Wilson, Alfred James;
(2020)
Thermodynamic properties of a terrestrial magma ocean.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
A variety of early solar system processes provide a route to melting the majority of the Earth’s already differentiated mantle, creating a magma ocean. This makes the differentiation of the mantle to produce today’s structure reliant entirely on the properties of the liquids which would have constituted this molten history. The modern mantle is known to be composed mostly of the magnesium perovskite mineral, bridgmanite, with the calcium counterpart also being a significant contributor and the second most abundant mineral is that of periclase. The liquid counterparts to these compositions are therefore crucial to our understanding of how a magma ocean cooled to produce the solid Earth. For this goal the melting curves of these minerals, and associated mixtures, are the primary relations. I apply first principles molecular dynamics to calculate the thermodynamic properties of both solid and liquid phases. In order to calculate melting temperatures, Gibbs free energies of each phase must be found, which requires entropy to be known. Entropy is calculable for the solid using existing techniques but liquid entropy proves to be one of the most challenging thermodynamic quantities. I refine and evaluate the recently developed two-phase thermodynamic method of calculating liquid entropy from first principles molecular dynamics simulations before applying this to calculating the whole mantle liquidus for Mg-Ca perovskites, completely independently from experiment. I also investigate the structural properties for these liquids under compression to super-earth relevant pressures. Finally, I apply similar scrutiny to carbonate liquids, which possess low melting temperatures and extremely low viscosity which makes them relevant liquids in today’s mantle as well as the upper portions of the ancient magma ocean.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Thermodynamic properties of a terrestrial magma ocean |
| Event: | UCL (University College London) |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | © The Author 2020. Original content in this thesis is licensed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) Licence (https://creativecommons.org/licenses/by/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10089294 |
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