Exploring lithological assemblages and structural styles of granite-greenstone belts
Upper-level undergraduate or graduate level course in structural geology or tectonics
Skills and concepts that students must have mastered
Students need to know:
- some structural geology including fault types and folding;
- how to read and interpret geologic maps and cross-sections;
- some basic geophysical (seismic) methods.
How the activity is situated in the course
This activity could be placed as a 1 week case study in a structural geology or tectonics course.
Content/concepts goals for this activity
- Learn typical structural patterns of granite-greenstone terranes.
- Evaluate different tectonic models for granite-greenstone belts.
- Learn that all geologic maps and cross-sections contain data but also require interpretations.
Higher order thinking skills goals for this activity
- Synthesize and evaluate competing models
- Evaluate uncertainty in scientific data
- 3-dimensional spatial thinking
Other skills goals for this activity
- Reading professional literature
- Improving map and cross-section skills
Description of the activity/assignment
1. Day 1: End of class Mini lecture (15 minutes) on:
- a. what greenstone belts are (where in the world, rock assemblages, structures)
b. vertical vs. horizontal tectonic models (old arguments and current details).
c. Superior Province (one example) introduction
2. Homework and Jigsaw Activity: Looking at "typical" structures within greenstone belts.
This assignment asks students to compare papers with folding models vs. thrusting models. One set of papers that provides a good contrast focuses on the Beardmore-Geraldton greenstone belt in the Superior Province, Canada. Students will also use a paper with Lithoprobe seismic data across the Superior Province.
a. Folding model: Kehlenbeck, M. M. 1986. Folds and folding in the Beardmore-Geraldton fold belt. Canadian Journal of Earth Sciences (CJES) 23, 158-171.
b. Thrusting model: Devaney, J. R. & Williams, H. R. 1989. Evolution of an Archean subprovince boundary: a sedimentological and structural study of part of the Wabigoon-Quetico boundary in northern Ontario. CJES 26 1013-1026.
c. Percival, J. A. et al. 2006. Tectonic evolution of the western Superior Province from NATMAP and Lithoprobe studies. CJES 43(7): 1085-1117.
Divide the class into 3 "expert" groups and assign one paper to each group. Students need to create an outline of the major structures (faults, folds, both) described and the evidence provided for the structural interpretation. Students should bring two copies of their outline to class.
3. Day 2
Turn in one copy of outline (to be assessed for grade) and meet with the group to create a composite, master outline (30 minutes). Students break up into small groups (one from each "expert" group), discover very different structural style interpretations, and try to determine WHY there are the discrepancies (lack of data, preconceived notions influencing interpretations, etc). The goal of the new group is to prepare each student to write a short paper. Each student is assigned to write a 1-page paper exploring reasons why there are discrepancies between the models. Students are also encouraged to speculate on what other evidence or future research might help resolve the apparent conflict. Students begin paper in class and finish outside of class.
4. Day 3
Students hand in paper (to be graded). Mini lecture/ discussion on key related questions.
a. Does either model (folding or faulting) support or negate either vertical or horizontal tectonic models?
b. Are there any modern analogues to greenstone belts? If so, what are the differences or limitations to the comparisons (lithological and structural)?
Determining whether students have met the goals
- 1. Pass/fail grading on outline
2. Grade on final paper
Teaching materials and tips
Goodwin, A. M., 1977, Archean basin-craton complexes and the growth of Precambrian shields. Canadian Journal of Earth Sciences, v. 14, p. 2737-2759.
Gorman, B. E., Pearce, T. H., and Birkett, T. C., 1978, On the structure of Archean greenstone belts. Precambrian Research, v. 6, p. 23-41.
Wilson, H. D. B., Morrice, M. G., and Ziehlke, D. V., 1974, Archean continents. Geoscience Canada, v. 1, p. 12-20.
Young, G. M., 1978, Some aspects of the evolution of the Archean crust. Geoscience Canada, v. 5, p. 140-149.
Burke, K., Dewey, J. F., and Kidd, W. S. F., 1976, Dominance of horizontal movements, arc and microcontinental collisions during the later permobile regime. in Windley, B. F., ed The Early History of the Earth, New York, John Wiley & Sons, p. 113-129.
Card, K. D., 1990, A review of the Superior Province of the Canadian Shield, a product of Archean accretion. Precambrian Research, v. 48, p. 99-156.
Hoffman, P. F., 1989, Precambrian geology and tectonic history of North America. in Bally, A. W., and Palmer, A. R., eds., The geology of North America; an overview: The geology of North America: A, Boulder, CO, Geological Society of America, p. 447-512.
Hoffman, P. F., 1990, On accretion of granite-greenstone terrane. in Robert, F., Sheahan, P. A., and Green, S. B., eds., Greenstone gold and crustal evolution; NUNA conference volume, St. John's, NF, Geological Association of Canada, p. 32-45.
Langford, F. F., and Morin, J. A., 1976, The development of the Superior Province of northwestern Ontario by merging island arcs. American Journal of Science, v. 276, p. 1023-1034.
Talbot, C. J., 1973, A plate tectonic model for the Archaean crust. Philosophical Transactions of the Royal Society of London, v. A273, p. 413-428.
Example of fairly recent articles that cites both possibilities
Ayres, L D; Corfu, F., 1991. Stacking of disparate volcanic and sedimentary units by thrusting in the Archean Favourable Lake greenstone belt, central Canada. Precambrian Research 50, 221-238.
Parmenter, A. C.. et al., 2006. Can. J. Earth Sci. 43(7): 767-787.
Other granite-greenstone belts
Carlson, R. W. 2000. Continental growth, preservation, and modification in Southern Africa. GSA Today 10, 1-7.
Coward, M. P., James, P. R., and Wright, L., 1976, Northern margin of the Limpopo mobile belt, southern Africa. Geological Society of America Bulletin, v. 87, p. 601-611.
de Wit, M. J., 1991, Archaean greenstone belt tectonism and basin development; some insights from the Barberton and Pietersburg greenstone belts, Kaapvaal Craton, South Africa. Journal of African Earth Sciences, v. 13, p. 45-63.
de Wit, M. J., Armstrong, R., Hart, R. J., and Wilson, A. H., 1987, Felsic igneous rocks within the 3.3-3.5 Ga Barberton greenstone belt: high crustal level equivalents of the surrounding tonalite-trondhjemite terrain, emplaced during thrusting. Tectonics, v. 6, p. 529-549.
Archibald, N. J., Bettenay, L. F., Binns, R. A., Groves, D. I., and Gunthorpe, R. J., 1978, The evolution of Archaean greenstone terrains, Eastern Goldfields Province, Western Australia. Precambrian Research, v. 6, p. 103-131.
And many more.
- South Africa: