# Continental Crust Mass Balance Calculation

**This activity was selected for the On the Cutting Edge Reviewed Teaching Collection**

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### This activity has benefited from input from a review and suggestion process as a part of an activity development workshop.

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This page first made public: Oct 23, 2009

#### Summary

The exercise uses geochemical data for average quartz monzonite and diorite from the Mineral Mountains in Utah. The students do mass balance calculations and are asked to relate their calculations to continental crust formation.

## Learning Goals

- to connect arithmetic calculations to physical reality and real questions in geology
- to apply quantitative geochemical techniques to other sub-disciplines of geology
- to increase student familiarity with spreadsheet programs

## Context for Use

The exercise requires some familiarity with the concepts of density and buoyancy. It also requires some understanding of incompatibility of elements (distribution coefficients). By the time they take my course, students have taken Lithology (the introductory "rock" course at Oshkosh) -- a key point since this exercise requires some familiarity of the IUGS classification scheme.

This exercise helps to lead the class into the second half of the course -- isotopes and their uses in studying the crust, etc.

This exercise can be used in class as a group exercise. Working through the entire problem can take up to an hour, if you include a discussion of the implications of the calculations (see question #4 in Student handout).

## Description and Teaching Materials

*This file is the handout I give to my students. It includes the exercise, data and some hints for working through the problems*

*This file walks one through the steps of calculation involved in the exercise*

*This file contains more comprehensive notes on teaching this exercise.*

*This PDF file has answers in Excel format.*

## Teaching Notes and Tips

- Students struggle with this exercise because often they do not know how to apply the math they already know to a new problem. Help them to recognize and enjoy the challenge of applying geochemical and quantitative skills to real problems.
- A workthrough of each step is provided in the Teaching materials section below. This document does not provide answers; thus, it may be provided to the students.
- Because this exercise uses data from a real place, the mathematics can be made even more accessible with maps and field shots.
- This problem set can be adapted to use data for diorites and intermediate rocks from other places (for example, I have used the Sierra Nevada in CA).
- Data and/or figures from papers about continental crust such as Rudnick and Fountain, 1995, or Taylor and McClennan, 1985, may help students to make connections between the calculations they have made and what the crust looks like.
- This is an excellent exercise to reinforce the idea that Excel (and other spreadsheet programs) can be a powerful tool in the geosciences. Bob McKay, Clark College, has an excellent website that gives a number of tutorials on the use of Excel.

## References and Resources

*Igneous Petrology*, 2001, by Myron G. Best and Eric H. Christiansen. The classification scheme is from IUGS.

Several excellent tutorials on Excel can be found on pages designed by Robert McKay.