Cutting Edge > Petrology > Teaching Activities > Progressive metamorphism of pelitic rocks: A lab assignment to facilitate translation from AFM space to P-T space

Progressive metamorphism of pelitic rocks: A lab assignment to facilitate translation from AFM space to P-T space

Jane Selverstone
,
University of New Mexico
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Summary

This is an example of a lab activity aimed at teaching students how to go from natural samples to AFM diagrams to P-T conditions of equilibration.

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Context

Audience

This exercise is designed for a sophomore or junior level petrology course that is required for majors.

Skills and concepts that students must have mastered

How the activity is situated in the course

The lab is designed to be completed in two 3-hour lab sessions, at the end of which the students will be able to: The lab follows an in-class lecture in which we graphically derive the AFM projection and talk in general terms about pelitic schists.

Goals

Content/concepts goals for this activity

Higher order thinking skills goals for this activity

This activity involves critical thinking and data analysis.

Other skills goals for this activity

Description of the activity/assignment

This lab assignment helps students to develop a detailed understanding of AFM diagrams and how they relate to pressure-temperature conditions of metamorphism of pelitic rocks. The lab is designed to be completed in two 3-hour lab sessions, at the end of which the students will be able to: The lab follows an in-class lecture in which we graphically derive the AFM projection and talk in general terms about pelitic schists. The lab emphasizes going from real rocks to the phase diagrams to pressure-temperature space. I particularly emphasize extracting P-T information from pelitic schists using the AFM diagram (we revisit this qualitative approach after going through a quantitative thermobarometry exercise later in the course). I introduce the laboratory assignment via a PowerPoint presentation that is available from the Teaching Petrology website. My own version of this PowerPoint file includes several slides on the tectonic histories of the orogens from which my lab samples are derived (New England, Alps, New Mexico, etc.).
The lab as written is obviously not directly transferable to other users as it is tied to specific thin sections and hand samples. However, the section below on Adaptations (in the instructors' notes, see below) suggests ways for other instructors to achieve the same goals, using their own sample suites. The lab as included in this volume contains brief answers in order to show the nature of the samples that I use and the level of expertise that I expect of my students.
The AFM diagrams and P-T diagram are redrafted after Spear (1993). The AFM movie in the PowerPoint presentation is from Worley and Powell (1998), but similar movies can also be obtained from Spear (1999).

Determining whether students have met the goals

Students have successfully completed this exercise if they completely and accurately answer the questions and follow instructions given in the exercise handout.

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