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Christopher Gerbi - Current projects

My current projects center around transferring field observations to quantifiable rheological properties.  I think of it as providing “ground truth” and insight for geodynamic models.  Thus my projects span the gamut of field to analytical to modeling approaches.  And as with all of us in the Geodynamics group, most of this work is in collaboration with students.

Speaking of which, I am always looking for strong, motivated students (either M.S. or Ph.D).  So if you are interested in any of the projects below, please contact me.  I am also always open to discussing and likely supervising projects related to SEM-EBSD-CL microanalysis, rheology, U-Pb geochronology, metamorphic petrology, and Appalachian tectonics.

An example of hydration-induced weakening from a granulitic block to an amphibolite-facies shear zone

An example of hydration-induced weakening during retrogression from a granulitic block to an amphibolite-facies shear zone

1. Mechanisms and magnitude of syntectonic weakening. This is a nearly ubiquitous process, but most geodynamic models do not account for it.  This work is the centerpiece of my research program at the moment, with several subprojects.  The essential question is:

How (and by how much) does the middle to lower orogenic crust change strength? We are currently exploring a number of shear zones to identify whether the operative mechanisms were dominated by or a combination of metamorphic reactions, water infiltration, stress concentration, and textural change.

The field area is primarily southern Ontario (see maps of near Parry Sound and the Grenville Front Tectonic Zone).  Most of the work to date is based out of the Ontario field area. (Which, by the way, is a great place to work!  Extensive exposure, travel by boat, beautiful rocks…) 

2. Evaluating the effect of (1) on orogen development.

A natural shear zone (white) system whose bulk properties depend on the strength contrast between the shear zones (white) original rock (black), their modal fractions, and their geometrical arrangement.

A natural shear zone (white) system whose bulk properties depend on the strength contrast between the shear zones (white) original rock (black), their modal fractions, and their geometrical arrangement.

Using numerical modeling, we are evaluating the importance of different scales and magnitudes of synorogenic weakening on orogen evolution.

3. Characterizing the bulk rheological properties of multi-phase materials. Having good constraints on the rheology of the various parts of the crust is paramount for addressing problems of crustal deformation from post-glacial rebound to orogen development.  Using numerical modeling, we are exploring methods for evaluating the bulk properties of regions that contain strength heterogeneities.

4. Characterizing natural ice microstructures. Ice plays an important role in the climate system, yet several large unknowns exist regarding its physcial properties, and particularly how they change with microstructure. These unknowns hamper predictions of, for example, calving and flow rates. We are developing the capability to analyze ice in the SEM and are looking forward to working with this new material.

5. Student understanding of the movement of Earth materials. Movement in the Earth is what makes the system a system. Whether it is the mantle, magma, glaciers, oceans, or air, the movement of materials is a balance of the driving and resisting forces. This is a cross-cutting concept, but students rarely see through the descriptions of specific systems to understand why the systems work. We are looking to evaluate the effectiveness of instructional interventions and measure students conceptions of forces as they relate to the Earth.

 


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