Central American Arc Volcanoes, Petrology, and Geochemistry

Bob Stern, Ben Edwards, Mike Carr, Jim Walker

Summary

This is one component of the Subduction FactoryMini Lesson set

This activity is designed to teach upper division undergraduate students basic concepts in igneous petrology that relate hand specimen identification of lavas (including phenocryst mineralogy) to major element geochemistry using the Central American volcanic arc (CAVA) (a MARGINS Subduction Factory focus site) as an example. The module includes an overview powerpoint presentation to describe CAVA and two volcanoes used as specific examples, a supplemental document with additional reading, and a guided activity sheet that can be used as a handout which students work through to practice the skills and concepts central to the lesson. Comments from students and TA are included, along with an instructor answer sheet.

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Learning Goals

After completing the activity students should demonstrate the ability to:·

  • Understand the relationships between large-scale tectonic feature (convergent margins), a specific example (Central America) of that tectonic feature, individual volcanoes, the composition of lavas (both petrography and chemistry), and the processes that control these compositions.·
  • Calculation of important geochemical parameters such as the Mg# (Magnesium number)· Visual estimation of mineral percentages (modes)·
  • Calculation of normative mineralogies·
  • Connection between rock mineralogy and geochemistry via comparison of modal and normative mineralogies,·
  • Recognition that arc magmas are generated by melting of different sources (crust vs. mantle), and·
  • Understanding that certain major element compositions can be used to as first order differentiators to identify primary mantle magmas.

 

Context for Use

This module is intended to provide a multiscale, quantitative introduction to subduction zone magmatism for an upper division course such as igneous petrology or volcanology. Students should have basic knowledge of properties of common igneous minerals, hand sample description and identification, volcano types and plate tectonics.

The lesson can be done over two classes or in a long lab (min 3 hours).

Description and Teaching Materials

This mini-lesson consists of 4 parts: Handout 1 (to be read by the student before class; a powerpoint with slides that the instructor can use in lecture; Handout 2, which walks the student through the exercises of Handout 3 with exercises (to be completed in lab as small groups or as homework).

  1. Handout 1 (Microsoft Word 2007 (.docx) 1.7MB Sep10 15) should be read by the student before class. It introduces the student to the Central American convergent margin.
  2. CAVA Overview (PowerPoint 2007 (.pptx) 10MB Sep28 15) contains maps and figures intended to be used by the instructor to familiarize the class with the Central American arc. Many of the slides contain explanatory notes. The instructor is advised to choose whichever slides are useful, this powerpoint is a resource that is not intended to be shown in its entirety.
  3. Handout 2 (Microsoft Word 2007 (.docx) 1.3MB Sep10 15) should be read by the student after the instructor lectures. It walks the student through the exercises that will be done in Handout 3.
  4. Handout 3 - Exercises (Microsoft Word 2007 (.docx) 7.7MB Sep15 15) Exercises to be done by students and to be graded by instructor.

 

 

Teaching Notes and Tips

This "mini-lesson" is best done in "mixed mode", alternating between materials presented by the instructor (using powerpoint "Central America Powerpoint for Instructors") and student reading of material below, intended as two individual handouts. This is because color figures show well in a Powerpoint but perhaps will not be reproduced in the handout, and because we recommend group responses to questions on the Powerpoint. All of the figures in the handout are provided in the Powerpoint, but not all of the powerpoint figures are presented; Powerpoint slides are also labeled in the lower left if and how they occur in the handout. The instructor is encouraged to modify the Powerpoint as useful for their classes and syllabus. We recommend that students read "Handout Part 1" before the class, then the instructor present the Powerpoint segment "Part one: background" in class, then the students read "Handout 2" before undertaking the exercises in "Handout 3", either in lab or as homework.


Assessment

Students will complete a four-part exercise (Handout 3) which will be graded. An exam question could also be based on this exercise, for example to ask the student how different magmatypes are generated by melting in the crust or mantle?

Instructor Stories

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Teaching MARGINS Mini Lessons in Igneous and Metamorphic Petrology
Bob Stern, The University of Texas at Dallas
Minilesson used to reinforce student learning about convergent margin igneous activity and how both visual examination of volcanic rocks and using major element analyses are useful for characterizing these rocks and understanding the processes that formed them.

If you have used this mini-lesson in your course, you can submit your instructor storyto help others adopt and adapt this material. Want to discuss GeoPRISMS/MARGINS mini-lessons further with other educators?Join the Community.

 

References and Resources

  • Carr, M.J., Feigenson, M.D., Patino, L.C., and Walker, J.A., 2003. Volcanism and Geochemistry in Central America: Progress and Problems. Inside the Subduction Factory, Geophysical Monograph v. 138; p.153-179.
  • Carr, M. J., I. Saginor, G. E. Alvarado, L. L. Bolge, F. N. Lindsay, K. Milidakis, B. D. Turrin, M. D. Feigenson, and C. C. Swisher, III, 2007. Element fluxes from the volcanic front of Nicaragua and Costa Rica, Geochem. Geophys. Geosyst., 8, Q06001, doi:10.1029/2006GC001396.
     
  • Dull, R., Southon, J., Kutterolf, S., Freundt, A., Wahl, D., and Sheets, P. 2012. Evidence for the Ilopango TBJ eruption as the trigger of the AD 536 Event (abstract). Am. Assoc. Geographers 57
     
  • Kelley, K.A. and Cottrell, E., 2009. Water and the Oxidation State of Subduction Zone Magmas. Science 325, 605-607.
     
  • R. W. Le Maitre (editor), A. Streckeisen, B. Zanettin, M. J. Le Bas, B. Bonin, P. Bateman, G. Bellieni, A. Dudek, S. Efremova, J. Keller, J. Lamere, P. A. Sabine, R. Schmid, H. Sorensen, and A. R. Woolley, Igneous Rocks: A Classification and Glossary of Terms, Recommendations of the International Union of Geological Sciences, Subcommission of the Systematics of Igneous Rocks. Cambridge University Press, 2002
     
  • MacKenzie, L.S., Abers, G.A., Rondenay, S., Fischer, K.M., 2010. Imaging a steeply dipping subducting slab in Southern Central America Earth and Planetary Science Letters 296 (2010) 459–468.
     
  • Siebert L., Simkin T., 2002-. Volcanoes of the World: an Illustrated Catalog of Holocene Volcanoes and their Eruptions. Smithsonian Institution, Global Volcanism Program Digital Information Series, GVP-3, (http://www.volcano.si.edu).
     
  • Stoiber, R.E., and Carr, M.J., 1973. Quaternary volcanic and tectonic segmentation of Central America. Bull. Volc., 37:304-325.
     
  • Sugimura, A., 1960. Zonal arrangement of some geophysical and petrological features in Japan and its environs. Jour. Fac. Sci., Univ. Tokyo, Sec. II, V. XII, Part. 2, p. 133-153.
     
  • Syracuse, E. M., and G. A. Abers (2006), Global compilation of variations in slab depth beneath arc volcanoes and implications, Geochem. Geophys. Geosyst., 7, Q05017, doi:10.1029/2005GC001045
     
  • Viramonte J.G. and Di Scala, L. 1970. Summary of the 1968 Eruption of Cerro Negro, Nicaragua. Bull. Volcan.
     
  • Workman, R.K. and Hart, S.R., 2005. Major and trace element composition of the depleted MORB mantle (DMM). Earth and Planetary Science Letters 231, 53-72.
     

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