Boudinaged quartz vein in shear foliation, Starlight Pit, Fortnum Gold Mine, Western Australia. The competent bed begins to break up, forming sausage-structural geology fossen pdf boudins. In lithospheric-scale tectonics, boudinage of strong layers can signify large-scale creep transfer of rock matter. The study of boudinage can, also, help provide insight to the forces involved in tectonic deformation of rocks and their strength.
Boudinage can develop in two ways: planar fracturing into rectangular fragments or by necking or tapering into elongate depressions and swells. This causes the resulting boudin to take a characteristic sausage or barrel shape. They can also form rectangular structures. Boudins can become separated by fractures or vein material, this zone of separation is known as boudin necks.
In three dimensions, the boudinage may take the form of ribbon-like boudins or chocolate-tablet boudins, depending on the axis and isotropy of extension. They range in size from about 20 m thick to about 1 cm. There are three different types of boudinage. These include no-slip boudinage, s-slip boudinage, and a-slip boudinage. No-slip boudinage occurs when there is no slip, resulting in a symmetrical structure. S-slip boudinage occurs when the boudin moves in opposition to the shear movement, where A-slip occurs when it moves with the direction of the shear.