Boudinage

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Boudinaged jasperoid in sheared basalt, Fortnum Gold Mine, Australia. Typical example of shear boudinage.

Boudinaged quartz vein in shear foliation, Starlight Pit, Fortnum Gold Mine, Western Australia.

Banded gneiss with dike of granite orthogneiss; competent banded gneiss is boudinaged by ductile shear.

Boudinage is a geological term for structures formed by extension, where a rigid tabular body such as a bed of sandstone, is stretched and deformed amidst less competent surroundings. The competent bed begins to break up, forming sausage-shaped boudins.

Boudins are typical features of sheared veins and shear zones where, due to stretching along the shear foliation and compression perpendicular to this, rigid bodies break up. Ductile deformation conditions also encourage boudinage rather than imbricate fracturing.

In three dimensions, the boudinage may take the form of ribbon-like boudins or chocolate-tablet boudings, depending on the axis and isotropy of extension.

Examples: Evolution of the mullions (boudins) of the Eifel-Ardennes by Prof. Janos Urai. PDF

Etymology
Boudinage derives from the French word "boudin", meaning sausage.

[edit] References

Urai, J. L., Spaeth, G., van der Zee, W. & Hilgers, C. 2001. Evolution of Mullion (Boudin) structures in the Variscan of the Ardennes and Eifel. In: Jessell, M. J. 2001. General Contributions: 2001. Journal of the Virtual Explorer, 3, 1-16.