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: