Papers by Michel Gregoire
Marine Pollution Bulletin
In the early XXth century, the Gulf of Gabes in SE Tunisia used to host the most extended Posidon... more In the early XXth century, the Gulf of Gabes in SE Tunisia used to host the most extended Posidonia oceanica seagrass beds in the Mediterranean basin and was a highly productive hotspot of benthic species. Since the 70's, >500 million t of wet toxic phosphogypsum discharges from a fertilizer industrial complex have led to the gradual loss of ~90 % of its initial surface. This drastic shrinkage is accompanied by significant value losses originated from the direct and indirect-use services of which the most important ones are small scale fisheries and carbon storage function. Using market valuations of a number of services we estimate economic losses at 105 million € in 2014 (~915€/ha), i.e., around 115 % of the added value of the gabesian fertilizer factories for the same year. Value losses should increase in the near future in relation with the COP26 agreements which boosted the open carbon credit market. Without actions to reduce negative production externalities caused by the fertilizer industry in the Gulf of Gabes it would not be possible to recover Posidonia ecosystems in this region leading to further economic, ecologic, and cultural losses.
Geochimica et Cosmochimica Acta
The direct determination of silicate melts iron and silicon isotopes signature remains a major ch... more The direct determination of silicate melts iron and silicon isotopes signature remains a major challenge of high-temperature isotope geochemistry. For this reason, melts are often approximated by silicate glasses. Calculation of precise equilibrium Si and Fe isotopes fractionation factors between minerals and melt would indeed allow us to distinguish equilibrium fractionation from diffusion-driven kinetic fractionation involved in the iron and silicon isotopes signatures of Earth and other planets. In this study, we use for the first time, first-principles molecular dynamics based on density functional theory to determine iron and silicon isotope compositions of different silicate melts, namely: iron-rich basalt, iron-depleted basalt, basanite, trachyte and phonolite. The 57 Fe/ 54 Fe reduced partition function ratios (-factors) of the different melts span over a 1.1 ‰ range at 1000 Kelvin (K) while 30 Si/ 28 Si-factors are much less influenced by the melt composition with a 0.5 ‰ fractionation range at the same temperature. The main parameter controlling iron isotope fractionation in silicate melts having similar iron oxidation state is, after temperature, the average Fe-O bond length. The chemical environment around iron (e.g. Fe-Fe distances) is suggested to contribute to Fe isotope fractionation as well. Silicon isotopes fractionation seems also affected, but to a lesser extent, by its local chemical composition with decreasing Si-Fe distances leading to slightly higher Si-factor in the melt. From these melts Fe and Si-factors, a new set of equilibrium fractionation factors between a variety of minerals and melts has been calculated. These new ∆ 57 Femin-melt and ∆ 30 Simin-melt sets allow us to discuss whether processes such as fractional crystallization, partial melting and diffusion could be responsible for the documented Fe and Si isotopes variations in igneous rocks. Our results suggest that: 1) fractional crystallization may explain at least part of the Fe and Si isotopic evolution during magmatic differentiation, for values up to 57 Fe = 0.65 ‰ and 30 Si =-0.1 ‰, respectively, 2) partial melting of the upper mantle can produce the Mid-Ocean Ridge Basalts (MORB) iron isotopes signature. Finally, we calculated that olivine at equilibrium with a basaltic melt could display an iron isotope composition down to-0.1 ‰ for 57 Fe. Hence, the lower isotopic compositions ( 57 Fe <-0.1 ‰) observed in natural olivines are most likely due to diffusion-driven kinetic fractionation.
International Geology Review
The Norian magmatic rocks of Jabuka, Brusnik and Vis Islands (Croatia) and their bearing on the e... more The Norian magmatic rocks of Jabuka, Brusnik and Vis Islands (Croatia) and their bearing on the evolution of Triassic magmatism in the Northern Mediterranean. The magmatic rocks from Jabuka, Brusnik, Vis Islands and the submerged Brusnik plateau have been investigated to define their age and genetic affinity, identifying their role in the geodynamics of the Adria Plate. The plutonic and lava flow samples have been characterized for their petrography, mineral chemistry, whole rock major and trace elements, and Sr and Nd isotopic compositions. The two samples with the freshest plagioclase crystals have been selected for 40 Ar/ 39 Ar analysis, which gave ages of 221.5 ± 2.5 Ma (Brusnik) and 227 ± 5 Ma (Jabuka), similar to those of the Triassic magmatism from the northern part of the Adria Plate and neighbouring territories. Geochemical and isotopic data suggest that the magmatism dominantly sourced from spinel peridotites variously metasomatized during pre-Mesozoic subduction events. Furthermore, the investigated rocks evidence interactions of the magmas with Mid-Late Triassic evaporites. The comparison with other coeval magmatic occurrences from the Adria Plate and its edges shows that the subduction signature of the Triassic within-plate magmatism is mainly related to the evolution of the upper mantle of the Adria Plate.
Lithos
Rodingite represents a particular metasomatic rock type that occurs as dykes or lenses in associa... more Rodingite represents a particular metasomatic rock type that occurs as dykes or lenses in association with serpentinized ultramafic rocks and typically consists of Ca-rich, often hydrated silicate minerals. Rodingites have been recognized as a source of information on fluid compositions and their circulation in both ocean floor and subduction environments. Yet, the nature of the protoliths, the chemistry and the origin of fluids, the details of fluid-rock interaction, and the metamorphic context remain often obscure. This work investigates some of these questions in the case of rodingites from the Western Carpathians through petrological, mineralogical and geochemical studies. Rodingites are here associated in the field with serpentinized tectonically dismembered bodies of ultramafic rocks embeded into Carboniferous metasediments. They mostly consist of vesuvianite, diopside, and hydrated garnet with minor titanite, chlorite, epidote, calcite and Fe-Ti oxides. Three successive hydrothermal events were recognized: 1) formation of diopside, vesuvianite and garnet, 2) formation of a second generation of vesuvianite and garnet together with titanite and minor chlorite, and 3) formation of a mineral assemblage consisting of epidote, chlorite and calcite. The first two events represent a pervasive and intense rodingitization process, whereas the third one represents late, channeled, fluid circulation under greenschist facies conditions. The presence of Fe-Ti oxides influences the mineralogy and the whole rock chemistry of the investigated rodingites. Rutile and ilmenite are commonly associated with titanite and garnet, and whole rock analyses can reach up to 9.2 wt.% TiO2. Vesuvianite and garnet also incorporate a significant amount of titanium. The lack of primary minerals, the mineral composition as well as high CaO and low SiO2 contents demonstrate high extent of Ca-metasomatism. The high modal amount of vesuvianite and the immobility of Al during metasomatic processes suggest that the protolith was relatively Al-rich. Taking into account the REE patterns of whole-rock and minerals, the high TiO2 content and the local Fe-Ti-rich accumulations, we suggest that the protoliths were more or less Fe-Ti-rich gabbroic rocks initially occurring in association with the serpentinized ultramafic body.
Journal of Hazardous Materials
Mismanaged plastic waste interacts with secondary environmental pollutants, potentially aggravati... more Mismanaged plastic waste interacts with secondary environmental pollutants, potentially aggravating their impact on ecosystems and human health. Here we characterized the natural and artificial radionuclides in polyethylene terephthalate (PET) bottles collected from the industrial littoral discharge of a phosphate fertilizer plant. The activity concentrations in littered bottles ranged from 0.47 (208Tl) to 12.70 Bq⋅kg-1 (226Ra), with a mean value of 5.30 Bq⋅kg-1. All the human health risk assessment indices (annual intake, annual effective dose, and excess lifetime cancer risk) estimated for radionuclides associated with ingestion and inhalation of microplastics were below international safety limits. Our results demonstrated that PET can be loaded with natural and artificial radionuclides, and potentially act as a carrier to transfer radionuclides to humans, posing a new potential health risk. Increased use, mismanagement and fragmentation of plastic waste, and continued interaction of plastic waste with radioelements may lead to enhanced radiation exposure in the future.
Key Engineering Materials
Abrasive water jet machining is a process that removes material using sand and water. This versat... more Abrasive water jet machining is a process that removes material using sand and water. This versatile process uses a high-pressure water jet loaded with abrasive particles of mineral origin. It allows the machining of all materials and is particularly suitable for machining or stripping applications on hard metal sheets. Due to a local action, the abrasive water jet limits heating and deformation. During machining, the removal of material occurs abrasion and erosion [1]. The identification of the respective importance of this abrasion and this erosion conditions the precision of the modeling of the machined depth. In this study, these mechanisms are presented and characterized for machining on 6mm thickness TiAl6V titanium alloys sheets with or without inclination of the jet. It is possible to model an elementary passage and it allows predicting the pocket bottom profile obtained after a succession of passages. During machining, two mechanisms appear. Abrasion occurs when machining a...
International Journal of Geosciences
Volcanic deposits from the lake Nyos contain ultramafic xenoliths: lherzolites, harzburgites and ... more Volcanic deposits from the lake Nyos contain ultramafic xenoliths: lherzolites, harzburgites and wehrlites, sometimes containing amphiboles and phlogopites. The lithospheric mantle beneath Nyos, as inferred from chemical diagrams, has experienced partial melting and variably cryptic and modal metasomatism of the two groups of samples that have been distinguished: Group 1 samples are characterized by spoon-shaped REE patterns, and Group 2 samples show light (L) REE-enriched patterns. Metasomatic events were associated with pervasive infiltration of volatile (Ti, CO 2 , H 2 O) or alkali-rich small melts fractions and fluids. Later on, hydrous phases, Ti-rich Cpx, CaO-rich Ol, Ti-rich Ol, Cr poor and low values of NiO and F O (%) in wehrlite compared to other xenoliths, precipitated from alkali enrichments due to the percolation of the mantle by basaltic magmas. The metasomatic liquid which percolates the Nyos mantle column was a dense alkaline silicate rich in volatile, displaying low HFSE abundances in the metasomatic hydrous melts compared to the LILE. It is suggested that 1) cryptic metasomatism affected Group 1 samples, 2) the spinel-free wehrlite is a Group 2 sample corresponding to a cumulate of a similar melt and 3) amphibole may be a potassiumbearing mineral in addition to phlogopite at shallower levels of Nyos upper mantle. P-T estimated indicates that xenoliths were initially equilibrated in the garnet stability field, at depth of 85 Km, and then they were re-equilibrated in the spinel field owing to isobaric heating up to 1000˚C. Adiabatic decompressions occur from 85 to 50 Km materialized by sample NK14 showing transitional porphyroclastic to equigranular texture and displaying pyroxene-Cr How to cite this paper: Teitchou, M.I.,
Open Journal of Geology
Xenoliths enclosed in Lavas of the Nyos volcano (Cameroon Volcanic Line, continental sector) rang... more Xenoliths enclosed in Lavas of the Nyos volcano (Cameroon Volcanic Line, continental sector) range from fertile lherzolites to harzburgites. One spinel-free wehrlite has been also sampled. The occurrence of phlogopites and pargasites in some harzburgites together with specific textural rock-type (lherzolites transitional porphyroclastic to equigranular), including major and trace element compositions both in peridotites bulk rocks and minerals point out interactions between the mantle and basaltic magmas responsible for the formation of wehrlites beneath the Nyos volcano. Hydrous minerals (phlogopites and pargasites) and metasomatic events are their main petrogeochemical signatures different from group 1 samples which are characterized by spoon-shaped REE patterns. Later on, hydrous phases, Ti-rich Cpx, CaO rich Ol, Ti, and V rich Ol wehrlite precipitated from melt enrichments due to the percolation of the mantle by basaltic magmas of alkaline affinity. The metasomatic liquid which percolates the Nyos mantle column was a dense alkaline silicate rich in volatile, displaying low HFSE abundances in the metasomatic hydrous melts compared to the LILE. It is suggested that Nyos mantle peridotites have experienced: 1) variable metasomatic events related to the percolating of the depleted mantle by a alkaline silicate liquid, 2) the spinel-free wehrlite is a group 2 sample corresponding to a cumulate of a similar melt, 3) amphibole may be a potassium-bearing mineral instead of or in addition to phlogopite at shallower levels of Nyos upper mantle and 4) transitional textural rock facies express also the fingerprint of rising mantle plume which were percolated by alkaline magma during their transit to the surface.
Comptes Rendus. Géoscience, 2021
An alkaline volcanic activity with a relative Plio-Quaternary age (based on the succession of lay... more An alkaline volcanic activity with a relative Plio-Quaternary age (based on the succession of layers on the field) occurred in the northern part of Uromieh Dokhatar magmatic belt, Iran. Hornblendite xenoliths mostly displaying cumulitic texture occur in the trachyandesites from this magmatic episode. The thermobarometric results indicate that these xenoliths formed within the crust. Based on mineralogical and chemical characteristics, these xenoliths are divided into two groups. In Group 1, plagioclase (andesine) modal content is less than 10% while amphibole (magnesiohastingsite) and biotite are the main minerals. In Group 2, plagioclase (labradorite) modal content is higher than 20% while amphibole (pargasite) and biotite are the main minerals. Positive anomalies of U, Ba, Ti, and K in hornblendite xenoliths are probably related to the accumulation process of amphibole and biotite. The study of the chemical composition of amphiboles indicates crystallization of amphibole from Grou...
Re-Os and Lu-Hf isotope constraints on the origin and age of pyroxenites from the Beni Bousera pe... more Re-Os and Lu-Hf isotope constraints on the origin and age of pyroxenites from the Beni Bousera peridotite massif: Implications for mixed peridotite-pyroxenite mantle sources.
The EGU General Assembly, 2016
ABSTRACT The Pacific margin of East and NE Asia is part of the circum-Pacific orogenic system and... more ABSTRACT The Pacific margin of East and NE Asia is part of the circum-Pacific orogenic system and could be considered as a tectonic collage of nappes, displaced terrenes, accreted island arcs and accretionary complexes. This tectonic environment is the consequence of the convergence between the Palaeo-Pacific plate and the eastern Eurasian continent. It could be divided into three main units; the Koryak-Kamachatka fold belt, the Sikhote-Alin fold belt and the Okhotsk volcanic belt. The broadly defined Sikhote-Alin fold belt here refers to a nearly N-S belt extending north from the southern shoreline of the Okhotsk Sea south to the northern margin of the Japan Sea. The Mantle xenoliths come from Tuttochi, a locality close to Khabarovsk, Sikhote-Alin. The xenoliths are spinel peridotites, their sizes vary from 3 to 8 cm in diameter and they are exceptional fresh. The majority of the samples are coarse grained with protogranular texture. However a number of xenoliths have transitional textures from relatively coarse grained protogranular to fine grained equigranular textures. Hydrous phases such as phlogopite and/or amphibole were not found so far. The most striking feature is the fact that part of the xenoliths show heavy infiltration of melts. These melts circulate intergranular and react with the neighbor minerals creating veinlets with variable thickness that consists of glass and new forming minerals. Especially, their interaction with orthopyroxene results often to its almost entirely consumption, indicating that the invaded melt was silica undersaturated but rich in alkalies. According to their modal composition the xenoliths are fertile spinel lherzolites as also can be inferred from the compositions of the constituent minerals. Olivine is forsteritic with Fo varying from 89.3 to 90.1 and the average NiO content is 0.37 wt%. The mg# of orthopyroxene and clinopyroxene vary from 0.895-0.904 and 0.904-0.915, respectively and the spinel is Al2O3-rich with an average of cr# = 0.100. According to the REE abundances in cpx the spinel peridotites could be divided into three groups; group 1 has chondrite normalized REE with s concave upwards pattern. The LREE depletion expressed by the La/SmN ratio is medium to strong and varies from 0.11 to 0.53. The group 2 does not show any enrichment or depletion in LREE (La/SmN=0.64-1.05) and the group 3 shows an enrichment in LREE (La/SmN=1.85). While the chondrite normalized LREE abundances in cpx demonstrate variable enrichments and depletions, the HREE do not show significant differences among the three groups. Their overall Dy/YbN ratios vary from 1.05-1.16. In the primitive mantle normalized incompatible trace elements clinopyroxens show moderate negative Ti anomaly in respect to their neighbor elements. Same behavior has been observed for Zr. The lithospheric mantle underneath Tuttochi is a fertile spinel lherzolith, which experienced low degrees of partial melting. Model calculation has shown that the lithospheric mantle in this area, according to model calculations, has experienced 1-5 % batch melting. Also the calculated equilibrium temperatures for the xenoliths at 1.5 GPa are relative low and range from 780° to 940°C.
Journal of Petrology, 2020
Eclogite xenoliths, together with garnet pyroxenites and some mafic garnet granulites, found in k... more Eclogite xenoliths, together with garnet pyroxenites and some mafic garnet granulites, found in kimberlites located along the southern margin of the Kaapvaal craton in southern Africa have been analysed by electron microprobe and mass spectrometry techniques to determine their geochemical characteristics. The majority of eclogites are bimineralic with garnet and omphacitic clinopyroxene in subequal proportions, with rutile as the main accessory phase; a few contain kyanite. Based on K2O in clinopyroxene and Na2O in garnet, the eclogites can be classified as Group II eclogites, and the majority are high-Ca in character. Garnet pyroxenites comprise garnet clinopyroxenites and garnet websterites. Major and trace element concentrations and isotope ratios of reconstituted bulk rock compositions of the eclogites and garnet pyroxenites allow constraints to be placed on depth of origin and likely protolith history. Calculated Fe–Mg exchange equilibration temperatures for the eclogites range...
Geological Society, London, Memoirs, 2021
We present a summary of peridotite in the Subantarctic (46–60° S) surrounding the Antarctic Plate... more We present a summary of peridotite in the Subantarctic (46–60° S) surrounding the Antarctic Plate. Peridotite xenoliths occur on the Kerguelen Islands and Auckland Islands. The Kerguelen Islands are underlain by a plume, whereas the Auckland Islands are part of continental Zealandia, which is a Gondwana-rifted fragment. Small amounts of serpentinized peridotite has been dredged from fracture zones on the Southeast Indian Ridge, Southwest Indian Ridge and Pacific Antarctic Ridge, and represent upwelled asthenosphere accreted to form lithosphere. Suprasubduction-zone peridotite was collected from two locations on the Sandwich Plate. Peridotites from most subantarctic occurrences are moderately to highly depleted, and many show signs of subsequent metasomatic enrichment. Os isotopes indicate that subantarctic continental and oceanic lithospheric mantle contains ancient fragments that underwent depletion long before formation of the overlying crust.
Journal of Petrology, 2021
Oceanic island basalts and related magmatic rocks from Hawaii are derived from a compositionally ... more Oceanic island basalts and related magmatic rocks from Hawaii are derived from a compositionally heterogeneous mantle plume. Here we describe how this heterogeneity results from the transport of filaments of a specific composition in the plume, representing a relatively small volume of rocks (~15 %) interbedded inside a dry peridotite mantle. Four types of filaments are considered: sub-primitive mantle, ultralow-velocity zone, fertilized-harzburgite and eclogite type filaments. We present a model that describes the flow within a plume and the stress field in the overriding viscoelastic lithosphere and that can determine, from depth to the surface, the melting rate, composition and trajectory of melts produced within each type of filament. Our model shows that (1) the filaments melt at a depth corresponding to >5 GPa, where the temperature gap between the solidus and liquidus is narrow (~40–80 °C), and (2) the volume of filaments is small relative to the total volume of mantle, wh...
Geochemistry, 2021
Abstract A suite of mafic pyroxenite xenoliths and clinopyroxene megacrysts was brought to the su... more Abstract A suite of mafic pyroxenite xenoliths and clinopyroxene megacrysts was brought to the surface by Cenozoic nephelinites of the Jbel Saghro Volcanic Field (Anti-Atlas, Morocco). The large population of samples was subdivided into five groups: (i) clinopyroxenites sensu stricto; (ii) olivine clinopyroxenites; (iii) mica-bearing clinopyroxenites; (iv) kaersutite-bearing clinopyroxenites; (v) clinopyroxene megacrysts. These xenoliths display a cumulate texture (adcumulate, heteradcumulate with poikilitic clinopyroxene including olivine). The clinopyroxenes have the composition of augite and show an appreciable variation of MgO (7.02-14.80 wt.%), TiO2 (0.58-5.76 wt.%) and Al2O3 (2.81-12.38 wt.%) contents in grains. The clinopyroxenes are characterized by convex upward chondrite-normalized REE patterns, they display very similar trace element compositions with low contents of incompatible elements such as Rb (0-0.9 ppm), Ba (0.1-8.3 ppm), Th (0.1-0.3 ppm), U (0.01-0.04 ppm) and Nb (1.3-3.2 ppm). REE contents of the calculated melts in equilibrium with the clinopyroxene megacrysts and clinopyroxene from pyroxenite xenoliths are similar to those of the nephelinites exposed in Jbel Saghro. Crystallization temperatures of pyroxenite xenoliths and clinopyroxene megacrysts range from 950 °C to 1150 °C. Clinopyroxene barometry yielded pressure of crystallization ranging from 0.4 to 0.8 GPa for pyroxenite xenoliths and 0.3 to 0.7 GPa for clinopyroxene megacrysts. This pressure range is in agreement with pyroxenite xenoliths and clinopyroxene megacrysts being crystallized from their parental melts at the lower and upper crust.
European Journal of Mineralogy, 2000
Alkali basalts from the Kerguelen Islands have entrained numerous phlogopite- and amphibole-beari... more Alkali basalts from the Kerguelen Islands have entrained numerous phlogopite- and amphibole-bearing ultramafic to mafic xenoliths. These are subdivided into mantle harzburgites, dunites and associated composite xenoliths that represent mantle wall-rock (Type-I) and high pressure (10–15 kbar) segregates (Type II). A lamprophyric dyke containing phlogopite megacrysts has been also studied. Chemical compositions of amphiboles and phlogopites from both xenolith types are similar to those recognized in many ultramafic and mafic volatile-bearing xenoliths from kimberlites and alkali basalts and in peridotites and pyroxenites from orogenic lherzolite massifs. Interstitial amphibole and phlogopite in harzburgites and dunites probably formed during diffuse percolation of highly alkaline basic silicate melt within the upper mantle (porous flow). Evidence from composite xenoliths suggest that similar mantle melts migrated through a network of dykes generated by hydraulic fracturing in the Kerg...
Deep-seated meta-igneous xenoliths brought to the surface by alkali basaltic magmas from the Kerg... more Deep-seated meta-igneous xenoliths brought to the surface by alkali basaltic magmas from the Kerguelen Islands reveal that basaltic magmas have intruded the upper mantle beneath the Kerguelen Islands throughout their geological evolution. These record volcanic activity associated with their early mid-ocean ridge (South East Indian Ridge) location and subsequent translation away from the ridge to an intraplate setting over the Kerguelen Plume. The metaigneous xenoliths sample two distinctive magmatic episodes distinguished by major, trace element and isotope compositions: one tholeiitic transitional episode and one alkaline episode. Ultrasonic measurements of compressional wave speed Vp have been carried out at pressures up to 1 GPa, and densities measured, for representative samples of these two suites of metaigneous xenoliths. A spinel harzburgite that represents the Kerguelen peridotitic upper mantle has been incorporated in the study. Vp and density have also been calculated usin...
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Papers by Michel Gregoire