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Crystallization-Differentiation of Basaltic Magma

Kent Ratajeski
,
Montana State University
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Summary

In this exercise, students use geochemical data from volcanic glasses and minerals in lavas and drill cores from the solidified Kilauea Iki lava lake to learn about the petrologic processes related to the eruption and in situ crystallization-differentiation of basaltic magma.

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Context

Audience

undergraduate- or graduate-level petrology course

Skills and concepts that students must have mastered

This exercise assumes that the student is already familiar with plotting data in Excel. The student should have some basic knowledge of chemical variation diagrams, and how they work in situations of simple fractionation or binary magma mixing. No prior knowledge of the mineralogy and petrology of basalts is required.

How the activity is situated in the course

This activity could supplement class lectures on basaltic volcanism or magmatic differentiation.

Goals

Content/concepts goals for this activity

Students who complete this exercise should be able to make useful geochemical plots (Harker diagrams) from geochemical data in an Excel spreadsheet, and interpret geochemical plots to suggest or rule out possible petrogenetic processes that may have contributed to the geochemical diversity among erupted and differentiated products of basaltic volcanism at Kilauea Iki, Hawaii.

Higher order thinking skills goals for this activity

This exercise requires students to formulate hypothesis based on geochemical data.

Other skills goals for this activity

Students gain practice in using an Excel program to plot geochemical data, interpreting geochemical plots, and writing answers to open-ended questions.

Description of the activity/assignment

In this exercise, students use major-element compositions of whole-rocks, volcanic glasses, and minerals in lavas and drill cores from the solidified Kilauea Iki lava lake. The data is presented in the form of a "precompiled" spreadsheet which contains selected analyses culled from the GEOROC database and a USGS Open File report. Students make graphs from the data to learn about the petrologic processes related to the eruption and in situ crystallization of basaltic magma.

Determining whether students have met the goals

This activity is formatted as a self-paced exercise where students can check their own answers by clicking on "Show answer" tabs. The exercise could be reformatted as a normal homework assignment without the answers given and graded by the instructor using his/her own evaluation scheme.

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