Introduction to Petrology

Elizabeth Johnson
,

johns2ea@jmu.edu

James Madison University
a

Public four-year institution, primarily undergraduate

Summary

Igneous and metamorphic processes explained using crystallization theory, phase diagrams, thermodynamics and geochemistry; laboratory study of rocks, their chemical and mineralogical signatures, and their geologic origins.

Course URL:
Course Size:

15-30

Course Context:

This is a course for undergraduate majors in the BS program. Prerequisites are mineralogy and chemistry. The class has a lecture and lab component, and meets for two 2hr, 15min-long blocks per week. There is a 2-day required field trip plus shorter optional field trips.

Course Goals:

Students should be able to

describe the types and relative abundances of phases in a rock based on observations from hand specimens and thin sections.
classify a rock based on mineral abundances or chemical composition.
describe crystallization history and textures of the rock based on thin section observations.
interpret textures and crystallization history using appropriate phase diagrams.
explain magma differentiation and observations of layered mafic instrusions using a fractional crystallization model.
identify the layers of the Earth, describe the approximate composition for each layer of the Earth and bulk Earth, and relate these to observations from meteorites.
use geochemical data (partition coefficients, REE plots, etc) to constrain petrogenetic processes.
use metamorphic mineral assemblages and textures to constrain deformation history and P-T conditions.

How course activities and course structure help students achieve these goals:

The course is structured around case studies. I assess the course with labs (traditional and jigsaw-type group work), quizzes, and tests. I am new to teaching this course, and I found that a traditional grading scheme has made students feel more comfortable with a completely new syllabus and instructor. In particular, biweekly quizzes are a motivator for students to study and/or read, and gives students examples of questions for the short-answer section of the tests.

I would like to move to something more effective / efficient, especially with grading labs. I find the labs to be tedious to grade, and it is difficult to effectively give students feedback for these larger assignments.

Skills Goals

interpretation of "messy" data
reading geologic literature (I'm in the process of developing this one)

How course activities and course structure help students achieve these goals:

The labs provide students with the opportunity to make observations of complicated rock textures and produce hypotheses to tie these textures to regional geology or tectonics. Right now, I include interpretation as part of the petrographic description worksheet, and I grade these along with mineral and texture ID.

Attitudinal Goals

Improving students' ability to create relatively simple hypotheses about complicated systems, and then build logically upon these initial hypotheses.

How course activities and course structure help students achieve these goals:

I try to address a concept (ie, fractional crystallization) with one or two simple models (ie, fractional crystallization, or Bowen's reaction series), then apply this to a real system (ie, the Bushveld igneous complex). Labs are a combination of observations of hand samples and thin sections, plus thought questions based on the data they collect in the lab (ie., does the plagioclase composition in our samples follow the predicted trends from the base to top of the Bushveld)?