Calculating Pressures and Temperatures of Petrologic Events: Geothermobarometry

Donna L. Whitney

University of Minnesota

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Initial Publication Date: July 15, 2008 | Reviewed: January 19, 2015 (see revision history: 2 events)

Summary

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.

PTt Relationships, Geology | College Lower (13-14), College Upper (15-16)

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Context

Audience

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).

Goals

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)

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.

More information about assessment tools and techniques.

Teaching materials and tips

Activity Description/Assignment (Acrobat (PDF) 216kB Jan16 04)