Fault gouge

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Salmon-colored fault gouge and associated fault separates two different rock types on the left (dark grey) and right (light grey). From the Gobi of Mongolia.

Fault gouge is a tectonite (a rock formed by tectonic forces) with a very small grain size. Fault gouge has no cohesion and it is normally an unconsolidated rock type, unless cementation took place at a later stage. A fault gouge forms in the same way as fault breccia, the latter also having larger clasts.[1] In comparison to fault breccia, which is another incohesive fault rock, fault gouge has less visible fragments (less than 30% visible fragments regarding fault gouges, and more than 30% regarding fault breccia).[2]

Gouge-filled faults can be weak planes in rock masses. If compressive stresses are enough these can cause compressive yielding or eventually rock fracture. [3]


Fault gouge forms by tectonic movement along a localized zone of brittle deformation (a fault zone) in a rock. The grinding and milling that results when the two sides of the fault zone move along each other results in a material that is made of loose fragments. First a fault breccia will form, but if the grinding continues the rock becomes fault gouge.

See also[edit]


  1. ^ Twiss, R.J. & Moores, E.M., 2000 (6th edition): Structural Geology, W.H. Freeman & co, ISBN 0-7167-2252-6; p. 55
  2. ^ Sibson, R. H. (1977). "Fault rocks and fault mechanisms". Journal of the Geological Society of London. 133: 191–213. doi:10.1144/gsjgs.133.3.0191.
  3. ^ Bertuzzi, R., 2015: Tunnel Support Loading Mechanism, UNSW, Sydney, Australia; p. 1