Saturday, May 17, 2014

Geo 730: May 17, Day 503: Bluedinage

The correct term is actually boudinage, but, hey, it's in blueschist, so there's your geo-pun for the day. Boudinage forms when two components of a strained rock have different competencies, with one more plastic, the other less so. The more plastic component tends to deform more easily, shearing due to the stress it experiences, while the other tends to deform more brittley, breaking up into discrete blocks and pieces. There are a large number of boudins visible in the above photo, and I've annotated just a few below to help clarify the idea for those not familiar with it.
In this case, the more plastic component is the mica-rich regions, probably mostly chlorite. The more brittle component is the glaucophane-rich regions, which are dark blue.

Photo unmodified. March 9, 2012. FlashEarth location.

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