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Transtension is the state in which a rock mass or area of the Earth's crust experiences both ''extensive'' and ''transtensive'' shear. As such, transtensional regions are characterised by both extensional structures (
''Releasing bends'' are transtensional structures that form where the orientation of a strike-slip fault becomes oblique to the regional slip vector causing local extension (such as a right stepping bend on a right-lateral fault). They also form where two segments of a strike-slip fault overlap, and the relay zone between the segments experiences transtension. Releasing bends often form negative flower structures or
normal faults
Normal(s) or The Normal(s) may refer to:
Film and television
* ''Normal'' (2003 film), starring Jessica Lange and Tom Wilkinson
* ''Normal'' (2007 film), starring Carrie-Anne Moss, Kevin Zegers, Callum Keith Rennie, and Andrew Airlie
* ''Norma ...
, graben
In geology, a graben () is a depression (geology), depressed block of the Crust (geology), crust of a planet or moon, bordered by parallel normal faults.
Etymology
''Graben'' is a loan word from German language, German, meaning 'ditch' or 't ...
s) and wrench structures (strike-slip fault
In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...
s). In general, many tectonic regimes that were previously defined as simple strike-slip shear zones are actually transtensional. It is unlikely that a deforming body will experience 'pure' extension or 'pure' strike-slip.
Transtensional shear zones are characterized by the co-existence of different structures, related to both strike-slip shear and extension. End member structures include pure strike-slip faults and purely extensional ("normal") dip-slip fault
In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic f ...
s. Faults which have components of both (termed 'oblique' slip faults) are abundant.
Releasing bend
''Releasing bends'' are transtensional structures that form where the orientation of a strike-slip fault becomes oblique to the regional slip vector causing local extension (such as a right stepping bend on a right-lateral fault). They also form where two segments of a strike-slip fault overlap, and the relay zone between the segments experiences transtension. Releasing bends often form negative flower structures or pull-apart basin
In geology, a basin is a region where subsidence generates accommodation space for the deposition of sediments. A pull-apart basin is a structural basin where two overlapping (en echelon) strike-slip faults or a fault bend create an area of crust ...
s. Geologists may also refer to a releasing bend as a right bend.
Transtensional regions
*Dead Sea
The Dead Sea (; or ; ), also known by #Names, other names, is a landlocked salt lake bordered by Jordan to the east, the Israeli-occupied West Bank to the west and Israel to the southwest. It lies in the endorheic basin of the Jordan Rift Valle ...
Kearey, Philip and Frederick J. Vine, ''Global Tectonics,'' Blackwell Science, 2nd ed., 1996, pp. 131-133
* Salton Sea
The Salton Sea is a shallow, landlocked, highly salinity, saline endorheic lake in Riverside County, California, Riverside and Imperial County, California, Imperial counties in Southern California. It lies on the San Andreas Fault within the S ...
* Sea of Marmara
The Sea of Marmara, also known as the Sea of Marmora or the Marmara Sea, is a small inland sea entirely within the borders of Turkey. It links the Black Sea and the Aegean Sea via the Bosporus and Dardanelles straits, separating Turkey's E ...
on the North Anatolian Fault
The North Anatolian Fault (NAF; ) is an active right-lateral strike-slip fault in northern Anatolia, and is the transform boundary between the Eurasian plate and the Anatolian sub-plate. The fault extends westward from a junction with the Ea ...
* Vienna Basin Royden, Leigh H., The Vienna Basin: a Thin-Skinned Pull-Apart Basin ''in'' N. Christie-Blick and K.T. Biddle (eds.), ''Strike-Slip Deformation, Basin Formation, and Sedimentation''. SEPM Special Publications, 37.
See also
*Pull-apart basin
In geology, a basin is a region where subsidence generates accommodation space for the deposition of sediments. A pull-apart basin is a structural basin where two overlapping (en echelon) strike-slip faults or a fault bend create an area of crust ...
* Rift
In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics. Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-graben ...
* Strike-slip tectonics
Strike-slip tectonics or wrench tectonics is a type of tectonics that is dominated by lateral (horizontal) movements within the Earth's crust (and lithosphere). Where a zone of strike-slip tectonics forms the boundary between two tectonic plates, t ...
* Structural geology
Structural geology is the study of the three-dimensional distribution of rock units with respect to their deformational histories. The primary goal of structural geology is to use measurements of present-day rock geometries to uncover informati ...
* Transpression
In geology, transpression is a type of Strike-slip fault, strike-slip deformation that deviates from simple shear because of a simultaneous component of shortening perpendicular to the fault plane. This movement ends up resulting in oblique shear. ...
References
Structural geology {{tectonics-stub