Fonction : Thèse soutenue le 02/12/2022
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CRPG UMR 7358 CNRS-UL
15 rue Notre Dame des Pauvres
54500 Vandœuvre les Nancy – France
2022 |
Ardoin, L., Broadley, M. W., Almayrac, M., Avice, G., Byrne, D. J., Tarantola, A., Lepland, A., Saito, T., Komiya, T., Shibuya, T., Marty, B. The end of the isotopic evolution of atmospheric xenon (Article de journal) Dans: Geochemical Perspectives Letters, vol. 40, 2022. @article{Ardoin_etal2022,Noble gases are chemically inert and, as such, act as unique tracers of physical processes over geological timescales. The isotopic composition of atmospheric xenon, the heaviest stable noble gas, evolved following mass-dependent fractionation throughout the Hadean and Archaean aeons. This evolution appears to have ceased between 2.5 and 2.1 Ga, around the time of the Great Oxidation Event (GOE). The coincidental halting of atmospheric Xe evolution may provide further insights into the mechanisms affecting the atmosphere at the Archaean-Proterozoic transition. Here, we investigate the isotopic composition of Xe trapped in hydrothermal quartz from three formations around the GOE time period : Seidorechka and Polisarka (Imandra-Varzuga Greenstone Belt, Kola Craton, Russia) with ages of 2441thinspacetextpmthinspace1.6 Ma and 2434thinspacetextpmthinspace6.6 Ma, respectively, and Ongeluk (Kaapvaal Craton, South Africa) dated at 2114thinspacetextpmthinspace312 Ma (Ar-Ar age) with a host formation age of 2425.6thinspacetextpmthinspace2.6 Ma (upper bound). From these analyses we show that Xe isotope fractionation appears to have ceased during the time window delimited by the ages of the Seidorechka and Polisarka Formations, which is concomitant with the disappearance of mass-independent fractionation of sulfur isotopes (MIF-S) in the Kola Craton. The disappearance of Xe isotope fractionation in the geological record may be related to the rise in atmospheric oxygen and, thus, can provide new insights into the triggering mechanisms and timing of the GOE. |
Almayrac, M. G., Bekaert, D. V., Broadley, M. W., Byrne, D. J., Piani, L., Marty, B. The EXCITING experiment exploring the behavior of nitrogen and noble gases in interstellar ice analogs (Article de journal) Dans: The Planetary Science Journal, vol. 3, p. 252, 2022. @article{Almayrac_etal2022,Comets represent some of the most pristine bodies in our solar system and can provide a unique insight into the chemical makeup of the early solar system. Due to their icy volatile-rich nature, they may have played an important role in delivering volatile elements and organic material to the early Earth. Understanding how comets form can therefore provide a wealth of information on how the composition of volatile elements evolved in the solar system from the presolar molecular cloud up until the formation of the terrestrial planets. Because noble gases are chemically inert and have distinct condensation temperatures, they can be used to infer the temperatures of formation and thermal history of cometary ices. In this work, we present a new experimental setup called EXCITING to investigate the origin and formation conditions of cometary ices. By trapping nitrogen and noble gases in amorphous water ice, our experiment is designed to study the elemental and isotopic behavior of volatile elements in cometary ice analogs. We report new results of noble gas and nitrogen enrichment in cometary ice analogs and discuss the limitations of the experimental conditions in light of those supposed for comets. We show that forming ice analogs at â`u70 K best reproduce the noble gas and N2 abundances of comet 67P/Churyumov--Gerasimenko, considering a solar-like starting composition. This formation temperature is higher than previous estimates for cometary ices and suggests that the formation of cometary building blocks may have occurred in the protosolar nebula rather than in the colder molecular cloud. |
2020 |
Marty, B., Almayrac, M., Barry, P. H., Bekaert, D., Broadley, M. W., Byrne, D. J., Ballentine, C. J., Caracausi, A. An evaluation of the C/N ratio of the mantle from natural CO2-rich gas analysis : Geochemical and cosmochemical implications (Article de journal) Dans: Earth and Planetary Science Letters, vol. 551, p. 116574, 2020. @article{Marty_etal2020,The terrestrial carbon to nitrogen ratio is a key geochemical parameter that can provide information on the nature of Earthtextquoterights precursors, accretion/differentiation processes of our planet, as well as on the volatile budget of Earth. In principle, this ratio can be determined from the analysis of volatile elements trapped in mantle-derived rocks like mid-ocean ridge basalts (MORB), corrected for fractional degassing during eruption. However, this correction is critical and previous attempts have adopted different approaches which led to contrasting C/N estimates for the bulk silicate Earth (BSE) (Marty and Zimmermann, 1999 ; Bergin et al., 2015). Here we consider the analysis of CO2-rich gases worldwide for which a mantle origin has been determined using noble gas isotopes in order to evaluate the C/N ratio of the mantle source regions. These gases experienced little fractionation due to degassing, as indicated by radiogenic ⁎ values (where 4He and 40Ar* are produced by the decay of U+Th, and 40K isotopes, respectively) close to the mantle production/accumulation values. The C/N and ratios of gases investigated here are within the range of values previously observed in oceanic basalts. They point to an elevated mantle C/N ratio (�`u350-470, molar) higher than those of potential cosmochemical accretionary endmembers. For example, the BSE C/N and ratios (160-220 and , respectively) are higher than those of CM-CI chondrites but within the range of CV-CO groups. This similarity suggests that the Earth accreted from evolved planetary precursors depleted in volatile and moderately volatile elements. Hence the high composition of the BSE may be an inherited feature rather than the result of terrestrial differentiation. The and ratios of the surface (atmosphere plus crust) and of the mantle cannot be easily linked to any known chondritic composition. However, these compositions are consistent with early sequestration of carbon into the mantle (but not N and noble gases), permitting the establishment of clement temperatures at the surface of our planet. |
2018 |
Broadley, M. W., Hagi, H., Burgess, R., Zedgenizov, D., Mikhail, S., Almayrac, M., Ragozin, A., Pomazansky, B., Sumino, H. Plume-lithosphere interaction, and the formation of fibrous diamonds (Article de journal) Dans: Geochemical Perspectives Letters, vol. 2018, no. 8, p. 26–30, 2018. @article{Broadley_etal2018_2,Fluid inclusions in diamond provide otherwise inaccessible information on theorigin and nature of carbonaceous fluid(s) in the mantle. Here we evaluate therole of subducted volatiles in diamond formation within the Siberian cratoniclithosphere. Specifically, we focus on the halogen (Cl, Br and I) and noble gas(He, Ne and Ar) geochemistry of fluids trapped within cubic, coated and cloudyfibrous diamonds from the Nyurbinskaya kimberlite, Siberia. Our data show Br/Cl and I/Cl ratios consistent with involvement of altered oceanic crust, suggestingsubduction-derived fluids have infiltrated the Siberian lithosphere. 3He/4Heranging from 2 to 11 RA, indicates the addition of a primordial mantle componentto the SCLM. Mantle plumes may therefore act as a trigger to re-mobilisesubducted carbon-rich fluids from the sub-continental lithospheric mantle, andwe argue this may be an essential process in the formation of fluid-rich diamonds,and kimberlitic magmatism. |