Damien Guillaume - Academia.edu (original) (raw)
Papers by Damien Guillaume
... électronique à balayage et en transmission (imagerie haute résolution, EDS et EELS), microson... more ... électronique à balayage et en transmission (imagerie haute résolution, EDS et EELS), microsondeélectronique, spectroscopie Mössbauer ... mots-clés : Argile stockage expérimentation système fer-smectite minéralogie et cristallochimie des minéraux argileux MET-EDS ...
The Kerguelen Archipelago (South Indian Ocean) is mostly made up of piles of Oligocene basaltic t... more The Kerguelen Archipelago (South Indian Ocean) is mostly made up of piles of Oligocene basaltic traps (≈ 25 Ma) forming cliffs of about 1000m in height, which are cross cut by a dense network of large and deep valleys. The basaltic traps are intruded by numerous plutonic complexes; the largest being the plutonic complex of the Rallier du Baty peninsula in the southern western part of the main island. The Rallier du Baty plutonic complex is mainly constituted of syenites with minor occurrence of gabbros and monzonites. This plutonic complex can be divided into two plutonic complexes emplaced at different times. The southern complex was emplaced between about 15 and 7 Ma, and then the magmatic activity migrated northward to form the northern plutonic complex between 7 and 4,5 Ma. The plutonic rocks were probably emplaced at shallow depth between several hundred meters to a few kilometers. We report the first data using the (U-Th)/He thermochronometer on apatite crystals from syenites in the southern Rallier du Baty plutonic complex in order to constrain the timing of erosion in a geological context where tectonic activity is weak and where climatic conditions have drastically changed since Oligocene. The preliminary results indicate very reproducible (U-Th)/He ages (AHe) between 6.7±1.1 Ma et 4.4±0.4 Ma. These AHe ages suggest a cooling history of the syenites that can be explained by the removal of the upper volcanic rock pile by erosion at the end of Miocene and beginning of Pliocene. The preliminary data also suggest that the exhumation is rapid and corresponds to a period where climatic conditions changed from humid and hot to cold, windy and humid at the end of Miocene-beginning of Pliocene. More AHe ages are currently under way and U/Pb and (U-Th)/He ages on zircon will be obtained, as well as barometric estimations, in order to provide better constraints on the thermal history of the plutonic complexes since their emplacement, and thus the timing of exhumation.
European Journal of Mineralogy, Dec 1, 1998
Mineralogy and Petrology, 2016
The Kerguelen Archipelago (South Indian Ocean) is mostly made up of piles of Oligocene basaltic t... more The Kerguelen Archipelago (South Indian Ocean) is mostly made up of piles of Oligocene basaltic traps (≈ 25 Ma) forming cliffs of about 1000m in height, which are cross cut by a dense network of large and deep valleys. The basaltic traps are intruded by numerous plutonic complexes; the largest being the plutonic complex of the Rallier du Baty peninsula in the southern western part of the main island. The Rallier du Baty plutonic complex is mainly constituted of syenites with minor occurrence of gabbros and monzonites. This plutonic complex can be divided into two plutonic complexes emplaced at different times. The southern complex was emplaced between about 15 and 7 Ma, and then the magmatic activity migrated northward to form the northern plutonic complex between 7 and 4,5 Ma. The plutonic rocks were probably emplaced at shallow depth between several hundred meters to a few kilometers. We report the first data using the (U-Th)/He thermochronometer on apatite crystals from syenites ...
AGU Fall Meeting …, 2009
... most widespread mineral in earth sciences, especially for fluid inclusions studies[1]. We use... more ... most widespread mineral in earth sciences, especially for fluid inclusions studies[1]. We used a commercial Ti:Sapphire femtosecond pulsed ... Experiments have been realized on polished andunpolished single synthetic and natural (Campério, Swiss Alps) crystals, with a laser ...
European Journal of Mineralogy, 2011
A commercial femtosecond laser system operating at its fundamental wavelength (l ¼ 800 nm, near I... more A commercial femtosecond laser system operating at its fundamental wavelength (l ¼ 800 nm, near Infra-Red) was used to ablate both synthetic and natural quartz on polished and unpolished surfaces. Ablation rates and maximum depths were determined using two distinct optical setups: a 25 mm focal length Cassegrain reflecting objective, and a 50 mm focal length convergent coated lens. All samples were ablated with the same laser beam at E 0 ¼ 1 mJ, t ¼ 60 fs, f ¼ 5 Hz and N ¼ 10-8000 shots. The depth of ablation craters obtained with the lens shows a linear increase with shot number N up to N ¼ 2000 shots. Then the depth increases much less with N and reaches a plateau above N ¼ 3000 shots. Maximum depth was close to 1300 mm for N ¼ 3000 shots. Using the reflecting objective, ablation rate starts from 0.42 mm/shot and decreases rapidly to 0.02 mm/shot at a maximum depth of 350 mm for N ¼ 1500 shots. Ablation thresholds (F th ) were calculated for 1 and 10 consecutive shots with energy increasing from E 0 ¼ 0.1-2 mJ/ pulse. Threshold values varies from F th ¼0.1 J.cm À2 (unpolished, 10 shots) to F th ¼ 2.9 J.cm À2 (polished, single shot). The energy penetration of IR-femtosecond laser pulses in quartz has been calculated at l ¼ 271 nm. The low absorption of IR wavelengths in quartz affects the ablation efficiency in the first shots. The associated non-linear effects are visible on a crater FIB foil observed with TEM as progressive high-pressure photomechanical damage developing under the ablation pit. The present study emphasizes the potential of IR-femtosecond laser for ablation of highly transparent material, and provides reliable data for LA-ICP-MS applications in earth sciences.
Cement and Concrete Research, 2008
Natural pozzolans have been widely used as substitutes for Portland cement, because of their bind... more Natural pozzolans have been widely used as substitutes for Portland cement, because of their binding properties. Some of them are natural volcanic rocks which contain secondary minerals such as clays and zeolites corresponding to products of the alteration of the rock. The objective of this study was to document the potential effect of the secondary minerals on the strength development of pozzolanic mortars. We chose to investigate this effect by thermally destabilising these minerals in three different pozzolanic deposits (poz-1, poz-2 and poz-3). We first did a detailed mineralogical study, to identify the occurrence and the nature of the different secondary minerals. Kaolinite is abundant in poz-1 and different types of zeolite were identified in poz-2 and poz-3. Thermal treatments were monitored by X-ray Diffraction (XRD) analysis, in order to document mineralogical transformations. The effect on the pozzolanic activity has been tested by strength measurements on normalised mortars at 1, 7 and 28 days. Strength of all blended cements is enhanced while destabilising secondary alteration minerals. For kaolinite, we showed that a strength improvement occurs as soon as it is destructured, even if it is not transformed in metakaolin. For zeolites, destabilisation takes place at low temperature (350°C), but as recrystallisation products are easily formed, activation temperature window is narrow. Endly, we have evidence that the presence of calcite in pozzolans has an effect on early strength. Therefore this study is giving new perspectives for a better use of natural pozzolanic materials in the cement industry.
Clay Minerals, Sep 1, 2003
A B S T R A C T : The alteration and transformation behaviour of montmorillonite (bentonite from ... more A B S T R A C T : The alteration and transformation behaviour of montmorillonite (bentonite from Wyoming, MX-80) in low-salinity solutions (NaCl, CaCl 2 ) in the presence of metallic Fe (powder and 86461 mm plate) and magnetite powder was studied in batch experiments at 300ºC to simulate the mineralogical and chemical reactions of clays in contact with steel in a nuclear waste repository. The evolutions of pH and solution concentrations were measured over a period of 9 months. The mineralogical and chemical evolution of the clays was studied by XRD, SEM, Transmission Mössbauer Spectroscopy and TEM (EDS, HR imaging and EELS). Dissolution of the di-octahedral smectite of the starting bentonite was observed, in favour of newly formed clays (chlorite and saponite), quartz, feldspars and zeolite. The formation of Fe-chlorite was triggered by contact with the metallic Fe plate and Fe-Mg-chlorite at distance from the Fe plate (>2 mm).
Lithos, 2009
The upper end of the CH 4-zone in the External part of the Central Alps of Switzerland results fr... more The upper end of the CH 4-zone in the External part of the Central Alps of Switzerland results from an oxidation reaction of methane into water and carbon dioxide at 270 ± 5 °C [Tarantola, A., Mullis, J., Vennemann, T., Dubessy, J., de Capitani, C., 2007. Oxidation of methane at the CH 4 / H 2O-(CO 2) transition zone in the external part of the Central Alps, Switzerland: Evidences from stable isotope investigations. Chemical Geology 237, 329-357.]. Petrographic investigations of the North-Helvetic Flysch revealed the presence of detrital biotite, muscovite and chlorite in the CH 4-zone. At the transition from the methane to the water zone, the sudden increase of CO 2 in the fluid is associated with the formation of chlorite and muscovite in replacement of detrital biotite. In the H 2O-zone, biotite is entirely replaced by chlorite-muscovite interlayered stacks. Mössbauer spectroscopy showed a minimum decrease of XFe 3+ from 0.18 to 0.09 within the sheet silicate fraction at the transition from the CH 4- to the H 2O-(CO 2) dominated fluid zone. Detrital biotite of the investigated host rocks incorporates at the same conditions larger amounts of Fe 3+ than chlorite in its structure and XFe 3+ (biotite) > XFe 3+ (new-chlorite) > XFe 3+ (detrital chlorite). The reaction of chloritization of detrital biotite is interpreted as a fluid controlled mineralogical isograde at 270 ± 5 °C, marking the transition from the low to the high grade anchizone, and allowing the oxidation of up to 36 moles of CH 4 per cubic meter of rock.
Geochimica Et Cosmochimica Acta, May 1, 2010
The kinetics of abiotic redox reactions induced by hydrogen are poorly documented although it rep... more The kinetics of abiotic redox reactions induced by hydrogen are poorly documented although it represents a growing area of interest in terms of both nuclear waste storage assessment and the comprehensive study of hydrogen-rich fluid in mid-ocean ridge hydrothermal systems. We present an experimental kinetics study of pyrite reduction into pyrrhotite under significant H 2 pressure and mid-hydrothermal conditions. We describe the mechanism and kinetic behavior of this reaction by combining textural and solution analyses under various conditions of temperature, pyrite particles size, H 2 pressure and pH. When pH is controlled by calcite, the reaction presents all the characteristics of a coupled dissolution-precipitation mechanism occurring at the pyrite-pyrrhotite interface. By considering the chemical affinity of the coupled reaction as a function of reaction extent, we demonstrate that the spatial coupling is induced both by pyrite as a substrate for pyrrhotite nucleation and by the role of fluid chemistry at the reaction front. Far from equilibrium with respect to pyrite, the kinetics of sulfide production associated with the reaction are linearly related to the square root of time with an activation energy of 53 kJ/mol. This value is higher than what is expected for a diffusion-controlled kinetic regime. We suggest that the reaction rate is controlled both by pyrite reductive dissolution and by sulfide diffusion through the porous pyrrhotite microstructure. We provide a simple sulfide production-rate expression on the basis of our measured rate constants that can be used in geochemical modeling to further evaluate the impact of hydrogen on pyrite under nuclear waste disposal conditions.
Geochmica et Cosmochimica Acta
The Maevatanana deposits consist of gold-bearing quartz-sulphide veins crosscutting banded iron f... more The Maevatanana deposits consist of gold-bearing quartz-sulphide veins crosscutting banded iron formation (BIF) within a metamorphosed 2.5 Ga greenstone belt. The host rocks are dominated by a sequence of migmatites, gneisses, amphibolites, magnetite-rich quartzites and soapstones, intruded by large granitoid batholiths (e.g. the 0.8 Ga Beanana granodiorite). In the mineralised rocks, pyrite is the dominant sulphide, in addition to accessory chalcopyrite and galena. Outside the immediate ore zone, the BIF is dominated by quartz + magnetite ± hematite, accompanied by cummingtonite, albite and biotite. Gold occurs as globular grains (usually <500 μm) within quartz crystals close to the sulphides and as invisible inclusions within pyrite and chalcopyrite (up to 2,500 ppm Au content). Fluid inclusion textural and microthermometric studies indicate heterogeneous trapping of a low-salinity (∼3.6 wt.% eq. NaCl) aqueous fluid coexisting with a carbonic fluid. Evidence for fluid-phase immiscibility during ore formation includes variable L/V ratios in the inclusions and the fact that inclusions containing different phase proportions occur in the same area, growth zone, or plane. Laser Raman spectroscopy confirms that the vapour phase in these inclusions is dominated by CO 2 but shows that it may contain small amounts of CH 4 (<1 mol%), H 2 S (<0.05 mol%) and traces of N 2 . Fluid inclusion trapping conditions ranged from 220 to 380°C and averaged 250°C. Pressure was on the order of 1-2 kbar. The abundant CO 2 and low salinity of the inclusions suggest a metamorphic origin for the fluid. Likewise, the presence of H 2 S in the fluid and pyritisation of the wall-rock indicate that gold was likely transported by sulphide complexing. Fluid immiscibility was probably triggered by the pressure released by fracturing of the quartzites during fault movements due to competence differences with the softer greenstones. Fracturing greatly enhanced fluid circulation through the BIF, allowing reaction of the sulphide-bearing fluids with the iron oxides. This caused pyrite deposition and concomitant Au precipitation, enhanced by fluid phase separation as H 2 S partitioned preferentially into the carbonic phase.
Pegmatites are exceptional igneous rocks and, to this day, there is still no clear consensus abou... more Pegmatites are exceptional igneous rocks and, to this day, there is still no clear consensus about their origin. To obtain some insight on the chemical interactions between a pegmatitic melt and the leucogranite melt hosting it, we compared the trace-element composition of quartz-hosted, unheated melt inclusions (50 -70 μm) from several well-characterised peraluminous (ASI ≥ 1) pegmatites in the Ehrenfriedersdorf Complex (Erzgebirge, Germany), with that from homogenized inclusions (700 -900°C, 100 -300 MPa; 40 -500 μm) of leucogranite melts from the Ehrenfriedersdorf mining district, the Kymi leucogranite (Finland), and the Erongo leucogranite (Namibia). Trace-element data were collected by near-infrared femtosecond Laser Ablation -Inductively Coupled Plasma -Quadrupole Mass Spectrometry (Agilent 7500 ce ICP-QMS). The results show that these melts are extremely enriched in boron, rare metals and metalloids such as Li, Be, Zn, Ga, As, Rb, Nb, Cd, Sn, Sb, Cs, Ta and U, and that these are heterogeneously distributed throughout the melts. The high solubility of metals (Ga, Cd) and metalloids (As, Sb) in the peraluminous melts can be explained by the depolymerized structure of hydrous melts rich in P, F and B (Borisova et al., 2010). Except for Ta and Be, the pegmatitic melt inclusions (Type A) show similar rare-metal enrichment and distribution as the host Ehrenfriedersdorf granitic melts, suggesting the absence of a boundary layer effect during pegmatitic segregation. Heterogeneous distribution of Nb and Ta in granitic melts from Greifenstein, Erongo and Kymi could indicate the presence of either submicron-size Nb-Ta oxides (inclusion E7, 120 μm in size, from the Greifenstein granite), or complex Nb-Y-Th-REE-Zr-Ta-U (Nb,Ta-rich zircon in inclusion KB, 500 μm in size, from the Kymi granite) or Nb-Ta-Zn-V-Sr-Y-Th-REE phase ), which is possibly complex Y,REE,Nb,Ta-oxide as described in a granitic pegmatite by Škoda & Novák (2007). The compositional heterogeneities (e.g., from 30 -40 ppm (018, 020) to~1000 ppm (019, ) of Nb in three point analyses of inclusion E2) clearly indicate that Nb and Ta contents of melt inclusions in peraluminous systems cannot be regarded as indication of melt saturation with respect to a simple phase. Figure 1: LA-ICP-MS spectra for one point analysis (019) of homogenized melt inclusion (inclusion E2, 200 μm in size, see inset) in quartz from the Greifenstein granite. The growing 23 Na, 27 Al, 39 K and 85
American Mineralogist, 2014
The chemical forms of sulfur in geological fluids control the behavior of this element and associ... more The chemical forms of sulfur in geological fluids control the behavior of this element and associated base and precious metals in magmatic, hydrothermal, and metamorphic environments. However, these forms are insufficiently known at elevated temperature (T) and pressure (P). In this study, sulfur speciation in model aqueous solutions of thiosulfate and sulfur (~3 wt% of total S) was examined by in situ Raman spectroscopy on synthetic fluid inclusions at T-P-pH-redox conditions typical of porphyry Cu-Au-Mo deposits. Fluid inclusions were entrapped at 2 kbar and 600 or 700 °C in quartz that served as a container for the high T-P fluid. Then, the inclusion-bearing quartz samples were re-heated and examined by Raman spectroscopy as a function of T and P (up to 500 °C and ~1 kbar). At T < 200 °C, all fluid inclusions show sulfate (SO 4 2-± HSO 4 -) and sulfide (H 2 S ± HS -) in the aqueous liquid phase and elemental sulfur (S 8 ) in the solid/molten phase; these results agree both with thermodynamic predictions of sulfur speciation and the common observation of these three S forms in natural fluid inclusions. At T > 200-300 °C, in addition to these S species, the S 3ion was found to appear and grow with increasing temperature to at least 500 °C. The formation of S 3is rapid and fully reversible; its Raman signal disappears on cooling below 200 °C, and re-appears on heating. These new data confirm the recent findings of S 3in similar aqueous solutions at P of 5-50 kbar and T > 250 °C; they suggest that S 3may account for some part of dissolved sulfur and serve as a ligand for chalcophile metals in fluids from subduction zones and related Cu-Au-Mo deposits. This work demonstrates that in situ approaches are required for determining the true sulfur speciation in crustal fluids; it should encourage future spectroscopic investigations of natural fluid and melt inclusions at high temperatures and pressures close to their formation conditions.
Mineralium Deposita, 2007
The Maevatanana deposits consist of gold-bearing quartz-sulphide veins crosscutting banded iron f... more The Maevatanana deposits consist of gold-bearing quartz-sulphide veins crosscutting banded iron formation (BIF) within a metamorphosed 2.5 Ga greenstone belt. The host rocks are dominated by a sequence of migmatites, gneisses, amphibolites, magnetite-rich quartzites and soapstones, intruded by large granitoid batholiths (e.g. the 0.8 Ga Beanana granodiorite). In the mineralised rocks, pyrite is the dominant sulphide, in addition to accessory chalcopyrite and galena. Outside the immediate ore zone, the BIF is dominated by quartz + magnetite ± hematite, accompanied by cummingtonite, albite and biotite. Gold occurs as globular grains (usually <500 μm) within quartz crystals close to the sulphides and as invisible inclusions within pyrite and chalcopyrite (up to 2,500 ppm Au content). Fluid inclusion textural and microthermometric studies indicate heterogeneous trapping of a low-salinity (∼3.6 wt.% eq. NaCl) aqueous fluid coexisting with a carbonic fluid. Evidence for fluid-phase immiscibility during ore formation includes variable L/V ratios in the inclusions and the fact that inclusions containing different phase proportions occur in the same area, growth zone, or plane. Laser Raman spectroscopy confirms that the vapour phase in these inclusions is dominated by CO 2 but shows that it may contain small amounts of CH 4 (<1 mol%), H 2 S (<0.05 mol%) and traces of N 2 . Fluid inclusion trapping conditions ranged from 220 to 380°C and averaged 250°C. Pressure was on the order of 1-2 kbar. The abundant CO 2 and low salinity of the inclusions suggest a metamorphic origin for the fluid. Likewise, the presence of H 2 S in the fluid and pyritisation of the wall-rock indicate that gold was likely transported by sulphide complexing. Fluid immiscibility was probably triggered by the pressure released by fracturing of the quartzites during fault movements due to competence differences with the softer greenstones. Fracturing greatly enhanced fluid circulation through the BIF, allowing reaction of the sulphide-bearing fluids with the iron oxides. This caused pyrite deposition and concomitant Au precipitation, enhanced by fluid phase separation as H 2 S partitioned preferentially into the carbonic phase.
Journal of Geochemical Exploration, 2003
This study confirms the ability of Raman spectroscopy for the quantification of methane in aqueou... more This study confirms the ability of Raman spectroscopy for the quantification of methane in aqueous fluids trapped in inclusions. The procedure is based on the use of reference synthetic inclusions for calibration at various salinities. The temperature effect, which was suspected to be weak, has been confirmed using a natural metastable liquid inclusion. No temperature correction is needed between 80 and 175 °C. The Raman decomposition of the water stretching band using methane as an internal reference gives us the opportunity to follow the state of liquid water between 24 and 278 °C. The decrease of the hydrogen bonding contribution with temperature is responsible for the increase of the Raman CH4/H20 peak area ratio.
Journal of African Earth Sciences, 2013
Incipient charnockitisation of an A-type granite protolith has been recognized in a spectacular o... more Incipient charnockitisation of an A-type granite protolith has been recognized in a spectacular outcrop 35 km north of Antananarivo. The charnockites form structurally-controlled dark greenish patches suggesting channelized fluid transfer, during and after partial reworking of the granite coeval with the Antananarivo virgation zone (ca 560 Ma) and/or the Angavo shear zone of late-Panafrican age (ca 550 Ma). They are characterized by a significant increase of the bulk magnetic susceptibility. The granitic protolith contains quartz, perthitic alkali feldspar, high-Ti hastingsitand accessory minerals (apatite, allanite, magnetite and zircon). The charnockitic granite contains quartz, perthitic alkali feldspar and ghost (altered) orthopyroxene crystals, as well as secondary low-Ti hastingsite surrounding orthopyroxene. The large increase of magnetic susceptibility magnitudes is related to the formation of pockets of secondary magnetite, spatially associated with quartz and other accessories, such as fluorine, calcite, bastnaesite, sphalerite, Ti-oxide and (Ca, REE)fluor-carbonates, in fluid percolation zones or in reaction rims around ghost orthopyroxene. Fluid inclusions entrapped in quartz grains witness the presence of CO 2 -rich hydrocarbonic fluids of low salinity, that are more abundant in charnockites than in granites. It is suggested that the rocks underwent a rather long history of fluid percolation, leading to prograde and then retrograde transformations. The corresponding metasomatic changes point to the mobility of Ti, Fe, Ca, Zn, F and REE. These changes are consistent with the CO 2 -rich nature of the percolating fluids.
Geochimica et Cosmochimica Acta, 2010
The kinetics of abiotic redox reactions induced by hydrogen are poorly documented although it rep... more The kinetics of abiotic redox reactions induced by hydrogen are poorly documented although it represents a growing area of interest in terms of both nuclear waste storage assessment and the comprehensive study of hydrogen-rich fluid in mid-ocean ridge hydrothermal systems. We present an experimental kinetics study of pyrite reduction into pyrrhotite under significant H 2 pressure and mid-hydrothermal conditions. We describe the mechanism and kinetic behavior of this reaction by combining textural and solution analyses under various conditions of temperature, pyrite particles size, H 2 pressure and pH. When pH is controlled by calcite, the reaction presents all the characteristics of a coupled dissolution-precipitation mechanism occurring at the pyrite-pyrrhotite interface. By considering the chemical affinity of the coupled reaction as a function of reaction extent, we demonstrate that the spatial coupling is induced both by pyrite as a substrate for pyrrhotite nucleation and by the role of fluid chemistry at the reaction front. Far from equilibrium with respect to pyrite, the kinetics of sulfide production associated with the reaction are linearly related to the square root of time with an activation energy of 53 kJ/mol. This value is higher than what is expected for a diffusion-controlled kinetic regime. We suggest that the reaction rate is controlled both by pyrite reductive dissolution and by sulfide diffusion through the porous pyrrhotite microstructure. We provide a simple sulfide production-rate expression on the basis of our measured rate constants that can be used in geochemical modeling to further evaluate the impact of hydrogen on pyrite under nuclear waste disposal conditions.
... électronique à balayage et en transmission (imagerie haute résolution, EDS et EELS), microson... more ... électronique à balayage et en transmission (imagerie haute résolution, EDS et EELS), microsondeélectronique, spectroscopie Mössbauer ... mots-clés : Argile stockage expérimentation système fer-smectite minéralogie et cristallochimie des minéraux argileux MET-EDS ...
The Kerguelen Archipelago (South Indian Ocean) is mostly made up of piles of Oligocene basaltic t... more The Kerguelen Archipelago (South Indian Ocean) is mostly made up of piles of Oligocene basaltic traps (≈ 25 Ma) forming cliffs of about 1000m in height, which are cross cut by a dense network of large and deep valleys. The basaltic traps are intruded by numerous plutonic complexes; the largest being the plutonic complex of the Rallier du Baty peninsula in the southern western part of the main island. The Rallier du Baty plutonic complex is mainly constituted of syenites with minor occurrence of gabbros and monzonites. This plutonic complex can be divided into two plutonic complexes emplaced at different times. The southern complex was emplaced between about 15 and 7 Ma, and then the magmatic activity migrated northward to form the northern plutonic complex between 7 and 4,5 Ma. The plutonic rocks were probably emplaced at shallow depth between several hundred meters to a few kilometers. We report the first data using the (U-Th)/He thermochronometer on apatite crystals from syenites in the southern Rallier du Baty plutonic complex in order to constrain the timing of erosion in a geological context where tectonic activity is weak and where climatic conditions have drastically changed since Oligocene. The preliminary results indicate very reproducible (U-Th)/He ages (AHe) between 6.7±1.1 Ma et 4.4±0.4 Ma. These AHe ages suggest a cooling history of the syenites that can be explained by the removal of the upper volcanic rock pile by erosion at the end of Miocene and beginning of Pliocene. The preliminary data also suggest that the exhumation is rapid and corresponds to a period where climatic conditions changed from humid and hot to cold, windy and humid at the end of Miocene-beginning of Pliocene. More AHe ages are currently under way and U/Pb and (U-Th)/He ages on zircon will be obtained, as well as barometric estimations, in order to provide better constraints on the thermal history of the plutonic complexes since their emplacement, and thus the timing of exhumation.
European Journal of Mineralogy, Dec 1, 1998
Mineralogy and Petrology, 2016
The Kerguelen Archipelago (South Indian Ocean) is mostly made up of piles of Oligocene basaltic t... more The Kerguelen Archipelago (South Indian Ocean) is mostly made up of piles of Oligocene basaltic traps (≈ 25 Ma) forming cliffs of about 1000m in height, which are cross cut by a dense network of large and deep valleys. The basaltic traps are intruded by numerous plutonic complexes; the largest being the plutonic complex of the Rallier du Baty peninsula in the southern western part of the main island. The Rallier du Baty plutonic complex is mainly constituted of syenites with minor occurrence of gabbros and monzonites. This plutonic complex can be divided into two plutonic complexes emplaced at different times. The southern complex was emplaced between about 15 and 7 Ma, and then the magmatic activity migrated northward to form the northern plutonic complex between 7 and 4,5 Ma. The plutonic rocks were probably emplaced at shallow depth between several hundred meters to a few kilometers. We report the first data using the (U-Th)/He thermochronometer on apatite crystals from syenites ...
AGU Fall Meeting …, 2009
... most widespread mineral in earth sciences, especially for fluid inclusions studies[1]. We use... more ... most widespread mineral in earth sciences, especially for fluid inclusions studies[1]. We used a commercial Ti:Sapphire femtosecond pulsed ... Experiments have been realized on polished andunpolished single synthetic and natural (Campério, Swiss Alps) crystals, with a laser ...
European Journal of Mineralogy, 2011
A commercial femtosecond laser system operating at its fundamental wavelength (l ¼ 800 nm, near I... more A commercial femtosecond laser system operating at its fundamental wavelength (l ¼ 800 nm, near Infra-Red) was used to ablate both synthetic and natural quartz on polished and unpolished surfaces. Ablation rates and maximum depths were determined using two distinct optical setups: a 25 mm focal length Cassegrain reflecting objective, and a 50 mm focal length convergent coated lens. All samples were ablated with the same laser beam at E 0 ¼ 1 mJ, t ¼ 60 fs, f ¼ 5 Hz and N ¼ 10-8000 shots. The depth of ablation craters obtained with the lens shows a linear increase with shot number N up to N ¼ 2000 shots. Then the depth increases much less with N and reaches a plateau above N ¼ 3000 shots. Maximum depth was close to 1300 mm for N ¼ 3000 shots. Using the reflecting objective, ablation rate starts from 0.42 mm/shot and decreases rapidly to 0.02 mm/shot at a maximum depth of 350 mm for N ¼ 1500 shots. Ablation thresholds (F th ) were calculated for 1 and 10 consecutive shots with energy increasing from E 0 ¼ 0.1-2 mJ/ pulse. Threshold values varies from F th ¼0.1 J.cm À2 (unpolished, 10 shots) to F th ¼ 2.9 J.cm À2 (polished, single shot). The energy penetration of IR-femtosecond laser pulses in quartz has been calculated at l ¼ 271 nm. The low absorption of IR wavelengths in quartz affects the ablation efficiency in the first shots. The associated non-linear effects are visible on a crater FIB foil observed with TEM as progressive high-pressure photomechanical damage developing under the ablation pit. The present study emphasizes the potential of IR-femtosecond laser for ablation of highly transparent material, and provides reliable data for LA-ICP-MS applications in earth sciences.
Cement and Concrete Research, 2008
Natural pozzolans have been widely used as substitutes for Portland cement, because of their bind... more Natural pozzolans have been widely used as substitutes for Portland cement, because of their binding properties. Some of them are natural volcanic rocks which contain secondary minerals such as clays and zeolites corresponding to products of the alteration of the rock. The objective of this study was to document the potential effect of the secondary minerals on the strength development of pozzolanic mortars. We chose to investigate this effect by thermally destabilising these minerals in three different pozzolanic deposits (poz-1, poz-2 and poz-3). We first did a detailed mineralogical study, to identify the occurrence and the nature of the different secondary minerals. Kaolinite is abundant in poz-1 and different types of zeolite were identified in poz-2 and poz-3. Thermal treatments were monitored by X-ray Diffraction (XRD) analysis, in order to document mineralogical transformations. The effect on the pozzolanic activity has been tested by strength measurements on normalised mortars at 1, 7 and 28 days. Strength of all blended cements is enhanced while destabilising secondary alteration minerals. For kaolinite, we showed that a strength improvement occurs as soon as it is destructured, even if it is not transformed in metakaolin. For zeolites, destabilisation takes place at low temperature (350°C), but as recrystallisation products are easily formed, activation temperature window is narrow. Endly, we have evidence that the presence of calcite in pozzolans has an effect on early strength. Therefore this study is giving new perspectives for a better use of natural pozzolanic materials in the cement industry.
Clay Minerals, Sep 1, 2003
A B S T R A C T : The alteration and transformation behaviour of montmorillonite (bentonite from ... more A B S T R A C T : The alteration and transformation behaviour of montmorillonite (bentonite from Wyoming, MX-80) in low-salinity solutions (NaCl, CaCl 2 ) in the presence of metallic Fe (powder and 86461 mm plate) and magnetite powder was studied in batch experiments at 300ºC to simulate the mineralogical and chemical reactions of clays in contact with steel in a nuclear waste repository. The evolutions of pH and solution concentrations were measured over a period of 9 months. The mineralogical and chemical evolution of the clays was studied by XRD, SEM, Transmission Mössbauer Spectroscopy and TEM (EDS, HR imaging and EELS). Dissolution of the di-octahedral smectite of the starting bentonite was observed, in favour of newly formed clays (chlorite and saponite), quartz, feldspars and zeolite. The formation of Fe-chlorite was triggered by contact with the metallic Fe plate and Fe-Mg-chlorite at distance from the Fe plate (>2 mm).
Lithos, 2009
The upper end of the CH 4-zone in the External part of the Central Alps of Switzerland results fr... more The upper end of the CH 4-zone in the External part of the Central Alps of Switzerland results from an oxidation reaction of methane into water and carbon dioxide at 270 ± 5 °C [Tarantola, A., Mullis, J., Vennemann, T., Dubessy, J., de Capitani, C., 2007. Oxidation of methane at the CH 4 / H 2O-(CO 2) transition zone in the external part of the Central Alps, Switzerland: Evidences from stable isotope investigations. Chemical Geology 237, 329-357.]. Petrographic investigations of the North-Helvetic Flysch revealed the presence of detrital biotite, muscovite and chlorite in the CH 4-zone. At the transition from the methane to the water zone, the sudden increase of CO 2 in the fluid is associated with the formation of chlorite and muscovite in replacement of detrital biotite. In the H 2O-zone, biotite is entirely replaced by chlorite-muscovite interlayered stacks. Mössbauer spectroscopy showed a minimum decrease of XFe 3+ from 0.18 to 0.09 within the sheet silicate fraction at the transition from the CH 4- to the H 2O-(CO 2) dominated fluid zone. Detrital biotite of the investigated host rocks incorporates at the same conditions larger amounts of Fe 3+ than chlorite in its structure and XFe 3+ (biotite) > XFe 3+ (new-chlorite) > XFe 3+ (detrital chlorite). The reaction of chloritization of detrital biotite is interpreted as a fluid controlled mineralogical isograde at 270 ± 5 °C, marking the transition from the low to the high grade anchizone, and allowing the oxidation of up to 36 moles of CH 4 per cubic meter of rock.
Geochimica Et Cosmochimica Acta, May 1, 2010
The kinetics of abiotic redox reactions induced by hydrogen are poorly documented although it rep... more The kinetics of abiotic redox reactions induced by hydrogen are poorly documented although it represents a growing area of interest in terms of both nuclear waste storage assessment and the comprehensive study of hydrogen-rich fluid in mid-ocean ridge hydrothermal systems. We present an experimental kinetics study of pyrite reduction into pyrrhotite under significant H 2 pressure and mid-hydrothermal conditions. We describe the mechanism and kinetic behavior of this reaction by combining textural and solution analyses under various conditions of temperature, pyrite particles size, H 2 pressure and pH. When pH is controlled by calcite, the reaction presents all the characteristics of a coupled dissolution-precipitation mechanism occurring at the pyrite-pyrrhotite interface. By considering the chemical affinity of the coupled reaction as a function of reaction extent, we demonstrate that the spatial coupling is induced both by pyrite as a substrate for pyrrhotite nucleation and by the role of fluid chemistry at the reaction front. Far from equilibrium with respect to pyrite, the kinetics of sulfide production associated with the reaction are linearly related to the square root of time with an activation energy of 53 kJ/mol. This value is higher than what is expected for a diffusion-controlled kinetic regime. We suggest that the reaction rate is controlled both by pyrite reductive dissolution and by sulfide diffusion through the porous pyrrhotite microstructure. We provide a simple sulfide production-rate expression on the basis of our measured rate constants that can be used in geochemical modeling to further evaluate the impact of hydrogen on pyrite under nuclear waste disposal conditions.
Geochmica et Cosmochimica Acta
The Maevatanana deposits consist of gold-bearing quartz-sulphide veins crosscutting banded iron f... more The Maevatanana deposits consist of gold-bearing quartz-sulphide veins crosscutting banded iron formation (BIF) within a metamorphosed 2.5 Ga greenstone belt. The host rocks are dominated by a sequence of migmatites, gneisses, amphibolites, magnetite-rich quartzites and soapstones, intruded by large granitoid batholiths (e.g. the 0.8 Ga Beanana granodiorite). In the mineralised rocks, pyrite is the dominant sulphide, in addition to accessory chalcopyrite and galena. Outside the immediate ore zone, the BIF is dominated by quartz + magnetite ± hematite, accompanied by cummingtonite, albite and biotite. Gold occurs as globular grains (usually <500 μm) within quartz crystals close to the sulphides and as invisible inclusions within pyrite and chalcopyrite (up to 2,500 ppm Au content). Fluid inclusion textural and microthermometric studies indicate heterogeneous trapping of a low-salinity (∼3.6 wt.% eq. NaCl) aqueous fluid coexisting with a carbonic fluid. Evidence for fluid-phase immiscibility during ore formation includes variable L/V ratios in the inclusions and the fact that inclusions containing different phase proportions occur in the same area, growth zone, or plane. Laser Raman spectroscopy confirms that the vapour phase in these inclusions is dominated by CO 2 but shows that it may contain small amounts of CH 4 (<1 mol%), H 2 S (<0.05 mol%) and traces of N 2 . Fluid inclusion trapping conditions ranged from 220 to 380°C and averaged 250°C. Pressure was on the order of 1-2 kbar. The abundant CO 2 and low salinity of the inclusions suggest a metamorphic origin for the fluid. Likewise, the presence of H 2 S in the fluid and pyritisation of the wall-rock indicate that gold was likely transported by sulphide complexing. Fluid immiscibility was probably triggered by the pressure released by fracturing of the quartzites during fault movements due to competence differences with the softer greenstones. Fracturing greatly enhanced fluid circulation through the BIF, allowing reaction of the sulphide-bearing fluids with the iron oxides. This caused pyrite deposition and concomitant Au precipitation, enhanced by fluid phase separation as H 2 S partitioned preferentially into the carbonic phase.
Pegmatites are exceptional igneous rocks and, to this day, there is still no clear consensus abou... more Pegmatites are exceptional igneous rocks and, to this day, there is still no clear consensus about their origin. To obtain some insight on the chemical interactions between a pegmatitic melt and the leucogranite melt hosting it, we compared the trace-element composition of quartz-hosted, unheated melt inclusions (50 -70 μm) from several well-characterised peraluminous (ASI ≥ 1) pegmatites in the Ehrenfriedersdorf Complex (Erzgebirge, Germany), with that from homogenized inclusions (700 -900°C, 100 -300 MPa; 40 -500 μm) of leucogranite melts from the Ehrenfriedersdorf mining district, the Kymi leucogranite (Finland), and the Erongo leucogranite (Namibia). Trace-element data were collected by near-infrared femtosecond Laser Ablation -Inductively Coupled Plasma -Quadrupole Mass Spectrometry (Agilent 7500 ce ICP-QMS). The results show that these melts are extremely enriched in boron, rare metals and metalloids such as Li, Be, Zn, Ga, As, Rb, Nb, Cd, Sn, Sb, Cs, Ta and U, and that these are heterogeneously distributed throughout the melts. The high solubility of metals (Ga, Cd) and metalloids (As, Sb) in the peraluminous melts can be explained by the depolymerized structure of hydrous melts rich in P, F and B (Borisova et al., 2010). Except for Ta and Be, the pegmatitic melt inclusions (Type A) show similar rare-metal enrichment and distribution as the host Ehrenfriedersdorf granitic melts, suggesting the absence of a boundary layer effect during pegmatitic segregation. Heterogeneous distribution of Nb and Ta in granitic melts from Greifenstein, Erongo and Kymi could indicate the presence of either submicron-size Nb-Ta oxides (inclusion E7, 120 μm in size, from the Greifenstein granite), or complex Nb-Y-Th-REE-Zr-Ta-U (Nb,Ta-rich zircon in inclusion KB, 500 μm in size, from the Kymi granite) or Nb-Ta-Zn-V-Sr-Y-Th-REE phase ), which is possibly complex Y,REE,Nb,Ta-oxide as described in a granitic pegmatite by Škoda & Novák (2007). The compositional heterogeneities (e.g., from 30 -40 ppm (018, 020) to~1000 ppm (019, ) of Nb in three point analyses of inclusion E2) clearly indicate that Nb and Ta contents of melt inclusions in peraluminous systems cannot be regarded as indication of melt saturation with respect to a simple phase. Figure 1: LA-ICP-MS spectra for one point analysis (019) of homogenized melt inclusion (inclusion E2, 200 μm in size, see inset) in quartz from the Greifenstein granite. The growing 23 Na, 27 Al, 39 K and 85
American Mineralogist, 2014
The chemical forms of sulfur in geological fluids control the behavior of this element and associ... more The chemical forms of sulfur in geological fluids control the behavior of this element and associated base and precious metals in magmatic, hydrothermal, and metamorphic environments. However, these forms are insufficiently known at elevated temperature (T) and pressure (P). In this study, sulfur speciation in model aqueous solutions of thiosulfate and sulfur (~3 wt% of total S) was examined by in situ Raman spectroscopy on synthetic fluid inclusions at T-P-pH-redox conditions typical of porphyry Cu-Au-Mo deposits. Fluid inclusions were entrapped at 2 kbar and 600 or 700 °C in quartz that served as a container for the high T-P fluid. Then, the inclusion-bearing quartz samples were re-heated and examined by Raman spectroscopy as a function of T and P (up to 500 °C and ~1 kbar). At T < 200 °C, all fluid inclusions show sulfate (SO 4 2-± HSO 4 -) and sulfide (H 2 S ± HS -) in the aqueous liquid phase and elemental sulfur (S 8 ) in the solid/molten phase; these results agree both with thermodynamic predictions of sulfur speciation and the common observation of these three S forms in natural fluid inclusions. At T > 200-300 °C, in addition to these S species, the S 3ion was found to appear and grow with increasing temperature to at least 500 °C. The formation of S 3is rapid and fully reversible; its Raman signal disappears on cooling below 200 °C, and re-appears on heating. These new data confirm the recent findings of S 3in similar aqueous solutions at P of 5-50 kbar and T > 250 °C; they suggest that S 3may account for some part of dissolved sulfur and serve as a ligand for chalcophile metals in fluids from subduction zones and related Cu-Au-Mo deposits. This work demonstrates that in situ approaches are required for determining the true sulfur speciation in crustal fluids; it should encourage future spectroscopic investigations of natural fluid and melt inclusions at high temperatures and pressures close to their formation conditions.
Mineralium Deposita, 2007
The Maevatanana deposits consist of gold-bearing quartz-sulphide veins crosscutting banded iron f... more The Maevatanana deposits consist of gold-bearing quartz-sulphide veins crosscutting banded iron formation (BIF) within a metamorphosed 2.5 Ga greenstone belt. The host rocks are dominated by a sequence of migmatites, gneisses, amphibolites, magnetite-rich quartzites and soapstones, intruded by large granitoid batholiths (e.g. the 0.8 Ga Beanana granodiorite). In the mineralised rocks, pyrite is the dominant sulphide, in addition to accessory chalcopyrite and galena. Outside the immediate ore zone, the BIF is dominated by quartz + magnetite ± hematite, accompanied by cummingtonite, albite and biotite. Gold occurs as globular grains (usually <500 μm) within quartz crystals close to the sulphides and as invisible inclusions within pyrite and chalcopyrite (up to 2,500 ppm Au content). Fluid inclusion textural and microthermometric studies indicate heterogeneous trapping of a low-salinity (∼3.6 wt.% eq. NaCl) aqueous fluid coexisting with a carbonic fluid. Evidence for fluid-phase immiscibility during ore formation includes variable L/V ratios in the inclusions and the fact that inclusions containing different phase proportions occur in the same area, growth zone, or plane. Laser Raman spectroscopy confirms that the vapour phase in these inclusions is dominated by CO 2 but shows that it may contain small amounts of CH 4 (<1 mol%), H 2 S (<0.05 mol%) and traces of N 2 . Fluid inclusion trapping conditions ranged from 220 to 380°C and averaged 250°C. Pressure was on the order of 1-2 kbar. The abundant CO 2 and low salinity of the inclusions suggest a metamorphic origin for the fluid. Likewise, the presence of H 2 S in the fluid and pyritisation of the wall-rock indicate that gold was likely transported by sulphide complexing. Fluid immiscibility was probably triggered by the pressure released by fracturing of the quartzites during fault movements due to competence differences with the softer greenstones. Fracturing greatly enhanced fluid circulation through the BIF, allowing reaction of the sulphide-bearing fluids with the iron oxides. This caused pyrite deposition and concomitant Au precipitation, enhanced by fluid phase separation as H 2 S partitioned preferentially into the carbonic phase.
Journal of Geochemical Exploration, 2003
This study confirms the ability of Raman spectroscopy for the quantification of methane in aqueou... more This study confirms the ability of Raman spectroscopy for the quantification of methane in aqueous fluids trapped in inclusions. The procedure is based on the use of reference synthetic inclusions for calibration at various salinities. The temperature effect, which was suspected to be weak, has been confirmed using a natural metastable liquid inclusion. No temperature correction is needed between 80 and 175 °C. The Raman decomposition of the water stretching band using methane as an internal reference gives us the opportunity to follow the state of liquid water between 24 and 278 °C. The decrease of the hydrogen bonding contribution with temperature is responsible for the increase of the Raman CH4/H20 peak area ratio.
Journal of African Earth Sciences, 2013
Incipient charnockitisation of an A-type granite protolith has been recognized in a spectacular o... more Incipient charnockitisation of an A-type granite protolith has been recognized in a spectacular outcrop 35 km north of Antananarivo. The charnockites form structurally-controlled dark greenish patches suggesting channelized fluid transfer, during and after partial reworking of the granite coeval with the Antananarivo virgation zone (ca 560 Ma) and/or the Angavo shear zone of late-Panafrican age (ca 550 Ma). They are characterized by a significant increase of the bulk magnetic susceptibility. The granitic protolith contains quartz, perthitic alkali feldspar, high-Ti hastingsitand accessory minerals (apatite, allanite, magnetite and zircon). The charnockitic granite contains quartz, perthitic alkali feldspar and ghost (altered) orthopyroxene crystals, as well as secondary low-Ti hastingsite surrounding orthopyroxene. The large increase of magnetic susceptibility magnitudes is related to the formation of pockets of secondary magnetite, spatially associated with quartz and other accessories, such as fluorine, calcite, bastnaesite, sphalerite, Ti-oxide and (Ca, REE)fluor-carbonates, in fluid percolation zones or in reaction rims around ghost orthopyroxene. Fluid inclusions entrapped in quartz grains witness the presence of CO 2 -rich hydrocarbonic fluids of low salinity, that are more abundant in charnockites than in granites. It is suggested that the rocks underwent a rather long history of fluid percolation, leading to prograde and then retrograde transformations. The corresponding metasomatic changes point to the mobility of Ti, Fe, Ca, Zn, F and REE. These changes are consistent with the CO 2 -rich nature of the percolating fluids.
Geochimica et Cosmochimica Acta, 2010
The kinetics of abiotic redox reactions induced by hydrogen are poorly documented although it rep... more The kinetics of abiotic redox reactions induced by hydrogen are poorly documented although it represents a growing area of interest in terms of both nuclear waste storage assessment and the comprehensive study of hydrogen-rich fluid in mid-ocean ridge hydrothermal systems. We present an experimental kinetics study of pyrite reduction into pyrrhotite under significant H 2 pressure and mid-hydrothermal conditions. We describe the mechanism and kinetic behavior of this reaction by combining textural and solution analyses under various conditions of temperature, pyrite particles size, H 2 pressure and pH. When pH is controlled by calcite, the reaction presents all the characteristics of a coupled dissolution-precipitation mechanism occurring at the pyrite-pyrrhotite interface. By considering the chemical affinity of the coupled reaction as a function of reaction extent, we demonstrate that the spatial coupling is induced both by pyrite as a substrate for pyrrhotite nucleation and by the role of fluid chemistry at the reaction front. Far from equilibrium with respect to pyrite, the kinetics of sulfide production associated with the reaction are linearly related to the square root of time with an activation energy of 53 kJ/mol. This value is higher than what is expected for a diffusion-controlled kinetic regime. We suggest that the reaction rate is controlled both by pyrite reductive dissolution and by sulfide diffusion through the porous pyrrhotite microstructure. We provide a simple sulfide production-rate expression on the basis of our measured rate constants that can be used in geochemical modeling to further evaluate the impact of hydrogen on pyrite under nuclear waste disposal conditions.