Strike-slip tectonics: Difference between revisions

===Riedel shear structures===

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, forms at about 15° to the underlying fault with the same shear sense. The R shears are then linked by a second set, the R' shears, 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|accessdate=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, often with the development of a further set of shears known as 'P shears', which are roughly symmetrical to the R shears relative 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>

 

===Flower structures===

In detail, many strike-slip faults at surface consist of en echelon and/or braided segments in many cases 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'', 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===