Models of deformation and texture inheritance at the base of the mantle

<div>A poster presented at the 15th Symposium of the Study of the Earth's Deep Interior (SEDI 2016); 24-29th July, Nantes, France</div><div><b><br></b></div><div><b>Abstract</b></div><div><br></div><div>The profound changes in physical properties across the Earth’s core-mantle boundary makes this region key for the understanding of global-scale dynamics. As well as moderating any interaction between the metallic core and rocky mantle, the lowermost mantle also hosts the basal limb of mantle convection acting as a kind of inaccessible inverse lithosphere. In principle, knowledge of seismic anisotropy permits us to probe mantle flow in this region. However, in order to understand anisotropy in terms of flow, we need to know how the minerals present in the lowermost mantle deform and generate the textures that lead to bulk anisotropy. Previously, by combining predictions of mantle flow with the simulation of texture development in deforming post-perovskite aggregates, we have explored how different slip system activities give different predictions for the long-wavelength anisotropy in the lowermost mantle. By converting these results into models compatible with global scale radially anisotropic seismic tomography we have shown how different predictions correlate with tomographic inversions. We found that the most recent experimental indication of the active slip systems in post-perovksite, where dislocations gliding on (001) are most mobile, give predictions that were anti-correlated with results from tomography at long wavelengths. This means that it is difficult to explain the observed patterns of seismic anisotropy in the lowermost mantle as being due to the generation of lattice-preferred orientation in post-perovskite. A possible resolution to this difficulty is offered by experiments on analogues, which show that texture can be inherited during the perovskite to post-perovskite phase transition. Here we modify our previous approach to include this effect. This results in distributions of predicted seismic anisotropy that are in better agreement with tomography. In particular, we find that models where texture is generated by deformation of post-perovskite dominated by dislocations gliding on (001) followed by texture inheritance during the phase transition to perovskite driven by increasing temperature results in models that correlate with tomography at spherical harmonic degrees 1-5. In particular, texture inheritance in our models results in a better match to tomography in regions where the vertically polarised shear waves propagate more quickly than horizontally polarised shear waves.</div

Neutrinos as a geophysical tool

<p>Oral presentation on the various uses of neutrinos as a means of sounding planetary interiors, principally as an introduction to the novel concept of using coherent scattering to obtain information about the crystal structure of the core.</p> <p>See also</p> <p>Fortes, A. D., I. G. Wood, & L. Oberauer (2006): Using neutrino diffraction to study the Earth's core <em>Astronomy & Geophysics</em> <strong>47</strong>(5), 31-33 (doi:10.1111/j.1468-4004.2006.47531.x)</p