MAGMATIC VOLATILES ACROSS PLANETARY DIFFERENTIATION: FROM THE CORE TO THE ATMOSPHERES – GASTON

What makes a planet habitable? This question drives scientific enquiry and human curiosity, and links many domains in geo-astro-bio-sciences. In addition to the stability of liquid water, the availability of the volatile elements (C-O-H-S-N), which dominate surficial biochemical, climatic, and geochemical processes, is crucial. Isotopic constraints indicate that the major part of these elements was delivered on Earth during the accretion stage. We may also postulate that this is at least partly the case for other terrestrial planets. In that case, volatile elements have been processed and redistributed among planetary reservoirs through the different stages of planetary differentiation. As a matter of fact, all of these stages involved magmatic processes: the magma ocean, where the core formed leaving a residual mantle; the onset of the solid mantle convection where partial melting occurred yielding the crusts; the degassing of magma that shaped the past and present atmosphere.
GASTON associates researchers in French laboratories working on the behaviour of magmatic volatiles at all these stages. They will address the fate of C-O-H-S-N elements during this sequence of differentiation events marking the Earth’s construction. How the C-O-H-S-N elements partition during core-mantle equilibration, during mantle melting or during basalt degassing and what sort of isotopic signature such processes may have left in the present geological records constitutes the poorly addressed topics that GASTON will tackle. The consortium proposes to gather their unique sets of experimental and analytical facilities to produce: (i) samples from sophisticated experiments in a poorly explored range of (high)pressure-temperature-redox conditions. (ii) these samples will then be analysed using state-of the-art measurements of light elements at high spatial resolution and sensitivity. (iii) in situ lab measurements (at pressure and temperature) will be deployed to monitor magmatic degassing and volatile speciations. These are challenging tasks, but the project achievability is either demonstrated by previous work led by the consortium or by fall-back solutions involving alternative measurements remaining innovative.
The future dataset, together with available literature data, will be assimilated in a comprehensive thermodynamic model linking speciation and solubility of C-O-H-S-N elements in basaltic melts within a prime comprehensive formalism of uncertainty propagations. This model will become the tool for the simulation the “magmatic pipeline”, that is to say, the process linking the dissolution of volatiles in the magmatic melt at depth and their release during degassing in the atmospheres.
By construction, GASTON will relate the geochemical behaviour of the C-O-H-S-N elements, eg. volatiles, lithophile, magmatophile, chalcophile or siderophile, to the pressure, temperature and redox conditions (fO2) prevailing in the magmatic pipeline. The achievement of this ambitious purpose lies in the methodology of modelling: relating redox speciation in silicate melts to fluid/melt/metal partitioning of the C-O-H-S-N elements.
Overall, GASTON should define the magmatic processes building habitable worlds by linking two domains of research, the geochemistry of the Earth and planetary interiors to the concept of habitable worlds. A strategy of dissemination and communication is planned to fulfil this ambition. In order to achieve this goal, GASTON will have a significant support from the involved host infrastructures and requests here funding for two engineers (tot 44 months) and one postdoc research associate (24 months) in addition to consumables for the experimental and analytical costs.