My research aims to determine and quantify the interactions between processes at the microscale (e.g. microstructural and compositional evolution) and those at macroscopic tectonic scales (e.g. fault zone processes, mantle deformation and plate motion). Currently, I am working on application of methods based on electron backscatter diffraction (EBSD) to questions of rock rheology during deformation in the upper mantle and in crustal shear zones. In particular, I am adapting high angular-resolution electron backscatter diffraction (HR-EBSD), developed in the materials sciences, to quantify dislocation densities, residual stress and elastic strain in geological materials. More generally my research interests include crustal evolution, deformation during orogeny, and interpretation of fault zone behaviour from deformation microstructures.
View Selected Publications
Qi, C., Hansen, L.N., Wallis, D., Holtzman, B.K., Kohlstedt, D.L. (in press) Crystallographic preferred orientation of olivine in sheared partially molten rocks: the source of the “a-c switch”. Geochemistry, Geophysics, Geosystems, 2017GC007309R.
Wallis, D., and Searle, M.P. (in press) Spatial and temporal distributions of deformation in strike-slip faults: The Karakoram Fault in the India-Asia collision zone. Duarte, J.C. (Ed.) Transform Plate Boundaries and Fracture Zones. Elsevier.
Wallis, D., Parsons A.J., and Hansen, L.N. (in press) Quantifying geometrically necessary dislocations in quartz using HR-ESBD: Application to chessboard subgrain boundaries. In: Hippertt, J. (Ed.) Back to the Future: 40 years of Structural Geology and Beyond, Journal of Structural Geology 40th Anniversary Special Issue, DOI: 10.1016/j.jsg.2017.12.012.
Wallis, D., Lloyd, G.E., and Hansen, L.N. (2018) The transition from dislocation-mediated to frictional deformation of marbles within the Karakoram Fault, NW India. Journal of Structural Geology, 107, 25–37, DOI: 10.1016/j.jsg.2017.11.008.
Kumamoto, K.M., Thom, C., Wallis, D., Hansen, L.N., Armstrong, D.E.J., Warren, J.M., Goldsby, D.L., and Wilkinson A.J. (2017) Size effects resolve debate in 40 years of work on low-temperature plasticity in olivine. Science Advances, 3, e1701338, DOI: 10.1126/sciadv.1701338.
Wallis, D., Hansen, L.N., Britton, T.B., and Wilkinson, A.J. (2017) Dislocation interactions in olivine revealed by HR-EBSD. Journal of Geophysical Research: Solid Earth, 122, 7659–7678, DOI: 10.1002/2017JB014513.
Boneh, Y., Wallis, D., Hansen, L.N., Krawczynski, M.J., and Skemer, P. (2017) Oriented grain growth and modification of ‘frozen anisotropy’ in the lithospheric mantle. Earth and Planetary Science Letters, 474, 368–374, DOI: 10.1016/j.epsl.2017.06.050.
Wallis, D., Hansen, L.N., Britton, T.B., and Wilkinson, A.J. (2016) Geometrically necessary dislocation densities in olivine obtained using high-angular resolution electron backscatter diffraction. Ultramicroscopy, 168, 34–45, DOI: 10.1016/j.ultramic.2016.06.002.
Britton, T.B., Jiang, J., Guo, Y., Vilalta-Clemente, A., Wallis, D., Hansen, L., Winkelmann, A., and Wilkinson, A.J. (2016) Tutorial: Crystal Orientations and EBSD – or which way is up? Materials Characterization, 117, 113–126, DOI: 10.1016/j.matchar.2016.04.008.
Wallis, D., Carter, A., Phillips, R.J., Parsons, A.J., and Searle, M.P. (2016) Spatial variation in exhumation rates across Ladakh and the Karakoram: new apatite fission track data from the Eastern Karakoram. Tectonics, 35, 704–721, DOI: 10.1002/2015TC003943.
Wallis, D., Lloyd, G.E., Phillips, R.J., Parsons, A.J., and Walshaw, R.D. (2015) Low effective fault strength due to frictional-viscous flow in phyllonites, Karakoram Fault Zone, NW India. Journal of Structural Geology, 77, 45–61, DOI: 10.1016/j.jsg.2015.05.010.
Wallis, D., Phillips, R.J., and Lloyd, G.E. (2014) Evolution of the Eastern Karakoram Metamorphic Complex, Ladakh, NW India, and its relationship to magmatism and regional tectonics. Tectonophysics, 626, 41–52 DOI: 10.1016/j.tecto.2014.03.023.
Wallis, D., Parsons, A.J., Phillips, R.J., Searle, M.P., and Ferré E. (2014) Comment on “Interplay of deformation and magmatism in the Pangong Transpressional Zone, Eastern Ladakh, India: Implications for remobilization of the trans-Himalayan magmatic arc and initiation of the Karakoram Fault” by K. Sen, B.K. Mukherjee and A.S. Collins, Journal of Structural Geology 62 (2014) 13–24. Journal of Structural Geology, 65, 117–119, DOI: 10.1016/j.jsg.2014.03.008.
Wallis, D., Phillips, R.J., and Lloyd, G.E. (2013) Fault weakening across the frictional-viscous transition zone, Karakoram Fault, NW Himalaya. Tectonics, 32, 5, 1227–1246, DOI: 10.1002/tect.20076.