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National audience; A detailed analysis of the petrographic relations and mineral chemical zoning combinedwith the use of calculated psuedosections is a powerful tool to unravel cryptic, yetimportant details of the P–T evolution of rocks, with a potential impact on theinterpretation of the geodynamic context.A mafic kyanite-bearing eclogite from the Haut-Allier displays garnet-rich layers thathave intriguing similarities and differences with respect to the surrounding eclogites.Chemical zoning of garnet inside and outside the layers is similar, but the layers areenriched in rutile and ilmenite, and lack kyanite, common in the eclogite. Threesuccessive metamorphic stages, M1, M2 and M3, are characterized by assemblagescomprising garnet1-omphacite- kyanite, garnet2-plagioclase, and amphiboleplagioclase,respectively, and define a clockwise P–T path. These events occurred atthe conditions of eclogite (M1; ∼ 20 kbar, 650 °C to ∼22.5 kbar, 850 °C), high-pressure granulite (M2; 19.5 kbar and 875 °C) and hightemperatureamphibolite facies (M3; < 9 kbar, 750– 850 °C), respectively. Phasediagrammodelling of garnet growth zoning and mineralogy of the inclusions reveal aprograde M1 stage, first dominated by burial and then by near-isobaric heating.Subsequent garnet1 resorption, prior to a renewed growth of garnet2 is interpreted interms of a decompression during M2. High- pressure partial melting is predicted forboth the M1 temperature peak and M2, due to focussed influx of H2O-rich fluids orexternal melts, probably associated with localized deformation. It is inferred thatsubsequent melt loss resulted in the formation of the garnet- rich layers. Despite theabsence of clear accumulations of crystallised melts in the eclogite, high-pressuremelting may he linked to the existence of HP trondhjemitic melts, described elsewherein the Massif Central. M3 testifies to further strong decompression associated withlimited cooling. The preservation of garnet growth zoning indicates the short-livedcharacter of the temperature increase, decompression and cooling cycle. We argue thatsuch P–T evolution is compatible with the juxtaposition of the asthenosphere againstthe subducted crust prior to exhumation driven by slab rollback.

International audience; Les cartes géologiques évènementielles, conceptualisées et réalisées dans le cadre du Programme « Référentiel Géologique de la France » (RGF), sont des cartes numériques qui permettent de retracer l’histoire géologique des objets représentés. Les roches acquièrent leurs caractéristiques (minéralogiques, structurales et texturales) à travers une suite d’évènements qui leurs sont propres, depuis leur genèse jusqu’à l’affleurement, en passant par tous les phénomènes de transformation qu’elles subissent (métamorphisme, déformation, altération). Au cours du projet RGF-Pyrénées la compilation de plusieurs milliers de ces évènements géologiques en base de données, et leur assignation à des géométries, a permis de générer des cartes de ces évènements géologiques.Dans les Pyrénées, l’amiante existe à l’état naturel dans certaines lithologies, dont en particulier : les roches ultrabasiques ; les roches plutoniques et filoniennes basiques à intermédiaires et les marbres. Certains évènements métamorphiques (hydothermalisme, métamorphisme en faciès schiste vert, …) vont rendre davantage probable la cristallisation de minéraux amiantifères dans ces roches. Lors de cette étude, un traitement SIG appliqué sur les lithologies et les évènements métamorphiques, a permis de produire une carte prédictive des lithologies potentiellement porteuses d’amiante naturel dans les Pyrénées. Un travail de cartographie sur le terrain couplé à des analyses en laboratoire (MOLP, microsonde électronique, MEB), s’est ensuite focalisé sur l’identification et la caractérisation des espèces minérales fibreuses présentes dans les roches échantillonnées. Le travail présenté ici, montre une carte de la susceptibilité de présence d’amiante naturel, à l’échelle 1/50 000, des Pyrénées.Les résultats de cette étude soulignent: (i) l’importance de l’actinolite-amiante dans les roches doléritiques, et (ii) la présence de trémolite-amiante dans les skarns et certains marbres dolomitiques. Ce travail illustre une utilisation innovante de la cartographie géologique événementielle, comme puissant outil de prédiction. Cette approche sera utile dans un contexte d’évolution de la règlementation en France, qui dès la fin de l’année, imposera la recherche d’amiante naturel avant tout types de travaux, dans l’environnement naturel.

International audience; The Aiguilles-Rouges Massif (ARM) basement is mostly composed of migmatitic gneisses and micaschists hosting metric boudins of retrograded eclogites and amphibolites. In the SW part of the massif, these high-grade rocks are overlaid by low-grade metamorphosed Carboniferous volcano-detritic sediments Three main deformations, named D1, D2 and D3, have been described in the Variscan basement of the ARM. When D1 relicts are preserved in low-D2 strain domains, they correspond to a flat-lying S1 foliation only preserved in the gneissic core. This D1 is associated with partial melting metamorphic event M1. D2 is characterized by three main orientations of planar fabrics, oriented toward N160, N0 and N20 directions and forming S2- C2-C2’ structures, respectively. They are related to a bulk non-coaxial anastomosed system developed under dextral transpression. D3 corresponds to a flat-lying cleavage associated to vertical shortening and folding of previous foliations. This deformation has only been observed in the upper structural levels of the gneissic basement and within the Visean sediments.Field observations and EBSD data on eclogitic boudins indicate that D1 deformation is posterior to the relictual high pressure paragenesis, while D2 is synchronous with the retrogression of the eclogites into amphibolites. U-Th-Pb LA-IC-PMS datings on Zircon, Monazite and Rutile indicate that high-pressure metamorphism is recorded at ca. 335-330 Ma in the eclogitic boudins, whereas the M2 peak of temperature in surrounding metapelites ranges between 325 and 315 Ma. The exhumation of the Variscan basement, related to D2 dextral shearing and D3 crustal thinning, occurred between 315 and 300 Ma. These new results indicate a Variscan geodynamic evolution from high pressure conditions to late exhumation ranging between ca. 335 and 300 Ma in the ARM.

International audience

International audience; La dimension temporelle est une composante intrinsèque de la géologie. Toutes les roches résultent de processus de formation et de transformations qui se relayent dans le temps. Les cartes géologiques restituent l'état actuel des objets géologiques, pour ne représenter que le "faciès" dominant des roches. Elle privilégie, dans sa représentation, un évènement marquant enregistré dans une roche (génétique ou de transformation) au détriment des autres. Ainsi, les roches altérées sont sous représentées au bénéfice de leur protolithe ; certains orthogneiss sont identifiés comme des granites ; des marbres figurent comme calcaires et les roches métamorphiques apparaissent avec leur faciès dominant. Le choix de la représentation cartographique est donc arbitraire et dépend de la finalité de la carte géologique, de son contexte de réalisation et de la sensibilité du géologue. Aujourd'hui, les technologies numériques permettre de dépasser les limites imposées par la représentation graphique de la carte géologique. L'un des principes de la nouvelle carte géologique du Référentiel Géologique de la France (RGF) est de pouvoir intégrer toutes les caractéristiques d'une roche en fonction de son histoire géologique. Ce nouveau concept, développés dans le cadre du projet RGF-Pyrénées, est appelé "carte géologique évènementielle". Cette carte numérique s'appuie sur une base de données hiérarchisée contenant l'essentiel des évènements affectant les roches et constitue le « Référentiel évènementiel » des Pyrénées. Pour chaque polygone de la carte géologique RGF est associé un ou plusieurs évènements. Cette approche permet ainsi, selon les besoins des utilisateurs, de décliner autant de produits cartographiques que nécessaire. La carte événementielle laisse à l'utilisateur le choix de proposer sa propre interprétation, sans affecter la donnée brute et son organisation en base de données. Elle permet d'intégrer les nouvelles données, de défaire/faire de nouveaux liens entre ces données au gré des questions et progrès scientifiques.

International audience; The term asbestos is a commercial term referring to six silicate minerals, listed as human carcinogen by world hearth authorities. Asbestos was banned in France since 1996 but since a decade, a new focus was done on Naturally Occurring Asbestos (NOA). NOA are fibrous minerals that occur as natural components in some rocks and soils, as opposed to asbestos in commercial products. Human activities (such as mining, agriculture, construction or urban development) and natural weathering processes are likely to release NOA in the air. Because NOA forms in specific rocks and geologic conditions, it is possible to predict geologic environments that may host NOA. A multi-scale geological mapping program is going on in France to identify lithologies that are likely to contain asbestos-like minerals leading to the establishment of maps of potential asbestos-bearing rocks at different scales. Major occurrences concern ultrabasic, basic and dolomitic rocks affected by greenschist to amphibolite-facies metamorphism and/or hydrothermal metasomatism. Unusual occurrences were also identified, as in alkaline metagranitoids, dolerites and talcschists. To manage NOA-related risks and control worker exposures to asbestos, new upcoming regulations will come into force in France, including the prior identification of asbestos in natural soils or rocks likely to be impacted by the execution of works. Maps of potential NOA occurrences will therefore constitute reference documents for such studies. Moreover, regulations will lead to the standardisation of protocols for sampling, analysis and characterization of natural materials likely to contain asbestos.

International audience; The P–T evolution of a mafic eclogite sample from the Haut-Allier was studied in order to constrain the dynamic of the Variscan subduction in the eastern French Massif Central. Three successive metamorphic stages M1, M2 and M3, are characterized by assemblages comprising garnet1-omphacite-kyanite, garnet2-plagioclase, and amphibole-plagioclase, respectively, and define a clockwise P–T path. These events occurred at the conditions of eclogite (M1; ∼ 20 kbar, 650 °C to ∼ 22.5 kbar, 850 °C), high-pressure granulite (M2; 19.5 kbar and 875 °C) and high-temperature amphibolite facies (M3

International audience; The French Massif Central (FMC) forms the hinterland of the west-European Variscan belt and was subject to numerous tectonic and metamorphic events from Devonian to Permian times. The accreted tectonic units belonging to Gondwana and Laurussia were variably involved in subduction, nappe stacking and syn-to post-orogenic extension. Besides, plutons and migmatites showing syn-collision crust melting are very common in the Variscan belt. Such orogenic evolution implies that the resulting finite structure likely reflects the interference between fabrics formed at different stages of the orogenic cycle with different degrees of overprinting, depending on e.g. the spatial strain gradients, lithologies, structural level or partial melting grade. We present a model of finite strainfield of the western FMC based of the analysis/interpolation of ductile and brittle fabrics, at regional to local scale, using geostatistics. Ductile fabrics within autochthonous units and syn-collisional plutons are poorly disturbed and reflect the transition from syn-thickening to extensional lateral flow of the partially molten mid-lower crust. In contrast, allochtonous units are affected by numerous perturbations including polyphased ductile shearing, folding and faulting inducing local bloc tilting and rotations. Taking into account the overprint of late tectonic events, we show that early fabrics related to High Pressure metamorphism or nappes' stacking have suffered intense reorientations. The finite trend of the related lineations L1 must be treated with extreme caution and may not reflect the original direction of stretching and shearing that occurred during the initial compressional stages. Taking into account i) the spatial distribution and amount of reorientation of these D1 fabrics and ii) the deconvolution of these disturbances, we propose that:-The high dispersion of lineation trend can be simply explained by passive rotations, during late isoclinal folding, rather than two superposed tectonic phases, as previously inferred.-The allochtonous units formed one single tectonic unit.-This D1 event looks related to the exhumation of the subducted continental crust due to partial melting-The formation of Variscan orogenic prism in western FMC only results of continuous south-directed thrusting rather than a switch from NE-SW to NW-SE thrusting.

International audience; In France, the asbestos banning is subject to a national decree (n° 96-1133), published in 1996. The regulatory texts and standards adopted to control this banning concern in particular asbestos-bearing manufactured products, but remain difficult to apply to asbestos-bearing natural materials (ie. rocks, soils). Considering problems related to such asbestos-bearing natural materials, the Ministry of Ecological and Solidary Transition has mandated the French Geological Survey to locate the impacted areas. Mappings were priority carried out in geological domains where NOA was predictable (French Alps, Corsica). These studies integrated field expertise, sampling and laboratory analyses, in order to characterize the potential of geological units to contain NOA. Furthermore, some expertises were carried out on geological formations exploited in France to produce aggregates. These studies concerned the quarries exploiting massive basic or ultrabasic rocks, likely to contain NOA, and quarries exploiting alluvium likely to contain asbestos-bearing rock pebbles. These studies highlight the difficulty of establishing robust diagnoses for natural materials. Indeed, distinction between cleavage fragments resulting from the fragmentation of non-asbestos particles and proper asbestos fibers is particularly problematic for laboratories. Thus, a recent study of the National Agency for Health Safety, Food, Environment and Work (2015) recommends to apply the asbestos regulation for elongated mineral particles (L/D > 3:1, L > 5 μm, D < 3 μm) with chemical composition corresponding to one of the five regulated amphibole species, irrespective of their mode of crystallization (asbestiform or non-asbestiform). The upcoming regulatory changes are part of a decree published in 2017, including the prior identification of asbestos in natural soils or rocks likely to be impacted by the execution of work. Specific protocols will be defined for sampling, analysis and characterization of natural materials that may contain asbestos.

National audience; Dans les Pyrénées, le métamorphisme hercynien dominant estde type haute température (HT) et basse pression (BP). Ce typede métamorphisme est présent partout dans le reste de la chaînehercynienne, mais il est généralement tardif et précédé par unmétamorphisme de plus haute pression, typiquement barrovien.Dans les Pyrénées, les évidences d’un métamorphisme barroviensont rares. Du disthène a été décrit et interprété comme le résultatd’un métamorphisme de moyenne pression antérieur au métamorphismerégional HT-BP, p.ex. dans le Canigou. Néanmoins,le disthène a également été interprété comme un minéral tardif,postérieur au métamorphisme HT-BP (p.ex. Cap de Creus, Albères).Le massif du Canigou est dominé par un orthogneiss ordovicienformant un dôme. Des micaschistes situés au coeur du massif,sous l’orthogneiss, enregistrent deux évènements métamorphiquesassociés au développement de deux schistosités (S1 et S2). Lepremier évènement est caractérisé par le développement syn-S1de porphyroblastes de staurotide et de grenat avec des tracesd’inclusion sigmoidales. Ces porphyroblastes sont partiellementrésorbés et entourés d’andalousite dont les caractéristiques texturalestémoignent d’une cristallisation syn-S2. Des pseudosections(calculées avec THERMOCALC et Theriak/Domino) permettentde montrer que le premier évènement, prograde, est associé à unpic de pression, enregistré par la zonation du grenat, de l’ordrede 7 kbar à 550C. La paragenèse à staurotide + grenat indiqueun pic de température autour de 600C pour 6,5 kbar, dans ledomaine de stabilité du disthène. Cela correspond à un gradientthermique d’environ 30C/km, typique du métamorphismebarrovien. Le second évènement métamorphique est défini parla stabilité de l’andalousite et localement une seconde phase decristallisation du grenat. Il est contemporain du développementde la schistosité régionale S2 et témoigne d’une décompression,entre 3 et 5 kbar à environ 550C. Le gradient thermique, lors dece second évènement métamorphique, est de l’ordre de 60C/km.Cette séquence d’évènements métamorphiques implique au premierordre l’existence d’un épisode d’épaississement qui a précédéune phase d’exhumation d’origine tectonique dans les Pyrénées.Néanmoins, la seconde phase de croissance du grenat témoigned’une évolution plus complexe avec une décompression et un refroidissementsuivant le premier pic de température et précédantle métamorphisme dominant syn-S2 de HT-BP.Ce travail a été réalisé dans le cadre du chantier Pyrénées duprogramme RGF.

National audience; Plusieurs exemples de terrains issus de différents cratonsarchéens et paléoprotérozoïques (Afrique du Sud, Canada, Finlande,Terre Adélie) démontrent que les modalités de la déformationdes lithosphères continentales chaudes diffèrent fortementde celles connues dans les zones orogéniques modernes. Ceci estparallèlement argumenté par la modélisation analogique. Modélisationet terrain nous ont ainsi conduits à proposer un nouveaumodèle tectonique des structures compressives observées dans leszones de déformation affectant les cratons archéens ou paléoprotérozoïques[1]. Ce modèle montre que beaucoup de structuressont interprétables en termes de descente de portions de croûtesupérieure qui s’empilent le long de zones de déformation verticales.Ce processus purement tectonique ne nécessite pas d’effetgravitaire, comme précédemment proposé dans les modèles desagduction souvent invoqués pour les ceintures de roches vertesarchéennes. Une condition nécessaire est une lithosphère molleavec un manteau lithosphérique ductile, lithosphère molle danslaquelle la croûte supérieure fragile descend sous le simple effetde la compression. Les zones le long desquelles s’empilentpréférentiellement les portions de croûte supérieure descendantessont des zones de forte déformation potentiellement connectéesavec le manteau ductile sous-jacent. Elles sont caractérisées pardes foliations très pentues et des linéations d’étirement fortementplongeantes. Leur caractère durable et leur géométrie subverticale,impliquant l’incorporation et le métamorphisme de sédimentssyntectoniques, en font des zones particulièrement favorables auxtransferts de fluides d’origines variées, de la surface au manteau,et aux interactions fluides-roches.Nous présentons des exemples de terrain (Afrique du Sud, Canada)qui montrent que ce processus tectonique peut être un supportclé pour la localisation de minéralisations variées (e.g. Sb, Au,Ni) à différents niveaux structuraux (de la croûte supérieure auxdomaines de fusion crustale) dans les cratons archéens et paléoprotérozoïques.D’autres exemples, incluant le cas des gisementsd’uranium à la base du bassin de l’Athabasca (Canada) sont aussidiscutés.Références:[1] Gapais D. et al. (2014) Tectonophysics 618: 102–106.

International audience; As a continuation of the national programme of geological map of France at 1:50,000, the French Geological Survey (BRGM) engaged in the Geological Reference of France (Référentiel Géologique de la France, RGF). Over the next decades, this programme aims at developing a three dimensional knowledge of the eleven different geological regions through a continuous, homogeneous and consistent description permanently updated as well as understanding the mechanisms governing their evolution over time.All existing and newly acquired information, currently in the Pyrenees, are integrated within the RGF spatial data infrastructure (SDI). It provides the associated scientific programme with the necessary information system (data structure, computer means, applications and tools) to meet the various needs of contributors and end-users, from acquisition to dissemination of public data and knowledge. The RGF SDI must deliver the best available geological information over the territory, whatever the producer, i.e. research works, applied geology projects, both internal and external to the RGF programme. It must also abide by French and European legislation in terms of interoperability and open access to public data.The quality and reliability of the data and knowledge capitalised in the RGF SDI are primarily based on a thematic reference system including detailed lithostratigraphy, chronostratigraphy, structures and geological events. Both 2D and 3D geometries are also part of the references so that the RGF SDI can be used by other information systems e.g. hydrogeology, mineral resources and geohazards. This involves a dedicated architecture of data sets and applications as well as innovative data structures to capture the complexity of the geological objects and processes. A description-oriented method was used for building original master data sets from textual descriptions in natural language. For example, it was applied to lithology and also its transformation by diagenesis, metamorphism or supergene alteration, as many sub-processes of the event references. This essential foundation for a consistent description and interpretation in 2D-3D is associated to validation workflows involving the RGF Scientific Committee. Several data status i.e. input/proposed/ labelled/disseminated allow to manage appropriately the access and publication of the RGF data and references both within the RGF community and to the public.The multi-stakeholder dimension of RGF drives the technical implementation through a collaborative approach of the SDI platform. It complies with the European INSPIRE Directive while offering a series of web services based on GeoSciML. This enables the RGF SDI contents to be disseminated both through web-enabled geoscientific portals (rgf.brgm.fr) and data processing tools.

International audience; The Armorican belt is part of the westernEuropean Variscan belt. Although the region was oneof the world leader producers of antimony at thebeginning of the 20th century, the geological controlsbehind these deposits remain badly constrained. Herewe present a spatial statistical analysis of the Sbmineralisation,together with geophysical andgeological data [1]. Results show that the Sbmineralisationis spatially associated with strongpositive gravity and magnetic anomalies which mustbe linked to the presence of mafic/ultramafic bodiesat depth. This spatial link is further supported by thenumerous outcropping occurrences of dolerite dykesand sills close to the Sb-deposits and sometimeshosting the mineralisation. This mafic magmatism,dated by in-situ U-Pb analyses on apatite at ca. 360Ma, appears as a regional-scale event at theDevonian-Carboniferous boundary. In addition, newdata suggests that mafic magmatism may haveprobably played a role in the early distribution orredistribution processes of metal stock in thesubsequent history of the antimony in the VariscanArmorican belt.[1] Pochon et al. (2016). Terra Nova, doi:10.1111/ter.12201

International audience

International audience; The localization and strike of compressional structures developed in the Pyrenees during the Iberian-Eurasiancollision are strongly controlled by structures inherited from earlier tectonic events. This structural inheritanceresults in the first place from the Variscan orogeny, then from the Cretaceous rifting episode. The consequencesof this extension are particularly well developed in the North Pyrenean Zone (NPZ), a relatively narrow domainthat focussed strong localization during subsequent shortening. The position of the Internal Metamorphic Zone(IMZ) that makes the southern part of the NPZ is debated. The IMZ displays very specific structure and lithologies(foliated marbles, sometimes brecciated, peridotites...) within a narrow stripe with a width limited to a fewkilometers, from the Agly massif in the east, all the way to the Spanish Basque massifs where it forms the "Nappedes Marbres". These marbles result from the metamorphic transformation of the carbonate series of extensionalbasins presumably of Jurassic to lower Cretaceous age. The HT-LP metamorphism reached temperatures of550-600C in the IMZ and the Nappe des Marbres and surrounding formations, represented by the Paleozoicbasement or Mesozoic series are not exempt of metamorphism, with measured maximum temperatures up to350C. The temperature contrasts measured within the NPZ and the deformation intensity contrasts imply latepost-metamorphic movements bringing the high-temperature and low-temperature domains into close contacts.This observation and the geometrical relations observed in the field suggest the allochthony of the IMZ. Wepresent a new interpretation of the 3D geometry of the NPZ following this hypothesis and discuss the implicationsfor the overall geometry of the Pyrenees.