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Silicate Liquids in Extreme Conditions: Giant Impacts and Super-Earth Interiors

Bardon, Lee R.; (2018) Silicate Liquids in Extreme Conditions: Giant Impacts and Super-Earth Interiors. Masters thesis (M.Phil), UCL (University College London). Green open access

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Abstract

In this work, I use first-principles molecular dynamics (FPMD) to examine the structural, thermodynamic and transport properties of silicate liquids in the extreme conditions associated with giant impacts and super-Earth interiors, with temperatures ranging between 3000 K and 20,000 K, and pressures of up to ~4 TPa. I focus primarily on MgSiO3 liquid, with some initial results reported for the hydrated form of approximately 10 wt% water. I found that mean Si-O coordination in MgSiO3 increases linearly with pressure, from between 4 and 4.5 at upper Earth mantle conditions (~2 GPa), to between 6 and 6.5 in Earth’s lower mantle (~130 GPa), and finally to between 8 and 8.5 in the conditions associated with super-Earth mantles and giant impacts (~2.5 to 3 TPa). Average heat capacity, in the case of MgSiO3 decreases on compression from ~4.6 N k at the reference volume of V/Vx=1 to ~3.35 N k at the highest compression level of V/Vx=0.2. My analysis of self-diffusion over a very large pressure-temperature range may reveal the limitations of the Arrhenius form, when applied to self-diffusion in liquid silicates. Although the Arrhenius form describes diffusive behaviour across the temperature-pressure regime of Earth’s mantle, I discovered that self-diffusion coefficients in the conditions of super-Earth mantles are much larger than those obtained via Arrhenius extrapolation from lower-pressure. This suggests that chemical exchange between magma oceans and the crystals freezing out of them are not as limited as what once might have been thought. This work represents the first step toward a complete set of results for all materials studied, including MgSiO3, and hydrated MgSiO3, across a wide temperature and pressure regime. The results may have important implications for our understanding of the behaviour of silicate liquids in super-Earth magma oceans, and as the result of high velocity impacts. The work will motivate experimental studies of structure and physical properties of amorphous silicates over a wider temperature-pressure regime than has previously been explored.

Type: Thesis (Masters)
Qualification: M.Phil
Title: Silicate Liquids in Extreme Conditions: Giant Impacts and Super-Earth Interiors
Event: UCL (University College London)
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © The Author 2018. 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 > 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
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/10064567
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