WHY AND HOW TO INCLUDE GRAIN-SCALE DEFORMATION MECHANISMS, MICROSTRUCTURES, AND RHEOLOGY IN UNDERGRADUATE STRUCTURAL GEOLOGY COURSES

Only 50% of the 70 structural geologists surveyed at the recent Cutting Edge workshop on Teaching Structural Geology in the 21st Century include grain-scale deformation mechanisms, microstructures, and rheology in their courses, yet the case for including these topics is strong. Fundamentally, microscopic processes accomplish all macroscopic deformation. There are only a few distinct grain-scale deformation mechanisms; each one dominates at different P,T conditions, produces characteristic microstructures, and has a different form of constitutive relation between stress and strain or strain rate. Understanding the different mechanisms informs the most fundamental questions in our discipline. Interpretation of the microstructures preserved in deformed rocks allows us to infer the physical conditions and history of deformation. Knowledge of rock rheology allows us to predict the deformation style and rock strength in different tectonic settings, and provides critical input to geodynamics questions.

The study of deformation mechanisms, microstructures and rheology allows students to correlate grain-scale features and processes to those developed at hand sample, outcrop and regional scales, and to confront how deformation rates relate to rock strength at different depths in the crust. Students trained to recognize and understand the actual processes of both brittle and ductile deformation are better able to critically analyze the bulk behavior of rocks in different geologic settings.

To facilitate the incorporation of deformation mechanisms and microstructures into structural geology courses, our working group has developed short teaching modules on critical concepts (e.g. cataclastic flow, diffusion and pressure solution, dislocation creep) that can be incorporated into existing courses during discussion of related topics (e.g. faults, foliations, folds). These modules include instructor’s notes, key diagrams, annotated photos, possible handouts, and ideas for class or lab demonstrations and activities. The modules and supplemental resources (e.g. animations, analogs, articles) can be found at http://serc.carleton.edu/NAGTWorkshops/structure04. Additional contributions to this resource bank from all geoscientists are welcome.