13 December 2011
Dikes crossing dikes
Posted by Callan Bentley
A pretty cool outcrop I saw on my pre-GSA structural geology field trip to the Superior Craton:
Can you see what caught my eye here?
It’s a nice series of cross-cutting relationships. A series of sedimentary rocks were sheared out and metamorphosed, transforming into schists with internal boudins, and then they were cross-cut by first a felsic dike, and then a mafic dike, as seen in this modified version of the same photo:
Outcrops like this are great for teaching the relative timing of geologic events.
Here’s a close up of some of the itty-bitty boudins in the schist adjacent to the margin of the felsic dike:
Callan Bentley is Associate Professor of Geology at Piedmont Virginia Community College in Charlottesville, Virginia. He is a Fellow of the Geological Society of America. For his work on this blog, the National Association of Geoscience Teachers recognized him with the James Shea Award. He has also won the Outstanding Faculty Award from the State Council on Higher Education in Virginia, and the Biggs Award for Excellence in Geoscience Teaching from the Geoscience Education Division of the Geological Society of America. In previous years, Callan served as a contributing editor at EARTH magazine, President of the Geological Society of Washington and President the Geo2YC division of NAGT.
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