STABLE ISOTOPE GEOCHEMISTRY RESEARCH PROJECTS IN A PETROLOGY COURSE

The replacement of traditional lecture format with inquiry-based projects requires trading off breadth of material covered (more passively) for the excitement and frustration of hands-on research. I have been slow to move in this direction because time spent on projects reduces coverage of other petrologic topics. Three changes have encouraged me to shift toward research projects in my petrology course; these are (1) changes in my mineralogy course, (2) acquisition of a new scanning electron microscope (SEM) with EDS system, and (3) addition of vacuum lines for stable isotope work. The prerequisite for petrology is my Rocks and Minerals course (formerly mineralogy), which is a traditional mineralogy course modified so the last four weeks cover igneous and metamorphic classifications and processes. This provides a head start for petrology and relieves some guilt about topics not covered more thoroughly in the petrology course. The new SEM is easy for students to manipulate. They can quickly obtain semi-quantitative analyses and X-ray maps. Two projects are spread over the semester. One focuses on igneous processes utilizing the SEM and XRF data. The other, the stable isotope project, focuses on metamorphic processes. Students are introduced to stable isotope geochemistry through readings and problem sets available on my website (http://www.mtholyoke.edu/courses/sdunn/geol201/index.html). These readings include an overview of the Alta aureole, the stable isotope data of Bowman, Willett and Cook (1994), and implications for fluid-rock interactions. Class projects have included contact metamorphism of carbonate rocks, formation of talc skarn, calcite-graphite carbon isotope geothermometry, and shear zones in marble. Groups of two or three students (assigned by me) are responsible for specific tasks and data collection. All data are compiled and students can work together or alone to interpret and summarize the results. Stable isotope-based projects have particular advantages, including a rich literature base (from classics to current), quantitative problem solving that is mathematically accessible to most students, the content connects nicely with other fields of geology, and students are exposed to a wide range of interesting petrological and geochemical processes and investigative methods.