Abstract: Communication atMicrobiOccinatnie 2017 – 1ère reconcontre des Microbiologistes Région Occinatie, 24-26 Avril 2017, Toulouse.

Abstract: Abstract Observations of seismic anisotropy near the core?mantle boundary may yield constraints on patterns of lowermost mantle flow. We examine seismic anisotropy in the lowermost mantle beneath Australia, bounded by the African and Pacific Large Low Shear Velocity Provinces. We combined measurements of differential splitting of SKS?SKKS and S?ScS phases sampling our study region over a range of azimuths, using data from 10 long?running seismic stations. Observations reveal complex and laterally heterogeneous anisotropy in the lowermost mantle. We identified two subregions for which we have robust measurements of D??associated splitting for a range of ray propagation directions and applied a forward modeling strategy to understand which anisotropic scenarios are consistent with the observations. We tested a variety of elastic tensors and orientations, including single?crystal elasticity of lowermost mantle minerals (bridgmanite, postperovskite, and ferropericlase), tensors based on texture modeling in postperovskite aggregates, elasticity predicted from deformation experiments on polycrystalline MgO aggregates, and tensors that approximate the shape preferred orientation of partial melt. We find that postperovskite scenarios are more consistently able to reproduce the observations. Beneath New Zealand, the observations suggest a nearly horizontal [100] axis orientation with an azimuth that agrees well with the horizontal flow direction predicted by previous mantle flow models. Our modeling results further suggest that dominant slip on the (010) plane in postperovskite aggregates provides a good fit to the data but the solution is nonunique. Our results have implications for the mechanisms of deformation and anisotropy in the lowermost mantle and for the patterns of mantle flow.

Abstract: Summary The seismologically observed structures of both the solid inner core and the liquid outer core are the ground truth for the material properties of solid and liquid iron and its alloying elements. The key properties, from a materials science standpoint, are density, seismic wave speeds, and anisotropy. The anisotropy of the inner core does not appear to be simple; it varies laterally at the same radial level as well as varying radially. Four themes including uncertainty, model variability, virtues of solid vs. liquid properties, and composition, are the focus of this chapter. Their elaboration hopefully help present and future investigators of the physical state and composition of the core understand the problems associated with certain types of data and to focus experimental work on avenues of research providing tight observational constraints on the core's character.