REBUILDING PETROLOGY FROM THE GROUND UP

The 2003 Teaching Petrology Workshop in Bozeman, Montana was a turning point in my teaching career. I started teaching at the university level in 1981 and taught petrology the way it had been taught to me—in a desultory manner, using books that were not very good. In spite of those handicaps, petrology was a vibrant field at the time, integrating well into the relatively new field of plate tectonics, benefitting from newly applied technologies such as the electron microprobe and TIMS, and linking to the similarly energetic field of cosmochemistry. The future seemed bright, indeed.

Any yet it wasn’t. Fundamental themes that emerged from the 2003 workshop included “students don’t like petrology much anymore” and “I feel like I’m doing a terrible job teaching.” Evenings were spent drinking beer during long ad hoc discussions in the dorms, weeping, and wondering what was wrong and how to bring life back into the subject.

Many excellent ideas, practices, and materials came out of the workshop, but for me the main "aha!" moment was the realization that we were teaching the subject in a way that is fundamentally wrong. To this day petrology texts and classes usually follow the organization of the influential 1951 (i.e., pre-plate tectonics) text Igneous and Metamorphic Petrology by Turner and Verhoogen; material is presented and taught in the same order (heavy on classification and phase diagrams early, followed by a survey of rocks with lots of emphasis on weird ones; igneous rocks first--STOP--then metamorphic rocks). Plate tectonics, isotope geochemistry, geochronology, etc. are added almost as afterthoughts. Imagine a modern biology book that used the same organizational scheme as one written before DNA had been discovered! Petrology classes need to be rebuilt from the ground up, using major Earth systems as a backbone and conceding that igneous and metamorphic petrology, so often treated as estranged siblings, are two facets of the same processes.