Steven Dutch, Natural and Applied Sciences, University
of Wisconsin - Green Bay
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Location: 56o 48' 05" N, 005o 27' 30" W. (approximate)
These rocks were once deep in the crust during the formation of a mountain range about 1.8 billion years ago. The geologist in the center of the picture describes rocks like these as "looking like they've been stirred with a spoon." How in the world do we make sense out of such contorted rocks?
Geologists make use of the fact that when rocks are deformed, small structures in the rock reflect larger structures. When rocks fold, the rocks in the center of the fold slip by the rocks on the outside, and small layers within the rock get crumpled. On one side of the fold they tend to crumple into S-shapes, on the other side they fold into Z-shapes. By mapping those small folds, the geologist who's pointing out the rocks was able to zero in on a place where it was actually possible to see how the rocks are folded.
The topmost colored drawing shows the scene as it appears in nature. The bottom has two of the layers in the rock colored. We can see that, as contorted as they are, the layers basically form a U-shaped fold called a syncline.
(author's image)
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Created 19 February 2008, Last Update 01 March 2008
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