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International audience; The North Pyrenean Zone (NPZ) belongs to the northern flank of the Pyrenean chain and continuously outcrops to the north of the AZ from Perpignan to the Basque Country. It is essentially composed of Mesozoic sediments associated with Paleozoic basement massifs (North Pyrenean massifs) and results from the inversion and northward thrusting of the basins formed during the Cretaceous rifting phase. The geology of the NPZ is unique in the world and of major interest for the study of the formation of passive continental margins and, in particular, for better constraining the thermal conditions of crustal thinning. The NPZ is the result of the inversion of extensional and transcurrent structures distributed along the Iberian–Eurasian plate boundary. Along the Iberia–Eurasia boundary itself, the Basque–Cantabrian basin was connected to the North Pyrenean basins (future NPZ). The evolution of the Pyrenean smooth-slope basins contrasts with brittle-dominated models of crustal thinnings, as exemplified along the Iberian–Newfoundland passive margins.

International audience; Examples of fossil and present-day passive margins resulting from mantle exhumation at the ocean–continent transition appear to have developed under conditions of high mantle heat flow. The pattern of geothermal gradients along these hyperextended margins at the time of rifting is of interest for exploration of geothermal and petroleum resources, but is difficult to access. The fossil rift in the North Pyrenean Zone, which underwent high temperature–low pressure metamorphism and alkaline magmatism during Early Cretaceous hyperextension, was studied to explore the geothermal regime at the time of rifting. Data from a set of 155 samples from densely spaced outcrops and boreholes, analyzed using Raman spectroscopy of carbonaceous material, shed light on the distribution of geothermal gradients across the inverted hyperextended Mauléon rift basin during Albian and Cenomanian time, its period of active extension. The estimated paleogeothermal gradient is strongly related to the structural position along the Albian-Cenomanian rift, increasing along a proximal-distal margin transect from ~34°C/km in the European proximal margin to ~37–47°C/km in the two necking zones and 57–60°C/km in the hyperextended domain. This pattern of the paleogeothermal gradient induced a complex competition between brittle and ductile deformation during crustal extension. A numerical modeling approach reproducing the thermal evolution of the North Pyrenees since 120 Ma suggests that mantle heat flow values may have peaked up to 100 mW.m-2 during the rifting event. We demonstrate that the style of reactivation during subsequent convergence influences the thermal structure of the inverted rift system.

International audience; Sapphirine-bearing rocks are described in the Aulus Basin (Ariège, France) in a contact zone between the Lherz peridotitic body and Mesozoic metasediments which underwent the Pyrenean Cretaceous high-temperature, low-pressure metamorphic event (Monchoux, 1970, 1972a, 1972b). Sapphirine crystals occur in layered clastic deposits characterized by an uncommon suite of Al-Mg-rich minerals. A detailed petrographic study of sixteen samples representative of the diversity of the Lherz sapphirine-bearing rocks is presented. These rocks include breccias and microbreccias with various compositions. Some samples are composed of polymineralic clasts and isolated minerals that derive from regionally well-known protoliths such as ultramafic rocks, meta-ophites, “micaceous hornfels”, and very scarce Paleozoic basement rocks. Nevertheless, a large portion of the sapphirine-bearing clastic suite is composed of mono- and polymineralic debris that derive from unknown protolith(s). We define a "sapphirine-bearing mineral suite” (SBMS) composed of monomineralic debris including: sapphirine + enstatite + aluminous spinel + Mg-amphiboles + Ca-amphiboles + kornerupine + accessory minerals (apatite, diopside, rutile, serpentine, smectite, tourmaline, vermiculite and a white mica). We highlight the dominance of metamorphic Keuper clastic materials in the studied rocks and the presence of inclusions of anhydrite and F-, Cl-, Sr-rich apatite in minerals of the Al-Mg-rich suite. The brecciated texture and the presence of unequivocal sedimentary features suggest that the sapphirine-bearing rocks were mechanically disaggregated and then experienced winnowing in underwater conditions with poor mixing between the different sources. We measured U-Pb rutile age data in order to provide constraints on the age of (one of) the protolith(s) of those clastic deposits. The obtained age (98.6 + 1.2 Ma) is interpreted as the age of metamorphism of this protolith of the SBMS. Previous works interpreted the Lherz sapphirine-bearing rocks as crustal protoliths modified at depth along the contact with the ultramafic rocks of the Lherz body during their ascent towards shallower depths. These new data imply: (i) an Upper Triassic to Lower Jurassic origin for the main protolith of the sapphirine-bearing rocks; (ii) the metamorphism of this protolith along an active hot crust–mantle detachment during Cenomanian times with the involvement of metasomatic, brine-type fluids; and (iii) its brecciation during the exhumation of the material due to the evolution of the detachment, followed by subsequent sedimentary reworking of the metamorphic material.; Des roches contenant de la saphirine ont été décrites dans le Bassin d’Aulus (Ariège, France), au sein d’une zone de contact entre le corps de péridotites de Lherz et les métasédiments mésozoïques affectés au Crétacé par un métamorphisme de haute température et de basse pression (Monchoux, 1970, 1972a, 1972b). La saphirine se trouve dans des dépôts clastiques lités caractérisés par une association minérale rare, riche en Al et Mg. Nous présentons ici les résultats de l’étude pétrographique détaillée de 16 échantillons représentatifs de la diversité des roches à saphirine de Lherz. Ces brèches et microbrèches sont constituées de clastes monominéraux et polyminéraux de composition variable. Les protolithes de certains de ces clastes sont aisément identifiables : roches ultramafiques, méta-ophites, « cornéennes micacées », socle paléozoïque. Néanmoins, une grande partie des roches à saphirine est composée de débris mono- et polyminéraux dont le ou les protolithes sont inconnus dans la région et restent à identifier. Ces protolithes énigmatiques sont nécessairement composés des minéraux de l’ensemble que nous appelons « assemblage minéralogique à saphirine » (sapphirine-bearing mineral suite : SBMS) et qui comprend les espèces suivantes : saphirine + enstatite + spinelle alumineux + Mg-amphiboles + Ca-amphiboles + kornérupine + minéraux accessoires (apatite, diopside, rutile, serpentine, smectite, tourmaline, vermiculite et mica blanc). Nous mettons en évidence la présence d’inclusions d’anhydrite et d’apatite riche en F, Cl et Sr dans les espèces minérales du SBMS, ainsi qu’une proportion dominante d’éléments clastiques issus du métamorphisme de roches du Keuper dans l’ensemble des échantillons étudiés. La texture bréchique ainsi que la présence de figures sédimentaires dans les roches à saphirine montrent que leur(s) protolithe(s) a (ont) été soumis à un processus de désagrégation mécanique suivi du vannage des clastes en milieu aqueux. Un faible mélange entre les différentes sources est établi par la composition lithologique des roches étudiées. Une étude géochronologique par la méthode U-Pb sur rutile a été réalisée afin d’apporter des contraintes sur l’âge d’une (ou de la) source de ces dépôts clastiques. L’âge obtenu (98,6 + 1,2 Ma) est interprété comme l’âge du métamorphisme de ce protolithe du SBMS. Les roches à saphirine ont jusqu’à présent été interprétées comme du matériel crustal modifié en profondeur au contact des roches ultramafiques du corps de Lherz lors de leur remontée vers la surface. Les nouvelles contraintes géologiques apportées par cette étude impliquent : (i) l’origine triasique supérieure à jurassique inférieure du protolithe principal des roches à saphirine ; (ii) le métamorphisme de ce protolithe en présence de saumures le long d’un détachement croûte-manteau actif et chaud au Cénomanien ; et (iii) sa bréchification au cours de la remontée du matériel associée au fonctionnement du détachement, suivie du remaniement sédimentaire ultérieur de ce matériel métamorphique.

International audience; The Pyrenean range results from the collision between the Iberian and Eurasian plates which started during the Santonian. Iberia has shown no more relevant motion with respect to Europe since Early Miocene times. In this regard, the Pyrenees can no longer be considered as an active plate boundary from Miocene onwards. Dissected remnants of a high elevation low relief surface (HELRS) are encountered all along the Pyrenean range. All authors agree on the tardi- to post-shortening age of this surface, but doubt remains on its original elevation. In particular, whether a substantial post-shortening uplift occurred after the generation of the Pyrenean planation surface is still debated.Based on a geomorphological study of the entrenchment of the Aspe River in the North-Western Pyrenees, we evidence a Lower Miocene to present-day multi-stage history of dissection of the HELRS in the North-Western Pyrenees. Each incision stage is recorded by erosional triangular facets and associated stepped remnants of palaeovalleys. Compared analysis of the patterns of incisions characterizing (i) the Axial Zone of the range and (ii) its northern border allows to evidence differential vertical motion. We finally discuss the process(es) controlling the deduced uplift of the Western Pyrenean Axial Zone.

In two companion papers, we report the detailed geological and mineralogical study of two emblematic serpentinized ultramafic bodies of the western North Pyrenean Zone (NPZ), the Urdach massif (this paper) and the Saraille massif (paper 2). The peridotites have been exhumed to lower crustal levels during the Cretaceous rifting period in the future NPZ. They are associated with Mesozoic pre-rift metamorphic sediments and small units of thinned Paleozoic basement that were deformed during the mantle exhumation event. Based on detailed geological cross-sections and microprobe mineralogical analyses, we describe the lithology of the two major extensional fault zones that accommodated: (i) the progressive exhumation of the lherzolites along the Cretaceous basin axis; (ii) the lateral extraction of the continental crust beneath the rift shoulders and; (iii) the decoupling of the pre-rift cover along the Upper Triassic (Keuper) evaporites and clays, allowing its gliding and conservation in the basin center. These two fault zones are the (lower) crust-mantle detachment and the (upper) cover decollement located respectively at the crust-mantle boundary and at the base of the detached pre-rift cover. The Urdach peridotites were exposed to the seafloor during the Late Albian and underwent local pervasive carbonation and crystallization of calcite in a network of orthogonal veins (ophicalcites). The carbonated serpentinized peridotites were partly covered by debris-flows carrying fragments of both the ultramafics and Paleozoic crustal rocks now forming the polymictic Urdach breccia. The mantle rocks are involved in a Pyrenean overturned fold together with thin units of crustal mylonites. Continent-derived and mantle-derived fluids that circulated along the Urdach crust-mantle detachment led to the crystallization of abundant metasomatic rocks containing quartz, calcite, Cr-rich chlorites, Cr-rich white micas and pyrite. Two samples of metasomatized material from the crust-mantle detachment yielded in situ zircon U/Pb ages of 112.9 +/- 1.6 Ma and 109.4 +/- 1.2 Ma, thus confirming the Late Albian age of the metasomatic event. The cover decollement is a 30-m thick fault zone which also includes metasomatic rocks of greenschist facies, such as serpentinecalcite association and listvenites, indicating large-scale fluid-rock interactions implying both ultramafic and continental material. The lowermost pre-rift cover is generally missing along the cover decollement due to tectonic disruption during mantle exhumation and continental crust elision. Locally, metasomatized and strongly tectonized Triassic remnants are found as witnesses of the sole at the base of the detached pre-rift cover. We also report the discovery of a spherulitic alkaline lava flow emplaced over the exhumed mantle. These data collectively allow to propose a reconstruction of the architecture and fluid-rock interaction history of the distal domain of the upper Cretaceous northern Iberia margin now inverted in the NPZ.

International audience; The Pyrenean range results from the collision between the Iberian and Eurasian plates which started during theSantonian (e.g. Handy et al., 2010; Olivet, 1996; Rosenbaum et al., 2002). Iberia has shown no more relevantmotion with respect to Europe since Early Miocene times (e.g. Srivastava et al., 1990; Macchiavelli et al., 2017).In this regard, the Pyrenees can no longer be considered as an active plate boundary from Miocene onwards.Previous studies on the post-shortening relief evolution of the Pyrenees have emphasized the existence of highlyelevated – low relief planation surfaces (hereafter referred to as HELRS) all along the chain (see Bosch, 2016for a complete review). Even though the origin of the HELRS is still strongly discussed, all authors agree thatthe HELRS are relicts of planation surfaces which were shaped during the post-shortening period. We identifyremnants of these surfaces on top of the Aspe River flanks, thus questioning the modality and timing of thedissection of a former smooth topography in the North Western Pyrenees.We recognize in the field and from Google Earth and Digital Elevation Model (DEM) data a complex landscapecomprised of poorly preserved and stepped low relief relict surfaces associated with imbricated erosional triangularfacets. Geomorphic attributes of the Aspe Valley flanks are extracted from a 5-m Digital Elevation Model (DEM;RGE ALTI® 5 m IGN) and used to characterize the entrenchment of the hydrographical network which led to thedissection of the Pyrenean planation surface. We attempt to reconstitute the landscape prior to the well preservedlast incision episode in order to quantify the subsequent erosion. This incision attained more than 600 m in themost internal portion of the valley. Our aim is to link the observed progressive incision to foreland deposits. Wethen discuss the timing and processes able to cause this high amount of localized erosion. The combination of aLate Miocene humidification of the climate as well as Late Miocene to present-day relative uplifts evidenced inthe Pyrenees by various authors account for the dissection of the Pyrenean planation surface.This work is funded and carried out in the framework of the BRGM-TOTAL project Source-to-Sink

International audience; The North Pyrenean Zone recorded lithospheric mantle exhumation and its local exposure to the seafloor duringmid-Cretaceous rifting in response to the eastward drift of the Iberian plate. However, the pre-Cretaceous crustalconfiguration and the role of pre-Mesozoic (Variscan) thinning events remain unconstrained. With the aim toconstrain the pre-Mesozoic crustal structure in the region, we carried out a comprehensive petrochronologicalstudy on the granitoid intrusions emplaced in the Hercynian granulitic envelope of the Lherz peridotite (AulusBasin, France). Field work, meso- and micro-scale investigation, multiequilibrium thermobarometry and zirconand titanite U-(Th)-Pb geochronology were combined to define the P-T-t-deformation history of the granitoids,in the transition from magma emplacement to solid-state deformation. Magmatic mineralogy consists of Kfs +Pl1 + Qz + Amp1 + Bt and Ttn1 + Zrc as accessory minerals. The application of Al-in-Hbl barometry and Zrin-Ttn1 thermometry models constrains magma emplacement at 0.5 GPa and 780C. The tectonic fabric isattested by distributed and narrow (up to 25 cm wide), sub-vertical bands of S-(L) tectonites, developed during thesub-solidus mylonitisation of the granitoid. Ductile shearing was accompanied by Amp-Ttn-Pl recrystallization,which occurred at shallower crustal levels and temperatures compatible with the greenschist- facies metamorphicconditions (450-500C and P 0.2 GPa). The U-(Th)-Pb dating of the magmatic zircon clusters around 280Ma, indicating that the Pyrenean continental crust was already significantly thinned during the Permian (Variscan)post-orogenic collapse. The U-(Th)-Pb dating of the REE-poor metamorphic (syn-shearing) titanite (Ttn2) grainsconstrains the activation of ductile shearing on the envelope of the Lherz peridotites around the Albian-Cenomanianboundary (100 Ma). The major implication of this study is that the Pyrenean continental crust was alreadyattenuated and the Hercynian metamorphic envelope of the Lherz peridotites resided at upper crustal levels inpre-Mesozoic times. We infer that the pre-Cretaceous crustal configuration was likely the result of a polyphasethinning, resulted from the cumulated effects of the Permian post-orogenic collapse and of the Triassic and Liassicaborted rifting events. The polyphase evolution unraveled by this study has major implications for the amount ofstretching required during the Cretaceous Pyrenean rifting to exhume the lithospheric mantle and, more in general,for the long-term post-orogenic evolution of the Variscan domain around the Iberian plate

International audience; In two companion papers, we report the detailed geological and mineralogical study of two emblematic serpentinized ultramafic bodies of the western North Pyrenean Zone (NPZ), the Urdach massif (this paper) and the Saraillé massif (paper 2). The peridotites have been exhumed to lower crustal levels during the Cretaceous rifting period in the future NPZ. They are associated with Mesozoic pre-rift metamorphic sediments and small units of thinned Paleozoic basement that were deformed during the mantle exhumation event. Based on detailed geological cross-sections and microprobe mineralogical analyses, we describe the lithology of the two major extensional fault zones that accommodated: (i) the progressive exhumation of the lherzolites along the Cretaceous basin axis; (ii) the lateral extraction of the continental crust beneath the rift shoulders and; (iii) the decoupling of the pre-rift cover along the Upper Triassic (Keuper) evaporites and clays, allowing its gliding and conservation in the basin center. These two fault zones are the (lower) crust-mantle detachment and the (upper) cover décollement located respectively at the crust-mantle boundary and at the base of the detached pre-rift cover. The Urdach peridotites were exposed to the seafloor during the Late Albian and underwent local pervasive carbonation and crystallization of calcite in a network of orthogonal veins (ophicalcites). The carbonated serpentinized peridotites were partly covered by debris-flows carrying fragments of both the ultramafics and Paleozoic crustal rocks now forming the polymictic Urdach breccia. The mantle rocks are involved in a Pyrenean overturned fold together with thin units of crustal mylonites. Continent-derived and mantle-derived fluids that circulated along the Urdach crust-mantle detachment led to the crystallization of abundant metasomatic rocks containing quartz, calcite, Cr-rich chlorites, Cr-rich white micas and pyrite. Two samples of metasomatized material from the crust-mantle detachment yielded in situ zircon U/Pb ages of 112.9 ± 1.6 Ma and 109.4 ± 1.2 Ma, thus confirming the Late Albian age of the metasomatic event. The cover décollement is a 30-m thick fault zone which also includes metasomatic rocks of greenschist facies, such as serpentine-calcite association and listvenites, indicating large-scale fluid-rock interactions implying both ultramafic and continental material. The lowermost pre-rift cover is generally missing along the cover décollement due to tectonic disruption during mantle exhumation and continental crust elision. Locally, metasomatized and strongly tectonized Triassic remnants are found as witnesses of the sole at the base of the detached pre-rift cover. We also report the discovery of a spherulitic alkaline lava flow emplaced over the exhumed mantle. These data collectively allow to propose a reconstruction of the architecture and fluid-rock interaction history of the distal domain of the upper Cretaceous northern Iberia margin now inverted in the NPZ.; Dans deux articles compagnons, nous décrivons la géologie et la minéralogie de deux massifs de péridotites serpentinisées représentatifs de la Zone Nord-Pyrénéenne (ZNP) occidentale, le massif d’Urdach (cet article) et le massif du Saraillé (article 2). Les péridotites ont été portées vers les niveaux crustaux supérieurs durant l’épisode de rifting pyrénéen crétacé qui a affecté la future ZNP. Elles sont associées à des sédiments métamorphiques pré-rift et à des lambeaux de croûte Paléozoïque déformée durant l’exhumation. En s’appuyant sur des descriptions de coupes géologiques et des analyses de minéraux à la microsonde, nous précisons la lithologie de deux failles extensives majeures qui ont permis : (i) la remontée des lherzolites sous l’axe du bassin ; (ii) l’extraction latérale de la croûte continentale sous les bordures du rift et ; (iii) le découplage et le glissement de la couverture pré-rift le long des évaporites et argiles du Keuper. Ces deux zones de faille sont le détachement croûte-manteau (inférieur) et le décollement de couverture (supérieur) situés respectivement à la limite croûte-manteau et à la base de de la série pré-rift glissée. Les péridotites d’Urdach ont été mises à l’affleurement sur le fond marin où elles ont subi une carbonatation interne partielle accompagnée de cristallisation de calcite dans un réseau de veines orthogonales (ophicalcites). Les serpentinites ont été recouvertes partiellement par la brèche d’Urdach formée d’écoulements de débris ultramafiques et paléozoïques. Les roches du manteau sont engagées avec de minces lentilles de mylonites crustales dans un pli deversé vers l’ouest. Des fluides d’origine mantellique et continentale ont circulé le long du détachement croûte-manteau et ont permis la cristallisation de roches métasomatiques renfermant : quartz, calcite, chlorite et mica riches en Cr, et pyrite. Deux échantillons de ces roches métasomatiques ont fourni des âges U/Pb in situ sur zircons de 112.9 ± 1.6 Ma et 109.4 ± 1.2 Ma confirmant ainsi l’âge Albien supérieur de cet événement métasomatique. Le décollement de couverture renferme aussi des roches métasomatiques (associations calcite-serpentine et listvénites), témoignant d’échanges fluide-roche à grande échelle à partir de matériel mantellique et crustal. La base de la couverture pré-rift a subi une troncature basale lors de l’exhumation du manteau et des résidus triasiques très déformés sont présents à la base de la série pré-rift décollée. Nous avons également découvert une coulée de lave sphérulitique alcaline mise en place sur le manteau exhumé. Cet ensemble de données sur le massif d’Urdach permet de proposer une reconstitution au Crétacé supérieur de l’histoire des fluides et de l’architecture du domaine distal de la marge nord ibérique aujourd’hui inversée dans la ZNP.

International audience; The Pyrenean Range results from the collision between Eurasia and Iberia plates that started during the Santonian. The Pyrenean orogeny is considered to end in Early Miocene times, since from that period onwards, Iberia shows no more differential motion with respect to the rest of Europe and becomes part of the Eurasian plate. This coincided with the slowing down of African-Eurasian convergence. Nevertheless, the Pyrenean relief still displays an unexpected strong relief and a combination of various geological methods highlights the occurrence of local Upper Miocene to present-day uplifts in the Pyrenees (low temperature thermochronological dating, sedimentology, karstology, palynology, palaeoaltimetry). While it has already been studied extensively in the Eastern Pyrenees, fewer works refer to the Western Pyrenean uplift. Depending on the method considered, the timing and the vertical amplitude of this uplift differs.We are initiating a geomorphological study of the incisions in the Western Pyrenees in order to constrain this post-shortening uplift. We focused on the Aspe Valley, where Miocene highly elevated – low relief erosion paleosurfaces observed as relicts on top of the interfluves have been strongly dissected. This dissection was achieved in several steps, including a low erosion episode, followed by an acceleration of erosion which could be attributed to the Late Miocene to actual Western Pyrenean uplift event. The sharp incisions are highlighted by erosion triangular facets which cannot be attributed to glacial erosion as they occur beyond the last glacial deposits. We attempt to reconstitute the landscape prior to this late incision in order to quantify the subsequent erosion and to try to link it with foreland deposits.Evidence of a Late Miocene to present-day uplift is well described in the Eastern Pyrenees and at a larger scale, in the Central Massif, the peri-alpine area and in northern and central Iberia thus suggesting an uplift at a lithospheric scale. However, discrepancies in the uplift rates indicated by already published data are found at a kilometric scale in the Western Pyrenees, which leads us to consider a possible contribution of both local and regional processes to explain the recent incisions in the Aspe Valley.This work is funded and carried out in the framework of the BRGM-TOTAL project Source-to- Sink.