Advanced steronet -finding rotation axes
Using stereonets to find rotation axes of tilted planes. Paleomagnetic vectors used as indicators of rotations of dikes and planes.
structural geology for majors, upper level
Skills and concepts that students must have mastered
simple use of stereonets, be able to project lines and planes, find great circles and measure angles.
How the activity is situated in the course
advanced extra credit exercise.
Content/concepts goals for this activity
Finding rotation axes and orignal orientation of planar features that have been deformed by one or more rotations. Visualizing the rotation in 3D and on a steronet.
Higher order thinking skills goals for this activity
3-D visualization, analysis of various kinds of field data.
Other skills goals for this activity
evaluating multiple results and choosing most likely
Description and Teaching Materials
Enclosed is a PDF with a description of a method to find arbitrary rotation axes given some orientation data - in this case a non-vertical dike with an initial and measured paleomagnetic direction associated with it.
Method for finding rotation on a steronet (Acrobat (PDF) 9kB Jun29 12)
Data and Hints for steronet exercise (Microsoft Word 24kB Jun29 12)
A second Word doc is attached with some questions that might come up, trouble spots and possible example data to be used.
Teaching Notes and Tips
A physical model consisting of a flat piece of wood (the plane or dike) with two dowels set into it (one perpendicular for the pole) and one at another angle is very helpful for visualizing the problem/solution. other suggestions in the Hints and data file.
Ask then to solve various test data including special cases (one rotation axis only, or none).
References and Resources