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International audience; The distribution of ultrahigh-pressure metamorphism (UHP) at the scale of a mountain belt is of primeimportance for deciphering its past subduction history. In the Western Alps, coesite has been recognized in thesouthern Dora-Maira massif, in the lens-shaped Brossasco-Isasca Unit, but has not been found up to now inthe other parts of the massif. We report the discovery of a new UHP unit in the northern Dora-Maira Massif(Western Alps), named Chasteiran Unit. It is only a few tens of metres thick and consists of garnet-chloritoidmicaschists. Garnet inclusions (chloritoid, rutile) and its growth zoning allow to precisely model the P-Tevolution. Coesite crystals, which are pristine or partially transformed to palisade quartz occur as inclusionsin the garnet outer cores. According to thermodynamic modelling, garnet displays a continuous record ofgrowth during the prograde increase in P and T (25-27 kbar 470-500°C) (stage 1), up to the coesite stabilityfield (27-28 kbar 520-530°C) (stage 2), as well as sub-isothermal decompression of about 10 kbar (down to15 kbar 500-515°C) (stage 3). The main regional, composite, foliation, marked by chloritoid and rutile, beganto develop during this stage, and was then overprinted by chlorite-ilmenite (stage 4). The Chasteiran Unit isdiscontinuously exposed in the immediate hangingwall of the Pinerolo Unit, and it is located far away from,and without physical links to the classic UHP Brossasco-Isasca Unit. Moreover, it records a different, muchcolder, P-T evolution, showing that different slices were detached from the downgoing subduction slab. TheChasteiran Unit is the fourth and the coldest Alpine UHP unit known so far in the entire Alpine belt. Its P-Tconditions are comparable to the ones of the Tian Shan coesite-chloritoid-bearing rocks.

Recent thermodynamic and experimental studies have suggested that volatile organic compounds (e.g., methane, formate, and acetate) can be produced and stabilized in subduction zones, potentially playing an important role in the deep carbon cycle. However, field evidence for the high-pressure production and storage of solid organic compounds is missing. Here, we examine forearc serpentinite clasts recovered by drilling mud volcanoes above the Mariana subduction zone. Notable correlations between carbon and iron stable-isotope signatures and fluid-mobile element (B, As and Sb) concentrations provide evidence for the percolation of slab-derived CO 2 -rich aqueous fluids through the forearc mantle. The presence of carbonaceous matter rich in aliphatic moieties within high-temperature clasts (>350°C) demonstrates that molecular hydrogen production associated with forearc serpentinization is an efficient mechanism for the reduction and conversion of slab-derived CO 2 -rich fluids into solid organic compounds. These findings emphasize the need to consider the forearc mantle as an important reservoir of organic carbon on Earth.

International audience; Metamorphic reactions can lead to drastic changes in rocks mechanical properties. Indeed, duringsuch transformations, the nucleation of new phases with different strength, grain size and/ordensity compared to the primary phases is enhanced, and transient processes due to the ongoingreaction are then activated.Eclogitization of lower crustal rocks during continental subduction constitutes an emblematictransformation illustrating these processes. In such tectonic context, it has been shown thateclogitization seems to be closely associated with the occurrence of seismogenic events. However,the mechanisms that trigger brittle failure in such high pressure environments remain highlydebated. Indeed, whether the change in density or the change in rheology can lead toembrittlement is still enigmatic.By using 2D compressible mechanical numerical models we studied the impact of the strongnegative volume change of the eclogitization reaction on the rocks rheological behaviour. We showthat eclogitization-induced density change occurring out of equilibrium can, by itself, generatessufficient shear stress to fail the rocks at high-pressure conditions.Rupture initiation at depth in continental subduction zones could therefore be explained byvolume changes, even without considering the modifications of the rheological properties inducedby the transformation. Our results also indicate that the negative volume change associated withbrittle failure can enhance the propagation of the eclogitization process by a runaway mechanismas long as the reaction is not limited by the lack of reactants.Powered by

Les Eléments de Terres Rares sont distribués à faibles teneurs dans grand nombre de roches. Pour en augmenter les concentrations et en faire une ressource exploitable, de multiples processus géologiques sont à l’œuvre. Charles et al. font l’inventaire exhaustif des domaines européens où des concentrations intéressantes en Eléments de Terres Rares sont reconnues.

International audience; The Western Gneiss Region in Norway is constituted by a crustal nappe stack that comprises someof the best-preserved exhumed ultra-high pressure (UHP) terranes on Earth. The UHP rocks resultfrom the subduction of the western edge of the Baltica craton beneath Laurentia during theCaledonian orogeny. Mafic eclogites form lenses within granitoid orthogneisses and show the bestrecord of the pressure and temperature evolution. Their exhumation from the UHP conditions hasbeen largely studied, but the prograde evolution has been rarely quantified in the eclogitesalthough it constitutes an important constraint on the tectonic history of this area. This studyfocused on an unaltered eclogite sample from Vågsøy in the Nordfjord region. This sample wasinvestigated using a large panel of methods including phase-equilibria modelling, trace-elementanalyses of garnet, trace- and major-element thermo-barometry and quartz-in-garnet barometryby Raman spectrometry. The eclogite comprises omphacite, garnet, white mica, epidote andamphibole and accessory rutile, quartz, zircon, carbonates and kyanite. Garnet shows a grossularrichcore with inclusions of quartz, epidote, white mica and amphibole, while grossular-poor rimsare enriched in pyrope and middle rare-earth elements and include omphacite and rutile.Inclusions in garnet core point to crystallisation conditions in the amphibolite facies at 550–600 °Cand 11–15 kbar, while chemical zoning in garnet suggests growth during isothermal compressionup to the peak pressure of 28 kbar at 600 °C, followed by near-isobaric heating to 640–680 °C.Isothermal decompression to 8–13 kbar is recorded in fine-grained clinopyroxene-amphiboleplagioclasesymplectites. The absence of a temperature increase during compression seemsincompatible with the classic view of crystallization along a geothermal gradient in a subductionzone and may question the tectonic significance of eclogite-facies metamorphism. Two maintectonic scenarios are discussed to explain such an isothermal compression: (1) either the maficrocks were originally at deep level within the lower crust and were then buried along theisothermal part of the subducting slab, or (2) the mafic rocks recorded significant tectonicoverpressure at constant depth and temperature conditions during the collisional stage of theorogeny. A multi-chronometer geochronological study is currently performed and expected tobring additional, discriminant constraints on this P–T evolution.

International audience; Crustal evolution is currently governed by plate tectonics and it has been shown that between the Archean and the Phanerozoic major changes in subduction styles occured. Among others, the chemistry of different plutonic rocks through time and the understanding of their petrogeneses have helped to define different stages in the evolution of plate tectonics. An important change around 2.7 Ga led to the formation of magmas within a metasomatized mantle: the sanukitoids. This diachronous event is interpreted as the result of the evolution from a shallow to a steep subduction style. Similar rocks are generated in the modern Earth, for example the Caledonian (Palaeozoic) high Ba-Sr plutons in northern Scotland [1].In this contribution, we aim to study this Caledonian sanukitoid-like suite and test the reliability of several isotopic systems within the abundant accessory minerals. Whole rock chemistry (including radiogenic and stable isotopes) is well constrained. We now present a multi-isotope study of three accessory minerals (titanite, zircon and apatite). New Sm-Nd in-situ isotopes in titanite and apatite and Hf in zircon results are discussed in the light of oxygen isotopes previously published on the same samples for all phases [2]. These data are then compared to previous WR data obtained on the same samples[3], [4].[1] M. Fowler & H. Rollinson (2012) Geology 40, 1079–1082.[2] E. Bruand et al. (2019) Geochim. Cosmochim. Acta 255, 144–162.[3] M. Fowler et al. (2001) J. Geol. Soc. London., 158, 521–534.[4] M. Fowler et al. (2008) Lithos 105, 129–148.

We present here a combined EMPA and EBSD study of the late Proterozoic massive magnetiteepidote-amphibole ore of Takab (NW Iran). Magnetite (Mt) forms large (≤1 mm) oscillatory dark and light grey zoned grains (BSE images). Bright Mt needles and bands crosscut or are aligned along cleavages and fracturing planes. Some bands contain relict hematite (Hem), and show, then, abundant porosity. EBSD inverse pole figure maps reveal inter-grain orientation changes in grey Mt. Moreover, intra-grain misorientations, similar to undulose extinction in other minerals, indicate dislocations in the crystal lattice formed through deformation. Relict Hem and bright Mt show the coincidence of the orientations of the planes {0001} Hem //{111} Mt and{11-20} Hem //{110} Mt , which is a good evidence for a direct transformation process. Grey Mt show low and variable Fe content (68.5-71.5 wt.%) with high Si (1 wt.%), Mg and Al (1500-4000 ppm) and Ca (2100-3300 ppm), these elements being likely trapped on the lattices of Mt during crystallization. Bright Mt has higher Fe content (~72 wt.%) and < 1000 ppm of the other elements. Both grey and bright Mt have low Ti and V contents (

France, like many countries, is facing the need to reduce the carbon dioxide production related to the energy consumption, particularly for heating. The Paris Basin is densely populated in the Île-de-France region and has interesting potential reservoirs for low-enthalpy geothermal energy exploiting geothermal waters between 300 m and 2500 m depth, for district heating. The carbonate formations of the Middle Jurassic located between 1200 m and 1800 m are a main target. However, the high density of wells exploiting this reservoir and the recent failure of a well near Evry show that there is a non-negligible and unquantified risk of low water flow or interference between geothermal doublets in urban areas with a high density of infrastructures. This geological risk constitutes an obstacle to the future development of geothermal energy in Île-de-France. Optimizing the use of geothermal energy requires an increased knowledge of the heterogeneity of the reservoir in terms of porosity/permeability or reservoir connectivity. The objective of the thesis is to build a detailed 3D geological model of sedimentological, diagenetic and petrophysical heterogeneities integrating all available well data and allowing to reduce geological risk. A database of logging and petrophysical data from 168 wells was compiled. This database wassupplemented with 129 m of core samples and 191 thin sections. The result is a high-resolution 3D model (12.2 million cells of 100 m x 100 m sides and 3.7 m height, proposing the spatial distribution of facies, porosity and permeability. Thin section studies show that diagenesis plays an important role in the heterogeneity of porosity, in particular the development or not of blocking calcite, or dolomitization and dissolution phenomena. An outcrop analogue provided a better understanding of the distribution of facies in a well constrained sequence stratigraphy framework (3rd order sequences). The use of a drone to photograph a quarry in the Yonne (sub-kilometer scale) coupled with photogrammetric modelling enabled work on a digital outcrop, analogous to the geothermal reservoir. From this digital outcrop, a methodology was developed to work on a geomodeller, and thus to better understand the distribution of facies and petrophysical properties at a finer scale. The 3D modelling of the reservoir in a part of Île-de-France and of an outcrop analogue allows to better predict and understand the distribution of the reservoir properties and to de-risk future operations (such as Grigny near Evry)., Résumé : La France fait face, comme de nombreux pays, à la nécessité de décarboner l'énergie qu'elle consomme, notamment la chaleur. Le Bassin de Paris a une forte densité de population dans la région de l'Ile-de-France et dispose de réservoirs intéressants pour la géothermie de basse énergie exploitant l'eau géothermale entre 300 m et 2500 m de profondeur, pour une utilisation directe de chaleur. Les formations carbonatées du Jurassique moyen situées entre 1200 m et 1800 m constituent une cible principale. Cependant, la densité importante de puits exploitant ce réservoir et l'échec récent d'un puits vers Evry montre qu'il existe un risque non négligeable et non quantifié, de faible débit d'eau ou encore d'interférence entre doublets géothermiques dans des zones urbaines à forte densité d'infrastructures. Ce risque géologique constitue un obstacle au développement futur de la géothermie en Ile-de-France. L'optimisation de l'utilisation de la géothermie nécessite une connaissance accrue de l'hétérogénéité du réservoir en termes de porosité/perméabilité ou de connectivité du réservoir. L'objectif de la thèse est de construire un modèle géologique 3D détaillé des hétérogénéités sédimentologiques, diagenétiques et pétrophysiques intégrant toutes les données de puits disponibles et permettant de réduire le risque géologique. Une base de données numérique rassemblant les données diagraphiques et pétrophysiques de 168 puits a été constituée sur un géomodelleur. Cette base de données a été complétée par l'observation de 129 m de carottes et 191 lames minces. Il en résulte une modélisation 3D à haute résolution (12,2 millions de cellules de 100 m x 100 m de côté et 3,7 m en verticale), proposant la répartition spatiale des faciès, porosité et perméabilité. L'étude de lames minces montre que la diagénèse joue un rôle important sur l'hétérogénéité des porosités, en particulier le développement ou non de calcite de blocage, ou encore des phénomènes de dolomitisation et de sa dissolution. Un analogue à l'affleurement a permis de mieux comprendre la répartition des faciès dans un cadre de stratigraphie séquentielle bien contraint (séquences de 3ème ordre). L'utilisation de drone pour photographier une carrière (échelle infra-kilométrique) couplée à la modélisation photogrammétrique a permis de travailler sur un affleurement numérique dans l'Yonne, analogue au réservoir géothermique. A partir de cet affleurement numérique, une méthodologie a été développée afin de le travailler sur un géomodelleur, et ainsi de mieux comprendre la répartition des faciès et des propriétés pétrophysiques à une plus fine échelle. La modélisation 3D du réservoir dans une partie de l'Ile-de-France et d'un analogue à l'affleurement permet de mieux prédire et comprendre la répartition des propriétés du réservoir et de dé-risquer les futurs opérations (comme celle de Grigny vers Evry).

International audience; The potential exhumation mechanisms of high-pressure rocks in subduction/collision belts is a longstandingquestion, that may be answered combining a wealth of sophisticated techniques. Geological mapping,combined with geophysical investigations, reveal the first-order geometrical features of the stacked units.In the Western Alps, the nappe stack has been ‘ordered’ by E. Argand and co-workers since more than onecentury. Two major additions to the proposed geometry include (i) the recognition of the gravimetric (positive)anomaly associated to the Ivrea Geophysical Body, thought to reflect the presence of the Adriatic mantle atlow depth, and (ii) the investigation of discontinuities in terms of P-T conditions and age between stackedunits. The first point is of major importance for understanding the crustal-scale reworking of the nappe stack(backfolding/backthrusting) during Adria indentation, while the second offers clues to the succession of eventsat depth before collision.HP/UHP rocks in oceanic and continental rocks have in common four characteristics:• They reveal a gradient of P-T conditions consistent with low to very low geothermal gradients (5 to 10°C/km) along the former subduction zone.• The ‘subduction gradient’ has been destroyed during exhumation. The latter is best interpreted as due to theupward displacement of an extrusion wedge, bounded by (north-westward) propagating ductile thrusts atthe base and (south-eastward) ‘normal shear sense’ ductile faults at the top.• Exhumation of HP/UHP rocks has taken place shortly after peak burial, i.e., before collision, with theimplication that the processes acting during exhumation may have been severely overprinted duringcollision.• Erosion only contributes significantly to the exhumation during the final stages of the history, when collisionis proceeding.New discoveries of UHP rocks (Manzotti et al., this meeting) and progress in P-T conditions, age and timingof HP/UHP metamorphism (Nosenzo et al., this meeting) will be used to constrain a geometrical-kinematicalmodel. Strengths and weaknesses of the model will be discussed.

International audience; Eclogitization reactions in mafic rocks involve large volume changes, porosity evolution and fluidtransfer. They impact many important geological processes such as the localization of deformationand fluid channeling at intermediate depth in subduction zone. The study of exhumed eclogiticbodies in orogens shows that eclogitization of the oceanic crust is heterogeneous from both astructural and metamorphic point of view. For example, in the European Alps, the Allalinmetagabbro shows high strain areas, consisting of hydrous metagabbros, fully equilibrated undereclogite-facies conditions during the Alpine orogeny. Conversely, large volumes of low strain, fluidundersaturatedgabbros remained largely unaffected by the high-pressure (HP) metamorphism,locally preserving igneous textures and even, occasionally, relics of their magmatic mineralogy.The intensity of deformation as well as the degree of eclogitization in the metagabbro have beenshown to be directly related to the extent of pre-Alpine hydration during high-temperaturehydrothermal alteration [1]. However, the influence of this degree of hydration on (1) reactionkinetics and/or (2) enhancing rheological contrasts leading to heterogeneous deformationpatterns and metamorphic conditions is still debated.In order to address this issue, we propose a multidisciplinary study involving petrographic andmicrotextural observations combined with 2D thermo-mechanical numerical models allowing todiscuss the role of pre-Alpine hydrothermal alteration on the development of HP metamorphicassemblages.We present petrographic and textural data from three different types of rocks from the Allalinmetagabbros: i) undeformed and mostly untransformed metagabbros, with relics of igneousaugite and plagioclase, ii) coronites, with olivine pseudomorphs showing different levels ofhydration, rimmed by a garnet corona, and iii) eclogitized metagabbros, with olivine andplagioclase sites fully replaced by high-pressure assemblages.The role of protolith hydration on the observed range in metamorphic facies is then tested byusing 2D thermo-mechanical models that allow to simulate the deformation of a strong and dryrock with several randomly oriented weak and hydrous zones. Our results show that the shearingof heterogeneous rock can lead to the formation of localized ductile shear zone within a matrixthat remains relatively undeformed but where plastic deformation can occur. The associated P field is also highly heterogeneous, with P ranging from 1 to 3 GPa. The deformation patterns and Pmodelled may suggest that locally hydrated portions of the gabbro acted as rheologicalperturbations sufficiently efficient in producing the structural and metamorphic record nowobserved in the field.[1] Barnicoat, A. C. & Cartwright, I. (1997) Journal of Metamorphic Geology 15, 93–104

It is well established that the major and minor element contents of chromites are subject to change during greenschist to amphibolite facies metamorphism. During upper amphibolite facies metamorphism, chromite can be completely converted to chrome magnetite. However, not all elements are affected to the same degree, the concentrations of +2 ions (e.g. Zn, Co, Mn) being particularly vulnerable to modification. The degree to which trace elements, particularly the platinum-group elements (PGE), are affected has not been closely examined. The compositions and textures of chromites from komatiites of the Gorumahishani greenstone belt of the Singhbhum Craton (India) have experienced a range of metamorphic conditions from greenschist to amphibolite facies, providing the opportunity to study the changes of trace and platinum-group element composition with metamorphic grade. Five types of altered chromites are identified from the komatiitic suite of rocks in the ~120-km-long greenstone belt. The type-I chromites are non-porous and characterized by the least modified cores. These chromites are mostly present in the northern Maharajgunj-Tua Dungri section where rocks show metamorphism from greenschist to greenschist-amphibolite transition facies. The type-II and type-III chromites are porous and mostly found in the southern Kapili section of the greenstone belt where rocks show metamorphism up to the mid-amphibolite facies. Type-IV and type-V chromites are completely modified to ferritchromit and chrome magnetite, respectively, and are present in the komatiitic rocks from the entire greenstone belt. The central cores of the type-I and type-II grains have relatively higher concentrations of mobile trace elements (e.g. Zn, Co, and Mn) with higher Mg# [Mg/(Mg + Fe2+)], lower Cr# [Cr/(Cr + Al)], and lower Fe3+/R3+ (R3+ = Fe3+ + Cr3+ + Al3+) ratios than their respective rims. Significantly higher concentrations of the immobile trace elements (e.g. Ti and V) in the cores of the type-II grains relative to their chrome magnetite rims from the Kapili section and to the type-I varieties from other sections might be due to the metamorphism of the komatiitic rocks under higher-grade conditions (amphibolite facies). In situ LA-ICPMS analysis for PGE reveals a relatively higher concentration of Ru and Rh in the rims of the type-I chromites than in the cores which is due to the diffusion of these elements from the normal spinel structure of the cores towards the bivalent octahedral sites of the inverse spinel structure of the chrome magnetite rims during metamorphic processes. The lower concentrations of Os, Ir, Ru, and Rh in the cores of the type-II chromites from the Kapili section might be related to the metamorphism of the rocks under higher-grade conditions that facilitated the diffusion of these elements to associated sulphide or platinum-group mineral or alloy phases. The calculated partition coefficients of Sc, Ti, V, Mn, Ni, Ga, Os, Ir, Ru, and Rh from the least altered chromite cores assuming equilibrium with the parental komatiitic melt also suggest the variable effects of metamorphism when compared with global experimental and empirical values of the natural samples

International audience; Polymorphic transformations are key tracers of metamorphic processes, also used to estimate thepressure and temperature conditions reached by a rock. In particular, the quartz-coesite transitionis commonly used to define the lower boundary of the ultrahigh-pressure (UHP) metamorphicfield. The partial preservation of coesite included in garnets from UHP rocks bring considerableinsights into the burial and exhumation mechanisms of the continental crust involved inconvergent zone. Coesite was first described in the Western Alps by Chopin[1], in the Dora-Mariawhiteschist, one of the most emblematic UHP rock worldwide. Although the partial preservation ofcoesite inclusions in garnet has long been attributed to the pressure vessel effect, theinterrelationship and relative timing between fracturing and retrogression is still contentious.Here we study the reaction-deformation relationships of coesite inclusions initially enclosed ingarnet and transforming into quartz during the decompression process. We combine 2Dnumerical thermo-mechanical models constrained by pressure-temperature-time (P-T-t) estimatesfrom the Dora-Maira whiteschist. The model accounts for a compressible visco-elasto-plasticrheology including a pressure-density relationship of silica based on thermodynamic data. Thisallows us to study the effect of reaction-induced volume increase during decompression. Ourresults capture the typical fracture patterns of the host garnet radiating from retrogressed coesiteinclusions and can be used to study the relative role of volume change associated with a change ofP-T conditions on the style of deformation during decompression.The mechanisms of the coesite-quartz transformation and geodynamic implications are presentedand validated against geological data. The effect of fluids on the phase transition and theconditions of access of fluids during the transformation are discussed in the light of the results ofthe thermo-mechanical models.This study demonstrates the high potential of thermo-mechanical modelling in enhancing ourunderstanding of the processes involved in the formation and evolution of metamorphic minerals.[1]Chopin (1984) Contributions to Mineralogy and Petrology 86, 2, 107-118

International audience; Le piège biogéochimique du gisement d’uranium de Zoovch Ovoo (Mongolie) : Importance de la matière organique.Dimitrios Rallakis1, Raymond Michels 1*, Marc Brouand 2, Olivier Parize2 et Michel Cathelineau1 1 Université de Lorraine, CNRS, GeoRessources, UMR 7359, CREGU - France2ORANO Mining, FranceDans les dépôts sableux non consolidés fluvio-lacustres crétacés du gisement d’uranium de type roll-front de Zoovch Ovoo (Mongolie), la matière organique se trouve exclusivement sous forme de kérogène de type III (plantes supérieures). Il s’agit de particules détritiques de moins de 5mm qui, selon leurs situations sédimentologiques, sont disséminées dans les bancs sableux ou argileux, concentrés dans des lamines sableuses ou présentes dans des intraclastes argileux concentrés en base de bancs sableux. Les structures biologiques de ces particules sont plus ou moins préservées en relation avec leurs distances de transport. Leur maturité thermique est très faible (%Ro

International audience; Delineating the evolution of the Earth’s dynamics and interactions between its different silicate reservoirs (ocean crust, continental crust, mantle) is key to understanding planetary differentiation and the conditions of surface habitability. Today, plate tectonic processes play a major role in creating and destroying the Earth’s crust, and modifying its silicate mantle. Reconstructing its long-term evolution is, however, extremely difficult since the Hadean record is essentially missing and most Archean rocks have experienced reworking and overprinting of their original signatures. An interesting source of information can be found in robust accessory minerals (e.g. zircon, apatite, monazite, titanite...). They can resist secondary processes and erosion, can be dated and incorporate important trace elements sensitive to magma conditions (temperature, SiO2 content, fO2). The properties of these tiny minerals are giving the opportunity to recover informations about igneous and metamorphic rocks at the grain scale using few microns spot sizes. These minerals are particularly interesting for Precambrian terranes that have been affected by secondary processes such as multiple metamorphic events, fluid circulation, alteration or erosion. In this contribution, I will present (i) recent development on our understanding of the chemical behaviour of accessory minerals in different magma types through geological time, (ii) new data on apatite inclusions armoured within zircons on Archean terrane and (iii) will discuss the advantages and limitations of using accessory minerals in Archean terranes. Altogether, these new petro-geochemical tools can help to better reconstruct continental crust through time and can be valuable for future work on provenance studies

International audience; Most of the intrusions in the Noril’sk-Talnakh region (Siberia) are hosted in thick sedimentary sequences including abundant evaporitic and terrigenous sedimentary rocks. Three mafic-ultramafic intrusions in this region contain unusually thick massive sulfide deposits that constitute one of the world’s largest economic concentrations of Ni, Cu and PGE. The interaction of Siberian magmas with sulfate and organic matter-rich sedimentary rocks has been proposed as a mechanism for the origin of these remarkable sulfide deposits. Here we fully investigate the interaction and reaction paths, by means of experiments at magmatic conditions and by thermodynamic modeling. We demonstrate how the assimilation of sulfate and organic matter in mafic-ultramafic magmas affects magma composition, crystallization and sulfide saturation. We identify the conditions that favored assimilation and ore formation in Noril’sk-Talnakh intrusions and conclude that the assimilation of sulfate-rich rocks enriched Siberian magmas in sulfur, while the carbonaceous rocks ensured the reduction of the oxidized sulfur and the segregation of exceptional amounts of sulfide melt.One of the consequences of the assimilation of organic material is the formation of an abundant fluid phase in the mafic magma. Our experimental work shows that the strong association between sulfide melt and fluid phase may have a major control on both the mobility and the metal enrichment of the sulfide melt. The fluid phase seems to play a critical role on the accumulation of the sulfide liquid by facilitating the coalescence of those sulfide droplets that are attached to gas bubbles. The experiments also reveal that the presence of a fluid phase consumes the sulfide melt concentrating metals in it. This process may have occurred during the formation of Norilsk-Talnakh sulfide ores and could explain the decreasing sulfide content and increasing metal content from the bottom to the top of the intrusions, i.e. from S-rich, PGE-poor massive sulfides at the base, to disseminated sulfides at intermediate levels and to S-poor, PGE-rich ores in the upper part.

International audience; Tungsten isotopes are the ideal tracers of core-mantle chemical interaction. Given that W is moderately siderophile, it preferentially partitioned into the Earth’s core during its segregation, leaving the mantle depleted in this element. In contrast, Hf is lithophile, and its short-lived radioactive isotope 182Hf decayed entirely to 182W in the mantle after metal-silicate segregation. Therefore, the 182W isotopic composition of the Earth’s mantle and its core are expected to differ by about 200 ppm. Here, we report new high precision W isotope data for mantle-derived rock samples from the Paleoarchean Pilbara Craton, and the Réunion Island and the Kerguelen Archipelago hotspots. Together with other available data, they reveal a temporal shift in the 182W isotopic composition of the mantle that is best explained by core-mantle chemical interaction. Core-mantle exchange might be facilitated by diffusive isotope exchange at the core-mantle boundary, or the exsolution of W-rich, Si-Mg-Fe oxides from the core into the mantle. Tung-sten-182 isotope compositions of mantle-derived magmas are similar from 4.3 to 2.7 Ga and decrease afterwards. This change could be related to the onset of the crystallisation of the inner core or to the initiation of post-Archean deep slab subduction that more efficiently mixed the mantle.

International audience

International audience; The Bou Jaber ore deposit is one of the numerous diapir-related Pb–Zn–F–Ba deposits of the Dome Zone in Northern Tunisia. Its location is controlled by the regional NE-SW Tajerouine Fault.Ore minerals are hosted in the Late Aptian limestones (Serdj Formation) as open space filling and stratabound replacement bodies. According to Bouhlel et al. (2016), the poly-phase mineralization resulted from the successive activity of three mineral systems, a Pb–Zn, then a barite, and eventually a fluorite deposition system. The latter, from the Late Miocene, is demonstrated in the present study.The fluorite system is characterized by the involvement of oil in the hydrothermal fluids. This oil was produced in the local environment of the deposit from the thermal maturation of the Albian Fahdene black shale source-rock at temperature range of~140 °C–~100 °C. Two brines were involved in the fluorite hydrothermal system. The first one (L1) is a Ca-rich brine (≥20 wt % bulk salinity), with Na/Ca ≤ 0.18, which is thought to have long resided in the basement, before its transfer into the Jurassic reservoir (Upper Nara Formation) and its eventual mobilization at the time of ore deposition. The second brine (L2), less saline (≤14 wt % bulk salinity) is more sodic, with Na/Ca up to 0.53, and represents unmodified brine originated from the nearby Triassic salt. The L1 brine was F-bearing, whereas the L2 brine was associated with oil. Fluorite deposition occurred at the estimated shallow depth of 1.7 km from cooling of the L1 brine due to the first isobaric cooling from ~160 °C to 135 °C under sub-lithostatic conditions (36 MPa). This stage is followed by mixing with the newly incoming L2 brines (transporting oil) along a sub-isochoric decompression path (down to the hydrostatic pressure at 17 MPa) and continuously cooling from 135 °C to 125 °C. The cooling and mixing caused fluorite deposition after which a transient heat advection episode (up to 145 °C) caused late calcite deposition prior to the end of hydrothermal circulation.

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International audience

Basket geothermal heat exchanger buried at shallow depth and connected to heat pumps can be used to heat and/or cool buildings. Heat transfers and performance related to geothermal basket are complex due to heterogeneous petrophysical properties of the soil, freezing of ground and surface environmental conditions e.g. air temperature variations. To study heat transfers, a geophysical monitoring of electrical conductivity and induced polarization has been developed using three experiments at different scales. First, a petrophysical model was designed from laboratory measurements. This model describes at the pore scale, the variation of electrical conductivity and chargeability according to the soil temperature and frost. This model was applied to an in-situ experiment to monitor the growth of an ice-core. We have also designed an analogic experiment at small scale and under controlled conditions in order to study the heat transfers and the effect of the soil freezing according to different environmental conditions. This study shows the importance of lateral flow and the influence of freezing during system operation. The petrophysical model was tested and validated with several datasets and geophysical monitoring was able to detect the formation and melting of the ice core., Les corbeilles géothermiques sont des échangeurs thermiques hélicoïdaux implantés dans le proche sous-sol qui couplés à une pompe à chaleur, permettent de chauffer et/ou de rafraichir les bâtiments. Comprendre les transferts thermiques liés à ces systèmes et étudier leurs performances requiert de prendre en compte les propriétés pétrophysiques hétérogènes du sol, les phénomènes de changement de phase et les conditions environnementales, dont les variations de température de l’air et la pluviométrie. Dans ce but un monitoring géophysique en conductivité électrique et en polarisation provoquée a été développé à l’aide de trois expériences à différentes échelles. Tout d’abord, un modèle pétrophysique a été élaboré à partir d’une série d’expériences en laboratoire. Ce modèle décrit la variation de la conductivité électrique et de la chargeabilité en fonction de la température et du gel du sol à l’échelle porale. Ce modèle a été appliqué à une expérience in-situ pour suivre la formation d’un noyau de glace. Nous avons aussi développé une expérience analogique à échelle réduite et en conditions contrôlée pour mieux comprendre les transferts de chaleur au sein du sol et étudier l’impact du gel dans différentes conditions environnementales. Ces études ont montré l’importance des apports thermiques latéraux et l’impact du changement de phase lors du prélèvement de chaleur par la corbeille. Le modèle pétrophysique a été validé sur plusieurs jeux de données et les résultats du monitoring géophysique permettent de détecter la formation et la fonte d’un noyau glace.

The 2 Ga-old Ihouhaouene alkaline complex (Western Hoggar, Algeria) is among the oldest known carbonatite occurrences on Earth. The carbonatites are calciocarbonatites hosted by syenites, the predominant rock type in the complex. Both rock types are characterized by medium-grained to pegmatitic textures and contain clinopyroxene, apatite, and wollastonite, associated with K-feldspar in syenites and a groundmass of calcite in carbonatites. The rock suite shows a continuous range of compositions from 57–65 wt.% SiO2 and 0.1–0.4 wt.% CO2 in red syenites to 52–58 wt.% SiO2 and 0.1–6.5 wt.% CO2 in white syenites, 20–35 wt.% SiO2 and 11–24 wt.% CO2 in Si-rich carbonatites (>10% silicate minerals), and 2 and 24–36 wt.% CO2 in Si-poor carbonatites (50), whereas clinopyroxene was precipitated from silicate liquids characterized by lower LREE/HREE (Ce/Lu = 49–234) and variable Nb/Ta ratios (Nb/Ta = 2–30). The Si-poor carbonatites resemble the Si-rich carbonatites and the white syenites with elevated REE contents in apatite equilibrium melts compared to clinopyroxene. However, apatite equilibrium melt in Si-poor carbonatite shows a majority of subchondritic values (Nb/Ta

The Athabasca region in western Canada is a metallogenic province hosting numerous uranium deposits that contain among the highest grades as known. The uranium mineralization is associated with the unconformity between the Archean basement and the overlying undeformed Athabasca sandstones. Some of the known economic deposits are located within basement faults that developed along inherited ductile shear zones. Development of these brittle fault zones is usually characterized by breccia, damage zones, and frequently by a vertical offset at the unconformity. Reactivated inherited basement structures allowed the development of structural traps in which the mineralization could be precipitated. The typical known model for these basement-hosted deposits, or “Ingress deposits”, implies that basin-derived fluids enriched in uranium flowing along basement faults. Interaction between these fluids and basement rocks leads to uranium precipitation in the structures.In a mineralizing system in which structural control is prominent, deformation zones may have been acted either as fluid conduits or barrier regarding the fluid circulations. Numerous studies mention such structures and their role played in uranium mineralization process in the basement, in the Athabasca region, in the Thelon and in the McArthur basin (Australia), with however lack of knowledge about the exact mechanisms and the conditions related to the development of the fertile structures. Distinction is not made between structures that may act as a fluid conduit or as fluid screen, which strongly limits the knowledge of the role played by different episodes of deformation and alteration into the setup of a fertile porosity network.This thesis focuses on the study of basement structures, U-mineralization and their alteration halo at different scales and allows to highlight the lead role played by the preexisting ductile fabric in the development of a favorable system for uranium-bearing fluid flow. Basement shear zones testify about a long fluid history (hydrothermal alteration, silicification, dissolution), and while reactivated later under brittle conditions made favorable environment for fluid flow beneath the Athabasca basin. Reactivation in the brittle domain leads to the development of a fractured corridors that are characterized by the reworking of ductile fabric into open fractures, accompanied with development of tensile jogs, which are suitable for mineral precipitation. The mineralization was emplaced lately within such structures that form a favorable porosity network within these strongly deformed and altered intervals.The present work allowed to define a structural signature that is common for two different prospects located at two opposite sides of the Athabasca basin. This signature can be qualified as a “structural footprint” is based on the overprinting of ductile shear zones by a network micro-fracture, in strongly deformed and altered basement rocks. The results also showed the importance of the structural approach at different scales (from project-scale, to drill core sample scale, and microstructures analysis) in the understanding of which mechanisms are critical in the emplacement of a favorable porosity network related with uranium mineralization., La région d’Athabasca au Canada concentre les gisements d’uranium de haute teneur les plus riches connus. Les minéralisations uranifères sont associées à la discordance entre le socle archéen à paléoprotérozoïque et les grès non-déformés de l’Athabasca. Une partie des gisements économiques connus sont situés au niveau de failles de socle qui se développent le long d’anciennes zones de cisaillement. Le développement de ces failles se traduit par la présence de brèches, zones de fracturation, et parfois d’un rejet vertical de la discordance. La réactivation des structures de socle héritées a permis la formation de pièges structuraux dans lesquels précipite la minéralisation. Le modèle de formation de ces gisements de socle, ou modèle « Ingress », propose la circulation de saumures de bassin chargées en uranium dissous le long des failles de socle. L’interaction entre ces fluides et les roches du socle entraine la précipitation de l’uranium dans les structures. Dans un système minéralisateur où le contrôle structural est fort, les zones de déformation peuvent agir comme chemin préférentiel ou écran vis-à-vis de la circulation fluide. De nombreux travaux décrivent ces structures et leurs rôles dans la mise en place des minéralisations d’uranium de socle dans l’Athabasca, le Thelon et le bassin de McArthur en Australie, mais les conditions et mécanismes de développement de ces structures sont peu contraints. La distinction n’est pas faite entre les différents types de structures dans la mise en place des minéralisations (drain ou piège), ce qui limite la compréhension de l’impact des différents épisodes de déformation et d’altération dans la mise en place d’un réseau de porosité fertile. Ces travaux de thèse, basés sur l’étude des structures de socle et des altérations associées à différentes échelles, ont mis en avant l’importance de l’héritage ductile dans le développement d’un système propice à la circulation de fluides et à la mise en place de minéralisations d’uranium. Les zones de cisaillement ductile témoignant d’une longue histoire fluide (altération hydrothermale, silicification, dissolution), et qui réactivées ultérieurement dans le domaine cassant sont des environnements favorables à la circulation de fluides sous le bassin. Des réactivations cassantes vont entrainer le développement d’une zone de fracturation et permettre, selon l’orientation des structures par rapport au champ de déformation, l’ouverture des plans de foliation. Le développement de ces fentes de tension ou « tensile jogs » créée l’espace adéquat à un remplissage minéral. La minéralisation se mets en place tardivement dans ces structures qui forment un réseau de porosité adéquat au sein de ces intervalles très déformés et altérés. Les travaux présentés ont permis de définir une signature structurale commune à deux gisements situés de part et d’autre du bassin d’Athabasca. Cette signature que l’on peut qualifier « d’empreinte structurale » repose sur la superposition de déformations cisaillantes ductiles et d’une zone de micro-fracturation, dans des roches de socle fortement déformé altéré. Les résultats obtenus ont aussi montré l’importance de l’approche structurale à différentes échelles (depuis l’échelle du projet, de l’observation des carottes jusqu’à celle des microstructures) dans la compréhension des mécanismes critiques pour la mise en place d’un réseau de porosité en relation avec des minéralisations d’uranium.

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National audience; Si l’histoire alpine du massif Dora-Maira a fait l’objet de nombreuses études, sonhistoire anté-alpine reste encore largement inexplorée. Mettant à profit l’existence dedomaines faiblement déformés durant l’orogenèse alpine, nous nous attacherons àdécrire l’évolution pré-orogénique de ce socle paléozoïque, où figurent deux lithologiesmajeures.La première lithologie est constituée par de rares orthogneiss à foliation pré-alpineconservée. De composition chimique peralumineuse (A/CNK = 1.28), l’orthogneisspréserve de son histoire magmatique (i) de rares enclaves microgrenues sombres, (ii)des porphyroclastes d’orthose, et (iii) des cristaux de zircon ayant fourni un âge U-PbLA-ICP-MS de 442 ± 2 Ma. La foliation de l’orthogneiss, à plagioclase – biotite – grenat– muscovite, témoigne d’une déformation ductile pervasive dans les conditions dufaciès des amphibolites.La seconde lithologie, de loin prédominante, est constituée de micaschistes à grenatcentimétrique et pseudomorphoses prismatiques allongées, à chloritoïde et mica,dérivant de porphyroblastes de staurotide. L’empreinte alpine, dans les échantillonsétudiés, est négligeable (préservation de la muscovite, surcroissances de grenat étroites,voire absentes, absence de foliation alpine). Le grenat contient des inclusions (quartz,ilménite, staurotide pseudomorphosée en bordure des grains) et une zonation chimiqueavec diminution de la teneur en Sps du coeur vers la bordure. Cette zonation autoriseune modélisation de la croissance du grenat anté-alpin, dont trois étapes sontreconstituées en modifiant la composition du volume d’équilibration dans la roche. Legrenat commence à croître vers 510- 530°C, 4-6 kbar, et achève sa croissance dans lechamp de stabilité de la staurotide vers 650- 660°C, 6-8 kbar, caractérisant ainsi unmétamorphisme barrovien.Un effort important a été effectué en vue de caractériser l’âge de ce métamorphismebarrovien. La distribution des inclusions d’apatite, de zircon, et de monazite dans legrenat, et la datation de la monazite et du zircon (U-Th-Pb, LA-ICP-MS) permet, en lienavec leur composition en éléments traces, de déterminer les étapes de l’évolution de cesroches au Carbonifère supérieur.Ainsi se dessine, pour le socle anté-alpin du massif Dora-Maira, une base de donnéesrobuste permettant de discuter la position anté-alpine de ce socle, avec des implicationssur les processus éventuels de ré-hydratation durant la subduction continentale alpine.

International audience; A fundamental assumption in the Earth Sciences is that the continental crust was mostly built by magmas at volcanic arcs above subduction zones. These magmas, belonging to the calc-alkaline series, are more oxidised than magmatic rocks formed in other tectonic settings. Calc-alkaline rocks are largely confined to the post-Archaean world with the implication that modern-style plate tectonics is also a post-Archaean phenomenon despite a number of studies suggesting that plate tectonics and subduction possibly have started in the Archaen. Nonetheless, the post-Archaean period doubtlessly fostered an oxygenated atmosphere, initially during the c.2.4 Ga Great Oxygenation Event (GOE) and subsequently during the Neoproterozoic Oxygenation Event (NOE), which led inexorably to the Cambrian explosion of life. Key outstanding issues though are the relationship between the Archaean-Proterozoic transition, the changing style of magmas, the rise of atmospheric oxygen, the development of an oxidised mantle and the development of subduction-driven plate tectonics. The difficulty in resolving this debate lies in the lack of an effective proxy for determining the oxygen fugacity of suitable magmatic rocks. We have used a new approach to address this question via a recently developed synchrotron-based proxy for determining relative magma oxidation state by μ-XANES (X‑ ray absorption near edge structure) analysis of S valence within the mineral apatite. We have applied this approach to apatite grains and apatite inclusions in zircon from our well-constrained samples of granitoids that range in age from the Archaean to the Phanerozoic to try and measure changes in redox-state through time that could have been controlled by atmospheric oxygenation and active plate tectonics.

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Copper porphyries represent complex alteration zones, hosting variable grades of Cu- (Au-Mo), but also Pb, Zn, Te, Bi and Ag. Processing of these ores becomes more difficult and more expensive as metal grades are lower and highly variable. Reducing the operational costs while increasing the resource efficiency at constant production is the challenge for the mining industries. Five samples from the Niaz porphyry copper (Mo)-deposit in northwest Iran, representing each a specific alteration zone were investigated by dual energy (DE) and multienergy (ME) X-ray transmission (XRT) as well as X-ray computed tomography (CT). Thesenon-destructive techniques are powerful tools for locating metal concentrations and evaluating porosities. Two samples come from the potassic phyllic zones: (1) A microgranular quartz-diorite is composed of sericitized albite, chloritized biotite and quartz veinlets. Ore phases are chalcopyrite, Fe-sulfides, galena. Magnetite, barite and Ti-oxides also occur. (2) A granular quartz-monzonite is composed of sericitized feldspars, quartz, amphibole, biotite, chlorite and ankerite. Ore phases are molybdenite and Cu-sulfides. Veins are filled with galena and Cu-Bi-sulfides (+Cd, Sb, As). A coarse-grained diorite composed of feldspars, amphiboles, epidotes, biotite, chlorite and calcite characterizes the propylitic alteration zone. Apatite, zircon, sphene, magnetite and ilmenite are present. Ore phases are molybdenite, galena, pyrite, Te-Bi phases and sphalerite. A microgranular quartz-diorite hosting quartz, feldspars, amphibole, biotite, kaolinite and siderite represents the phyllic-argillic mineralized zone. Ore phases are various Cu-sulfides. Minor barite, monazite, thorite and galena occur. The peripheral part of the porphyry is a coarse-grained skarn composed of chlorite, amphiboles, garnet, epidote, diopside, quartz, calcite and apatite. Ore phases are chalcopyrite, pyrite, Ag-sulfides and Te-Bi clusters attached to galena. Scheelite, magnetite, sphalerite and galena are observed in sulfides. Analysis of reconstructed three-dimensional CT volume data revealed structure information as well as two or three different groups of elements (low, medium and high effective atomic number). With these data, priorly calibrated by SEM, mine-geologists can assign grey values to minerals based on densities. Thus, it is possible to locate rapidly mineralization and evaluate porositiesin the alteration zones for unknown samples. With XRT, fractions of heavy and light materialscan be revealed in two-dimensional radiographs. While CT is useful for a small selection ofsamples due to its high time consumption, XRT can be used as a real-time process on conveyor belts. This information contribute to ore body modelling and predicting optimal process parameters like crushing or sorting.

International audience; The capture, storage and use of CO2 is still in a transitional phase, between research and pilot experiments. Nevertheless it has demonstrated technological know-how, and the large-scale commitment of states or industries to operate sites of significant importance in order to contribute to the reduction of greenhouse gas emissions.The awareness of the impact of atmospheric CO2 emissions on the climate in the 1980s and 1990s naturally led to the deployment of technological solutions. The actors (political, industrial, and academic) mobilized their means, according to more or less economically favorable conditions. Five main domains are concerned by CCUS: 1) the CO2 capture from different industrial plants (refineries, steel making, cement plants, power plants…), 2) CO2 transportation via pipelines towards surface units for (3) CO2 utilization or (4) CO2 injection for (5) CO2 deep storage in geological reservoirs for long term sequestration (Figure 1). CCUS covers a huge domain of competencies from humanities to technological sciences. Separation techniques, estimates of social and environment impact, consequences of fluid-rock interaction for mineralization or mechanical behavior, numerical modelling and monitoring are some of the important topics covered by more than twenty years of intensive research. Figure 1: Domains of interest for academy in the field of CCUSThe major technological and scientific advances in geological storage have concerned the development of miniaturized sensors, high pressure - high temperature measurement benches and triaxial cells with percolation of fluids to get as close as possible to in situ conditions, computer tools to model the behavior of complex fluids and the mechanical response of formations subjected to injections. Significant advances have enabled the CCUS sector to reach high levels of technological maturity. Thus the IPCC estimates that the CCUS could contribute to nearly 20% of the reduction in greenhouse gas emissions.It can be seen that the R&D activity is governed by the price per ton of CO2. In 2013, it collapsed to reach € 5, and EU reduced the support to CCUS projects. Today the price goes up and the actors regain hope. New projects are emerging and diversifying even if the fateful breakeven point of € 50 / ton has not yet been reached.Université de Lorraine and CNRS was involved in CCUS for several projects in France as in EU in connection with industrial partners. One of the most important was the TotalEnergies project of Lacq-Rousse. Between 2006 and 2013, TotalEnergies developed the unique on-shore CCS demonstrator in EU in the Southwest of France. CO2 was produced in a boiler using oxy-combustion technique and transported by pipeline on 30 km before to be stored in a deep dolomite reservoir of Jurassic age. The main objectives of this experiment were 1) to demonstrate the technical feasibility of an integrated chain coupling capture, transportation and storage into a depleted gas reservoir, 2) to acquire operating experience for oxy-combustion process and 3) to develop and apply geological storage with efficient monitoring technologies for long term including regulatory aspects and risk assessment [1]. The objective of this paper is to show some scientific results acquired on the CCS demonstrator by the academic teams of Nancy throughout a series of research projects supported by the French Research Agency (ANR), CNRS, Université de Lorraine and TotalEnergies.The reservoir where the CO2 has been stored is the depleted Mano reservoir that is part of the Rousse gas field where CH4 gas was produced for more than 40 years. This fractured dolomitic reservoir discovered in 1967 had an initial pressure of 480 bar at 4500 m depth, the residual pressure being close to 30 bar [2, 3]. Within 2 years of operation, up to 51 000 tons of CO2, produced by oxy-combustion, were injected in the reservoir inducing a recompression of several tens of bar. This injection was operated via the former operating well Rousse-1 (RSE-1) converted into injection well (Figure 2). Figure 2: Cross section of Rousse gas field in the Southwest of France with indications about the targets of research developed at Université de Lorraine/CNRS (GeoRessources lab).The gas reservoir of Rousse is located southward of the Aquitaine basin, specifically in the Adour-Arzacq sub-basin. The Rousse reservoir is located in a deep, isolated, faulted, Triassic to Jurassic siliciclastic and carbonate horst overlain by a 4500m thick overburden, which is composed of a series of turbiditic flysch deposits of Upper Cretaceous (Cenomanian) to Tertiary (Eocene) age. The petrophysical properties of the reservoir, marked by an intense fracture network, were acquired early during an extensional period (Albian), whereas the impact of fluids associated with a period of compression appears to have been limited in space to drainage of tectonic origin (Eocene). CO2 was recorded in fluid inclusions in close association with CH4 at these periods, traces of H2S are suspected to arrive later [4].Geological studies helped us to reconsider the geodynamic situation of the target reservoir. It was demonstrated that rocks in reservoir were in contact with CO2 in the past [4]. Such observation increases confidence in the project because it is suspected that re-injection of CO2 in the porosity of the rock should not react a lot with the minerals. This conclusion is solid if and only if the injected gas is pure CO2. However this is not always the case because purity of injected gas is depending on the capture strategy and technology. High purity achievement increases the cost of capture and could limit the volume of CO2 to be stored.To tackle the role of impurities co-injected with CO2, different scenarios have been tested in lab using a research pilot mimicking the conditions at great depth (150°C, several hundreds of bar). Geochemical impacts of CO2 and potentially co-injected gases have been tested on the reservoir and the cap-rock. The effect of SOx has been studied because the fuel burned by contact of pure O2 in the boiler can contain some amounts of sulfur [5]. In the same way, the presence of nitrogen oxides have been tested because nitrogen from the air can be present in small quantities in the boiler and can react with O2 to form NOx. And finally, the presence of O2 in excess after oxycombustion has been considered having potential impact on the stability of minerals and on residual hydrocarbons in the depleted gas reservoir [5, 6, 7, 8]. O2 that remains in the flue gas for injection can induce the oxidation of the hydrocarbons contained in the reservoirs. The effect of O2 must be studied in terms of benefit and/or risk for CCS. The top of the geological series is marked by molasses deposits where different shallow wells were drilled to monitor CO2 transfers between geosphere-biosphere-hydrosphere and atmosphere. One of them, of 3.5 m depth at 30 m far from the injection well was equipped with a gas collection chamber isolated from the atmosphere by a packer. Gases were collected through a membrane, non-permeable to water, and driven by a pump up to two spectrometers (FT-IR and Raman) in surface [9]. This equipment was created in cooperation with Solexperts Company. Each 30 minutes, temperature, pressure, and CO2 concentrations were measured into the shallow borehole as into the atmosphere. Water table level is measured in a neighboring piezometer. Gas concentration baseline collected overtime is driven by a limited number of parameters. By consequence, CO2 leakages from the reservoir or the surface devices containing CO2 could be marked by the baseline deviation.Another survey strategy has been developed through a baseline monitoring of the CO2 injection pilot to explore a wide geographical area of 35 km2. The measurements consisted of the joint determination, on a specified number of sites, of CO2 and CH4 gas fluxes at the soil-atmosphere interface and of their concentrations at one meter deep in soil (CO2, CH4, O2, 4He and 222Rn). The emission of CO2 followed an annual cycle with strongest fluxes during summer times and lower during winter ones. This seasonal pattern was consistent with the annual cycle of biological activity in soil. Therefore it was concluded the CO2 at the soil-atmosphere interface was mainly of organic origin [10].Risk assessment for CCS projects like the Lacq-Rousse project requires efficient tools to demonstrate there is no CO2 emanation in the form of a plume above the storage site. It is the reason why we developed methodologies to perform 2D and 3D cloud chemical imaging using passive remote sensing by Fourier-transform infrared (FTIR) spectrometry for environmental survey of industrial sites like gas storages and natural ecosystems [11]. We used a SIGIS 2 apparatus developed by Bruker Company. Measurements consist in IR emission acquisition over a 2D spatial grid, each pixel of which is converted in brightness temperature spectrum, depending on wavenumber. The identification and quantification of gases are based on radiative transfer equations and on the specific spectroscopic characteristics of each gas. With this equipment, it was possible to build a “cloud” of CO2 in 3D over the injection site of Rousse using a 3D modeler (Gocad software). At each point of the cloud a concentration of CO2 in ppm can be quantified.Research investment around the Lacq pilot which is the first in Europe to implement an end-to-end CO2 capture-transport-storage chain led to several important results:•Development of new remote sensors for survey of industrial sites and reconstruction of gas plumes above a CO2 storage site,•Combination of equipment for baseline acquisition showing high variations of CO2 with time and locations, •New completion/sensor combinations for in situ on-line gas measurements with acquisition of chronicles over time allowing to establish prediction law for CO2 content in soil,•First simulations of annex gas injection in carbonate gas reservoir. SOx, NOx behaviors in deep environment was described for the first time,•Mechanisms of oxidation of CH4 were quantified, improving geochemical models used for combustion risk assessment.All these results must be applied to facilitate the capture of CO2 in a variety of industrial installations, to develop the infrastructure required to transport CO2 from the capture site to a storage site and to qualify geological formations to store the quantities of CO2 necessary to achieve carbon neutrality.Acknowledgements: These works greatly benefited from cooperation or supports of TotalEnergies, BRGM, IFPEN, INERIS, Kaiser Optical Systems, Solexperts, LMD-EPSL, INRA, CREGU, IPGP, Mines ParisTech, ADEME, LRGP, ANR (Sentinelle project), French Ministry of Education and Research.References:1. Monne J. Carbon Capture and storage, The Lacq Pilot, ©TotalEnergies, 2015, 274 p.2. Gapillou C., Thibeau S., Mouronval G., Lescanne M. Building a geocellular model of the sedimentary column at Rousse CO2 geological storage site (Aquitaine, France) as a tool to evaluate a theorical maximum injection pressure, GHGT9, Energy Procedia 1, 2009, 2937–2944.3. Thibeau S., Chiquet P., Mouronval G., Lescanne M. Geochemical assessment of the injection of CO2 into Rousse depleted gas reservoir, GHGT9, Energy Procedia 1, 2009, 3383-3390.4. Renard S., Pironon J., Sterpenich J., Carpentier C., Lescanne M., Gaucher E.C. Diagenesis in Mesozoic carbonate rocks in the North Pyrénées (France) from mineralogy and fluid inclusion analysis: Example of Rousse reservoir and caprock. Chemical Geology, 2019, 508, 30-465. Renard S., Sterpenich J., Pironon J., Chiquet P., Randi A. Geochemical effects of an oxycombustion stream containing SO2 and O2 on carbonate rocks in the context of CO2 storage. Chemical Geology, 2014, 382, 140–152.6. Pacini-Petitjean C., Morajkar P., Burkle-Vitzthum V., Randi A., Lorgeoux C., Morel D., Pironon J., Faure P. Oxidation of n‑Alkane (n‑C8H18) under Reservoir Conditions, in Context of Gas Mixture Injection (CO2/O2): Construction of a Kinetic Model. Energy and Fuels, 2015, 29, 1913-1922.7. Pacini-Petitjean C., Faure P., Burkle-Vitzthum V., Randi A., Pironon J. Oxidation of n-hexadecane and crude oil in response to injection of a CO2/O2mixture under depleted reservoir conditions: Experimental and kinetic modeling preliminary results, International Journal of Greenhouse Gas Control, 2015, 35, 110–119.8. Pacini-Petitjean C., Morajkar P., Burkle-Vitzthum V., Randi A., Lorgeoux C., Pironon J., Faure P. Oxidation of n‑Alkane (n‑C8H18) under Reservoir Conditions in Response to Gas Mixture Injection (CO2/O2): Understanding Oxygenated Compound Distribution. Energy and Fuels, 2016, Vol. 30 Issue 9, p7560-7570.9. Taquet N., Pironon J., De Donato Ph., Lucas H., Barres O. Efficiency of combined FTIR and Raman spectrometry for online quantification of soil gases: application to the monitoring of carbon dioxide storage sites. International Journal of Greenhouse Gas Control, 2013, 12, 359-371.10 Gal F., Michel K., Pokryszka Z., Lafortune S., Garcia B., Rouchon V., De Donato Ph., Pironon J., Barres O., Taquet N., Radilla G., Prinet C., Hy-Billiot J., Lescanne M., Cellier P., Lucas H., Gibert F. Study of the environmental variability of gaseous emanations over a CO2 injection pilot—Application to the French Pyrenean foreland. International Journal of Greenhouse Gas Control, 2014, vol. 21, 177-190.11. de Donato Ph., Barres O., Sausse J., Martin D. Near real-time ground-to-ground infrared remote-sensing combination and inexpensive visible camera observations applied to tomographic stack emission measurements. Remote Sens. 2018, 10, 678.

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Geological and geophysical study of the Earth crust revealed, over the last decades, a complex rheological and seismological behavior. The geophysical monitoring of tectonic plates boundaries highlighted slow slip events (SSEs) occurring below the seismogenic zone, consisting in the intermittent succession of transient "low-frequency" seismic events (LFEs, Low-Frequency Earthquakes), whose accumulation over days/weeks allows stress releases comparable to those of big earthquakes. However, physical processes behind slow slips remain poorly constrained, since our knowledge of their geological record is still incomplete.Out study consists in a petrological analysis of shear zones, which are the main strain localization structures in the middle and lower crust. It is therefore crucial to study the processes involved in their development, and particularly in their nucleation, to determine whether SSEs are their geophysical expression; and to increase our ability to map them with passive methods of geophysical imaging, by quantifying their seismic anisotropy. In this goal, we study natural shear zones, fossilized at various stages of development within low strain domains.The petrological, microstructural study and thermodynamic modelling carried on centimeter-scale shear zones and on their brittle precursors show that brittle deformation and fluid-rock interactions involved in precursor forming occur at the same pressure-temperature conditions than ductile strain localization (0.5-1 GPa, 450-550 °C). Shear zones nucleation on brittle precursors therefore traduce the concomitance of brittle and ductile strain, and fluid-rock interactions, at P-T conditions similar to SSEs occurrence conditions. We suggest that the short-term development of shear zones in low-strain domains in the middle crust are a geological record of SSEs, and more particularly that LFEs are the seismological signature of fracturing and fluid-rock interactions involved in their nucleation. This suggests that SSEs are not restricted to subduction and strike-slip settings, but can also occur in orogenic settings.Quantification of meter-scale shear zones seismic anisotropy by laboratory experiments and EBSD-modelling shows that anisotropy increases with ductile strain, until ca. 10 %, but does not follow a linear evolution due to the competition between phyllosilicates and quartz. Symmetry of anisotropic fabrics evolves with strain from orthorombic to hexagonal symmetry, where the foliation is the fast propagation plane for P and S waves, and the plane of maximal shear wave splitting. We propose a new three-layered model for shear zones, which takes into account the major contribution of the intermediate strain zone in the seismic anisotropy of the whole shear zone., L’étude géologique et géophysique de la croûte terrestre a révélé, au cours des dernières décennies, un comportement rhéologique et sismologique complexe. La surveillance géophysique des frontières de plaques tectoniques a en effet mis en évidence des phénomènes de glissements lents (SSE, Slow Slip Events) survenant à la base de la zone sismogène, et qui correspondent à la succession intermittente d’événements sismiques transitoires de "basse fréquence" (LFE, Low-Frequency Earthquakes), dont l’accumulation sur plusieurs jours/semaines permet des relâchements de contraintes équivalents à ceux de grands séismes. Toutefois, les processus physiques à l’origine des glissements lents restent mal contraints, car notre connaissance de leurs enregistrements géologiques est encore lacunaire.Notre étude consiste en une analyse pétrologique des zones de cisaillement, qui sont les structures majeures de localisation de la déformation dans la croûte moyenne à inférieure. Il est donc essentiel d’étudier les processus impliqués dans leur développement, et en particulier dans leur initiation, afin de déterminer si les SSE peuvent en être l’expression géophysique ; mais également d’améliorer notre capacité à les cartographier grâce aux méthodes d’imagerie géophysique passive, en quantifiant leur anisotropie sismique. Nous étudions pour cela des zones de cisaillement naturelles, fossilisées à divers stades de développement au sein de domaines peu déformés.L’étude pétrologique, microstructurale et de modélisation thermodynamique menée sur des zones de cisaillement centimétriques et sur leurs précurseurs fragiles montre que la déformation fragile et les interactions fluides-roche impliquées dans la formation des précurseurs fragiles surviennent sous les mêmes conditions pression-température que la localisation de la déformation ductile (0.5-1GPa, 450-550°C). La nucléation des zones de cisaillement sur ces précurseurs fragiles traduit donc une concomitance des déformations fragile et ductile, ainsi que d’intenses interactions fluides-roche, sous des conditions P-T correspondant aux conditions d’occurrence des SSE. Nous proposons donc que le développement court-terme des zones de cisaillement dans les domaines faiblement déformés de la croûte moyenne constituent un enregistrement géologique des SSE et, plus particulièrement, que les LFE sont la signature sismologique de la fracturation et des interactions fluides-roche liées à leur nucléation. Cela suggère que les SSE ne sont pas limités aux contextes de subduction et de frontière décrochante, mais peuvent également survenir en contexte orogénique.La quantification expérimentale et la modélisation EBSD de l’anisotropie sismique de zones de cisaillement métriques montre que l’anisotropie augmente sous l’effet de la déformation ductile jusqu’à environ 10%, mais ne suit pas une évolution linéaire du fait de la compétition entre la contribution des phyllosilicates et celle du quartz. La symétrie de la fabrique anisotrope évolue sous l’effet;et de la déformation, depuis une symétrie orthorombique vers une symétrie hexagonale, où la foliation constitue le plan de propagation rapide des ondes P et S, et de biréfringence maximale des ondes S. Nous proposons un nouveau modèle de zone de cisaillement tricouche, qui prend en compte la contribution majeure de la zone de déformation intermédiaire dans l’anisotropie des zones de cisaillement.