QUICK-AND-DIRTY SANDBOX MODELS FOR TEACHING AND LEARNING STRUCTURAL GEOLOGY

Analogue models have long been used for structural geology research, and have been adapted for use in classes and training (e.g. Del Castello and Cooke, 2008; Davis, 2014). Complex research rigs can fill entire rooms and reproduce a variety of tectonic scenarios. Previous teaching rig designs can demonstrate pure extension or contraction but cannot handle oblique or lateral motion. We have developed methods using a simple commercial workbench that can effectively model all these scenarios and more.

The Black and Decker Workmate provides a 0.75 m square top that opens and closes like a large vise. Hand cranks provide the motive power. Various tectonic scenarios can be generated by clamping simple materials to either the fixed side or the moving side of the bench top. For strike slip, overlapping metal sheets can be clamped at right angles to the vise for pure lateral motion, or clamped at an angle for oblique motion. Metal or rubber sheets also provide the base for detached extension or contraction; wood blocks with pre-cut angled “faults” provide “basement-involved” tectonics. Multiple deformation phases or even reversal of displacements and tectonic inversion are all possible.

We have used both dry sand and wet clay as analog material with good results. These are easy to set up, remove, and repeat during a lab or training module. In fact, the entire lab can be transported to remote sites, or even to the outcrop. The ease of set-up makes it possible to quickly re-build the model to allow repeated experiments. Several workbenches can be set up simultaneously with slightly different conditions to allow smaller groups of students to work together. Analysis of the models can happen in individual papers, in jigsaw groups during lab, or in whole-class discussions.

These models are especially useful for developing 4D systems thinking. Focus on the model surface (as opposed to cross-sections) gives students practice thinking about the development of a surface through time, and is similar to visualizations of 3D seismic data. Because the sides of the model are open, students need to think explicitly about driving forces and boundary conditions, and about how conditions change across the 3D model. Observation of the model as it deforms (and video recording to allow later examination) allows students to observe how the model changes through time.