Major Element Control Presentation
Summary
The presentation is an introduction to the control of magma chemical compositions by the fractionation of crystallizing phases. It is followed by a lab exercise where students interpret volcanic rock petrology and a geochemical data set (from Iceland) in terms of sequences of fractionating phases.
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Context
Audience
This presentation is designed for a sophomore or junior level petrology course for majors.
Skills and concepts that students must have mastered
How the activity is situated in the course
In context, this presentation is shown after phase diagram lectures and exercises, and it is linked to them by examining phase diagrams that illustrate the crystallization sequence (Olivine-plagioclase-augite). Further, a following lab exercise has the students deduce somewhat similar crystal fractionation controls for a set of Iceland lavas (for phenocryst petrology) and geochemical data sets (with which control lines are plotted).
Goals
Content/concepts goals for this activity
The presentation itself is not enough to make the connection between liquid composition changes, phase diagrams, and chemistry, but in the context of earlier phase diagrams, presentation, return to phase diagrams, and the petrology-geochemistry Iceland exercise, it helps get across the idea of how crystal fractionation can control magma evolution.
Higher order thinking skills goals for this activity
Other skills goals for this activity
Description of the activity/assignment
The presentation is an introduction to the control of magma chemical compositions by the fractionation of crystallizing phases. It is followed by a lab exercise where students interpret volcanic rock petrology and a geochemical data set (from Iceland) in terms of sequences of fractionating phases.
It is a useful as an introduction because it shows clearly, with data points, interpreted lines, and oral explanation how fractionating crystals can, in principal, control the chemical composition of derivative magmas.
In context, this presentation is shown after phase diagram lectures and exercises, and it is linked to them by examining phase diagrams that illustrate the crystallization sequence (Olivine-plagioclase-augite). Further, a following lab exercise has the students deduce somewhat similar crystal fractionation controls for a set of Iceland lavas (for phenocryst petrology) and geochemical data sets (with which control lines are plotted).
The presentation itself is not enough to make the connection between liquid composition changes, phase diagrams, and chemistry, but in the context of earlier phase diagrams, presentation, return to phase diagrams, and the petrology-geochemistry Iceland exercise, it helps get across the idea of how crystal fractionation can control magma evolution.
It is a useful as an introduction because it shows clearly, with data points, interpreted lines, and oral explanation how fractionating crystals can, in principal, control the chemical composition of derivative magmas.
In context, this presentation is shown after phase diagram lectures and exercises, and it is linked to them by examining phase diagrams that illustrate the crystallization sequence (Olivine-plagioclase-augite). Further, a following lab exercise has the students deduce somewhat similar crystal fractionation controls for a set of Iceland lavas (for phenocryst petrology) and geochemical data sets (with which control lines are plotted).
The presentation itself is not enough to make the connection between liquid composition changes, phase diagrams, and chemistry, but in the context of earlier phase diagrams, presentation, return to phase diagrams, and the petrology-geochemistry Iceland exercise, it helps get across the idea of how crystal fractionation can control magma evolution.
Determining whether students have met the goals
Teaching materials and tips
- Kilauea major elements, PowerPoint presentation (PowerPoint 284kB Jun26 03)
Other Materials
Supporting references/URLs
- Teaching with the EarthChem Geochemical Database - Part of SERC Integrating Research and Education page; provides information about how to use EarthChem in the classroom.
- EarthChem - an international database that combines the assets of PetDB, NavDat, and GeoRoc. Search the database for analyses according to location, rock type, chemical parameters, or references in the literature.
- Crystallization-Differentiation of the Kilauea Iki Lava Lake - The first in a series of pages that make up a case-study module about Kilauea.