HAL-BRGM, les publications scientifiques en libre accès du BRGM
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Experimental determination of lithium partitioning between plagioclase and hydrous rhyolitic melt
No full textInternational audienceLithium concentrations and partition coefficients were determined in plagioclase and Li-doped (300, 500, and 1500 ppm) H2O-saturated rhyolitic melts experimentally produced at temperature of 800–875 °C and pressure of 50–150 MPa.High bulk Li concentration of 1500 ppm have remarkable effects on the crystallization of rhyolitic melts, comparatively to lower concentrations: i) Ca-rich clinopyroxene crystallizes at the expense of plagioclase and Ca-poor clinopyroxene, ii) plagioclase anorthite content decreases, and iii) melt H2O solubility increases significantly, resulting in lower crystallinities.The Li content of plagioclase (70–900 ppm) and rhyolitic melt (300–1700 ppm) both increase with bulk Li content. The Li content in plagioclase increases with decreasing plagioclase anorthite content. The aqueous phase contains a negligible fraction of Li.The plagioclase-rhyolitic melt partition coefficients (K) range from 0.2 to 0.6 and are mostly constant with bulk Li concentration. At 875 °C, the K increase from ∼0.3 to 0.6 with pressure decreasing from 150 to 50 MPa, while constant (0.2–0.4) with pressure at 800 °C. At 50–100 MPa, the K increase from 0.3 to 0.4 at 800 °C to 0.5–0.6 at 875 °C, while constant (0.3–0.4) with temperature at 150 MPa.These results give information to interpret Li gradients in natural plagioclases with regard to processes such as magma degassing, decompression, and cooling. In particular, opposite Li gradients are expected in plagioclase during decompression-induced degassing (Li outward-gradients) and isobaric cooling (Li inward-gradients)
A Kalman Filter Approach for Estimating Daily Discharge Using Space‐Based Discharge Estimates
No full textInternational audienceThe SWOT satellite mission is the first to conduct a global survey of the Earth's surface waters, measuring water surface height, river width, and water surface slope, based on which river discharge is estimated. At mid‐latitudes, the repeat orbit design of SWOT only allows a sampling of twice per repeat cycle, which is considered too low for most hydrological applications. To address the spatiotemporal limitations of SWOT, we develop a method that assimilates SWOT observations across continuous reaches within a single‐branch river network to obtain daily discharge estimates. Our model‐free assimilation method provides a linear dynamic system that includes a process model based on a physically based spatiotemporal discharge correlation model and observation equations utilizing SWOT products. We solve this dynamic system using a simple Kalman filter in the time domain, assimilating SWOT observations and incorporating the physically based prior to estimate daily discharge. Since SWOT discharge products were not yet available during the period of this research, we used synthetic SWOT data sets, introducing random and systematic errors through Monte Carlo simulation. The validation of the estimated discharge against true discharge over all test cases leads to a median correlation as high as 0.95, a median NSE for residuals (mean‐removed discharge) as high as 0.81, and a median relative bias as low as 5%, respectively. These promising results suggest that daily discharge for continuous reaches in a river network can be obtained through our data assimilation framework
Benchmarking probabilistic spatial machine learning models with complex sample distributions
No full textInternational audienceIn recent years, machine learning models (ML) have become increasingly key to spatial interpolation. The cornerstone of these approaches is prediction accuracy, i.e. the extent to which a prediction of the target variable is estimated with high quality given the geographical coordinates and/or the spatial features that have not been used in the training dataset. Beyond spatial prediction, the question of predictive uncertainty has emerged as a challenge. Though the connection between ML and uncertainty quantification is an active research field, developments for spatial data still present open questions. One of the major concerns stems from the specificities of the spatial context, i.e. spatial dependence, uneven sample distribution, presence of strong anisotropies or/and non-stationarities. In this study, we benchmark four types of probabilistic ML models adapted to the spatial context: (1) Kriging, (2) Deep Gaussian process regression, (3) Conformal approaches adapted to non-exchangeable data, and (4) Adversarial-based generative models. We define repeated random experiments using synthetic random fields as well as real cases. The latter are based on the high resolution L1B radiance data sets measured from the MODIS satellite instrument that present different degrees of non-stationarities and anisotropies depending on the presence of ice or clouds. We discuss the influence of the characteristics of the sample distribution (sparsity, degree of clustering, spatial dependence, nonstationary) on the quality of the predictive uncertainty by using multiple performance metrics (coverage of the prediction intervals, informativeness, sharpness and calibration of the full predictive probability distribution) as well as practical considerations (computational burden, stability of the results, implementation effort, degree of required expertise). Our results show the high importance of using multiple performance metrics, and highlight the strong influence of the validation procedure (random or structured cross validation), which impacts the selection of the most optimal model. Finally, these results are used to guide the selection of ML interpolation models for a highly clustered real case. The latter aims at mapping bedrock topography in order to model the land-sea continuum of the hard basement beneath sediment cover, in the Pays-De-Monts coastal dune system, Atlantic coast, France
Continental rifts and mantle convection
No full textInternational audienceContinental rifting is an important component of the Wilson cycle, and a process-level description requires integration of constraints from seismic tomography, seismic anisotropy, and non-isostatic topography in addition to geological observations. We discuss the evolution of the East African Rift (EAR) and the European Cenozoic Rift System (ECRIS) and define two end members. 1) a-type rifts, such as the EAR and ECRIS, form parallel to mantle flow above elongated, asthenospheric anomalies of low-seismic velocity, “fingers” (LVF) and stay at embryonic stage with slow extension mostly driven by gravitational potential energy. 2) b-type rifts, such as the Menderes and Corinth Rifts, form perpendicular to mantle flow and lead to oceanisation; the Gulf of Aden, Red Sea and Baikal are intermediate. We then propose a new model for the evolution of the short-lived ECRIS (~44–33 Ma) in the magma-poor period of transition between the Pyrenean orogeny and Mediterranean back-arc extension. The propagation of a LVF toward the north emanating from the Canaries hotspot, all the way to the Massif Central and the upper and lower Rhine region formed the rift on top of a positive anomaly of non-isostatic topography. Fast slab retreat from the end of the Eocene modified asthenospheric mantle flow, initiating the recent Mediterranean subduction regime with back-arc basin opening and dispersal of the asthenospheric anomaly. From ~8 Ma, slab retreat successively ceased in the central and western Mediterranean, giving way to compression and resumption of volcanism, possibly related to the reestablishment of a mantle LVF. We conclude speculating on the respective roles of a-type and b-type rifts for plate tectonics more general, including for the Mesozoic fragmentation of Pangea
Modelling Water Worlds
No full textInternational audienceModelling and models influence how water and its flows are understood and governed. It is thus essential to critically explore the roles that models play in producing or addressing uneven water distribution. In this introduction to the Special Issue, we discuss approaches to analysing models and modelling practices. We start by establishing that they deserve special attention because they produce knowledge of another nature than gained from observations and measurements -knowledge that abstracts, generalises and offers access to potential futures and remote places. The paper outlines the ways in which models can appear to have universal relevance because of how they are able to travel between contexts; it also stresses that the rationalisation they offer aligns with the idea of control that underpins the modern water paradigm and related techno-managerial interventions. Despite their widespread appeal and use, this introduction stresses that models remain rather opaque, difficult to understand and navigate for non-experts and even sometimes for experts. The paper goes on to show how, in the context of water research and governance, models derive authority from the networks and discourses that surround them as well as from the epistemic and non-epistemic values that are shared by particular modelling communities. We present three complementary entry points for engaging with models: first, by interrogating their function as tools of representation; second, by exploring how they are produced and operated within constellations of actors, practices, discourses and material artefacts; and third, by analysing how models are deployed to legitimise water governance decisions that are inherently political. We then expand our critical engagement with water modelling, placing it in the broader context of attacks on science and scientists, particularly in the context of rising post-truth politics. Finally, by discussing the papers in this Special Issue, we conclude that models not only contribute to reproducing water inequalities but that they can also be mobilised to understand and address them. We suggest that future critical water research on modelling should continue to ground models and modelling in local realities, while also being invested in models as knowledge practices. Future research would benefit from bringing the diverse approaches that are showcased in this Special Issue into conversation as they enable rich and plural accounts of the worlds of water modelling
Influence of high-voltage electrode shape on granular metal particle trajectories in a roll-type electrostatic separator
No full textInternational audienceElectrostatic separation is recognized as an effective and robust recycling method, offering advantages such as low cost, energy efficiency and simplicity in operation. Nevertheless, the process is complex and involves multiple factors, necessitating careful selection of geometric and electrical parameters to effectively handle various material combinations and achieve optimal results. This study investigates the effects of the shape of the electrode connected to the high voltage (HV), the variation in the distance between the HV electrode and the rotating grounded cylindrical electrode, and the angular position of the HV electrode on the trajectories of conductive metal particles in a roll-type electrostatic separator. For this purpose, the particle trajectories were visualized with a High-speed camera. Indeed, visualizing the particle trajectories proved useful and innovative in terms of electrode design. The position and shape of the HV electrode were found to be influential parameters in the particle trajectories. The visualization of these trajectories allowed the adjustment of the HV electrode’s position to prevent interference with low-mass aluminum particles. It was found that better control of the particle trajectories can be achieved by using an inverted S-shaped HV electrode as compared to using an elliptical HV electrod
Element Mobility in a Metasomatic System with IOCG Mineralization Metamorphosed at Granulite Facies: The Bondy Gneiss Complex, Grenville Province, Canada
No full textInternational audienceIn the absence of appropriate tools and a knowledge base for exploring high-grade metamorphic terrains, felsic gneiss complexes at granulite facies have long been considered barren and have remained undermapped and understudied. This was the case of the Bondy gneiss complex in the southwestern Grenville Province of Canada which consists of 1.39-1.35 Ga volcanic and plutonic rocks metamorphosed under granulite facies conditions at 1.19 Ga. Iron oxide-apatite and Cu-Ag-Au mineral occurrences occur among gneisses rich in biotite, cordierite, garnet, K-feldspar, orthopyroxene and/or sillimaniterich gneisses, plagioclase-cordierite-orthopyroxene white gneisses, magnetite-garnetrich gneisses, garnetites, hyperaluminous sillimanite-pyrite-quartz gneisses, phlogopitesillimanite gneisses, and tourmalinites. Petrological and geochemical studies indicate that the precursors of these gneisses are altered volcanic and volcaniclastic rocks with attributes of pre-metamorphic Na, Ca-Fe, K-Fe, K, chloritic, argillic, phyllic, advanced argillic and skarn alteration. The nature of these hydrothermal rocks and the ore deposit model that best represents them are further investigated herein through lithogeochemistry. The lithofacies mineralized in Cu (±Au, Ag, Zn) are distinguished by the presence of garnet, magnetite and zircon, and exhibit pronounced enrichment in Fe, Mg, HREE and Zr relative to the least-altered rocks. In discrimination diagrams, the metamorphosed mineral system is demonstrated to exhibit the diagnostic attributes of, and is interpreted as, a metasomatic iron and alkali-calcic (MIAC) mineral system with iron oxide-apatite (IOA) and iron oxide copper-gold (IOCG) mineralization that evolves toward an epithermal cap. This contribution demonstrates that alteration facies diagnostic of MIAC systems and their IOCG and IOA mineralization remain diagnostic even after high-grade metamorphism. Exploration strategies can thus use the lithogeochemical footprint and the distribution and types of alteration facies observed as pathfinders for the facies-specific deposit types of MIAC system
Les savoirs sur l’eau à l’épreuve des terrains. Synthèse d’une année de réflexion collective en ateliers
No full textInternational audienceThis article presents the ongoing results of a monthly seminar of the G-eau UMR held since 2022, focused on the diversity of knowledge about water and the challenges of articulating this diversity with the research project and practices. The paper outlines the development of this working group, the questions raised, and the methodologies implemented. We also discussed some difficulties and challenges that motivated us to pursue our exchanges beyond the results of the first year presented here. Although the working group started reflecting on ‘water knowledge’ as a study object, the discussion quickly identified ‘knowledge’ as a transversal topic, since research itself is a process of knowledge production. This prompted us to reflect on our roles as researchers, our interactions with other actors and knowledges, and our relationships with different disciplines. The following main themes were addressed during the first year of our seminar: i) the process of knowledge production; ii) the embeddedness of knowledge in power relationships and legitimacy processes; iii) the diversity and circulation of knowledge. Based on these thematic ‘entries’, we examined critically the concept of ‘knowledge’ itself and the way it is instrumentalized or marginalized in research projects relating to water. Using an inductive approach informed by fieldwork in various regions across the world, we aim to set up a collective (S’Eau) designed to serve not only as a space for interdisciplinary and collective reflection but also as a base to debate critical issues, articulate positions, share suitable methodologies, and promote reflexivity regarding the diverse research practices related to this essential element of life, i.e. water.Cet article propose un point d’étape des réflexions sur les « savoirs sur l’eau », menées par un groupe de doctorants et chercheurs dans le cadre d’un séminaire mensuel organisé depuis 2022 au sein de l’unité mixte de recherche (UMR) G-eau. La diversité des savoirs sur l’eau, ainsi que des manières de les concevoir impose une vraie réflexion sur leur prise en compte dans les dispositifs de recherche et de recherche-action. Nous explicitons d’abord le cadre d’interaction mis en place au sein de notre séminaire pour faciliter les échanges et l’expression d’une diversité des conceptions et pratiques de recherche. Nous développons ensuite les trois principaux thèmes issus de nos échanges : i) la « récolte » des savoirs sur le terrain, ii) les liens entre savoirs et pouvoirs et iii) la « rencontre » des savoirs. Espace de réflexion interdisciplinaire, le groupe « Savoirs sur l’eau » (S’Eau) tente de poser les bases d’un collectif à même de discuter des questions critiques, de partager des méthodes et d’expliciter des postures pour développer une réflexivité collective vis-à-vis de pratiques de recherche très diverses. Partager cette expérience est aussi une invitation à étendre cette réflexion au-delà de notre collectif, convaincu de la transversalité de la question des savoirs dans des projets et sur des terrains les plus divers
Deep crustal deformation driven by reaction-induced weakening
No full textInternational audienceDeep crustal shear zones, fundamental to the dynamics of terrestrial plate tectonics, exhibit complex processes of initiation and evolution that are yet to be comprehensively quantified across both long and short temporal scales. Conventionally, thermo-mechanical models posit that crustal rock behaviour is dominated by monomineralic aggregates undergoing processes like intracrystalline plastic deformation by dislocation creep. However, high-pressure and temperature conditions in crustal rocks involve minerals with extremely strong mechanical properties, challenging strain localization theories. Drawing on deformation experiments performed at eclogite-facies conditions, our research reveals that strain is efficiently localized through dissolution-precipitation creep, operating at notably lower stresses than dislocation creep. Strain accommodation and mass transfer are episodically accelerated by local transient fluid flow resulting from grain boundary movements, fracturing and densification reactions. Our results illuminate the interconnected thermo-hydro-mechanical-chemical processes underpinning crustal shear zone development, regardless of the plastic strength of mineral phases. We advocate that the inception and progression of subduction plate interfaces are predominantly steered by local transient changes of rheology beyond the seismogenic zone. Such changes are rooted in the chemical disequilibrium and fluid concentration of the slab materials, including sediments and mafic to ultramafic rocks.</div
Formation of Ru catalytic nanoparticles onto polyethylene glycol by plasma sputtering
No full textInternational audienceDevelopment of metallic nanoparticles (NPs) materials with high catalytic and electrocatalytic potential by using innovative methods is essential for hydrogen storage. For this application, we synthesized Ru metal NPs in polyethylene glycol (PEG) by the sputtering on liquid (SoL) method, which is a favorable technique for the synthesis of ultra-pure NPs, halfway between the physical and chemical methods. Therefore, this process does not require an additional stabilisation step, while still being capable of synthesising NPs of controlled size, shape and purity. The initial step of this study focuses on the diagnostic of the plasma phase by means of optical emission spectroscopy (OES). This allows for highlighting particularly the plasma/liquid interactions by showing the presence of excited species originating from the liquid, such as OH and Hα. Line emissions of excited Ru and Ar are also observed. Then, the PEG+NPs solution was characterized by various methods in order to verify the presence of nanoparticles and to determine their characteristics such as their morphology, concentration, size and size distribution as a function of the plasma generating power, the amount of liquid and the temperature of the latter. UV-Vis-NIR spectroscopy shows metallic or semi-metallic behaviour of the PEG+NPs solution, with the amount of NPs depending on the sputtering conditions. The main results of HRTEM and SAXS analysis show that the Ru NPs have a diameter of 2-5nm, but can aggregate to form larger particles during or after deposition, depending on both the sputtering conditions and the liquid characteristics