Calculating Pressures and Temperatures of Petrologic Events: Geothermobarometry
Donna L. Whitney
University of Minnesota
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In this lab exercise, students examine one or more metamorphic rocks and use various approaches to estimating and calculating the pressure-temperature conditions at which the rocks equilibrated. The exercise involves hand sample description, petrography, interpretation of phase diagrams, and calculations of a phase diagram or P-T conditions from given equations.
This activity is designed for a sophomore or junior level required course in petrology.
Skills and concepts that students must have mastered
To do this exercise, students need to understand the concept of equilibrium and be able to identify major rock-forming minerals with a petrographic microscope. Knowledge of basic thermodynamics is helpful, but optional.
How the activity is situated in the course
This is a stand-alone exercise. I use this exercise as a capstone that synthesizes many of the important concepts and skills that the students have learned after 6 (out of 7) weeks of lectures/labs/discussions of metamorphic petrology. At this point in the class, their experience with estimating P-T conditions consists of qualitative determinations: low/medium/high grade, metamorphic facies (metabasalts), and Barrovian zones (metapelites).
Content/concepts goals for this activity
A main goal of the lab is to connect observations from real rocks to inferences about metamorphic conditions and paths.
Higher order thinking skills goals for this activity
This activity involves analyzing data and synthesizing ideas.
Other skills goals for this activity
Description of the activity/assignment
The goal of this exercise is to calculate the pressure (P) â€
Determining whether students have met the goals
Students have met the goals of this activity if they are able to complete the laboratory assignment (write-up) completely and accurately.
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