Strike-slip tectonics: Difference between revisions

{{short description|StructureDeformation anddominated processesby associatedhorizontal with zones of lateral displacementmovement in the Earth's crustlithosphere}}

'''Strike-slip tectonics''' isor concerned'''wrench withtectonics''' theis structuresa formedtype by, and theof [[Tectonics|tectonictectonics]] processesthat associatedis with,dominated zones ofby lateral displacement(horizontal) movements within the Earth's [[Crust (geology)|Earth's crust]] or(and [[lithosphere]]). ItWhere isa onezone of thestrike-slip threetectonics mainforms typesthe ofboundary tectonic regime, the othersbetween beingtwo [[extensionalPlate tectonics]]|tectonic and [[thrust tectonicsplates]]., Thesethis matchis theknown threeas types of [[plate tectonics|plate boundary]],a [[transform fault|transform]] (strike-slip),or [[divergentconservative boundary|divergent]] (extensional) and [[convergentplate boundary|convergent]] (thrust). Areas of strike-slip tectonics are associatedcharacterised withby particular deformation styles including: ''stepovers'', ''Riedel shears'', ''flower structures'' and ''strike-slip duplexes''. This typeWhere the displacement along a zone of strike-slip deviates from parallelism with the zone itself, the style becomes either [[transpression]]al or [[transtension]]al depending on the sense of deviation. Strike-slip tectonics is characteristic of several geological environments, including oceanic and continental transform faults, zones of oblique collision and the deforming foreland of a zonezones of [[continental collision]].<ref>{{Cite book |last=Acocella |first=V. |title=Volcano-Tectonic Processes |publisher=Springer International Publishing |year=2021 |isbn=9783030659684 |pages=74}}</ref><ref name="Burg_2017">{{Cite web |last=Burg |first=J.-P. |date=2017 |title=Strike-slip and Oblique-slip tectonics |url=https://www.files.ethz.ch/structuralgeology/jpb/files/english/5wrench.pdf |access-date=26 September 2022}}</ref>

In the early stages of [[Fault (geology)#Strike-slip faults|strike-slip fault]] formation, displacement within [[Basement (geology)|basement]] rocks produces characteristic fault structures within the overlying cover. This will also be the case where an active strike-slip zone lies within an area of continuing sedimentation. At low levels of strain, the overall [[simple shear]] causes a set of small faults to form. The dominant set, known as R shears, formforms at about 15° to the underlying fault with the same shear sense. The R shears are then linked by a second set, the R' shearshears, that forms at about 75° to the main fault trace.<ref name="Katz">{{cite journal|last=Katz|first=Y.|author2=Weinberger R.|author3=Aydin A.|year=2004|title=Geometry and kinematic evolution of Riedel shear structures, Capitol Reef National Park, Utah|journal=Journal of Structural Geology|volume=26|issue=3|pages=491–501|doi=10.1016/j.jsg.2003.08.003|url=ftp://geos.gsi.gov.il/pub/Rami/Papers/Riedel.pdf|accessdateaccess-date=6 May 2011|bibcode=2004JSG....26..491K}}{{Dead link|date=June 2018 |bot=InternetArchiveBot |fix-attempted=no }}</ref> These two fault orientations can be understood as conjugate fault sets at 30° to the short axis of the instantaneous strain ellipse associated with the simple shear strain field caused by the displacements applied at the base of the cover sequence. With further displacement, the Riedel fault segments will tend to become fully linked, until a throughgoing fault is formed. The linkage often occurs with the development of a further set of shears known as 'P shears', which are roughly symmetrical to the R shears concerningrelative to the overall shear direction, until a throughgoing fault is formed.<ref name="Tchalenko">{{cite journal|last=Tchalenko|first=J.S.|year=1970|title=Similarities between Shear Zones of Different Magnitudes|journal=Geological Society of America Bulletin|volume=81|issue=6|pages=1625–1640|doi=10.1130/0016-7606(1970)81[1625:SBSZOD]2.0.CO;2|bibcode = 1970GSAB...81.1625T }}</ref> The somewhat oblique segments will link downwards into the fault at the base of the cover sequence with a helicoidal geometry.<ref>[http://adsabs.harvard.edu/abs/2001AGUFM.S52D0682U Ueta, K.; Tani, K. 2001. Ground Surface Deformation in Unconsolidated Sediments Caused by Bedrock Fault Movements: Dip-Slip and Strike-Slip Fault Model Test and Field Survey. American Geophysical Union, Fall Meeting 2001, abstract #S52D-0682]</ref>

In detail, many strike-slip faults at surface consist of [[en echelon]] and/or braided segments, which in many cases were probably inherited from previously formed Riedel shears. In cross-section, the displacements are dominantly reverse or normal in type depending on whether the overall fault geometry is [[transpression]]al (i.e. with a small component of shortening) or [[transtension]]al (with a small component of extension). As the faults tend to join downwards onto a single strand in basement, the geometry has led to these being termed ''flower structure''. Fault zones with dominantly reverse faulting are known as ''positive flowers'', while those with dominantly normal offsets are known as ''negative flowers''. The identification of such structures, particularly where positive and negative flowers are developed on different segments of the same fault, are regarded as reliable indicators of strike-slip.<ref>[http://search.datapages.com/data/doi/10.1306/0C9B2533-1710-11D7-8645000102C1865D Harding, T. P. 1990. Bulletin American Association of Petroleum Geologists. 74]</ref>

Strike-slip duplexes occur at the step overstepover regions of faults, forming a lens-shaped near parallel arrays of [[horse (geology)|horses]]. These occur between two or more large bounding faults which usually have large displacementdisplacements.<ref name = "D"/>

An idealized [[Fault (geology)#Strike-slip faults|strike-slip fault]] runs in a straight line with a vertical [[Strike and dip|dip]] and has only horizontal motion, thus there is no change in topography due to motion of the fault. In reality, as strike-slip faults become large and developed, their behavior changes and becomes more complex. A long strike-slip fault follows a staircase-like trajectory consisting of interspaced fault planes that follow the main fault direction.<ref name = "A">{{Citation

}}</ref> These sub-parallel stretches are isolated by offsets at first, but over long periods of time, they can become connected by step overstepovers to accommodate the strike-slip displacement.<ref name = "D"/> In long stretches of strike-slip, the fault plane can start to curve, giving rise to structures similar to step overs.<ref name = "C"/>

[[Sinistral and dextral|Right lateral]] motion of a strike-slip fault at a right step overstepover (or overstep) gives rise to [[Extensional tectonics|extensional]] bends characterised by zones of [[subsidence]], local [[normal faultsfault]]s, and [[pull-apart basinsbasin]]s.<ref name = "D"/> On extensional duplexes, normal faults will accommodate the vertical motion, creating negative relief. Similarly, left stepping at a dextral fault generates contractional bends; shorteningthis theshortens stepthe oversstepovers which isare displayed by local [[Fault (geology)|reverse faults]], push-up zones, and [[Fold (geology)|folds]].<ref name = "C"/> On contractional duplex structures, thrust faults will accommodate vertical displacement rather than being folded, as the uplifting process is more energy-efficient.<ref name = "C"/>

Strike-slip duplexes are passive structures; they form as a response to displacement of the bounding fault rather than by the stresses from plate motion.<ref name = "A"/> Each horse has a length that varies from half to twice the spacing between the bounding fault planes. Depending on the properties of the rocks and the fault, the duplexes will have different length ratios and will develop on either major or subtle offsets, although it is possible to observe duplex structures that develop on nearly straight fault segments.<ref name = "C"/> Because the motion of the duplexes may be heterogeneous, the individual horses can experience a rotation with a horizontal axis, which results in the formation of scissor faults. Scissor faults exhibit normal motion at one end of the horse and a thrust motion at the other end.<ref name = "C">{{Citation

An example of strike-slip duplexes wasis observed in the Lambertville sill, New Jersey.<ref name = "B"/> Flemington and the Hopewell faults, the two main faults in the region, experienced 3&nbsp;km of dip-slip and over 20&nbsp;km of strike-slip motions to accommodate regional extension. It is possible to trace the lensoidal structures which are interpreted as horses that form duplexes.<ref name = "B"/> The lens structures observed in the 3M quarry are 180 meters long and 10 meters wide. The main duplex is 30 m in length and other smaller duplexes are also present.<ref name = "B">{{Citation

[[File:Aerial-SanAndreas-CarrizoPlain.jpg|thumb|160px|San Andreas Transform Fault on the [[Carrizo Plain]]]]

In most zones of [[continental collision|continent-continent collision]], the relative movement of the plates is oblique to the plate boundary itself. The deformation along the boundary is normally partitioned into dip-slip contractional structures in the foreland with a single large strike-slip structure in the [[hinterland (geology)|hinterland]] accommodating all the strike-slip component along the boundary. Examples include the ''Main Recent Fault'' along the boundary between the [[Arabian plate|Arabian]] and Eurasian platesplate behind the [[Zagros]] [[fold and thrust belt]],<ref>Talebian, M. Jackson, J. 2004. [http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?db_key=AST&bibcode=2004GeoJI.156..506T&letter=0&classic=YES&defaultprint=YES&whole_paper=YES&page=506&epage=506&send=Send+PDF&filetype=.pdf A reappraisal of earthquake focal mechanisms and active shortening in the Zagros mountains of Iran] [[Geophysical Journal International]], 156, pages 506–526</ref> the [[Liquiñe-Ofqui Fault]] that runs through [[Chile]] and the [[Great Sumatran fault]] that runs parallel to the [[subduction]] zone along the [[Java Trench|Sunda Trench]].