Research interests: rock deformation; microstructural evolution; EBSD; structural geology
Many major geodynamic phenomena – including plate tectonics, mantle convection, mountain building, post-seismic rebound, and ice sheet flow – are controlled by microphysical (atom- or grain-scale) deformation processes in Earth materials. These small-scale processes enable the solid Earth to flow over very long timescales, like a viscous fluid.
My research explores the rheology (flow and deformation) of rocks and minerals, in order to understand the geodynamic evolution of the Earth. The key to understanding rock rheology is through the study of microstructures – grain size and shape, or the alignment of crystal lattices, for example – that evolve during deformation, and record crucial information about the conditions and mechanisms of flow in the Earth’s interior. To decipher this information, I combine field-based, numerical, and experimental approaches, to reveal how microstructures observed in exhumed rocks relate to stress, temperature, and strain-rate conditions deep within the Earth.
As a postdoc in the ESPM group, my main focus is the ongoing development of the Large Volume Torsion (LVT) solid-medium apparatus. The LVT is capable of generating much higher pressures than conventional (gas-medium) torsion apparatus, allowing us to reproduce a range of conditions representative of the middle crust to upper mantle (P < 6 GPa; T < 1500 K). Using the LVT, I am investigating the mechanisms that lead to the intermixing of different mineral phases, which is thought to be an essential ingredient in the formation and persistence of tectonic plate boundaries. I am also involved in ongoing research, based on my Ph.D. studies, regarding the quantification of stress states within the Earth’s lithosphere, particularly around the Alpine Fault zone of New Zealand.
Some snapshots of my current and recent research (click to enlarge):
For research updates, musings and mishaps:
- Cross, A. J., Hirth, G. & Prior, D. J. (in press). Effects of secondary phases on crystallographic preferred orientations in mylonites. Geology. doi:10.1130/G38936.1
- Cross, A. J., Prior, D. J., Stipp, M. & Kidder, S. (2017). The recrystallized grain size piezometer for quartz: an EBSD-based calibration. Geophysical Research Letters, 44, 6667–6674
- Cross, A. J. & Skemer, P. (2017). Ultramylonite generation via phase mixing in high strain experiments. Journal of Geophysical Research: Solid Earth, 122(3), 1744-1759.
- Cross, A. J., Ellis, S. & Prior, D. J. (2015). A phenomenological numerical approach for investigating grain size evolution in ductiley deforming rocks. Journal of Structural Geology, 76, 22-34.
- Cross, A. J., Kidder, S. & Prior, D. J. (2015). Using microstructures and TitaniQ thermobarometry of quartz sheared around garnet porphyroclasts to evaluate microstructural evolution and constrain an Alpine Fault zone geotherm. Journal of Structural Geology, 75, 17-31.
- Cross, A. J. (2015). Microstructural evolution under non-steady state deformation in mid-crustal ductile shear zones. PhD thesis. University of Otago.
- Wheeler, J., Cross, A., Drury, M., Hough, R. M., Mariani, E., Piazolo, S., & Prior, D. J. (2011). Time-lapse misorientation maps for the analysis of electron backscatter diffraction data from evolving microstructures. Scripta Materialia, 65(7), 600-603.