View source for Earth:Slickenside

[[File:Slickenslides at 500m depth in a Permian sandstone.jpg|right|thumb|400x400px|Slickenlines at 500m depth in a Permian sandstone]]
In [[Earth:Geology|geology]], a '''slickenside''' is a smoothly polished surface caused by frictional movement between [[Earth:Rock (geology)|rocks]] along a [[Earth:Fault (geology)|fault]]. This surface is typically [[Earth:Striation (geology)|striated]] with linear features, called '''slickenlines''', in the direction of movement.<ref>Tjia, H. D. "Slickensides and fault movements." Geological Society of America Bulletin 75.7 (1964): 683-686.
</ref>
== Geometry of slickensides ==
A slickenside can occur as a single surface at a fault between two hard surfaces. Alternatively, the [[Earth:Fault gouge|gouge]] between the fault surfaces may contain many anastamosing slip surfaces that host slickensides.<ref>Scholz, Christopher H. "The Mechanics of Earthquakes and Faulting." 3rd Edition. (2019): 128.</ref> These slip surfaces are on the order of 100 micrometers thick,<ref>Sagy, Amir, and Emily E. Brodsky. "Geometric and rheological asperities in an exposed fault zone." Journal of Geophysical Research: Solid Earth 114.B2 (2009).</ref> and the size of the grains that constitute the surface are ultra-fine (0.01-1 micrometers in diameter).<ref name="Power-1989">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.</ref> These grains are unlike typical grains of fault rock in that they have irregular [[Physics:Grain boundary|grain boundaries]] and few [[Chemistry:Crystal structure|crystal lattice]] defects (termed dislocations).<ref name="Power-1989" />

Slickensides have conspicuous shapes that can be used to determine the direction of movement along the fault. 
<ref>Doblas, Miguel. "Slickenside kinematic indicators." Tectonophysics 295.1-2 (1998): 187-197.</ref> Straight slickenlines indicate linear-translational fault motion. They are parallel to the direction of fault motion and serve as a kinematic indicator.<ref>Nibir Mandal and Chandan Chakraborty (1989) Fault motion and curved slickenlines: a theoretical analysis, Journal of Structural Geology</ref> Curved slickenlines have recently been studied for their potential to preserve the direction of [[Earth:Earthquake rupture|earthquake rupture propagation]]. <ref name="Kearse-2019">Kearse, J., Kaneko, Y., Little, T., and Van Dissen, R., 2019, Curved slickenlines preserve direction of rupture propagation: Geology, https://doi.org/10.1130/G46563.1</ref>

=== Surface 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. <ref> Emily E. Brodsky, James D. Kirkpatrick, Thibault Candela; Constraints from fault roughness on the scale-dependent strength of rocks. Geology 2016;; 44 (1): 19–22. doi: https://doi.org/10.1130/G37206.1 </ref> 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).<ref> Candela, T., Renard, F., Klinger, Y., Mair, K., Schmittbuhl, J., and Brodsky, E. E. (2012), Roughness of fault surfaces over nine decades of length scales, J. Geophys. Res., 117, B08409, doi:10.1029/2011JB009041. </ref>  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 ==
[[File:Fairview Fault mirror at Dixie Valley Nevada.jpg|thumb|450x450px|Mirror slickenside on scarp of Fairview Fault, Dixie Valley, Nevada, USA]]

The unique geometry of a slickenside can be created in a variety of ways,<ref name="Means-1987" /> 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.<ref name="Toy etal-2017">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</ref> When the particle size is reduced so dramatically that the surface becomes shiny, it can be characterized as a '''fault mirror'''.<ref name="Toy etal-2017" /> 

A fault mirror may also be the result of fluid being present at the fault surface during slip.<ref name="Kirkpatrick-2013">Kirkpatrick, J. D., et al. "Silica gel formation during fault slip: Evidence from the rock record." Geology 41.9 (2013): 1015-1018.</ref> Once slip has stopped, this fluid solidifies as a [[Chemistry:Silicon dioxide|silica gel]], which appears shiny and hosts slickenlines.

===Asperity plowing===
An [[Asperity (materials science)|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.<ref name="Means-1987">Means, W. D. "A newly recognized type of slickenside striation." Journal of Structural geology 9.5-6 (1987): 585-590.</ref> Asperity plowing is thus a result of permanent deformation in the brittle regime at a small scale.<ref name="Kirkpatrick-2014">Kirkpatrick, J. D., &amp; 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/S0012821X14006037 </ref>

===Debris 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.<ref name="Means-1987" /> 

===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 the lee side of the hard particle will be protected from wear. This creates a ''tail'' that starts abruptly as a ''crag'' where the hard particle was located and is elongated parallel to the direction of movement down-slip from the particle.<ref name="Means-1987" />

[[File:Slicks.png|left|thumb|400x400px|How slickenfibre steps form and show sense of movement on a fault.]]

===Fibre growth===

The fault plane may be coated by [[Earth:Mineral|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.

[[File:Calcite-chlorite slickenfibres on a small fault slickenside.jpg|thumb|450x450px|Calcite-chlorite slickenfibres on a small fault cutting greenschist-facies metavolcanic rocks of the Saddlebag Lake Roof Pendant, Sierra Nevada, California]]

Slickenfibres are secondary minerals that make up the slickensides rather than the rock itself. Slickenfibres form in areas where the rock slowly [[Earth:Aseismic creep|creep]] past one another rather than sliding suddenly as a result of an [[Earth:Earthquake|earthquake]].<ref name="Ishii-2017">Ishii, Eiichi. (2017). Estimation of the highest potential transmissivity of discrete shear fractures using the ductility index. International Journal of Rock Mechanics and Mining Sciences. 100. 10-22. 10.1016/j.ijrmms.2017.10.017.</ref> Unlike slickenlines, which give two possibilities for slip direction, slickenfibres preserve the true slip direction.<ref name="Ishii-2017" />

== Implications ==

Slickensides provide useful insight into earthquake processes. [[Chemistry:Calcite|Calcite]] slickenfibres have recently been used to constrain the depth of [[Earth:Aseismic creep|aseismic creep]] in the [[Place:Zagros Mountains|Zagros Mountains]] as well as the orientation of stress acting on the fault.<ref>Sarkarinejad, Khalil, Maryam Mottahedi, and Maryam Nori. "Aseismic slip on the active Sabz-Pushan and Sepidar thrusts, Iran: microstructural and kinematics evidence of the slickenline fibre creep." International Journal of Earth Sciences 110.8 (2021): 2831-2848.</ref> It has also been suggested that when multiple slickenfibre or slickensteps orientations are present, it can indicate that the ongoing shear is not strain softening so slip does not have a constant direction. <ref name="Toy etal-2017" />

In addition to the direction of slip, slickenlines have also been used to constrain the timing of fault slip.<ref>Norris, D. K. "Slickenlines and the kinematics of the Crowsnest Deflection in the Southern Rocky Mountains of Canada." Journal of Structural Geology 23.6-7 (2001): 1089-1102.</ref> They also preserve any complexity in the geometry of the earthquake rupture.<ref>Macklin, Clarrie, Yoshihiro Kaneko, and Jesse Kearse. "Coseismic slickenlines record the emergence of multiple rupture fronts during a surface-breaking earthquake." Tectonophysics 808 (2021): 228834.</ref>

== Other types of slickensides ==

=== Slickensides in soils ===
In pedology, the study of [[Chemistry:Soil|soils]] in their natural environments, a '''slickenside''' is a surface of the cracks produced in soils containing a high proportion of swelling [[Earth:Clay|clays]].  Slickensides are a type of [[Earth:Cutans|cutan]].
In the [[Earth:Australian Soil Classification|Australian Soil Classification]], slickensides, along with lenticular structural [[Earth:Aggregate (geology)|aggregates]], are an indicator of a [[Earth:Vertisol|vertisol]].<ref>Isbell, Raymond F. (1996). The Australian Soil Classification (1st ed.). Collingwood, Victoria: CSIRO Publishing. {{ISBN|0-643-05813-3}}.</ref>

=== Slickensides on the Moon ===
On the [[Astronomy:Moon|Moon]], a boulder with slickensides, discovered in a debris-strewn small crater at Station 9 near Rima Hadley, was photographed during a [[Engineering:List of spacewalks and moonwalks 1965–1999#1970–1979 spacewalks and moonwalks|moonwalk]] by the crew of [[Engineering:Apollo 15|Apollo 15]].<ref>https://www.lpi.usra.edu/resources/apollo/catalog/70mm/magazine/?82 Apollo Image Atlas (Lunar and Planetary Institute), 70 mm Hasselblad Image Catalog, Apollo 15 photographs AS15-82-11101, AS15-82-11102, AS15-82-11103 and AS15-82-11104</ref><ref>https://www.hq.nasa.gov/alsj/a15/a15.sta9.html Apollo 15 Lunar Surface Journal – Instant Rock at Station 9</ref><ref>https://history.nasa.gov/alsj/a15/A15SampleCat_1.pdf Catalog of Apollo 15 Rocks – Part 1. 15015-15299  </ref>





== Gallery ==
{{Gallery|File:PySlick.JPG|Dextral slickenside of [[Chemistry:Pyrite|pyrite]]|image:Slickensides.JPG|Slickensides developed on the surface of a small [[Earth:Fault (geology)|fault]] in [[Earth:Quartzite|quartzite]] in the Alpujarras|Image:Bear Valley Slickensides.jpg|Slickensides on a fault plane, south wall of Bear Valley Strip Mine. Lens cap 5.8cm wide.|File:East Kilve slickenfibres.JPG|Calcite slickenfibres on the surface of a normal fault, east of Kilve, Somerset.|File:Slickenside - Corona Heights, San Francisco.jpg|Slickensides on a fault plane in Corona Heights Park, San Francisco|File:Outcrop of Dalupirip Schist, Benguet, Philippines.jpg|Greenschist with slickensides in Itogon, Benguet, Philippines.}}



== Notes ==
{{reflist}}

== 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 CD

== External links ==

* {{Cite Americana|wstitle=Slickensides|year=1920|short=x}}

{{Structural geology}}

[[Category:Pedology]]
[[Category:Structural geology]]

{{Sourceattribution|Slickenside}}