Helium partitioning between the mantle and the core at the early Earth

Noble gases have the particularity that each one of them has at least one stable non-radiogenic isotope and at least one radiogenic isotope. The ratio of non-radiogenic and radiogenic isotopes of the noble gases arriving at the surface is essential to understand processes occurring on various timescale in the Earth interior.

The isotopic signature of the noble gases in the mid-ocean ridge basalts (MORB) is different than in the ocean island basalts (OIB) such as in Iceland, Hawaii, Galapagos, Réunion, or Samoa. One such example is the high ³He/⁴He ratio observed in OIB, which is explained as a signature of the core, which in this case becomes a hidden geochemical reservoir. Here, we determine the chemical behavior of helium in the magma ocean during the core formation. We employ molecular dynamics simulations based on the density functional theory as implemented in the VASP package. We perform the simulations at several temperatures and pressures that sample the magma ocean adiabat.

These calculations will enable us to derive some trends on the preference of helium in the silicate or iron melts. In the long term, they will confirm or inform the existence of a hidden reservoir deep inside the Earth.

We acknowledge support from the Research Council of Norway, project number 223272. RC acknowledges support from the European Research Council under EU Horizon 2020 research and innovation program (grant agreement 681818 – IMPACT) and access to supercomputing facilities via the eDARI gen6368 grants, the PRACE RA4947 grant, and the Uninet2 NN9697K grant.