Areas of Active Research

Using both field and experimental techniques, I investigate how geochemistry relates to rheology and the physical processes that result in plate tectonics.

 
 

 
 

Water in mantle minerals

The majority of my research focuses on the effects of water on deformation processes. Volatiles are fascinating species that have drastic effects on whatever material contains them. In melts, the presence of water decreases the viscosity of the melt, while the presence of carbon dioxide makes explosive eruptions more likely. In hard rocks, trace amounts of water in nominally anhydrous minerals (minerals with non-stoichiometric water contents) also reduces viscosity, in addition to causing melting at lower temperatures. The crystal preferred orientation (CPO) that develops during the deformation of anisotropic minerals like olivine and pyroxene can also change depending on the amount of water in the system, affecting interpretations of seismic anisotropy.

 
 

Laboratory investigations of mineral strength

Unlike field studies, where conditions are inferred based on chemical and microstructural analyses, the conditions of deformation experiments can be precisely controlled. This allows us to learn the effects of specific conditions, such as temperature or pressure, on properties like mineral strength. Experimental findings can then be applied to naturally deformed rocks in new field studies.

I utilize nanoindentation and deformation-DIA experiments to look at the behavior of minerals at low-temperature and high-stress conditions. I am particularly interested in understanding the strength profile of Earth’s lithosphere (aka tectonic plates) as this has implications for the processes behind earthquakes and friction on faults, the bending of plates beneath glacial loads and at subduction zones, and the tectonic styles of other planets.

Related methods:
Nanoindentation  D-DIA  HR-EBSD

Want to know more about nanoindentation in geology? Keep an eye out for a new website soon!

An example of a Berkovich (3-sided pyramid) indent in olivine. This secondary electron image was taken using a scanning electron microscope.

 

Mantle rocks in the Klamath Mountains! The horizontal pyroxene layering in this outcrop is common across the Fresno Bench area.

Field studies in the Josephine

Most of my Ph.D. research focused on understanding small-scale deformation in the mantle, which can tell us about the beginnings of plate boundary formation. I have a field site in the Josephine Peridotite of southwestern Oregon, USA. The outcrop I examine, called Fresno Bench, contains dozens of shear zones (areas of localized deformation), each a few centimeters to tens of meters wide. These shear zones are small and have accommodated less strain than deformed peridotites from established plate boundaries like oceanic transform faults. By analyzing samples from transects across these shear zones, I link chemical and rheological properties to understand how the shear zones formed millions of years ago.

Related methods:
SEM/EBSD  EPMA  SIMS  LA-ICPMS  TLS  SfM