The influence of the grain boundary network and grain size on seismic properties of Earth’s mantle


   Department of Earth Sciences

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  Prof Hauke Marquardt  No more applications being accepted  Competition Funded PhD Project (Students Worldwide)

About the Project

The geological evolution of our planet is tightly linked to deep geodynamic processes, which, themselves, are governed by the physical and chemical properties of the Earth’s mantle. Our current understanding of the thermo-chemical structure of the Earth’s mantle largely relies on the interpretation of geophysical remote sensing observations. Accurate interpretations of these observations, and hence a quantitative understanding of deep geodynamical processes, require experimental constraints on the elasticity of polycrystalline mantle materials at relevant pressure and temperature conditions. Previous high-pressure experimental studies have shown that polycrystalline materials exhibit an elastic behaviour that deviates from that predicted based on single-crystal properties (Wang et al. 2023). Yet, the underlying reasons, including the effects of grain size in polycrystalline mantle materials remain poorly understood (Marquardt et al. 2011). In this project, we will systematically study the physical properties and compression behaviour of sintered polycrystalline olivine samples, having different grain sizes and grain boundary networks (e.g. Marquardt & Faul, 2018). Seismic wave velocity measurements on mantle minerals in the diamond-anvil cell. The diamond-anvils are illuminated by the probing green laser light. The results will contribute to understanding the effects of grain boundaries on ceramics with application for the design of novel materials, and will facilitate the interpretation of geophysical observables in terms of the structure, dynamics and properties of Earth’s deep interior. Methodology A sample of a sintered polycrystalline olivine ceramics with an average grain size of about 0.17 micrometres. Synthetic sintered samples will be characterized by a variety of techniques available at the Department of Materials in Oxford, including Scanning Electron Microscopy, Transmission Electron Microscopy, Electron Backscatter Diffraction (EBSD). Physical properties at room conditions, as well as at high pressure and temperature, will be characterised by X-ray diffraction experiments at Synchrotron facilities (such as Diamond Light Source) as well as optical Brillouin spectroscopy measurements in the Department of Earth Sciences (e.g. Marquardt & Thomson, 2020). Complementary modelling will be conducted to quantitatively understand the measured material behaviour and their dependence on the observed microstructure (grain size, grain boundary network etc.)

Geology (18)

References

Marquardt, H., A. E. Gleason, K. Marquardt, S.
Speziale, L. Miyagi, G. Neusser, H. R. Wenk and R.
Jeanloz (2011). Elastic Properties of MgO Nanocrystals and Grain Boundaries to High Pressures.
Physical Review B 84: 064131.
Marquardt, H. and A. R. Thomson (2020).
Experimental elasticity of Earth’s deep mantle.
Nature Reviews Earth & Environment 1(9): 455-
469.
Marquardt, K. and U. H. Faul (2018). The structure
and composition of olivine grain boundaries: 40
years of studies, status and current developments.
Physics and Chemistry of Minerals 45(2): 139-172.
Wang, B., J. Buchen, A. S. J. Méndez, A. Kurnosov,
G. Criniti, H.-P. Liermann and H. Marquardt (2023).
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