Teaching Notes


Audience: undergraduate- or graduate-level petrology course.

Skills and concepts that students must have mastered: Some basic knowledge of plate tectonic settings (e.g., arcs and continental hotspots) is assumed for this exercise, but no advanced knowledge of the mineralogy and petrology of volcanic rocks beyond what is normally covered in introductory courses is required. No advanced knowledge of chemical variation diagrams is necessary, but it would probably be best if the instructor had covered the basics of whole-rock data and variation diagrams previously in lecture. This exercise does not assume that every student knows how to plot data in Excel spreadsheets, so I have included several pull-down text boxes (marked by 'Show me' tabs), as well as a separate page on plotting chemical variation diagrams in Excel, in order to help these students.

How the activity is situated in the course: This activity could supplement class lectures on compositional diversity or volcanic caldera complexes.


Content/concepts goals for this activity: Students who complete this exercise should be able to:
  1. use the GEOROC online geochemical database to extract useful whole-rock major- and trace-element data from precompiled datasets
  2. make useful geochemical plots (Harker diagrams)
  3. interpret geochemical plots to suggest or rule out possible petrogenetic models

Higher order thinking skills goals for this activity: This exercise requires students to formulate hypothesis based on geochemical data, and to compare/contrast two different volcanic suites.

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. In addition, the act of obtaining and using data from online databases like GEOROC informs the students about the powerful resources that have recently become available to the scientific community via the creation of digital cyberinformatics and cyberinfrastructure. A carefully guided approach of guiding students into these databases, through the various steps required to screen, download, import, and use their data, empowers the students in a tangible, practical way to think and act like scientists.

Evaluation and Answer Keys

This activity is formatted as a self-paced exercise that can be used as a homework assignment or in-class exercise. Instructors may obtain an answer key by emailing kent.ratajeski@uky.edu from their official college or university email address. Please include the title of this exercise and the URL for a webpage (or webpages) showing (1) your position of employment at an institution of higher learning and (2) your current email address.