KBBS, KINK-BAND BOUNDARIES
When a sharp deflection in otherwise planar anisotropic laminated
material of constant orientation occurs, it is called a kink-band.
Kink-bands are also produced by flexural slip like chevron folds. The
axial plane of a kink-band is the plane that bisects the angle between
deflected and un-deflected portions of the layers and is usually called a
kink plane. Kink-bands normally occur on a small scale such as the scale
of a hand specimen or on microscopic scale or even on the electron
microscopic scale or on the scale of an atomic lattice of a mineral When
these structures are developed on large scale outcrops or on the
mappable scale, they are called monoclines.
Two kink-bands in opposite directions may join to form what are known as
conjugate
kink-bands, or if developed on larger scales, conjugate
or box folds. The axial planes of
conjugate kink bands
occur in pairs and are either inclined towards each other (antiforms) or
away from each other (synforms) and the obtuse angle between them faces
the direction of
maximum shortening in rocks or it faces the direction of maximum
principal compressive stress s1
. Thus
the conjugate kink-bands are important in the sense that they allow the orientations
of principal stresses to be determined simply by plotting orientations
of axial planes on an equal area net as in case
of conjugate shear zones. .
Modified after Jiang.
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