KINK-BANDS
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 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. Kink-bands are
usually related to late stage movements of an orogenic pulse and therefore
developed on a schistosity, slaty cleavage etc. in phyllites or slates
developed during a previous episode of deformation and metamorphism.
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