KINK AXES

Since kink-bands are formed by interlayer slip, they are of subclass 1B style i.e. the orthogonal thickness within the kink-band and in the un-deflected layering remains the same. Such kink-bands are called REVERSE OR CONTRACTIONAL KINK-BANDS. Conversely, if the orthogonal thickness within the kink-band is systematically reduced than that in the un-deflected layering the kink-bands are called NORMAL OR EXTENSIONAL KINK-BANDS. The difference between the normal and reverse kink bands is shown in figure accompanying this text. If the compressive stress acts parallel to the layering, conjugate kink-bands or box folds are produced but if it acts at an angle to the layering, a single set of kink-bands are developed more or less at the exclusion of the other. Patterson and Weiss (1966) produced conjugate and single kink-bands experimentally and one of their significant conclusions has been that under large shortening, kink-bands are converted into chevron folds. Dewey (1966) made significant contribution towards our understanding of the nature and origin of kink-bards and Arvid Johnson and his coworkers have presented through a series of papers (see 1976 numbers of Tectonophysics) the origin of kink-bands by extensive theoretical treatment of the problem of their origin and geometry.