ATSC application to NERC

<p>Application case for support to the UK Natural Science Research Council under the Advanced Training Short Course scheme, 2014.</p> <p>We were granted funding to provide modified Software Capentry training to early career researchers and PhD students from the envrionmental sciences. Further details of the course content can be found at the links below.</p

Fractionation of magnesium isotopes in the lower mantle: insights from density functional theory

<p>Poster presented at the Geological Socitey of London meeting "Deep Earth Processes: windows on the working of a planet", 15 September 2014.</p> <p> </p

MSAT: a new Matlab toolbox for the analysis and modelling of seismic anisotropy

<p>Poster presented at the 2011 Fall meeting of the AGU outlining MSAT, an open source Matlab toolbox designed to aid the analysis of seismic and elastic anisotropy.</p

Interpolation and Inversion – New Features in the Matlab Sesimic Anisotropy Toolbox

Poster presented at the 2015 AGU Fall Meeting (DI21A-2582)<br><br><b>Abstract<br><br></b>A key step in studies of seismic anisotropy in the mantle is often the creation of models designed to explain its physical origin. We previously released MSAT (the Matlab Seismic Anisotropy Toolbox), which includes a range of functions that can be used together to build these models and provide geological or geophysical insight given measurements of, for example, shear-wave splitting. Here we describe some of the new features of MSAT that will be included in a new release timed to coincide with the 2015 Fall Meeting.<p>A critical step in testing models of the origin of seismic anisotropy is the determination of the misfit between shear-wave splitting parameters predicted from a model and measured from seismic observations. Is a model that correctly reproduces the delay time "better" than a model that correctly reproduces the fast polarization? We have introduced several new methods that use both parameters to calculate the misfit in a meaningful way and these can be used as part of an inversion scheme in order to find a model that best matches measured shear wave splitting. Our preferred approach involves the creation, "splitting", and "unsplitting" of a test wavelet. A measure of the misfit is then provided by the normalized second eigenvalue of the covariance matrix of particle motion for the two wavelets in a way similar to that used to find splitting parameters from data. This can be used as part of an inverse scheme to find a model that can reproduce a set of shear-wave splitting observations.</p><p>A second challenge is the interpolation of elastic constants between two known points. Naive element-by-element interpolation can result in anomalous seismic velocities from the interpolated tensor. We introduce an interpolation technique involving both the orientation (defined in terms of the eigenvectors of the dilatational or Voigt stiffness tensor) and magnitude of the two end-member elastic tensors. This permits changes in symmetry between the end-members and removes anomalous intermediate velocity distributions.</p

Nitrogen aggregation in diamond: insights from density functional theory

<p>Presentation from the meeting "Blowing the Earth's trumpet: New insights into deep volatiles and volatile-rich magmas" held at the University of Bristol, 14th-15th July 2011. Early results from DFT calculations on the controls on nitrogen aggregation were discussed.</p

Deformation of phase D and Earth's deep water cycle

<div>Talk given at the AGU Fall Meeting 2016. Abstract number DI22A-03.</div><div><br></div><div><b>Abstract: </b>The stability of dense hydrous magnesium silicates such as phase D in subducting slabs provide a potential path for hydrogen transport from the Earth’s surface environment into the lower mantle. Recent analysis of source-side shear wave splitting for rays from deep earthquakes around slabs detected a signal of anisotropy that could be attributed to the deformation of phase D [Nowacki et al. 2015; <em>Geochem. Geophys. Geosyst.</em>, 16, 764–784]. If this is the case these observations could provide an estimate of the hydrogen flux into the lower mantle at depths beyond shallow recycling through the volcanic arc. However, the processes leading to the deformation of phase D and the generation of seismic anisotropy are not well known and this is a barrier to progress. Here we present initial results of simulations designed to reveal how easily different dislocations move in phase D during deformation and lead to the generation of seismic anisotropy measured by shear wave splitting. In particular, we use atomic scale simulations to calculate the energies of generalised stacking faults in phase D, which are used to parameterise Peierls-Nabarro models of dislocation structures and Peierls stresses at pressures up to 60 GPa. We then use results from these calculations as parameters for models of texture development in polycrystalline aggregates during deformation using the visco-plastic self-consistent approach. In combination with measurement of the distribution of seismic anisotropy around subducting slabs, and an analysis of the strain pattern expected as slabs pass through the transition zone, these results could constrain an important part of Earth’s deep water cycle. </div

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

Magnesium Vacancy Segregation and Fast Pipe Diffusion for the 1⁄2❬110❭{110} Edge Dislocation in MgO

<p>Talk at the 2009 AGU Fall Meeting. Abstract number MR23B-06</p

Incorporating history dependence and texture in models of mantle convection

<p><strong>Poster presented at AGU Fall Meeting 2012</strong></p> <p>The solid state deformation processes permitting convection of Earth's rocky mantle necessarily lead to strong feedbacks between the deformation history and the instantaneous flow field. Mechanisms leading to the history dependence include the alignment of mineral grains with the attendant generation of elastic and rheological anisotropy, as well as processes operating at larger and smaller length scales including phase sepa- ration, grain size reduction, changes to the defect chemistry and dislocation multiplication and entanglement. Despite their sophistication, current models of mantle dynamics frequently ignore history dependent rheologies, and the feedback between deformation, grain size, crystal orientation, chemistry and viscosity. These processes have huge effects on viscosity: in the crust, they lead to the development of shear-zones and highly localised deformation, whilst, in the mantle, they are nearly always ignored. Here, we describe an approach intended to introduce the consequences of history dependence into models of whole-mantle convection. We make use of existing technology that exists in several convection codes: the ability to track markers, or particles, through the evolving flow field. Tracers have previously been used to track attributes such as the bulk chemical composition or trace element ratios. Our modifica- tion is to use this technology to track a description of the current state of the texture and microstructure (encompassing an orientation distribution function, grain size parameters and dislocation density) such that we can advance models of polycrystalline deformation for many particles alongside and in sync with models of mantle convection. Our current implementation (called Theia coupling TERRA to DRex) is designed to allow the seismic anisotropy of the upper mantle to be studied, but in future we aim to extend the approach to allow a direct feedback between the development and evolution of microstructure, and the rheology used to advance the model of mantle convection.</p> <p>Abstract number <strong>T33G-2741</strong>.</p

Can global or regional scale seismic anisotropy in D″

<p>Slides for an invited talk at the 2011 Australian Academy of Science Elizabeth and Frederick White Research Conference "<strong>Minerals at extreme conditions – Integrating theory and experiment</strong>".</p