Geometry of slickensides
A slickenside can occur as a single surface at a fault between two hard surfaces. Alternatively, the gouge between the fault surfaces may contain many anastamosing slip surfaces that host slickensides. These slip surfaces are on the order of 100 micrometers thick, and the size of the grains that constitute the surface are ultra-fine (0.01-1 micrometers in diameter).Power, William L., and Terry E. Tullis. "The relationship between slickenside surfaces in fine-grained quartz and the seismic cycle." Journal of Structural Geology 11.7 (1989): 879-893. These grains are unlike typical grains of fault rock in that they have irregular grain boundaries and few crystal lattice defects (termed dislocations). Slickensides have conspicuous shapes that can be used to determine the direction of movement along the fault. Straight slickenlines indicate linear-translational fault motion. They are parallel to the direction of fault motion and serve as a kinematic indicator. Curved slickenlines have recently been studied for their potential to preserve the direction of earthquake rupture propagation. Kearse, J., Kaneko, Y., Little, T., and Van Dissen, R., 2019, Curved slickenlines preserve direction of rupture propagation: Geology, https://doi.org/10.1130/G46563.1Surface Roughness
Slickenside formation results in unique roughness on a slip surface. Fault surface roughness (or topography) is characterized by the aspect ratio of asperity height to scale of observation, and this roughness is a key parameter in the study of fault slip. In general, a fault surface appears rougher at smaller scales (i.e. rough and bumpy at approximately millimetre scales and smaller, and increasingly smooth with larger fields of view). This smoothing with larger observation scales is more pronounced in the slip-parallel direction than the slip-perpendicular direction and is commonly a result of slickenside formation.Mechanisms to create slickensides
The unique geometry of a slickenside can be created in a variety of ways, but the precise mechanisms that create them is not well understood. The grinding between two rocks produces granular material, and there is a change in the behaviour of wear material when the particle size is reduced to nanometers.Toy, V. G., A. Niemeijer, F. Renard, L. Morales, and R. Wirth (2017), Striation and slickenline development on quartz fault surfaces at crustal conditions: Origin and effect on friction, J. Geophys. Res. Solid Earth, 122, 3497–3512, doi:10.1002/2016JB013498 When the particle size is reduced so dramatically that the surface becomes shiny, it can be characterized as a fault mirror. A fault mirror may also be the result of fluid being present at the fault surface during slip.Kirkpatrick, J. D., et al. "Silica gel formation during fault slip: Evidence from the rock record." Geology 41.9 (2013): 1015-1018. Once slip has stopped, this fluid solidifies as a silica gel, which appears shiny and hosts slickenlines.Asperity plowing
An asperity on a fault surface is a bump or point with higher relief than the area around it. The asperity, when pressed into the opposing rock surface and then moved, digs into the opposing rock, forming troughs, grooves, and scratches.Means, W. D. "A newly recognized type of slickenside striation." Journal of Structural geology 9.5-6 (1987): 585-590. Asperity plowing is thus a result of permanent deformation in the brittle regime at a small scale.Kirkpatrick, J. D., & Brodsky, E. E. (2014, October 22). Slickenline orientations as a record of Fault Rock Rheology. Earth and Planetary Science Letters. Retrieved November 3, 2022, from https://www.sciencedirect.com/science/article/pii/S0012821X14006037Debris streaking
When an asperity plows into the opposing rock, it wears itself and the opposing rock down and produces fine debris. This debris, or wear product, accumulates both in front of and behind the asperity in a long, elongated shape. If the asperity is relatively hard, the debris will accumulate in front of the asperity. If the asperity is relatively soft, the debris will trail behind. This debris hardens over time and is preserved as a form of slickenline.Erosional sheltering
Some rocks may contain particles that are harder than the rest of the rock. When these rocks are worn, the harder particles will resist wear more than the softer rock, the rock on theFiber growth
The fault plane may be coated by mineral fibres that grew in during the fault movement, known as ''slickenfibres''. Due to irregularities in the fault plane, exposed slickenfibres typically have a stepped appearance that can be used to determine the sense of movement across the fault. Slickenfibres are secondary minerals that make up the slickensides rather than the rock itself. Slickenfibres form in areas where the rock slowlyImplications
Slickensides provide useful insight into earthquake processes.Other types of slickensides
Slickensides in soils
InSlickensides on the Moon
On the Moon, a boulder with slickensides, discovered in a debris-strewn small crater at Station 9 near Rima Hadley, was photographed during a moonwalk by the crew ofGallery
Notes
References
* Allaby, A. and Allaby, M. (Eds). 1990. ''The Concise Oxford Dictionary of Earth Sciences''. New York, USA: Oxford University Press. * McDonald, R. C. et al. 1990. ''The Australian Soil and Land Survey Field Handbook'', 2nd Ed. Melbourne, Australia: Inkata Press. * ''Microtectonics'', by C.W.Passchier and R.A.J.Trouw, 2nd rev. and enlarged ed., 2005, XVI, 366 p., 322 illus., with CDExternal links
* {{Structural geology Pedology Structural geology