Combining GIS, Rock Samples and Thin Sections in a Culminating Lab to Enhance Student Learning of Metamorphic Petrology

Metamorphic petrology is part of the traditional geology curriculum and it requires the combination of observations that range from the grain scale (e.g., mineral identification, determination of equilibrium textures) to the map scale (drawing isograds) to the abstract (phase equilibria). Professional petrologists keep these various scales in mind when working, but most classroom techniques focus on a single scale at a time, leaving students with little practice thinking on multiple scales simultaneously. As part of a curriculum-wide adoption of GIS tools and techniques, we have developed a metamorphic petrology exercise that utilizes student observations of microscopic, hand-specimen and map-scale features of metamorphic rocks. These students then use those observations (which they incorporate into their GIS database) to make interpretations about metamorphic facies and locations of isograds.

Following introductory lectures on metamorphic petrology, students are given a partially-completed GIS map with bulk-compositional lithologies and some completed stations with known equilibrium assemblages. They are then asked to determine the mineral assemblage for a set of specimens with known locations and add these to the supplied GIS data set. Using GIS software, students then estimate the locations of metamorphic isograds and infer a plausible pressure-temperature metamorphic field gradient. From these observations they must make further inferences about the nature of the metamorphic event and the sensitivity of various bulk compositions to changing metamorphic grade.

This project, when combined with our traditional curriculum, has several advantages over standard approaches for learning about metamorphic facies and isograds. Students consider a single petrologic problem on a variety of scales simultaneously, linking the individual components lecture and lab and simulating professional demands once they graduate. Additionally, students learn to use, or practice with, a technological tool that is quickly becoming a standard in all geo-careers.