Célia Dalou

@article{Dalou_etal2022,

title = {Redox controls on H and N speciation and intermolecular isotopic fractionations in aqueous fluids at high pressure and high temperature: Insights from in-situ experiments},

author = {C. Dalou and C. Le Losq and E. F\"{u}ri and M. C. Caumon},

doi = {10.3389/feart.2022.973802},

year  = {2022},

date = {2022-01-01},

journal = {Frontiers in Earth Science},

volume = {20},

pages = {10.973802},

abstract = {Aqueous magmatic fluids are essential to the transport of hydrogen (H), carbon (C), and nitrogen (N) from the mantle to the surface, during which changes in pressure, temperature, and redox conditions affect the chemical speciation and intermolecular isotopic fractionations of H, C, and N. Here, we performed a series of hydrothermal diamond-anvil cell experiments to evaluate the role of pressure, temperature, and redox conditions on the speciation and intermolecular fractionations of H and N during the decompression and cooling of aqueous fluids from 780 MPa to 800textdegreeC to 150 MPa and 200textdegreeC. We used Raman spectroscopy to investigate the distribution and exchange reactions of H and N isotopologues between water, methane, ammonia, and dinitrogen molecules under changing physicochemical conditions. Our experiments show that upon decompression, a C- and N-bearing fluid will preferentially degas D-rich methane and 15N-rich N2, depleting the residual aqueous fluid in those isotopes. If this fluid precipitates N-rich (i.e., NH4 +- bearing) minerals, the observed N isotopic fractionation is opposite to that during N2 degassing, enriching the aqueous fluid in 15N. Because these fractionations result from changes in H, C, and N speciation in the aqueous fluid, their magnitudes depend on redox conditions as well as pressure and temperature. Our new in-situ experimental results are consistent with the large H and N isotopic fractionations observed between water, methane, and ammonia species in aqueous fluids at high pressures and temperatures, although the magnitude of the fractionations in our experiments cannot be quantified. Nonetheless, our results suggest that statistical thermodynamic models likely underestimate isotopic fractionation effects for isotopic molecules under these conditions, and should account for solubility and isotopic effects of the solvent associated with the solvation of water, methane, and ammonia isotopologues in aqueous fluids.This work has significant implications for interpreting isotopic measurements of natural samples from hydrothermal systems because it offers insights into isotopic fractionations in multicomponent and multiphase systems under hydrothermal temperatures and pressures.},

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@article{Boulliung_etal2021,

title = {Nitrogen diffusion in silicate melts under reducing conditions},

author = {J. Boulliung and C. Dalou and L. Tissandier and E. F\"{u}ri and Y. Marrocchi},

doi = {10.2138/am-2021-7799CCBYNCND},

year  = {2021},

date = {2021-01-01},

journal = {American Mineralogist},

volume = {106},

pages = {662--666},

abstract = {The behavior of nitrogen during magmatic degassing and the potential kinetic fractionation between N and other volatile species (H, C, O, noble gases) are poorly known due to the paucity of N diffusion data in silicate melts. To better constrain N mobility during magmatic processes, we investigated N diffusion in silicate melts under reducing conditions. We developed uniaxial diffusion experiments at 1 atm, 1425 textdegreeC, and under nominally anhydrous reducing conditions (fO2 ≤ IW-5.1, where IW is oxygen fugacity, fO2, reported in log units relative to the iron-wüstite buffer), in which N was chemically dissolved in silicate melts as nitride (N3--). Although several experimental designs were tested (platinum, amorphous graphite, and compacted graphite crucibles), only N diffusion experiments at IW-8 in compacted graphite crucibles for simplified basaltic andesite melts were successful. Measured N diffusivity (DN) is on the order of 5.3 textpm 1.5 texttimes 10--12 m2 s--1, two orders of magnitude lower than N chemical diffusion in soda-lime silicate melts (Frischat et al. 1978). This difference suggests that nitride diffusivity increases with an increasing degree of melt depolymerization. The dependence of N3-- diffusion on melt composition is greater than that of Ar. Furthermore, N3-- diffusion in basaltic-andesitic melts is significantly slower than that of Ar in similarly polymerized andesitic-tholeiitic melts at magmatic temperatures (1400--1450 textdegreeC ; Nowak et al. 2004). This implies that N/Ar ratios can be fractionated during reducing magmatic processes, such as during early Earthtextquoterights magma ocean stages.},

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@article{Baudouin_etal2020,

title = {Trace element partitioning between clinopyroxene and alkaline magmas: parametrization and role of M1 site on HREE enrichment in clinopyroxenes},

author = {C. Baudouin and L. France and M. Boulanger and C. Dalou and J. L. Devidal},

doi = {10.1007/s00410-020-01680-6},

year  = {2020},

date = {2020-01-01},

journal = {Contributions to Mineralogy and Petrology},

volume = {175},

pages = {42},

abstract = {Trace element partitioning between minerals and liquids provides crucial constraints on igneous processes. We quantified trace element concentrations in clinopyroxene (Cpx) phenocrysts and their phonolite melt inclusions from the 2007--08 erup-tion of Oldoinyo Lengai (Tanzania), and report Cpx-melt partition coefficients (D) and corresponding partitioning equations for rare earth elements (REE) and high field strength elements (HFSE) in alkaline magmas. Heavy REE (HREE: Er, Tm, Yb, Lu) are enriched relative to middle REE in alkaline Cpx and display a specific partitioning behavior that is characteristic of alkaline systems. HFSE (Ti, Zr, Hf) and HREE have similar D values (DHf = 0.25; DLu = 0.4) that are significantly higher than MREE (DSm = 0.06). High DHREE/DMREE are strongly correlated with the high values of DZr and DHf relative to the low DMREE values. In this study, REE partitioning between phonolite melt and Cpx is not consistent with standard models assum-ing incorporation of all REE in the Cpx M2 site, but rather highlights HREE substitution in both the M1 and M2 sites. Here we highlight the preferential incorporation of HREE in the VI-coordinated M1 site, whereas light REE and MREE remain mostly distributed in the VIII-coordinated M2 site. REE partitioning is strongly dependent on Cpx chemistry: the ideal ionic radius and HREE incorporation in the M1 site increase with increasing Fe3+ content and decrease with increasing Mg2+ and AlVI content. In our study, we focus on alkaline evolved magmas, and update existing models to obtain adequate DHREE for alkaline evolved melts. We provide equations to quantify REE and HFSE partitioning, and HREE enrichment in Cpx that are based on Cpx major element composition and temperature. We propose a new model based on the lattice strain approach that predicts HREE partitioning between Cpx and alkaline magmas. The knowledge of the melt composition or of the trace element contents is not required to obtain DREE from the new model. An improved parameterization of HFSE partitioning between Cpx and phonolite and trachy--phonolite melts is also provided herein. We discuss the potential implications of the new data on our understanding of REE deposits that are commonly associated with igneous alkaline complexes.},

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}

@article{Boulliung_etal2020,

title = {Oxygen fugacity and melt composition controls on nitrogen solubility in silicate melts},

author = {J. Boulliung and E. F\"{u}ri and C. Dalou and L. Tissandier and L. Zimmermann and Y. Marrocchi},

doi = {10.1016/j.gca.2020.06.020},

year  = {2020},

date = {2020-01-01},

journal = {Geochimica et Cosmochimica Acta},

volume = {284},

pages = {120--133},

abstract = {Knowledge of N solubility in silicate melts is key for understanding the origin of terrestrial N and the distribution andexchanges of N between the atmosphere, the silicate magma ocean, and the core forming metal. To place constraints onthe incorporation mechanism(s) of N in silicate melts, we investigated the effect of the oxygen fugacity (fO2) and melt com-position on the N solubility through N equilibration experiments at atmospheric pressure and high temperature (1425textdegreeC).Oxygen fugacity (expressed in log units relative to the iron-wu ̈stite buffer, IW) was varied from IW --8 to IW +4.1, and meltcompositions covered a wide range of polymerization degrees, defined by the NBO/T ratio (the number of non-bridging oxy-gen atoms per tetrahedrally coordinated cations). The N contents of the quenched run products (silicate glasses) were ana-lyzed byin-situsecondary ion mass spectrometry and bulk CO2laser extraction static mass spectrometry, yielding resultsthat are in excellent agreement even for N concentrations at the (sub-)ppm level. The data obtained here highlight the fun-damental control offO2and the degree of polymerization of the silicate melt on N solubility. Under highly reduced conditions(fO2= IW --8), the N solubility increased with increasing NBO/T from 17.4 textpm 0.4 ppm.atm-1/2in highly polymerized melts(NBO/T = 0) to 6710 textpm 102 ppm.atm-1/2in depolymerized melts (NBO/T˜2.0). In contrast, under less reducing conditions(fO2\> IW --3.4), N solubility is very low (≤2 ppm.atm-1/2), irrespective of the NBO/T value. Our results provide constraintson N solubility in enstatite chondrite melts and in the shallow part of a planetary magma ocean. The nitrogen storage capacityof an enstatite chondrite melt, which may approximate that of planetesimals that accreted and melted early in the inner SolarSystem, varies between ˜60 and ˜6000 ppm at IW --5.1 and IW --8, respectively. In contrast, a mafic to ultra-mafic magmaocean could have incorporated ˜0.3 ppm to ˜35 ppm N under thefO2conditions inferred for the young Earth (i.e., IW --5 toIW). The N storage capacity of a reduced magma ocean (i.e., IW --3.4 to IW) in equilibrium with a N-rich atmosphere is ≤1 ppm, comparable to the N content of the present-day mantle. However under more reducing conditions (i.e., IW --5 toIW --4), the N storage capacity is significantly higher (˜35 ppm) ; in this case, Earth would have lost N to the atmosphereand/or N would have been transported into and stored within its deep interior (i.e., deep mantle, core).},

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@article{Rose-Koga_etal2020,

title = {In-situ measurements of magmatic volatile elements, F, S, and Cl, by electron microprobe, secondary ion mass spectrometry, and heavy ion elastic recoil detection analysis},

author = {E. F. Rose-Koga and K. T. Koga and J. L. Devidal and N. Shimizu and M. Le Voyer and C. Dalou and M. D\"{o}beli},

doi = {10.2138/am-2020-7221},

year  = {2020},

date = {2020-01-01},

journal = {American Mineralogist},

volume = {105},

number = {5},

pages = {616--626},

abstract = {Electron probe and ion probe are the two most used instruments for in situ analysis of halogens in geological materials. The comparison of these two methods on widely distributed glass standards (example: MPI-DING glasses, Jochum et al., G-cubed, 2006) provides a basis for establishing laboratory method, independent geochemical data sets for these elements. We report analyses of F, S, and Cl concentrations in three geological glass samples (EPMA) and 10 referenced standards (EPMA and SIMS). Furthermore, F and Cl absolute abundances have been determined independently for three of the standards (KL2-G, ATHO-G, and KE12), via heavy ion elastic recoil detection analysis (HIERDA), to certify the accuracy of the cross-calibration EPMA-SIMS. The detection limits for EPMA are a 150 $mu$gtextperiodcenteredg-1 for F, 20 $mu$gtextperiodcenteredg-1 for S and Cl, and for SIMS \< 48 $mu$gtextperiodcenteredg-1 for F, \< 3 $mu$gtextperiodcenteredg-1 for S, and \<19 $mu$gtextperiodcenteredg-1 for Cl. On SiO2-rich glass-standards, F and Cl measurements by HIERDA highlight a weak matrix effect during SIMS analysis of F and Cl. With the HIERDA independently measured value, we therefore propose an alternative calibration function to empirically correct this matrix effect on the SIMS measurements of F, S, and Cl.},

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tppubtype = {article}

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@article{Dalou_etal2019,

title = {Redox control on nitrogen isotope fractionation during planetary core formation},

author = {C. Dalou and E. F\"{u}ri and C. Deligny and L. Piani and G. Caumon and B. Laumonier and J. Boulliung and M. Ed\'{e}n},

doi = {10.1073/pnas.1820719116},

year  = {2019},

date = {2019-01-01},

journal = {Proceedings of the National Academy of Sciences of the United States of America},

abstract = {The present-day nitrogen isotopic compositions of Earthtextquoterights surficial (15N-enriched) and deep reservoirs (15N-depleted) differ significantly. This distribution can neither be explained by modern mantle degassing nor recycling via subduction zones. As the effect of planetary differentiation on the behavior of N isotopes is poorlyunderstood, we experimentally determined N-isotopic fractionations during metal--silicate partitioning (analogous to planetary core formation) over a large range of oxygen fugacities ($Delta$IW −3.1 \< logfO2 \< $Delta$IW −0.5, where $Delta$IW is the logarithmicdifference between experimental oxygen fugacity [fO2] conditions and that imposed by the coexistence of iron and wüstite) at 1 GPa and 1,400 textdegreeC. We developed an in situ analytical method to measure the N-elemental and -isotopic compositions of experimental run products composed of Fe--C--N metal alloys and basaltic melts.Our results show substantial N-isotopic fractionations between metal alloys and silicate glasses, i.e., from −257 textpm 22texttenthousand to −49 textpm 1texttenthousand over 3 log units of fO2. These large fractionations under reduced conditions can be explained by the large difference between N bonding in metal alloys (Fe--N) and in silicate glasses (asmolecular N2 and NH complexes). We show that the $delta$15N value of the silicate mantle could have increased by �`u20texttenthousand during core formation due to N segregation into the core.},

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pubstate = {published},

tppubtype = {article}

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@article{Dalou_etal2019_2,

title = {Raman spectroscopy study of C-O-H-N speciation in reduced basaltic glasses : Implications for reduced planetary mantles},

author = {C. Dalou and M. M. Hirschmann and S. D. Jacobsen and C. Le Losq},

doi = {10.1016/j.gca.2019.08.029},

year  = {2019},

date = {2019-01-01},

journal = {Geochimica et Cosmochimica Acta},

volume = {265},

pages = {32--47},

abstract = {To better understand the solution of volatile species in a reduced magma ocean, we identify via Raman spectroscopy the nature of C-O-H-N volatile species dissolved in a series of reduced basaltic glasses. The oxygen fugacity (f O2) during synthesis varied from highly reduced at two log units below the iron-wustite buffer (IW-2.1) to moderately reduced (IW-0.4), spanning much of the magmatic f O2 conditions during late stages of terrestrial accretion. Raman vibrational modes for H2, NH2 -- , NH3, CH4, CO, CN--, N2, and OH-- species are inferred from band assignments in all reduced glasses. The integrated area of Raman bands assigned to N2, CH4, NH3 and H2 vibrations in glasses increases with increasing molar volume of the melt, whereas that of CO decreases. Additionally, with increasing f O2, CO band areas increase while those of N2 decrease, suggesting that the solubility of these neutral molecules is not solely determined by the melt molar volume under reduced conditions. Coexisting with these neutral molecules, other species as CN--, NH2 -- and OH-- are chemically bonded within the silicate network. The observations indicate that, under reduced conditions, (1) H2, NH2 -- , NH3, CH4, CO, CN--, N2, and OH-- species coexist in silicate glasses representative of silicate liquids in a magma ocean (2) their relative abundances dissolved in a magma ocean depend on melt composition, f O2 and the availability of H and, (3) metal-silicate partitioning or degassing reactions of those magmatic volatile species must involve changes in melt and vapor speciation, which in turn may influence isotopic fractionation.},

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pubstate = {published},

tppubtype = {article}

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@article{Mosenfelder_etal2019,

title = {Nitrogen incorporation in silicates and metals: Results from SIMS, EPMA, FTIR, and laser-extraction mass spectrometry},

author = {J. L. Mosenfelder and A. Von Der Handt and E. F\"{u}ri and C. Dalou and R. L. Hervig and G. R. Rossman and M. M. Hirschmann},

doi = {10.2138/am-2019-6533},

year  = {2019},

date = {2019-01-01},

journal = {American Mineralogist},

volume = {104},

number = {1},

pages = {31--46},

abstract = {A quantitative understanding of nitrogen incorporation in Earth materials is important for constraining volatile evolution in planetary bodies. We used a combination of chemical (SIMS, EPMA, and laser-extraction mass spectrometry) and spectroscopic (FTIR) observations to study nitrogen contents and speciation mechanisms in silicate glasses, metal alloys, and an N-bearing silicate mineral (hyalophane). One suite of Fe-free basaltic glasses was studied by all four methods. Concentrations of N in these glasses determined by EPMA are systematically higher than those measured by laser extraction but agree within mutual 2s uncertainties, demonstrating the general veracity of the EPMA method. SIMS working curves based on measurement of 14N+ and 14N16O- as a function of N content determined by EPMA (or laser extraction) are best fit with exponential functions rather than the linear regressions that are most commonly applied to SIMS data. On the other hand, the relationship based on 12C14N- for C-poor, Fe-free glasses is exceptionally well fit to a linear regression (r2 = 1, p \< 0.001), in contrast to expectations from previous work on glasses with lower N contents. Matrix effects on the SIMS signals associated with Fe or H2O content are not justified by the data, but volatile data (both N and H) for hyalophane, which contains 20 wt% BaO, reveal matrix effects possibly induced by its high average molar mass. A combination of FTIR and chemical data, together with a thorough review of the literature, was used to determine incorporation mechanisms for N in the Fe-free glasses. We infer that under reducing conditions at high pressure and temperature N is dissolved in basaltic melts chiefly as NH−2 and NH2--, with N2 and/or nitride (X-N3--) complexes becoming increasingly important at low fO2, increasing N content, and decreasing H content. Our results have implications for future studies seeking to accurately measure N by SIMS and for studies of N partitioning at high pressure relevant to planetary accretion and differentiation.},

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pubstate = {published},

tppubtype = {article}

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@article{Dalou_etal2018,

title = {DOUBLE FIT: Optimization procedure applied to lattice strain model},

author = {C. Dalou and J. Boulon and K. T. Koga and R. Dalou and R. L. Dennen},

doi = {https://d10.1016/j.cageo.2018.04.013},

year  = {2018},

date = {2018-01-01},

journal = {Computers and Geosciences},

volume = {117},

pages = {49--56},

abstract = {Modeling trace element partition coefficients using the lattice strain model is a powerful tool for understanding the effects of P-T conditions and mineral and melt compositions on partition coefficients, thus significantly advancing thegeochemical studies of trace element distributions in nature. In this model, partition coefficients describe the strain caused by a volume change upon cation substitution in the crystal lattice. In some mantle minerals, divalent, trivalent,and tetravalent trace element cations are mainly substituted in one specific site. Lattice strain model parameters, for instance in olivine and plagioclase, are thus fit for one crystal site. However, trace element cations can be substituted intwo sites in the cases of pyroxenes, garnets, amphiboles, micas, or epidote-group minerals. To thoroughly study element partitioning in those minerals, one must consider the lattice strain parameters of the two sites. In this paper, we present a user-friendly executable program, working on PC, Linux, and Macintosh, to fit a lattice strain model by an error-weighted differential-evolution-constrained algorithm (Storn, R., and Price, K. 1997. Differential evolution ?\u{I} A simple and efficient heuristic for global optimization over continuous spaces. Journal of Global Optimization 11, 341--359). This optimization procedure is called DOUBLE FIT and is available for download on http://celiadalou.wixsite.com/website/double-fit-program. DOUBLE FIT generates single or double parabolas fitting experimentally determined trace element partition coefficients using a very limited amount of data (at minimum six experimental data points) and accounting for data uncertainties. It is the fastest calculation available to obtain the best-fit lattice strainparameters while accounting for the elastic response of two different sites to trace element substitution in various minerals.},

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tppubtype = {article}

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@article{Fri_etal2018,

title = {Nitrogen abundance and isotope analysis of silicate glasses by secondary ionization mass spectrometry},

author = {E. F\"{u}ri and E. Deloule and C. Dalou},

doi = {10.1016/j.chemgeo.2018.06.008},

year  = {2018},

date = {2018-01-01},

journal = {Chemical Geology},

volume = {493},

pages = {327--337},

abstract = {Chondritic meteorites preserve extreme intra-sample 15N/14N variations, which exceed, in some cases, the range of nitrogen isotope ratios observed at the Solar System scale. These observations are based on in situ analyses of CN− molecular ions by secondary ionization mass spectrometry (SIMS) in carbon-rich phases. The distribution of nitrogen and its isotopes in silicate minerals and glasses has not been investigated to this date due to the lack of an appropriate analytical protocol, as well as of suitable N-bearing standards. In order to improve our knowledge of the nitrogen signature of both extraterrestrial and terrestrial silicate samples, we have developed a protocol for determining precise and accurate nitrogen abundances (and isotope ratios) in basaltic glasses using high massresolution SIMS. Twelve (C-)N-bearing synthetic basaltic glasses, containing between\<1 and 18,443 textpm 966 ppm N, form the suite of reference materials for this study. By targeting the CN−, NO−, AlN−, and SiN− secondary molecular ions, nitrogen abundances can be detected down to the ppm level in both carbonbearing and carbon-free glasses. The analytical precision and reproducibility of isotope ratios in the form of 15N16O−/14N16O− is on the order of 11texttenthousand and 10 to 17texttenthousand (2$sigma$), respectively, for reference glasses containing �W100 ppm N. Thus, nitrogen isotope ratios can be determined with an uncertainty that is small enough to resolve nitrogen isotope variations in extraterrestrial silicates. The study of four chondrules of the ordinary chondrite Semarkona (LL3.0) reveals that the nitrogen distribution in the mesostasis is highly heterogeneous, with concentrations ranging from 0 to 1099 textpm 168 ppm. The $delta$15N values in mesostasis, olivine, and pyroxenevary between −36 textpm 50texttenthousand and +55 textpm 72texttenthousand, indicating that silicate phases in chondrules do not host particularly 15N-poor nitrogen},

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