Cameron Davidson

Carleton College

Mid to upper level undergraduate petrology course.

This activity assumes students have already had a course in mineralogy and are familiar with photomicrographs. Plotting mineral compositions on ternary diagrams, the phase rule, and Schreinemaker's rules should be introduced as part of this activity.

This activity is a stand-alone exercise and could be integrated anywhere into a petrology curriculum.

Students who complete this exercise should be able to:

1. Identify mineral assemblages common to metamorphosed siliceous dolostones.
2. Determine appropriate chemical systems to describe and plot minerals.
3. Infer metamorphic reactions from progressive changes in mineral assemblages.
4. Identify metamorphic reactions responsible for producing isograds mapped in the field.
5. Understand how rock and fluid compositions control mineral assemblages.
6. Infer the temperature and fluid composition evolution of the Alta stock aureole based on T-X(CO2)diagrams.

This exercise helps students to learn how to go from the concrete (mineral assemblages) to the abstract (metamorphic reactions) to infer the physical processes present during metamorphism. It also helps develop their geometrical thinking by plotting mineral compositions and using Schreinemaker's rules to generate Schreinemaker's bundles.

Students create figures and practice writing by answering open-ended questions.

This exercise, based on a suite of rocks from the contact metamorphic aureole of the Alta stock near Salt Lake City, Utah, is constructed for a mid to upper level undergraduate petrology course and does not require access to rocks and thin sections. It assumes students have already had a course in mineralogy and are familiar with photomicrographs, plotting mineral compositions on ternary diagrams, the phase rule, and Schreinemaker's rules. Some of these concepts (e.g., Schreinemaker's rules) could be introduced as part of this activity. Students who complete this exercise should be able to identify mineral assemblages common to metamorphosed siliceous dolostones, determine appropriate chemical systems to describe and plot minerals, infer metamorphic reactions from progressive changes in mineral assemblages, identify metamorphic reactions responsible for producing isograds mapped in the field, understand how rock and fluid compositions control mineral assemblages, and infer the temperature and fluid composition evolution of the Alta stock aureole based on T-X(CO2)diagrams.

Students create figures that can be easily checked against a key, and answer open ended questions that help the instructor decide if they get it or not.