Lou, Y, Stackhouse, S orcid.org/0000-0001-7605-3510, Walker, AM orcid.org/0000-0003-3121-3255 et al. (1 more author) (2020) Thermoelastic properties of MgSiO3-majorite at high temperatures and pressures: A first principles study. Physics of the Earth and Planetary Interiors, 303. 106491. ISSN 0031-9201
Abstract
As the major component of garnet, the second most abundant phase in Earth's transition zone, MgSiO3-majorite plays a fundamental role in controlling the state and dynamics of Earth's mantle. However, due to challenges of experiments and simulations, there are still very limited data on the elastic properties of MgSiO3-majorite at simultaneously high temperatures and pressures. In this study, we have carried out extensive first principles calculations to determine the thermoelastic properties of MgSiO3-majorite up to 2000 K and 40 GPa. We find that the elastic constants of MgSiO3-majorite change significantly over the temperature and pressure range studied, with noticeable non-linearities in their pressure dependences. The seismic anisotropy of MgSiO3-majorite is high and generally increases with pressure. It is much higher than that of the other end-members of garnet and ringwoodite, which makes it the most anisotropic mineral in assemblages expected in the lower transition zone. Based on our calculated elastic moduli and with careful elimination of systematic errors, we establish a third-order Birch-Murnaghan-Mie-Grüneisen model for MgSiO3-majorite with the parameters: V0 = 114.1 cm3/mol, K0 = 163.6 GPa, G0 = 86.4 GPa, K0′ = 4.44, G0′ = 1.16, γ0 = 1.08, q0 = 0.48, ηS0 = 0.76, and θ0 = 822.5 K. Integrating our results into a thermodynamic model able to predict the properties of mantle assemblages, we find that a pyrolite composition produces velocities that agree with the seismic model AK135 in the upper transition zone. In the lower transition zone, a pyrolite composition fits well with some specific local observations, but a mechanical mixture with 18% basalt and 82% harzburgite is in better agreement with the global seismic model PREM. The much larger abundance of MgSiO3-majorite in the garnet phase of harzburgite suggests that the anisotropy in the lower transition zone may not be negligible and would be observable at least in the heterogeneous zones near subducting slabs.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2020 The Authors. Published by Elsevier B.V.. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/. |
Keywords: | Majorite; Garnet; Elastic properties; Anisotropy; Transition zone; First principles |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Environment (Leeds) > School of Earth and Environment (Leeds) > Inst of Geophysics and Tectonics (IGT) (Leeds) |
Funding Information: | Funder Grant number NERC (Natural Environment Research Council) NE/M000044/1 |
Depositing User: | Symplectic Publications |
Date Deposited: | 15 Apr 2020 11:19 |
Last Modified: | 25 Jun 2023 22:13 |
Status: | Published |
Publisher: | Elsevier |
Identification Number: | 10.1016/j.pepi.2020.106491 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:159367 |