TEACHING STABLE ISOTOPE GEOCHEMISTRY IN AN UNDERGRADUATE PETROLOGY COURSE

Stable isotope geochemistry has become commonplace in petrologic literature and stable isotope data strongly influence interpretations of many petrologic processes. In spite of this, undergraduate petrology textbooks tend to present limited background on stable isotope fundamentals and applications. In addition, stable isotopes provide an opportunity for quantitative problem solving that is mathematically within reach of students and involves a variety of chemical and geological processes. We present a lesson plan that introduces students to the fundamentals of stable isotope geochemistry with particular application to contact metamorphism of carbonate rocks. The lesson plan consists of (1) an introductory reading assignment with embedded problems and suggestions for classroom activities, (2) a reading assignment covering coupled C-O isotopic trends due to Batch and Rayleigh volatilization and fluid infiltration exchange fronts with problems, and (3) a reading assignment introducing the Alta aureole, Utah, with stable isotope data from Bowman et al. (1994). These are in Excel spreadsheets that allow students to explore the effects of varying parameters on volatilization and one-dimensional fluid flow. Variables that can be manipulated include fractionation factors and the relation between F-carbon and F-oxygen for Rayleigh and batch volatilization, and porosity, Darcy flux, effective diffusion coefficient, and oxygen content of fluid and rock for one-dimensional flow models. The lesson plan can be incorporated entirely or partly into a petrology course, depending on time available and desired depth of coverage. The level of sophistication can be tailored to the ability of the students and would be useful for graduate students as well. The Alta aureole is a classic locality, ideal for this lesson because the chemistry of the rocks is relatively simple and much has been published about them. Problem assignments start out very structured and become more open-ended and inquiry based. Assignments lend themselves well to group projects or cooperative learning methods. See http://www.mtholyoke.edu/courses/sdunn/geol201/index.html for spreadsheets and readings.