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High-pressure experimental geochemistry; reactivity of inert gases and the composition of planetary cores


This proposal aims at investigating geochemical problems concerning the distribution of chemical elements deep within planets by means of high-pressure physics and chemistry techniques.
The studies will have two foci:
1) the reactivity of inert gases with planetary materials,
2) the composition of the core of terrestrial planets. P-T conditions up to 150 GPa-4000 K be investigated to cover the Earths mantle and outer core, and the whole of other planets.
The puzzlingly low concentration of Xe in the atmosphere of the Earth could be explained if the normally inert Xe could form compounds under the conditions of the deep Earth. All inert/rare gases could be similarly hiding, due to variations of their incompatible character with pressure and temperature.
This would question our current understanding of the formation of the atmosphere and of mantle dynamics, since it is based on rare gases isotope geochemistry assuming they are inert.
The proposal to study the reactivity of Xe, Ar, Ne, and He with planetary mate rials, oxides and Fe, at pressures and temperatures found in the interiors of planets. This study will imply in situ Raman spectroscopy and X-ray diffraction, combined with post mortem chemical analysis using the latest micro-analytical techniques.
A systematic investigation of the physical properties (density, structure) of binary Fe-light element melts is proposed. In ternary systems, the existence of miscibility gaps is ubiquitous at room pressure. The P-T conditions of miscibility gap closure are likely to control the chemical composition of planetary cores, depending on the size of the planet.
The proposed approach is to investigate in situ at pressure the structure of liquids using X-ray scattering techniques. This will also give information on element partitioning between silicate and iron melts. An important change in the structure of one or other liquid might profoundly affect partitioning, i.e. the lithophile vs siderophile character of an element.

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Old College, South Bridge
United Kingdom

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