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Origin of volatile elements in the inner Solar System

Periodic Reporting for period 2 - VOLATILIS (Origin of volatile elements in the inner Solar System)

Reporting period: 2018-08-01 to 2020-01-31

The objective of project VOLATILIS is to investigate the origin(s) of volatile elements on Earth and other planetary bodies in the inner Solar System. Since primitive and differentiated asteroids, planetary embryos, and the Earth-Moon system represent different stages of planet formation, studies of chondritic and achondritic meteorites, as well as of samples collected on the Moon and Earth, can provide constraints on the evolution of planetary volatiles from primordial to present-day compositions. However, indigenous volatiles in extraterrestrial samples are often masked by 'secondary' solar and cosmogenic contributions. Only combined analyses of noble gases and other volatiles (N, H) allow the observed volatile signatures to be resolved into constituent components (atmospheric, solar, cosmogenic, indigenous). The Centre de Recherches Pétrographiques et Géochimiques (Nancy, France), the PI’s host institute, is the only laboratory that is equipped with static noble gas mass spectrometers for coupled N-noble analyses of small-sized samples, and with two secondary ion mass spectrometers for quasi non-destructive volatile element measurements. By coupling these high-precision analytical techniques, we are able to reliably identify and characterize indigenous planetary volatiles, and to assess the importance of volatile storage during primary accretion or late addition via comets and asteroids. Furthermore, as part of project VOLATILIS, we have developed the protocols for N isotope analysis by ion microprobe and by static mass spectrometry in multi-collection mode; these methods now allow us to target micron-sized samples (such as melt inclusions) for N analyses and to improve the analytical precision for coupled N-noble gas studies, respectively. In parallel, experimental studies can provide fundamental insight on how various physical parameters (redox conditions, pressure, temperature) can affect the behaviour of volatile elements during planetary formation and evolution. High-pressure high-temperature experiments (using our newly installed piston cylinder apparatus and hydrothermal diamond anvil cell) allow us to better understand the nitrogen incorporation mechanism(s) in silicate melts, nitrogen isotope fractionation during mineral-fluid interaction and magma degassing, and the evolution of the nitrogen isotopic composition of planetary bodies during core formation. The new data obtained here can be integrated as critical parameters into geochemical and astrophysical models of volatile accretion and fluxes in the inner Solar System, and they are expected to be of great interest to the geo-/cosmochemistry, astrophysics, and astrobiology communities.
"The key objective of project VOLATILIS is to target various (extra-) terrestrial samples, as well as synthetic samples, for nitrogen-hydrogen-noble gas analyses using secondary ion mass spectrometry (SIMS) and static noble gas mass spectrometry. To this end, we have developed the protocols for nitrogen isotope analysis of silicate glasses by SIMS (Füri et al., Chem. Geol., 2018) and by static mass spectrometry in multi-collection mode. These tasks were carried out in collaboration with senior staff, as well as with two PhD students (Julien Boulliung and Cécile Deligny) and a post-doctoral researcher (Celia Dalou), all supported (at least in part) by project VOLATILIS. The new analytical protocols have successfully been applied for the study of extraterrestrial and synthetic nitrogen-rich samples, and three articles, discussing the results, have been published/submitted:

1) Boulliung et al. (in revision) performed nitrogen equilibration experiments on various silicate melt compositions over a wide range of oxygen fugacities to better understand the incorporation mechanism(s) of nitrogen in silicate melts, and to synthesize new calibrants for nitrogen analyses by SIMS. The results were presented at the 16th International Symposium on Experimental Mineralogy, Petrology and Geochemistry in Clermont-Ferrand, France, at the DINGUE (Developments In Noble Gas Understanding and Expertise) VI workshop in Zurich, Switzerland, and at the Goldschmidt Conference 2019 in Barcelona, Spain.

2) Deligny et al. (in revision) investigated the nitrogen and hydrogen isotopic signature of angrite melts by SIMS analyses of mineral-hosted melt inclusions and interstitial glass in the angrite meteorites D'Orbigny and Sahara 99555 to constrain the source(s) and timing of volatile delivery to planetary bodies in the inner Solar System. The findings were also presented at the 82nd Annual Meeting of the Meteoritical Society in Sapporo, Japan.

3) Dalou et al. (PNAS, 2019) experimentally determined nitrogen isotopic fractionation during metal-silicate partitioning (analogous to planetary core formation) to better understand how planetary differentiation processes may have modified the nitrogen isotopic composition of the proto-Earth. The results were presented at the Japan Geoscience Union Meeting 2018 in Chiba, Japan, and at the Goldschmidt Conference 2019, in Barcelona, Spain.

In parallel, the PI has continued her research on lunar volatiles (i.e. noble gases) by studying the He-Ne-Ar abundance and isotopic composition of single Apollo 15426 green glasses by CO2 laser extraction static mass spectrometry. Although we were unable to detect any indigenous noble gases in these lunar volcanic glasses, the results provided new insights into the irradiation history of the lunar regolith. The results were presented at the European Lunar Symposium in Toulouse, France, and at the 50th Lunar and Planetary Science Conference, Houston, The Woodlands, USA. The findings were also discussed at the DINGUE (Developments In Noble Gas Understanding and Expertise) VI workshop – co-organized by the PI – in Zurich, Switzerland. Our article discussing the data was published in Geochemical Perspective Letters in 2018 (Füri et al., GPL, 2018) and made the cover of Volume 8 of GPL.

In addition, the PI was invited to contribute to two review articles, which summarize our current knowledge of the origin of terrestrial carbon (Mikhail and Füri, Elements, in press) and of the chemical and isotopic evolution of the early Solar System (Bermingham et al., Space Sci. Rev., submitted). The first article will be included in the October 2019 issue (""Catastrophic Perturbations of Earth's carbon cycle"") of Elements Magazine. This special collection of scientific papers commemorates the 10-year anniversary of the Deep Carbon Observatory (DCO). The second article will be included in a Space Science Series of ISSI book, which reports the findings, discussions, and ideas that resulted from a Europlanet and International Space Science Institute (ISSI) workshop (""Reading terrestrial planet evolution in isotopes and element measurements"") in Bern, Switzerland, in 2018.
A new high-pressure high-temperature piston cylinder apparatus was recently installed at the CRPG; therefore, instead of preforming piston-cylinder experiments at the Laboratoire Magmas et Volcans (LMV, Clermont-Ferrand, France) as initially planned, we are now using our in-house apparatus to study nitrogen solubility in silicate melts of variable compositions at high pressure (1 GPa). These results can then be compared to those obtained by Boulliung et al. (in revision) at low pressure (1 atm). In this way, we can also synthesize additional nitrogen-bearing reference materials (i.e. silicate glasses) for SIMS analyses.
We have equipped the existing experimental petrology facility at the CRPG with a hydrothermal diamond anvil cell (HDAC) for in situ Raman spectroscopic studies of nitrogen-rich aqueous fluids, silicate melts, and minerals at high pressures (up to 30 GPa) and temperatures (up to 1000ºC). A first series of experimental tests was successfully performed, and in situ measurements will now be carried out using the LabRAM HR microspectrometer at GeoRessources (Nancy, France). This technique will allow us to investigate, for the first time, nitrogen isotope fractionation during fluid segregation from a magma, mineral-fluid interaction, and magma degassing.
We are also planning to target additional terrestrial (mid-ocean ridge and ocean-island basalts) and extraterrestrial samples (e.g. iron meteorites, aubrites, ureilites, Martian meteorites, lunar basalts) for nitrogen and/or noble gas analyses in order to better understand the volatile characteristics of Earth and other planetary bodies in the inner Solar System. Several samples from the Moon and Mars have already been acquired for these studies, and preliminary results have been obtained.