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Solubility, diffusivity, and speciation of nitrogen in silicate glasses and melts

Thèse de doctorat - date limite de candidature 28 mai 2017 (POSTE POURVU)

Solubility, diffusivity, and speciation of nitrogen in silicate glasses and melts

Supervision : Evelyn Füri and Yves Marrocchi

Laboratory : Centre de Recherches Pétrographiques et Géochimiques (CRPG)
CNRS-Université de Lorraine
15 rue Notre Dame des Pauvres
54500 Vandoeuvre-les-Nancy

Theme : Formation and evolution of the Solar System and planets

Financial support : ERC-2016-STG ’VOLATILIS’ (PI : Evelyn Füri)

Duration : 3 years (36 months)

Volatile elements (hydrogen, carbon, nitrogen) control the evolution of planetary bodies, and they have been essential ingredients for the development of life on Earth. Nonetheless, the origin of volatiles on inner Solar System planets remains a subject of debate and controversy in planetary science. Nitrogen isotopes offer a powerful tool for assessing the contribution from solar, meteoritic, or cometary volatile reservoirs to the terrestrial planets, as the relative proportion of the two isotopes of nitrogen (14N and 15N) varies dramatically across the Solar System. The caveat is that secondary processes (e.g., degassing, alteration, space exposure) may have altered the primary nitrogen signature of most available mantle-derived samples. Consequently, in order to accurately constrain the origin and abundance of nitrogen in planetary interiors, complex physical and petrological processes must first be understood.

The objective of this project is to investigate the underlying processes affecting the nitrogen abundance and isotopic signature of terrestrial and extraterrestrial samples by using a combination of state-of the art and novel analytical techniques, such as static noble gas mass spectrometry, secondary ionization mass spectrometry, and Raman spectroscopy. Specifically, the solubility, diffusivity, and speciation of nitrogen in silicate melts and/or glasses will be studied through a targeted experimental and analytical approach.

1) We are currently developing the protocol for nitrogen analyses in silicate samples by secondary ionization mass spectrometry (SIMS) ; this method will allow us to target micron-sized objects (such as melt inclusions and rare extraterrestrial samples collected during sample return missions) for nitrogen analyses. Additional glass standards with variable compositions and nitrogen concentrations will have to be synthesized. The effect of the major element composition, nitrogen content, and nitrogen speciation on the ionization efficiency of nitrogen will have to be determined. Subsequently, the method can be applied to a range of natural silicate samples.

2) The nitrogen speciation and diffusivity in silicate glasses and/or melts will be investigated for a range of chemical and physical parameters. The nitrogen diffusion coefficient is a fundamental parameter for evaluating the efficiency of nitrogen incorporation into planetary magma oceans, for understanding magma vesiculation and degassing, for assessing whether melt inclusions retain pristine nitrogen contents, and for quantifying the diffusive nitrogen loss from volcanic glasses. It is also critical for understanding the nitrogen release patterns observed during step-wise heating experiments of terrestrial and extraterrestrial samples.

Ultimately, upon completion, this project will provide key results that will improve our understanding of the origin of nitrogen on Earth and other planetary bodies, and it will form the basis for deciphering the data expected to be obtained by future space missions dedicated to the study and/or sampling of near-Earth planetary objects.

The candidate should have an interest in analytical and experimental work and development, as well as a solid background in geochemistry and petrology. Strong organisational, writing, and interpersonal skills are essential, and good English speaking and writing skills are advantageous. Interested candidates should submit a letter of motivation, a CV, and the names and contact information of two references to Evelyn Füri (efueri@crpg.cnrs-nancy.fr). The deadline for application is set for May 28, 2017.

publié jeudi 6 avril 2017