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"Missing Xenon" : experimental and theoretical study of Xe storage in crustal and upper mantle minerals

Abstract : Storage of Xe in silicate minerals has been proposed to explain the ‘Missing Xenon’ issue, i.e. the low Xe abundance in the Earth’s and Mars’ atmospheres compared to other noble gases and chondrites. However, data about Xe incorporation in minerals remain scarce due to high Xe volatility preventing studies at ambient conditions. Xe incorporation in silicates has been proposed based on experimental evidences at high pressures (P) and temperatures (T). In this PhD thesis we bring new constraints on Xe incorporation in major Earth minerals of the continental crust (quartz and feldspar) and upper mantle (olivine). Xe-bearing samples have been synthesized, characterized ex situ and investigated in situ at high P-T conditions. Theoretical calculations have been performed to propose Xe incorporation sites able to reproduce experimental observations. In olivine and quartz, a Xe for Si substitution is likely, with the formation of at least partially covalent Xe-O bonds of 1.98-2.09 Å. Up to 0.4 at% Xe could be stored in olivine at depth, and in quartz a phase transition toward a new (Xe,Si)O2 phase is evidenced at high T. In presence of Fe and Xe, a phase separation is observed between a Fe-rich phase and a Fe-poor phase for feldspars and olivine, with Xe and Fe stabilizing each other. In presence of excess water, Xe is going into the fluid phase for olivine, while it is retained in a feldspathic melt. Eventually Kr and Xe reactivity in feldspathic glass and melt is evidenced with the observation of Kr oxidation and Kr-O short bonds (2.49 ± 0.1 Å). These constraints on Xe incorporation in silicate melts and minerals at depths could be crucial in the ‘Missing Xenon’ issue.
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  • HAL Id : tel-02555239, version 2

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Céline Crépisson. "Missing Xenon" : experimental and theoretical study of Xe storage in crustal and upper mantle minerals. Mineralogy. Sorbonne Université, 2018. English. ⟨NNT : 2018SORUS095⟩. ⟨tel-02555239v2⟩

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