HAL-BRGM, les publications scientifiques en libre accès du BRGM
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Earth’s past and present mantle oxygen fugacity
No full textInternational audienceOxygen is the most abundant element in Earth’s mantle. Oxygen fugacity (fO2), which quantifies the availability of oxygen to mediate oxidation–reduction reactions, affects important mantle processes, such as depth of melting, extraction of volatiles to the atmosphere, crustal composition and ore body generation. Debate continues over modern and past variations in mantle fO2. In this Review, we compile thermobarometric data from mafic and ultramafic rocks at ridges, back-arcs, and arcs and show that the fO2 of subduction-influenced arc mantle is appreciably higher than the mantle supplying ocean ridges. We review the timing and mechanisms that might transfer redox budget to the arc mantle wedge. A new proxy for the redox-sensitive element vanadium confirms the higher oxidation state of arc mantle and can be used to show there is no conclusive evidence for oxidation of the ambient mantle since the Archaean (2,500–4,000 million years ago). Earlier, in the Hadean magma ocean (>4,000 million years ago), liquid silicate equilibrated with liquid metal alloy while the upper mantle was rapidly oxidized to higher fO2. Future research should focus on how mantle fO2 coevolved with Earth’s primitive atmosphere during core formation, magma ocean crystallization and degassing
Sedimentary Architecture Prediction Using Facies Interpretation and Forward Seismic Modeling: Application to a Mediterranean Land–Sea Pliocene Infill (Roussillon Basin, France)
No full textInternational audienceThis study predicts sedimentary architectures and facies distribution within the Pliocene prograding prism of the Roussillon Basin (Gulf of Lion, France), developed along an onshore–offshore continuum. Boreholes and outcrops provide facies-scale observations onshore, while seismic data capture basin-scale structures offshore. Forward seismic modeling bridges spatial and scale gaps between these datasets, yielding characteristic synthetic seismic signatures for the sedimentary facies associations observed onshore, used as analogs for offshore deposits. These signatures are then identified in offshore seismic data, allowing seismic profiles to be populated with sedimentary facies without a well tie. Predicted offshore architectures are consistent with shoreline trajectories and facies successions observed onshore. The Roussillon prism records passive margin reconstruction in the Mediterranean Basin following the Messinian Salinity Crisis, through the following three successive depositional profiles marking the onset of infilling: (1) Gilbert deltas, (2) wave- and storm-reworked fan deltas, and (3) a wave-dominated delta. Offshore, transitions in clinoform type modify sedimentary architectures, influenced by inherited Messinian paleotopography. This autogenic control generates spatial variability in accommodation, driving changes in depositional style. Overall, this multi-scale and integrative approach provides a robust framework for predicting offshore sedimentary architectures and can be applied to other deltaic settings with limited land–sea data continuity
Guide méthodologique pour la planification territoriale participative
No full textSource Agritrop Cirad (https://agritrop.cirad.fr/614997/) * Autres projets (id;sigle;titre): ;PACTE;(TUN) Programme d’adaptation au changement climatique des territoires vulnérables de Tunisie// * Collectivites auteurs : CIRAD-ES-UMR TETIS - FRA// CIRAD-ES-UMR G-EAU - FRA// INRAE - FRA//International audienceCe guide traite de planification territoriale, un processus stratégique et décisionnel visant à organiser et à programmer le développement d'un territoire en intégrant divers aspects tels que l'utilisation des terres, la gestion des ressources naturelles, l'accès aux biens et aux services publics, les infrastructures et les activités économiques. Il est issu de réflexions et d'expérimentations menées en Tunisie depuis plus de quinze ans par le Ministère de l'Agriculture, des Ressources Hydrauliques et de la Pêche et ses partenaires de l'enseignement supérieur et de la recherche agronomique tunisiens et français
Développement d'une approche dendrochimique multi-techniques pour l'analyse intra-cernes des traceurs et co-traceurs de la pollution dans les sites pollués.
No full textInternational audienceLe projet GESIPOL ARGOS, coordonné par le BRGM en partenariat avec TAUW, Chrono-Environnement et l'INRAE, vise à développer une méthode dendrochimique pour mesurer les traceurs de pollution présents dans les sites et sols pollués, en analysant les arbres cerne par cerne. Cette méthode, peu coûteuse et rapide, est adaptée aux zones difficiles d'accès et permet de retracer l'historique de la pollution d'un site et de son sol. Dans le cadre du projet ARGOS, les essences d'arbres échantillonnées pour retracer la pollution sont essentiellement des salicacées, en raison de leur capacité à bioaccumuler les éléments chimiques métalliques. Ces essences, dont le peuplier en particulier, présentent des limites de cernes difficilement identifiables par microdensitométrie.Afin d'obtenir une datation aussi précise et fiable que possible, l'analyse des échantillons prélevés dans le cadre du projet ARGOS est réalisée par micro-tomographie. Cette technique permet d'obtenir des images très précises (résolution < 10 µm) et donc de dater les échantillons avec une grande précision. En parallèle, un modèle de détection automatique des limites de cernes basé sur l'intelligence artificielle est développé, afin d'obtenir une datation plus rapide et fiable.Pour réaliser une analyse élémentaire quantitative aussi complète que possible, deux méthodes d'analyse ont été développées. D'une part, l'analyse par microfluorescence X (µXRF), et d'autre part, l'analyse par ablation laser couplée à la spectrométrie de masse à plasma inductif (LA-ICP-MS), permettent de détecter et de quantifier de nombreux éléments traces présents dans les cernes des arbres, avec des limites de détection faibles. Enfin, un programme a été développé afin de quantifier les données obtenues, de les visualiser, de réaliser des traitements statistiques, et également de fusionner les données issues des différentes techniques d'analyse
Constraints on the neon isotopic composition of the lower mantle by single vesicle analyses in Icelandic glasses
No full textInternational audienceThe origin of volatile elements on Earth is still debated. Noble gases, due to their chemical inertness, can serve as powerful proxies to study planetary formation processes and mantle evolution. Neon is particularly relevant for tracing the source of volatile elements of our planet as its isotopic composition varies greatly between reservoirs in the Solar System. The existence of a preserved (over 4.45 Ga), relatively undegassed, reservoir in the mantle has been inferred from noble gas isotopic systematics [1]. This reservoir is tapped by deeply rooted mantle plumes, namely Galapagos, Hawaii and Iceland plumes. Analysis of quenched glass, preserving magmatic gases, from these locations, revealed that the neon isotopic composition of the lower mantle is different to that of the upper mantle (source of the MORBs), particularly for the 21Ne/22Ne ratio. In both cases however, neon has a20Ne/22Ne ratio over 12, akin to a solar, primitive source, distinct from the atmospheric ratio of 9.8. Two models may explain Earth's mantle neon isotopic compositions: (1) the capture and dissolution of a primordial atmosphere in an early magma ocean, or (2) solar wind irradiation of pre-planetary dust yielding different 20Ne/22Ne ratios in a preserved reservoir. The exact neon isotopic compositions of the lower mantle is still unclear, however. Indeed, the step-heating or step-crushing analytical techniques leads to a mixing curve for neon isotopic ratios between air contained in cracks and open vesicles (20Ne/22Ne = 9.8) and the mantellic value, contained in closed vesicles. To address this, we analyzed single vesicles from undegassed Icelandic subglacial lavas and developed a statistical approach to determine the 20Ne/22Ne of the Icelandic source. This technic has been shown to be efficient to obtain the neon isotopic composition devoid of shallow atmospheric contamination Our findings support solar wind irradiation of protoplanetary disk dust as the mechanism for Earth's light volatile accretion, aligning with Péron et al. [2] for the Galapagos mantle source
Applied Geomicrobiology at the Service of Natural Resource Management
No full textInternational audienceBRGM, the French Geological Survey does more than map subsurface resources. Occupying a space between academia and industry, BRGM is active in key areas such as mineral resources and the circular economy, groundwater quality, and mining environments and contaminated land. Applied geomicrobiology has been at the heart of research and development in these fields at BRGM for half a century. This presentation will briefly cover historic and current development and application of ecotechnologies, and how these are underpinned by geomicrobiology. A particular focus will be placed on international collaborations, especially with countries on the African continent which have enabled these advances; these are the win-wins. Since the 1970's BRGM has been developing biotechnologies for mining: for example, biomining of cobalt from tailings in Uganda and using sulfate-reducing bacteria to remediateand valoriseacid mine drainage. Understanding the biogeochemical processes involved in the weathering of mine wastes is leading to the development of predictive models of their phytostabilisation, with the aim to improve long-term management. In parallel, novel indicators are being developed to diagnose and monitor former mining and other brownfield sites as part of their rehabilitation. Finally, and most recently, BRGM has been working with South African partners to develop a suite of bioindicator tools to monitor groundwater quality and aquifer health. Such tools should complement existing analytical techniques, coupling geochemistry and microbial ecology to define the biological heritage beneath our feet, diagnose ecosystem service capacity, and monitor groundwater management systems (for example managed aquifer recharge).</div
Rare-metal mineralization and crustal magmatism in a collisional orogen: protracted evolution of the Sioule metallogenic zone (Variscan French Massif Central)
No full textInternational audienceThe West European Variscan Belt (360-300 Ma) is a major metallogenic province for rare metals, hosting both magmatic and hydrothermal deposits. Magmatic mineralization occurs in granitic or pegmatitic intrusions enriched in Li-Sn-Nb-Ta, while hydrothermal deposits are found in quartz veins and metasomatic rocks containing Sn ± W. Although these two mineralization types are often spatially associated within the same deposit particularly at the margins of granitic batholiths, they typically exhibit complex, multiphase evolutionary histories that are difficult to reconcile with a single metallogenic event. This issue is well exemplified in the Sioule region, an archetypal metallogenic zone within the Variscan Belt. There, a large quartz vein system mineralized in wolframite (W) and minor cassiterite (Sn) was later intruded by the Beauvoir rare-metal granite, which notably hosts disseminated Li-micas along with magmatic cassiterite. While the late-orogenic nature of rare-metal magmatism (315-310 Ma) is well constrained, the timing of the hydrothermal W-Sn mineralizing events and their relationship to regional tectonic and magmatic processes remains controversial, with previously proposed ages ranging from 330 to 310 Ma, and even older than 360 Ma. To address this, a petro-geochemical study combined with U-Pb zircon-apatite geochronology was conducted on metasediments and felsic igneous rocks from the Sioule Metallogenic Zone (SMZ), along with direct U-Pb dating of ore minerals including cassiterite and wolframite. Our data indicate that the protoliths of Sioule series migmatites include Late-Ediacarian (< 540 Ma) detrital sediments as well as peraluminous orthogneisses dated at 510-490 Ma. Partial melting likely occurred during or before Early Variscan peraluminous magmatism at 354 ± 6 Ma, marked by the emplacement of now variably deformed biotite ± garnet ± cordierite granitoids (Chantelle and St-Gervais massifs). This magmatic event was subsynchronous with N110-trending dextral shearing, and early W hydrothermalism as confirmed by a wolframite U-Pb age at 351 ± 9 Ma. By 333 ± 6 Ma, the southern part of SMZ was exhumed, and metaluminous to peraluminous felsic magmas were either erupted as tracy-dacite tuffs or crystallized at depth as biotite microgranite (Pouzol-Servant massif). Further north, highly peraluminous and Li-rich granitic magmatism, a precursor of rare-metal granite magmatism, formed rhyolitic dykes and granitic pluton (Colettes massif), possibly linked to N60 senestral shearing. Such event was likely accompanied by a second W mineralizing phase, constrained by apatite U-Pb dating at 329 ± 5 Ma. Between 320 and 310 Ma, the southeastern part of the SMZ experienced a new plutonic-volcanic episode marked by the emplacement of biotite granite (Champs massif) and trachy-dacite tuff. Such volcanism appears geochemically similar to the regionally recognized Visean volcanic event at ca. 330 Ma. At this time, magmatic fluids exsolved from the crystallizing Beauvoir rare-metal granite precipitated hydrothermal cassiterite (319 ± 7 Ma) and a third generation of wolframite.This study highlights the protracted magmatic and hydrothermal history of a metallogenic zone of the Varican belt in relation to episodic peraluminous magmatism. It also supports the common temporal decoupling of Sn and W deposition events, even within the same deposit
Extraction d'Informations dans les réseaux sociaux par apprentissage de représentations textes/images : application à la gestion des catastrophes naturelles
No full textWith the increasing use of social media, platforms like Twitter have become pivotal for real-time crisis information. Posts on these platforms serve as critical data sources for situational awareness and emergency response. To efficiently exploit this information, previous works have focused on developing automated methods to filter and categorize social media posts, primarily processing either text or images (unimodal data). The present work aims to integrate both images and text from tweets by fusing information from both modalities. Firstly, this thesis explores multiple unimodal encoders with various fusion techniques, along with a deep analysis of multimodal crisis tweets, highlighting the uniqueness of multimodal tweets in terms of modality relations. Secondly, it introduces a caption-based method that translates images into a text-compatible representation space through captioning, allowing for more efficient fusion and thus achieving better and more robust performance. This method also supports hybrid usage, enabling the model to function in both unimodal and multimodal settings without compromising performance. Our experiments revealed the presence of a well-known problem in multimodal learning, namely modality imbalance, where one modality dominates the learning process. We tackle this issue with a data-driven method that adapts to the learning dynamics and allows the dominated modality to catch up. In addition to methodological advancements, this thesis introduces M-CATNAT, a French multimodal dataset that fills a linguistic and multimodal gap in crisis-related resources. M-CATNAT provides detailed annotations for text, images, and combined content, offering a nuanced foundation for French multimodal crisis-related tweet processing.L'essor des réseaux sociaux, comme Twitter, a rendu ces plateformes essentielles pour diffuser des informations en temps réel lors de crises. Des méthodes automatisées de filtrage et de catégorisation de ces publications, basées sur le texte ou les images, ont été développées pour exploiter ces données. Ce travail propose d'intégrer simultanément texte et images des tweets, en fusionnant ces deux modalités. Dans un premier temps, cette thèse explore l'utilisation de plusieurs encodeurs unimodaux et techniques de fusion, tout en procédant à une analyse des tweets afin de mieux comprendre les relations entre les modalités visuelle et textuelle. Cette thèse introduit ensuite une méthode qui convertit les images dans un espace de représentation compatible avec le texte, rendant ainsi la fusion des deux modalités plus efficace et améliorant la robustesse et la performance du modèle. Cette approche est également hybride, permettant au modèle de traiter aussi bien des tweets unimodaux que multimodaux. Cette étude met en évidence un problème courant en apprentissage multimodal : le déséquilibre des modalités, où l'une d'elles domine le processus d'apprentissage. Une méthode d'adaptation a été proposée pour réguler cette dynamique et permettre une progression d'apprentissage plus équilibrée entre les modalités. En plus des avancées méthodologiques, cette thèse présente M-CATNAT, un jeu de données multimodal français qui comble un manque linguistique et multimodal dans les ressources liées aux crises. M-CATNAT offre des annotations détaillées pour le texte, les images et le contenu combiné, fournissant une base pour le traitement des tweets de crise multimodaux en français
Effects of Spacing Between Stone-Rows on the Chemical and Biological Fertility of Lixisoils in Eastern Burkina Faso
No full textInternational audienceThis study assessed the effects of stone-rows spacing on soil fertility and the potential for a fertility gradient to occur in a farming setting. The study was conducted in a rural area of Sampieri, eastern Burkina Faso, within a Sudano-Sahelian environment on Lixisols with a medium slope of up to 5%. The experimental design included three plots, each with a different stone-rows spacing: 15.5 m (P1), 18.5 m (P2) and 22 m (P3). Soil samples were taken at depths of 0-10 and 10-20 cm, with interval ranging from 0 to 15 m from the rows. Soil organic carbon(C), total nitrogen (N), pH and soil microbiological activity were measured. The study showed that C, N, P and pH levels improved more on plots P2 and P1 than on plot P3. Although differences were noted for microbiology, they were not statistically significant. A correlation was found and most soil fertility parameters. However, no soil fertility gradient was evident as a function of slope when moving away from the first stone-rows line. It can be concluded that the optimal spacing between stone-rows is 18.5 m and that it is difficult to deduce a fertility gradient within this interval. However, further research is needed for validation and confirmation of these findings
Démarche de prévention du risque sismique en Auvergne-Rhône-Alpes : priorisation et évaluation des itinéraires routiers utilisables par les secours
No full textInternational audienceLa DREAL Auvergne-Rhône-Alpes (ARA) a engagé une démarche d’évaluation du risque sismique sur son territoire depuis 2019. Ce territoire comporte plusieurs zones de sismicité de niveau modéré à moyen (notamment dans les départements alpins et préalpins). Depuis 2020, une approche co-construite entre les services de l’Etat, les collectivités locales et différents opérateurs spécialistes du sujet a été engagée pour établir des plans d’actions visant à répondre aux besoins exprimés par les acteurs en termes de connaissance de l’aléa, d’impact sur les aménagements existants et futurs, de sensibilisation et de prévention. Les premières actions entreprises (2021-2023) ont principalement consisté en des sessions de sensibilisation, d’amélioration des cartes d’effets de site, des études de scénarios de dommages au bâti (villes de Montélimar, Bourg-En-Bresse, Nantua et Belley), et plus récemment des études de prémicrozonage.En parallèle de ces actions, la DREAL ARA a souhaité compléter l’étude de vulnérabilité sismique des territoires en intégrant les réseaux routiers, vecteurs essentiels de mobilité de population et d’acheminement des secours dans un contexte de crise sismique. Le Cerema a ainsi appliqué au département de l’Isère l’approche SISMET préalablement développée et éprouvée sur les territoires de Nice et de Lourdes pour la hiérarchisation des itinéraires routiers à renforcer pour garantir l’accès des secours et l’analyse de risque sismique des ouvrages (ponts, murs, tunnels ou talus) les plus critiques de ces itinéraires, à partir du croisement d’indices d’aléa, de vulnérabilité et d’importance. Une collaboration entre le BRGM et le Cerema a permis de déployer cette démarche entre Bourg-en-Bresse et Nantua (Ain), et entre Valence et Montélimar (Drôme) et des projets similaires sont également en cours sur les itinéraires des départements de Savoie et Haute-Savoie. L’objectif de la présente communication est de présenter les grands principes de l’approche mise en œuvre et les premiers résultats obtenus sur ces différents départements exposés au risque sismique