Metamorphic Minerals

Texture and Microstructure

Metamorphic Rocks

Kink bands

Kinking occurs when slip on a single slip plane is inadequate to maintain homogeneous deformation. The grain sharply bends (kinks) and the deformation localizes into kink bands, which enable shortening of the grain to continue. The whole grain may divide into kink bands or the kink bands may be separate and commonly lenticular or wedge-shaped. Kinking is common in minerals with strongly anisotropic crystal structures and consequently only one slip plane, such as biotite, kyanite and enstatite, but also occurs in minerals with several slip systems, such as quartz and olivine. Although kinking is primarily thought to accommodate shortening of a crystal parallel to maximum compressive stress, it may also take place in crystals stressed in tension. Crystals unfavorably orientated for slip are freed by kinking which rotates the lattice along the rotation axis, allowing further plastic deformation to occur.

A kink band may be defined as part of a grain that undergoes rotation with respect to the unkinked part of the grain, the axis of rotation coinciding with the line of intersection of the kink band and the slip plane, perpendicular to the slip direction (Fig.1).

Fig.1: Mechanism of deformation kinking in a mineral grain. Modified from Vernon, 2004.

Bibliography

• Bucher, K., & Grapes, R. (2011). Petrogenesis of metamorphic rocks. Springer Science & Business Media.
• Fossen, H. (2016). Structural geology. Cambridge University Press.
• Howie, R. A., Zussman, J., & Deer, W. (1992). An introduction to the rock-forming minerals (p. 696). Longman.
• Passchier, Cees W., Trouw, Rudolph A. J: Microtectonics (2005).
• Philpotts, A., & Ague, J. (2009). Principles of igneous and metamorphic petrology. Cambridge University Press.
• Shelley, D. (1993). Igneous and metamorphic rocks under the microscope: classification, textures, microstructures and mineral preferred-orientations.
• Vernon, R. H. & Clarke, G. L. (2008): Principles of Metamorphic Petrology. Cambridge University Press.
• Vernon, R. H. (2018). A practical guide to rock microstructure. Cambridge university press.

Kink bands in biotite. Tonalite from Adamello massif, Italy. XPL image, 2x (Field of view = 7mm)	Kink bands in biotite. Tonalite from Adamello massif, Italy. PPL image, 2x (Field of view = 7mm)	Kink bands in biotite. Tonalite from Adamello massif, Italy. PPL image, 2x (Field of view = 7mm)
Kink bands in biotite. Tonalite from Adamello massif, Italy. XPL image, 2x (Field of view = 7mm)	Kink bands in biotite. Tonalite from Adamello massif, Italy. XPL image, 2x (Field of view = 7mm)	Kink bands in biotite. Tonalite from Adamello massif, Italy. PPL image, 2x (Field of view = 7mm)
Kink bands in biotite. Tonalite from Adamello massif, Italy. XPL image, 2x (Field of view = 7mm)	Kink bands in biotite. Tonalite from Adamello massif, Italy. XPL image, 2x (Field of view = 7mm)	Kink bands in biotite. Tonalite from Adamello massif, Italy. PPL image, 2x (Field of view = 7mm)
Kink bands in biotite. Tonalite from Adamello massif, Italy. XPL image, 2x (Field of view = 7mm)	Kink bands in biotite. Tonalite from Adamello massif, Italy. XPL image, 2x (Field of view = 7mm)	Kink bands in olivine. Xenolith from Etna volcano, Italy. XPL image, 2x (Field of view = 7mm)
Kink bands in olivine. Xenolith from Etna volcano, Italy. XPL image, 2x (Field of view = 7mm)	Kink bands in olivine. Xenolith from Etna volcano, Italy. XPL image, 2x (Field of view = 7mm)	Kink bands in olivine. Xenolith from Etna volcano, Italy. XPL image, 2x (Field of view = 7mm)
Kink bands in quartz. XPL image, 2x (Field of view = 7mm)	Kink bands in quartz. XPL image, 2x (Field of view = 7mm)	Kink bands in quartz. XPL image, 2x (Field of view = 7mm)
Kink bands in biotite. Granulite from Migiandone, Val'dossola, italian Alps. PPL image, 1x (Field of view = 9mm)	Kink bands in biotite. Granulite from Migiandone, Val'dossola, italian Alps. PPL image, 2x (Field of view = 7mm)	Kink bands in biotite. Granulite from Migiandone, Val'dossola, italian Alps. XPL image, 2x (Field of view = 7mm)
Kink bands in biotite. Granulite from Migiandone, Val'dossola, italian Alps. PPL image, 2x (Field of view = 7mm)	Kink bands in biotite. Granulite from Migiandone, Val'dossola, italian Alps. PPL image, 10x (Field of view = 2mm)	Kink bands in biotite. Granulite from Migiandone, Val'dossola, italian Alps. XPL image, 10x (Field of view = 2mm)
Kink bands in biotite. Granulite from Migiandone, Val'dossola, italian Alps. PPL image, 10x (Field of view = 2mm)	Kink bands in biotite. Granulite from Migiandone, Val'dossola, italian Alps. PPL image, 20x (Field of view = 1mm)	Kink bands in biotite. Granulite from Migiandone, Val'dossola, italian Alps. XPL image, 20x (Field of view = 1mm)
Kink bands in biotite. Granulite from Migiandone, Val'dossola, italian Alps. PPL image, 20x (Field of view = 1mm)	Kink bands in biotite. Granulite from Migiandone, Val'dossola, italian Alps. PPL image, 20x (Field of view = 1mm)	Kink bands in biotite. Granulite from Migiandone, Val'dossola, italian Alps. PPL image, 20x (Field of view = 1mm)
Kink bands in kyanite. PPL image, 10x (Field of view = 2mm)	Kink bands in kyanite. XPL image, 10x (Field of view = 2mm)	Kink bands in kyanite. PPL image, 10x (Field of view = 2mm)
Kink bands in kyanite. XPL image, 10x (Field of view = 2mm)	Kink bands in kyanite. PPL image, 20x (Field of view = 1mm)	Kink bands in kyanite. XPL image, 20x (Field of view = 1mm)
Kink bands in calcite. Carbonatic schist from Praborna mine, Aosta valley, Italy. XPL image, 2x (Field of view = 7mm)	Kink bands in calcite. Carbonatic schist from Praborna mine, Aosta valley, Italy. XPL image, 2x (Field of view = 7mm)	Kink bands in calcite. Carbonatic schist from Praborna mine, Aosta valley, Italy. XPL image, 2x (Field of view = 7mm)
Kink bands in calcite. Carbonatic schist from Praborna mine, Aosta valley, Italy. XPL image, 2x (Field of view = 7mm)	Kink bands in calcite. Carbonatic schist from Praborna mine, Aosta valley, Italy. XPL image, 2x (Field of view = 7mm)	Kink bands in calcite. Carbonatic schist from Praborna mine, Aosta valley, Italy. XPL image, 2x (Field of view = 7mm)
Kink bands in calcite. Carbonatic schist from Praborna mine, Aosta valley, Italy. XPL image, 2x (Field of view = 7mm)	Kink bands in calcite. Carbonatic schist from Praborna mine, Aosta valley, Italy. XPL image, 2x (Field of view = 7mm)	Kink bands in calcite. Carbonatic schist from Praborna mine, Aosta valley, Italy. XPL image, 2x (Field of view = 7mm)
Kink bands in calcite. Carbonatic schist from Praborna mine, Aosta valley, Italy. XPL image, 2x (Field of view = 7mm)	Kink bands in calcite. Carbonatic schist from Praborna mine, Aosta valley, Italy. XPL image, 2x (Field of view = 7mm)	Kink bands in calcite. Carbonatic schist from Praborna mine, Aosta valley, Italy. XPL image, 2x (Field of view = 7mm)