Cutting Edge > Structural Geology > Teaching Activities > Contractional Strain: Calculations

# Contractional Strain: Calculations

Laurel Goodwin, UW-Madison, and Carol Ormand
,
SERC at Carleton College

#### Summary

In this exercise, students calculate bulk shortening and bulk thickening for a contractional deformation experiment. They then describe the specific structures accommodating that strain.

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## Context

#### Audience

Undergraduate required course in Structural Geology

#### Skills and concepts that students must have mastered

It is helpful, but not necessary, for students to know something about folds and reverse faults prior to this exercise.

#### How the activity is situated in the course

This exercise accompanies a lecture on contractional fault systems, convergent tectonics, and strain.

## Goals

#### Content/concepts goals for this activity

After completing this exercise, students will be able to describe and calculate the bulk strain within a foreland fold-and-thrust belt, if the undeformed geometry is known, and explain how that strain is accommodated by a suite of common structures. Specifically, students will recognize that horizontal shortening is accommodated by vertical thickening. They will also recognize that shortening within a specific lithological layer can be accommodated by multiple mechanisms.

#### Higher order thinking skills goals for this activity

If students complete the extra credit exercise at the end of this problem set, they will compare these contractional deformation experiments to extensional deformation experiments shown here: http://serc.carleton.edu/NAGTWorkshops/structure/activities/6662.html. In that case, students should be able to analyze these two types of deformation for similarities and differences. This makes an excellent introduction to extensional deformation.

## Description of the activity/assignment

In this exercise, students calculate bulk shortening and bulk thickening for a contractional deformation experiment. They then describe the specific structures accommodating that strain. This exercise can also be paired with an in-class gesture exercise, where students use gesture to describe the deformation.

## Determining whether students have met the goals

Student turn in their calculations and answers.