USING DATA TO TEACH THE PETROLOGY OF VOLCANIC ROCKS
The first example is associated with a laboratory exercise on "Basalts, Andesites, Rhyolites and Tuff." In this laboratory, students examine and describe each of the rocks using hand specimens and thin sections. Once the rock descriptions are complete, the students evaluate the similarities and differences between these rocks (e.g., all the samples are porphyritic and contain plagioclase, anorthite content of plagioclase varies with composition). Students then work in small groups to calculate magma ascent rates from amphibole reaction rim thickness according to methods described by Farver and Brabender (2001). The students collect, appraise, and interpret their own data in the context of a much larger data set and model developed by Rutherford and Hill (1993). This addition to the exercise allows students to make linkages with lecture discussions on magma ascent rates and how they may be determined for recent volcanic eruptions.
The second example relates to a laboratory exercise on "Basalts." Here, students examine and report descriptions on hand-samples and thin sections of three different basalts: an olivine tholeiite from Kilauea, an alkali basalt from the Gregory rift in Kenya, and a Mesozoic diabase (quartz-normative tholeiite) from New England. Whole rock and trace element data for these samples are also provided. Students use their rock descriptions and the geochemical data provided to answer questions regarding the degree of saturation of the magma, classification of the type of basalt (requiring normative calculations), and the tectonic setting of each rock (analyzing trace element data). This part of the exercise reinforces lecture materials on phase diagrams and geochemical tools used to decipher tectonic origin of rocks.
Assigning such activities allows students to retain materials learnt in lecture, have a better understanding of the lecture material, improve their ability to think critically, and gain experience in non-discipline skills such as writing, graphing, and working with peers.