Professor David J Prior

Research Interests

My research interests span from the understanding of the material processes that control behaviour of crystalline materials (including rocks, industrial ceramics, metals and ice), to the large-scale tectonic and thermo-chemical processes that control the evolution of the Earth's interior. I am widely known for my expertise in microstructural analysis, most specifically using Electron Backscatter Diffraction (EBSD) in the Scanning electron microscope and I will be establishing an EBSD laboratory at the University of Otago. I list below three major research areas that will occupy much of my time in the coming few years.

Grain Boundary Sliding (GBS) and Earth Rheology.

Understanding crust and mantle geodynamics underpins our ability to interpret and model the development of all geotectonic features from mountain belts to sedimentary basins, with implications for understanding the origins and distributions of Earth resources. The deformation and recrystallization mechanisms that occur during creep of the crust and mantle (and of glacial ice and industrial metals) control the development of lattice preferred orientations (LPO) and rock strength. My work on recrystallization has demonstrated that one mechanism that needs to be understood more fully is grain boundary sliding (GBS); this is essential to the interpretation of crust and mantle deformation kinematics, physical conditions and rheology from exhumed rock samples or from seismic velocity anisotropy data.

Up to now, few creep deformation experiments, of polycrystalline materials relevant to the crust or upper mantle, have succeeded in tracking the microstructural evolution of individual grains. Lacking this information limits severely our ability to understand processes such as GBS. Working with Dan Tatham and Elisabetta Mariani in Liverpool and Julian Mecklenburgh and Ernie Rutter in Manchester I have developed a new, relatively easy and inexpensive method to track the evolution of specific rock microstructures (e.g. individual grains) during laboratory creep experiments to high shear-strain at elevated pressure and temperature. The method allows us to examine the surface of a single cylinder sample, sequentially between increments of torsional shear and is now integral to a series of experiments I will be conducting whilst on sabbatical with Greg Hirth (Brown University) and Brian Evans (MIT) and parallel experiments by my colleagues in Liverpool and Manchester. I will be setting up the equipment for the microstructural aspect of this work in Otago so that extensive collaborations with experimentalists will continue.

The Alpine Fault Zone, South Island, New Zealand

Having spent more than a decade developing microstructural tools to understand processes in the Earth and to constrain conditions in the Earth I am now keen to apply these to larger-scale tectonic problems, and to use larger-scale tectonic settings to test and develop the understanding we have of grain-scale processes, together with their kinetics and driving forces. My main area of interest is the Southern Alps of New Zealand, where the Alpine Fault zone provides the world's best natural laboratory to document fault rock evolution; primarily because it exhumes its own fault rocks and active conditions at depth are representative of those that generated exhumed materials. I started work on the Alpine Fault for my PhD and been actively engaged in new Alpine Fault research, in collaboration with Richard Norris, Alan Cooper and Virginia Toy (Otago) and Tim Little (Wellington) since ~ 2003.

I am one of the principle scientists in an International Continental Drilling Programme (ICDP) initiative to drill the Alpine Fault zone. The first stage of drilling will start in January 2011 involving GNS and the Universities of Otago, Wellington, Canterbury, Auckland, Liverpool and Bremen. These partners are involved in fundraising for further, deeper drilling. I envisage that research that builds towards a major international initiative of drilling and allied science in the Southern Alps will be my priority over the next 5 to 10 years.

One key new area that links my expertise tightly to an Alpine Fault project is brittle fault rocks. These are the rocks formed in the seismogenic zone: the processes that contribute to the formation of brittle fault rocks and their resultant physical properties are key to understanding crustal strength, faulting and earthquakes. The new SEM based microstructural tools that I have been critical in developing have mainly been applied to rocks that are deformed by non-brittle, creep processes. Brittle rocks have largely been ignored, for a number of reasons. Furthermore, despite our broad understanding of changes in fault rocks and mechanics from depth to the surface, there are virtually no studies that document the changes within brittle fault rocks as a function of depth; although it is these rocks that are most relevant to processes in the seismogenic zone. The Alpine Fault affords the best opportunity to do this. One major goal of the next two years is to conduct a thorough analysis of a suite of brittle fault rocks from the Alpine Fault zone using modern microstructural methods, together with parallel studies of materials generated in laboratory experiments. The aim will be to generate a toolkit for the analysis of brittle fault rocks and a better understanding of processes and properties in seismogenic faults.

Ice microstructure and mechanics.

One problem in the analysis of rock rheology is the comparison of laboratory length and time scales with those in nature. Laboratory experiments are limited to small pieces of material (a few 10s of mm at most usually) and need to be complete in weeks at the longest, so that laboratory strain-rates are typically 5 orders of magnitude or more faster than natural ones; the faster strain-rate often facilitated by elevated temperatures. There are very few materials where we can compare laboratory results and larger-scale systems in a very quantitative way: the best opportunities lie in ice and rock-salt, where large-scale systems achieve significant strains on time-scales of weeks to years. Technology has now been developed to conduct EBSD on ice so that the full range of quantitative microstructural analyses we apply to rock forming minerals can be applied to ice. Thus there is the potential to assess stress, strain and kinematic fields in actively deforming large-scale systems (ice sheets, glaciers, sea-ice) and compare these systems and their products (deformed ice) directly with the results of small-scale laboratory experiments under equivalent conditions and under extrapolated conditions (from faster strain-rates etc). I am currently working with Dave Goldsby (Brown University) and Bill Durham and Sabrina Diebold (MIT) to link the mechanical behaviour of ice to its microstructural evolution. Ice EBSD is being conducted at Dartmouth College in collaboration with Ian Baker and Rachel Obbard. The data and models we will collect are also of considerable value in understanding the dynamics of natural ice systems. These are important components of the Earth System that responds to changes in climate and potentially influence the direction and rate of climate change.

Post-graduate student supervision

Current students

• Martin Forbes (PhD, Surveying) – Structural provinces and limits on rift propagation in the Ross Ice Shelf
• Rachel Worthington (MSc) – Mechanical properties of ice within shear margins and implications for ice shelf mechanics
• Tabitha German (BSc(Hons) – Evolution of air bubbles in ice during deformation
• Zoe MacClure (BSc(Hons) – Ice flow and deformation, Tasman Glacier, New Zealand

My Favourites from my Publications

• Prior, D.J., Knipe, R.J., & Handy, M.R., 1990. Estimates of rates of microstructural changes in mylonites. In Knipe et al (eds): Deformation mechanisms, rheology and tectonics. Special publication of the Geological Society of London, 54, 309-320.
• Prior, D.J., 1993. Sub-critical fracture and associated retrogression of garnet during mylonitic deformation. Contributions to Mineralogy and Petrology, 113, 545-556.
• Murdie, R.E.,Prior, D.J., Styles, P., Flint, S.S., Pearce, B., & Agar, S.M., 1994. Seismic responses to ridge-transform subduction: Chile Triple Junction. Geology, 21, 1095-1098.
• Prior, D.J., Trimby, P.W., Weber, U.D., Dingley, D.J. 1996. Orientation contrast imaging of microstructures in rocks using forescatter detectors in the scanning electron microscope. Mineralogical Magazine. 60 859-869.
• Trimby, P.W., Prior, D.J., and Wheeler, J.1998. Grain boundary hierarchy development in a quartz mylonite. Journal of Structural Geology, 20, 917-935.
• Prior, D.J., Boyle, A.P., Brenker, F., Cheadle, M.C., Day, A., Lopez, G., Peruzzo, L., Potts, G.J., Reddy, S.M., Spiess, R., Timms, N.E., Trimby, P.W., Wheeler, J., & Zetterström, L., 1999. The application of Electron Backscatter Diffraction and Orientation Contrast Imaging in the SEM to textural problems in rocks. American Mineralogist, 84, 1741-1759.
• Jiang, Z., Prior, D.J., & Wheeler, J. 2000. Albite CPO, grain misorientation distribution and granular flow in a low-grade mylonite. Journal of Structural Geology, 22, 1663-1675.
• Spiess, R., Peruzzo, L., Prior D.J., & Wheeler, J. 2001. Development of garnet porphyroblasts by multiple nucleation, coalescence and boundary misorientation driven rotations. Journal of Metamorphic Geology, 19, 269-290.
• Wheeler, J., Prior, D.J., Jiang, Z., Spiess, R., Trimby, P.W. 2001. The petrological significance of misorientations between grains. Contributions to Mineralogy and Petrology, 141, 109-124.
• Bestmann, M., & Prior, D.J., 2003 Intragranular dynamic recrystallization in naturally deformed calcite marble: diffusion accommodated grain boundary sliding as a result of subgrain rotation recrystallization. Journal of Structural Geology, 25, 1597-1613.
• Seward, G.G.E., Celotto, S., Prior, D.J., Wheeler, J. & Pond, R 2004. In-Situ SEM-EBSD Observations of the HCP to BCC Phase Transformation in Commercially Pure Titanium. Acta Materialia, 52, 821-832
• Bestmann, M., Piazolo, S., Spiers, C., & Prior, D. J., 2005. Microstructural development of rocksalt during in-situ heating experiments. Journal of Structural Geology. 27, 447-457.
• Ohfuji, H., Boyle, A., Prior, D.J. & Rickard, D., 2005. Structure of framboidal pyrite: a crystallographic study. American Mineralogist, 90, 1693-1704.
• Storey, C.D. and Prior, D.J., 2005. High strain deformation, recovery and recrystallization of garnet. Journal of Petrology, 46, 2593-2613.
• Haddad, S.C., Worden, R.H.W., Prior, D.J., & Smalley, C. 2006. Quartz overgrowths in the Fontainebleau sandstone, Paris basin, France; a study using electron backscatter diffraction (EBSD). Journal of Sedimentary Research. 76, 244-256
• Wightman, R., Prior, D.J & Little, T., 2006. Neotectonically deformed quartz veins in the Southern Alps orogen: possibility of diffusion accommodated grain boundary sliding as a dominant deformation mechanism under moderate P-T conditions. Journal of Structural Geology, 28, 902-918.
• Watt, L., Bland, P., Prior, D.J. & Russell, S.S. 2006. Fabric analysis of Allende matrix using EBSD. Meteoritics and Planetary Science, 41, 989-1001.
• Shigematsu, N., Prior, D.J. & Wheeler, J. 2006. First combined electron backscatter diffraction and transmission electron microscopy study of grain boundary structure of deformed quartzite. Journal of Microscopy, 224, 306-321.
• Toy, V., Prior, D.J., & Norris, R.J., 2008. Quartz fabrics in the Alpine Fault mylonites: Influence of pre-existing preferred orientations on fabric development during progressive uplift. Journal of Structural Geology. 30, 602-621.
• Barrie, C.D., Boyle, A.P. Cox, S.F. & Prior, D.J. 2008. Slip systems in pyrite: An electron backscatter diffraction (EBSD) investigation. Mineralogical Magazine, 72, 1181-1199.
• Hildyard, R., Prior, D.J. Faulkner, D.R. Mariani, E. 2009. Microstructural analysis of anhydrite rocks from the Triassic Evaporites, Umbria-Marche Appennines, Central Italy: an insight into deformation mechanisims and possible slip systems. Journal of Structural Geology. 31, 92-103.
• Mariani, E., Mecklenburgh, J., Wheeler, J., Prior, D.J. & Heidelbach F., 2009. Microstructure evolution and recrystallization during creep of MgO single crystals. Acta Materialia, 57, 1886–1898.
• Wheeler, J., Mariani, E., Piazolo, S., Prior, D.J. Trimby, P., Drury, M. 2009. The Weighted Burgers Vector: a new quantity for constraining dislocation densities and types using Electron Backscatter Diffraction on 2D sections through crystalline materials. Journal of Microscopy. 233. 482–494.
• Prior, D.J., Mariani, E., & Wheeler, J., 2009. EBSD in the Earth Sciences: applications, common practice and challenges. In: Electron Backscatter Diffraction in Materials Science: 2nd Edition. Editors Schwartz, A.J., Kumar, M., Adams B.L. & Field, D.P. Springer. ISBN-13: 978-0387881355.432p. Chapter 29. p345-357.
• Timms, N.E., Healy, D., Reyes-Montes J.M., Collins, D.S., Prior, D.J., Young, R.P. 2010. The effects of crystallographic anisotropy on fracture development and acoustic emission in quartz. Journal of Geophysical Research 115. doi:10.1029/2009JB006765
• Pearce, M., Wheeler, J., & Prior, D.J. (in Press). Quantitative microstructural constraints on the deformation of the Torridon high strain zone, NW Scotland. Journal of Structural Geology.
• Dempsey , E., Prior, D.J., Mariani, E., & Toy, V. (in Press). Mica fabrics and anisotropy from EBSD data: Mica controlled anisotropy within mid to upper crustal mylonites. Spec Publ Geol Soc London.
• Bland. P.A., Howard, L.E., Prior, D.J., Wheeler, J., & Hough, R.M. (in Press). The first rock fabric in the Solar System: Oriented sub-micron grains in a chondrule rim. Nature Geosciences.