13 July 2010
Folded Archean gneiss
Posted by Callan Bentley
Here’s a nice sample of folded gneissic banding in basement complex of the Gallatin Range, Montana. According to Dave Mogk of Montana State University (who I met in person for the first time on Saturday), these high grade metamorphic rocks are as old as 3.2 Ga (billion years old). They experienced temperatures as high as 750 degrees C, and pressures equivalent to 25 kilometers of depth in the crust. The lovely folds were what caught my eye, however:
Happy Tuesday!
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.
I was mapping this stuff today in the Pioneer Mountains. Pretty old stuff.