Temperature-dependent frictional healing processes

In my postdoctoral research, I collaborated with Dr. Chris Marone at Penn State University to experimentally investigate the role of thermally-activated deformation mechanisms on the mechanical evolution of quasi-stationary synthetic fault gouge. The repeating stress drops of the seismic cycle require that faults regain a portion of their strength during interseismic periods. Experimental data confirm that faults heal when stationary. However, existing laboratory data are limited, and additional data are essential for the interpretation of new high-precision seismic observations. Quantitative and mechanistic knowledge of fault healing processes is important for a wide range of applications from studies of global tectonics to studies of post-seismic healing in specific fault systems. Exploratory experiments have produced preliminary data indicating significant temperature dependence of frictional healing in a thin layer of olivine gouge. The results of these experiments could provide important constraints on fault behavior on oceanic transform faults near the base of the seismogenic zone. This project contributes to a broad range of research aimed at understanding the internal structure of fault zones and the fundamental micro-scale physical processes that determine the rheological properties of fault gouge.

Sample loaded into biaxial deformation apparatus at Penn State

Interactions between deformation and melt migration

Nearly all regions of the Earth where melt is produced and through which melt propagates are also areas of intense deformation (e.g. mid-ocean ridges, subduction zones, and hot spots). Knowledge of the interactions between deformation and melt migration is therefore essential to understanding the dynamics of these regions. Experiments in several studies have demonstrated that during deformation melt pockets align with a consistent orientation ~20° to the shear plane, antithetic to the shear direction. As predicted by two-phase flow theory, under certain conditions melt can segregate into distinct melt-rich bands in the same orientation as the aligned pockets. These melt-rich bands then act as high permeability pathways through which melt can travel. They can also develop into zones of highly localized deformation.
As the central part of my PhD research, I conducted a suite of experiments on partially-molten, olivine-rich rock at high-pressure and high-temperature in a gas-medium deformation apparatus. Samples were deformed in a torsion geometry, which allows for much larger sample sizes and different loading geometries that prior direct shear experiments. My research has focused on several aspects of this phenomenon: (1) How can we extrapolate experimental results to predict if this process is likely to occur in Earth and at what scale? (2) What is the importance of surface tension driven flow as a competing homogenization process? (3) How does stress-driven melt segregation interact with reaction driven melt channelization mechanisms?

High-pressure high-temperature gas medium deformation apparatus at the University of Minnesota

A polished section of a torsional deformation sample sheared top-to-the-right. The dark bands are melt-rich bands that formed in response to deformation

Deformation and magma transport at an evolving continental margin

Using structural data, microstructural analysis and U-Pb geochronology, collaborators and I (as part of my MSc thesis) have investigated the evolving tectonics of an exhumed continental margin in Fiordland, New Zealand. Fiordland offers a unique view of a crustal cross section with a nearly continuous section ranging from assemblages recording depths of >40 km in the south to the upper portion of the crust in the north. Like most continental margins, Fiordland records multiple, punctuated periods of contraction and crustal thickening followed by extension and crustal thinning. The continuous exposure makes this crustal section an ideal place to test hypotheses of physical processes associated with this transition from convergence to extension. These results from field studies in Fiordland provide important constrains for models of how strain is localized in convergent and extensional continental margins.

Shear zone analysis

Field work by boat in Fiordland