Crustal Rheology and Deformation Processes: From Micromechanics to Geodynamics

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The primary objective of the research program is to link the nano-/ micro-scale chemo-mechanical processes that control rock deformation with the macroscopic phenomena that define dynamic behaviour of Earth; that is, to elucidate how interactions of atom- to grain-scale mechanisms mediate plate-scale behaviour. At the core of this research is the first-order relationship of localized deformation, faults and shear zones, to crustal and lithosphere dynamics. Specific topics of focus include: deformation processes associated with high energy tsunamigenic faults; the role of plastic-brittle interactions in determining rock behaviour at the base of the seismogenic zone and the spatio-temporal evolution of fault-fluid interaction during earthquakes, including the formation of economic mineral deposits. Tectonic and geodynamic behaviour can be examined using a hierarchy comprising geometry, kinematics and process. The specific geometry (structural geology) of a phenomenon provides a global context, deformation history can be determined from the kinematic evolution, and the fundamental control of both of the latter resides in the chemo-mechanical processes. The latter tripartite approach enables robust retention of observations from natural systems. A primary requisite is to establish the context for the phenomena as appropriate e.g. field mapping, determination of fault zone architecture, utilization of the seismicity record. Secondly, material (rocks) from different crustal levels and deformation histories (i.e. different tectonic environments) are thoroughly examined through detailed microstructural and fabric analysis to characterize deformation mechanisms, mineralogical controls and probable rheology. The latter encompasses nanoscience techniques including analytical transmission electron microscopy (EDS, STEM, EELS), electron back-scattered diffraction and laser ICP mass spectroscopy, amongst others, which enable complete materials characterization. Finally, in order to refine and better constrain the natural deformation behaviour, observations are integrated with those of experimental deformation studies. The strength of the nanogeoscience program has the effect of attracting collaboration with experimentalists who require such expertise for analysis of their samples. The novelty of the research resides in its emphasis on a nano-scale, process-oriented approach that nevertheless remains rooted in classical field structural geology. This bottom-up approach reflects the importance that atom- to grain-scale processes, of necessity operating under far-from-equilibrium conditions, play in the development of emergent properties and structures. In general, the difficulties inherent in predicting fault rupture reflect complex non-linear interactions of chemo-mechanical processes that produce self-organized localization of deformation. To an important extent, the limited predictability of geological phenomena relates to the corresponding limited knowledge of the underlying processes that produce non-deterministic behaviour. The primary scientific contribution of the research is characterization of the materials and processes that control dynamic behaviour of the earth with all the ensuing implications for short- and long-term behaviour. Zones of localized deformation are inherently fine- to ultrafine-grained, requiring, at the most basic level, high-resolution materials characterization techniques such as TEM; for example, identification of fault products (melts, powders, gels) generated during seismic slip and/or gouge generation that control energy dissipation cannot be fully understood without such analyses. This knowledge can than be included to earthquake hazard assessment and mineral deposit models.