Physical transformation of layers of one orientation into another through isoclinal or very tight folding. If the shortening during formation of the crenulation foliation is very strong, the earlier foliation may become completely overprinted or transposed. In such cases the only evidence of the earlier foliation may be from inclusion trails trapped inside metamorphic porphyroblasts.
Crenulation Foliation and Differentiation :
Differentiation is a process that results in the concentration of certain minerals in one part of a rock and other minerals in another part of the rock. Crenulation foliation may occur under conditions that are also favorable for pressure solution. In such cases, as crenulations form, quartz may preferentially move from the limbs of the micro folds and be precipitated along the hinge areas of the folds.