Self-diffusion anisotropy in Zn at high pressure
Abstract
Earth's inner core has recently been revealed to be structurally complex, with significant seismic anisotropy - seismic waves traveling faster in the polar direction than in the equatorial plane - that varies in magnitude hemispherically and as a function of depth. This seismic anisotropy in Earth's inner core likely results from crystallographic preferred orientation of the hexagonal close-packed (hcp) iron-nickel alloy that is thought to be stable under inner core conditions, but how this texturing developed remains a subject of debate. Determining the self-diffusion coefficient of hcp-Fe as well quantifying the degree of anisotropy is essential for constraining the solid-state viscosity of the inner core and understanding the link between deformation and seismic anisotropy. However, direct diffusion experiments with hcp-Fe are not feasible at present because the phase is stable only at extreme pressure-temperature conditions. Therefore, we conducted piston-cylinder diffusion experiments using a structurally-analogous material, hcp-Zn, at P = 2 GPa and T = 573 - 673 K (T/Tm = 0.7 - 0.9). The diffusion couples consist of a 68Zn-enriched polycrystalline Zn foil sandwiched between two Zn single crystals, one oriented perpendicular to the crystallographic c-axis and one oriented parallel to the c-axis. Here we present the anisotropic 68Zn diffusion profiles obtained using secondary ion mass spectrometry and discuss the implications of self-diffusion anisotropy in Earth's inner core.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMMR51A2672P
- Keywords:
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- 3904 Defects;
- MINERAL PHYSICSDE: 3630 Experimental mineralogy and petrology;
- MINERALOGY AND PETROLOGYDE: 5120 Plasticity;
- diffusion;
- and creep;
- PHYSICAL PROPERTIES OF ROCKSDE: 5139 Transport properties;
- PHYSICAL PROPERTIES OF ROCKS