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In-situ studies of olivine-wadsleyite transformation and related microstructures between 12 to 22 GPa and 1500 to 1700 K

Abstract : The 410 km depth seismic discontinuity in the Earth is attributed to the transformation from olivine to its high pressure polymorph, wadsleyite (Ringwood, 1969). This phase transformation can be martensitic-like, i.e. with a crystallographic orientation relationship between the parent crystal and the transformed crystal, but not in all cases (Smyth et al., 2012). In a martensitic-like phase transformation wadsleyite inherits a lattice preferred orientation (LPO) from the starting olivine. Hence, a LPO in olivine will be inherited by wadsleyite and could give rise to seismic anisotropy to the mantle transition zone. However, in the case of a non martensitic-like transformation, no trace of the upper mantle olivine LPO will be preserved by the newly-formed wadsleyite. In order to determine which scenario applies at the conditions of the 410 km depth discontinuity, we reproduce the transformation in the laboratory. We use polycrystalline samples of pure olivine loaded in diamond anvil cells inside a pressure medium and apply combined pressure and temperature to induce the phase transformation. The evolution of the sample’s microstructure is followed using in-situ X-rays diffraction at the beamlines ID27 of the ESRF and P02 at PETRA III (DESY). Key steps of the transformation are documented by 3D-XRD data collections. Data processing of these 3D-RXD collections with the multigrain crystallography method give us information about orientations and positions of individual grains in the samples all along the experiment. Based on the orientation of these grains, we track the texture evolution during the experiments and search for evidences of a crystallographic orientation relationships between the two phases. This characterization will allow us to determine the transformation mechanism occurring at the conditions of the 410 km discontinuity and the effect of the transformation on the seismic anisotropy in the Earth’s mantle.
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https://hal.univ-lille.fr/hal-03160168
Contributeur : Lilloa Université de Lille Connectez-vous pour contacter le contributeur
Soumis le : vendredi 5 mars 2021 - 08:09:38
Dernière modification le : mardi 24 août 2021 - 10:20:04

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  • HAL Id : hal-03160168, version 1

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Estelle Ledoux, Julien Chantel, Nadege Hilairet, Volodymyr Svitlyk, Maxime Byka, et al.. In-situ studies of olivine-wadsleyite transformation and related microstructures between 12 to 22 GPa and 1500 to 1700 K. 17th International Symposium on Experimental Mineralogy, Petrology and Geochemistry (EMPG), Mar 2021, Online, Germany. ⟨hal-03160168⟩

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