Boudinage

division of rock strata or veins into separate blocks or lenses extending in the direction of the stratum or vein. It is formed during the crushing of a relatively more competent, flat geological body (stratum or vein) between two relatively more fluid layers under the influence of forces perpendicular to the layers. Such conditions arise, for example, on the limbs of strongly compressed folds, where the more plastic layers, being crushed and spreading in the direction of the axes of the folds, stretch the harder layers locked between them. The harder layers, being unable to flow with the same speed, at first divide into pinches—necks and swellings—lenses (lensing stage of boudinage), and then separate into pieces—boudins (boudinage proper). In the process of further deformation these pieces move farther and farther apart and the spaces between them fill up with material from adjacent plastic layers or with new mineral material (quartz, pegmatite). Boudinage is observed predominantly in metamorphic rocks.