Tension (geology)

File:Tens.tif In geology, the term "tension" refers to a stress which stretches rocks in two opposite directions. The rocks become longer in a lateral direction and thinner in a vertical direction. One important result of tensile stress is jointing in rocks. However, tensile stress is rare because most subsurface stress is compressive, due to the weight of the overburden.

## Jointing

Tensile stress forms joints in rocks. A joint is a fracture that forms within a rock, whose movement to open the fracture is greater than the lateral movement that takes place. Joints are formed in the direction perpendicular to the least principal stress, meaning that they are formed perpendicular to the tensile stress.[1] One way in particular that joints can be formed is due to fluid pressure, as well as at the crest of folds in rocks. This occurs at the peak of the fold or due to the fluid pressure because a localized tensile stress forms, eventually leading to jointing.[2] Another way in which joints form is due to the change in the weight of the overburden. Since rocks lay under a great deal of overburden, they undergo high temperatures and high pressures. Over time, the rocks are eroded and the weight of the overburden is lifted, so the rocks cool and are under less pressure, which causes the rock to change shape, often forming breaks. As the compression is lifted from the rocks, they are able to react to the tension on them by forming these breaks, or joints.

## Divergent boundaries

Geologic tension is also found in the tectonic regions of divergent boundaries. Here, a magma chamber forms underneath oceanic crust and causes sea-floor spreading in the creation of new oceanic crust.[3] Some of the force that pushes the two plates apart is due to ridge push force of the magma chamber.[4] Tension, however, accounts for most of the "opposite directions" pull on the plates. As the separating oceanic crust cools over time, it becomes more dense and sinks farther and farther away from the ridge axis. The cooling and sinking ocean crust causes a tensile stress that also helps drive the pulling apart of the plates at the ridge axis.

## References

1. ↑ Chrowder, Thomas and Rollin D. Salisbury Chamberlin. "Geology: Geologic Processes and their results." 2nd ed. New York: Henry Holt and Company, 1909. Print.
2. ↑ Secor, Donald T. (1965-10-01). "Role of fluid pressure in jointing" (in en). American Journal of Science 263 (8): 633–646. doi:10.2475/ajs.263.8.633. ISSN 0002-9599. https://www.ajsonline.org/content/263/8/633.
3. ↑ Watson, J. M. "Understanding Plate Motions [This Dynamic Earth, USGS]." Understanding Plate Motions. USGS Publications Warehouse, 5 May 1999. Web. <http://pubs.usgs.gov/gip/dynamic/understanding.html>
4. ↑ Weil, Arlo B. "Plate Driving Forces and Stress." Plate Driving Forces and Tectonic Stress. University of Michigan. Web. 22 Nov. 2010. <http://www.umich.edu/~gs265/tecpaper.htm>

* v
* t
* e

Structural geology

Underlying theory|

* Strain
* Stress
* Stress field
* Mohr–Coulomb theory
* Mohr's circle
* Lamé's stress ellipsoid
* Strain partitioning
* Tension
* Overburden pressure
* Deformation mechanism
* Rock mechanics

Measurement conventions|

* Strike and dip
* Rake
* Inclinometer
* Brunton compass
* Stereographic projection
* Orthographic projection

Large-Scale Tectonics|

* Plate tectonics
* Orogeny
* Structural basin
* Rift
* Extensional tectonics
* Graben
* Half-graben
* Décollement
* Obduction
* List of tectonic plate interactions
* Nappe
* Continental collision
* Convergent boundary
* Fenster
* Klippe
* Fold and thrust belt
* Foreland basin
* Accretionary wedge
* Terrane
* Mountain formation
* Fold mountains
* Fault block
* Horst
* Rift valley
* Mélange
* Thick-skinned deformation
* Thin-skinned deformation
* Thrust tectonics
* Passive margin
* Extensional tectonics
* Divergent boundary
* Back-arc basin
* Intra-arc basin
* Strike-slip tectonics
* Syneclise
* Suture
* Saddle
* Inversion
* Horst and graben
* Horse
* Pull-apart basin
* Autochthon
* Allochthon

Fracturing|

* Joint
* Exfoliation joint
* Vein
* Dike
* Columnar jointing

Faulting|

* Thrust fault
* Detachment fault
* Disturbance
* Fault mechanics
* Fault trace
* Fault scarp
* Transform fault
* Transfer zone
* Cataclastic rock
* Cataclasite

Foliation and Lineation|

* Rock microstructure
* Crenulation
* Cleavage
* Slickenside
* Pressure solution
* Stylolite
* Compaction
* Fissility
* Oblique foliation
* Tectonic phase
* Tectonite

Folding|

* Vergence
* Anticline
* Syncline
* Dome
* Monocline
* Chevron
* Homocline
* Detachment fold

Boudinage|

* Competence

Kinematic Analysis|

* 3D fold evolution
* Section restoration
* Paleostress
* Paleostress inversion

Shear zone|

* Shear
* Pure shear
* Mylonite

0.00

(0 votes)

Original source: https://en.wikipedia.org/wiki/Tension (geology). Read more

|

Retrieved from "https://handwiki.org/wiki/index.php?title=Earth:Tension_(geology)&oldid=497652"
*[v]: View this template
*[t]: Discuss this template
*[e]: Edit this template