20 June 2011

“Boudinage” is my favorite geology word

Posted by Callan Bentley

The current edition of the Accretionary Wedge geology blog carnival (hosted by Evelyn Mervine of Georneys) is built around the theme of favorite geology words.

My favorite geology word is derived from the French boudin, for sausage. It’s “boudinage,” and it’s best said with a heavy French accent and a leering, dirty expression.


I love pronouncing it; it’s a delicious word, like a good boudin itself.

So what is it?

Boudinage is when a rock unit (usually a tabular rock unit like a bed of sedimentary rock or an igneous dike or a mineral vein) gets stretched, and responds to that stress in a brittle/ductile fashion. It breaks into chunks, but those chunks show flow in between them. Like taffy, the strain is concentrated in the boudin “necks,” and the less competent surrounding rock flows into that accomodation space between the individual boudins. Viewed in cross-section, this creates a “sausage link” effect, as can be seen with this vertical example of boudinage (of a granitic dike) in the Lawhorne Mill High Strain Zone of Virginia’s Blue Ridge basement complex:

Here’s another one from the same spot, but further down the outcrop:

Sorry there’s no proper sense of scale in these photos — the outcrop wall was protected by a barricade of briers, ticks, and muck. I’ll go back in the winter sometime to document it properly.

Want more boudinage? Here’s some. Here’s some more.