks and have fault contacts with units of deformed Jurassic and Lower Cretaceous sediments belonging to the cover of the NPZ. These deformed Mesozoic formations are not older that the Aptian-early Albian. They are unconformably overlain by the Albian-Cenomanian flysch formations and have experienced high temperature-low pressure mid-Cretaceous metamorphism at variable grades. Such a tectonic setting characterizes most of the lherzolite bodies exposed in the western Pyrenees. These geological data first provide evidence of detachment tectonics leading to manle exhumation and second emphasize the role of gravity sliding of the Mesozoic cover in the preorogenic evolution of the Pyrenean realm. In the light of such evidence, a simple model of basin development can be inferred, involving extreme thinning of the crust, and mantle uprising along a major detachment fault. We demonstrate coeval development of a crust-mantle detachment fault and generalized gravitational sliding of the Mesozoic cover along lowangle faults involving Triassic salt deposits as a tectonic sole. This model accounts for the basic characteristics of the precollisional rift evolution in the Pyrenean realm. Citation: Lagabrielle, Y., P. Labaume, and M. de Saint Blanquat (2010), Mantle exhumation, crustal denudation, and gravity tectonics during Cretaceous rifting in the Pyrenean realm (SW Europe): Insights from the geological setting of the lherzolite bodies, Tectonics, 29, TC4012,

New evolutionary models for the Pyrenean orogeny must consider feedbacks between the midCretaceous hyperextension postulated recently and the Pyrenean inversion. We present a new crustal section of the Pyrenees through the Jaca basin, the western Axial Zone and the Chaînons Béarnais which allows identifying the ancient continental margins of the Iberian and European plates and a suture. A sequential restoration allows a reassessment of the style of convergence through time. Restoration leads to a progressively thinned crust in narrow continental margins separated by a domain of exhumed mantle peridotite and overlain by a detached sedimentary lid. Early convergence during the late Cretaceous and earliest Paleogene was accommodated by subduction of the peridotite domain. This was followed in the Eocene by initial collision involving overriding of the Iberian margin onto the European margin along the deep ramp of the NorthPyrenean Frontal thrust, which defines the suture. Subsequent full collision and strong relief generation from the late Eocene to the early Miocene were associated to thrust accretion of the Iberian plate, underlain by wedging and northward subduction of decoupled Iberian lower crust.

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

[1] In this work we combined apatite fission track and biotite/K-feldspar 40 Ar/ 39 Ar ages with tectonic data in the west central part of the Axial Zone of the Pyrenees. We discuss the exhumation ages and rates of the Néouvielle, Bordère-Louron, and Bielsa Variscan granites and their relationships with the timing and sequence of south vergent basement thrusting within the Pyrenean orogenic prism. The 40 Ar/ 39 Ar ages on K-feldspars from the Néouvielle massif (sample NV7) seem to indicate tectonic movements on the EauxChaudes thrust during the early middle Eocene. Fission track results suggest that the exhumation of the Néouvielle massif occurred around 35 Ma and exhumation of the Bordère-Louron massif around 32 Ma in relation to thrusting on the Gavarnie thrust. The Bielsa massif was exhumed from around 19 Ma by out-of-sequence movements on the Bielsa thrust. We thus show that whereas most of the Pyrenean basement thrust faults (here the Eaux-Chaudes, Gavarnie, and Guarga thrusts) were active in sequence toward the southern foreland from the early Eocene to the earliest Miocene, some of them (here the Bielsa thrust) were activated out of sequence in the hinterland, later than the generally accepted Aquitanian age for the end of the Pyrenean compression. Finally, the apatite fission track modeling indicate a last cooling episode starting around 5 Ma which is most certainly related to the Pliocene reexcavation of the southern and northern flanks of the Pyrenees. Citation: Jolivet, M., P. Labaume, P. Monié, M. Brunel, N. Arnaud, and M. Campani (2007), Thermochronology constraints for the propagation sequence of the south Pyrenean basement thrust system (France-Spain), Tectonics, 26, TC5007,

The South-Pyrenean Tertiary Basin was an east-west trending foreland trough which developed from Early Eocene to Miocene times in a north-south trending compressive regime.

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The Chaînons Béarnais is a salt-detached fold belt in the northern Pyrenees that formerly occupied the axis of the Cretaceous Pyrenean rift. Geological map revision and cross-section construction from surface geology and industrial well and seismic reflection data emphasize the role of salt diapirism in the folding of the belt during the Cretaceous extension and the subsequent Pyrenean orogeny. Pre-rift Triassic evaporites played a fundamental role during rifting, allowing the sedimentary basin lying above to detach and slide down the hyperextended margins onto a central exhumed mantle tract. Since the Early Cretaceous (and locally probably since the Jurassic) a system of low-amplitude salt walls evolved in shallow marine environments punctuated by episodic emersion. During the main stage of crustal extension, in late Aptian to early Cenomanian times, carbonate shelves rapidly drowned giving 2 rise to deeper marine sedimentation. This was a period of major rise of salt walls, progressively detached from their substratum. These salt walls enclosed minibasins that accumulated thick flysch deposits arranged in growth stratal patterns. Depocenter migration and foundering of previous diapiric highs controlled further flysch deposition during the Late Cretaceous, while moderate extension probably persited until the onset of the Pyrenean compression. During the late Santonian to Paleogene Pyrenean orogeny, the sedimentary lid of the Chaînons Béarnais basin climbed back along the Triassic detachment onto the colliding continental margins, leading to salt wall squeezing and further rising. Based on the Cretaceous timing and style of growth folding, we suggest that salt wall squeezing was not solely related to the Pyrenean compression, but shortening affected the diapiric ridges during the syn-rift sliding by gravity and crowding in the basin center, as the rifted margins were pulled apart from beneath. This makes the Chaînons Béarnais belt a unique field analog for contractional salttectonic systems in distal continental margins.