Thrust tectonics

Last updated
Cross-section diagram of the frontal part of a thin-skinned thrust zone Compressional decollement.pdf
Cross-section diagram of the frontal part of a thin-skinned thrust zone

Thrust tectonics or contractional tectonics is concerned with the structures formed by, and the tectonic processes associated with, the shortening and thickening of the crust or lithosphere.

Contents

Deformation styles

In areas of thrust tectonics two main styles are recognized; thin-skinned deformation and thick-skinned deformation. The distinction is important as attempts to structurally restore the deformation will give very different results depending on the assumed geometry. [1]

Thin-skinned deformation

Thin-skinned deformation refers to shortening that only involves the sedimentary cover. This style is typical of many fold and thrust belts developed in the foreland of a collisional zone. This is particularly the case where a good basal decollement exists such as salt or a zone of high pore fluid pressure. [2]

Thick-skinned deformation

Thick-skinned deformation refers to shortening that involves basement rocks rather than just the overlying cover. This type of geometry is typically found in the hinterland of a collisional zone. This style may also occur in the foreland where no effective decollement surface is present or where pre-existing extensional rift structures may be inverted. [3]

Geological environments associated with thrust tectonics

Collisional zones

The most significant areas of thrust tectonics are associated with destructive plate boundaries leading to the formation of orogenic belts. The two main types are: the collision of two continental tectonic plates (for example the Arabian and Eurasian plates, which formed the Zagros fold and thrust belt) and collisions between a continent and an island arc such as that which formed Taiwan. [4]

Restraining bends on strike-slip faults

When a strike-slip fault is offset along strike such that the resulting bend in the fault hinders easy movement, e.g. a right stepping bend on a sinistral (left-lateral) fault, this will cause local shortening or transpression. Examples include the 'Big Bend' region of the San Andreas fault, [5] and parts of the Dead Sea Transform. [6]

Passive margins

Passive margins are characterised by large prisms of sedimentary material deposited since the original break-up of a continent associated with formation of a new spreading centre. This wedge of material will tend to spread under gravity and, where an effective detachment layer is present such as salt, the extensional faulting that forms at the landward side will be balanced at the front of the wedge by a series of toe-thrusts. Examples include the outboard part of the Niger delta (with an overpressured mudstone detachment) [7] and the Angola margin (with a salt detachment). [8]

See also

Related Research Articles

Orogeny The formation of mountain ranges

An orogeny is an event that leads to both structural deformation and compositional differentiation of the Earth's lithosphere at convergent plate margins. An orogen or orogenic belt develops when a continental plate crumples and is pushed upwards to form one or more mountain ranges; this involves a series of geological processes collectively called orogenesis.

Thrust fault a type of reverse fault that has a dip of 45 degrees or less

A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks.

Tectonics The processes that control the structure and properties of the Earths crust and its evolution through time

Tectonics is the process that controls the structure and properties of the Earth's crust and its evolution through time. In particular, it describes the processes of mountain building, the growth and behavior of the strong, old cores of continents known as cratons, and the ways in which the relatively rigid plates that constitute the Earth's outer shell interact with each other. Tectonics also provides a framework for understanding the earthquake and volcanic belts that directly affect much of the global population. Tectonic studies are important as guides for economic geologists searching for fossil fuels and ore deposits of metallic and nonmetallic resources. An understanding of tectonic principles is essential to geomorphologists to explain erosion patterns and other Earth surface features.

Nappe A large sheetlike body of rock that has been moved a considerable distance above a thrust fault

In geology, a nappe or thrust sheet is a large sheetlike body of rock that has been moved more than 2 km (1.2 mi) or 5 km (3.1 mi) above a thrust fault from its original position. Nappes form in compressional tectonic settings like continental collision zones or on the overriding plate in active subduction zones. Nappes form when a mass of rock is forced over another rock mass, typically on a low angle fault plane. The resulting structure may include large-scale recumbent folds, shearing along the fault plane, imbricate thrust stacks, fensters and klippe.

Sevier orogeny Mountain-building episode in North America

The Sevier orogeny was a mountain-building event that affected western North America from Canada to the north to Mexico to the south.

The Lewis Overthrust is a geologic thrust fault structure of the Rocky Mountains found within the bordering national parks of Glacier in Montana, United States and Waterton Lakes in Alberta, Canada. The structure was created due to the collision of tectonic plates about 170 million years ago that drove a several mile thick wedge of rock 50 mi (80 km) eastwards, causing it to overlie softer Cretaceous age rock that is 400 to 500 million years younger.

Foreland basin A structural basin that develops adjacent and parallel to a mountain belt

A foreland basin is a structural basin that develops adjacent and parallel to a mountain belt. Foreland basins form because the immense mass created by crustal thickening associated with the evolution of a mountain belt causes the lithosphere to bend, by a process known as lithospheric flexure. The width and depth of the foreland basin is determined by the flexural rigidity of the underlying lithosphere, and the characteristics of the mountain belt. The foreland basin receives sediment that is eroded off the adjacent mountain belt, filling with thick sedimentary successions that thin away from the mountain belt. Foreland basins represent an endmember basin type, the other being rift basins. Space for sediments is provided by loading and downflexure to form foreland basins, in contrast to rift basins, where accommodation space is generated by lithospheric extension.

Décollement

Décollement is a gliding plane between two rock masses, also known as a basal detachment fault. Décollements are a deformational structure, resulting in independent styles of deformation in the rocks above and below the fault. They are associated with both compressional settings and extensional settings.

Transpression

In geology, transpression is a type of 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. It is generally very unlikely that a deforming body will experience "pure" shortening or "pure" strike-slip. The relative amounts of shortening and strike-slip can be expressed in the convergence angle alpha which ranges from zero to 90 degrees. During shortening, unless material is lost, transpression produces vertical thickening in the crust. Transpression that occurs on a regional scale along plate boundaries is characterized by oblique convergence. More locally, transpression occurs within restraining bends in strike-slip fault zones.

Strike-slip tectonics is concerned with the structures formed by, and the tectonic processes associated with, zones of lateral displacement within the Earth's crust or lithosphere.

Salt tectonics study of salt-controlled structures (like salt domes), mechanisms, and tectonic deformation involving salt or other evaporates

Salt tectonics, or halokinesis, or halotectonics, is concerned with the geometries and processes associated with the presence of significant thicknesses of evaporites containing rock salt within a stratigraphic sequence of rocks. This is due both to the low density of salt, which does not increase with burial, and its low strength.

Inversion (geology) Relative uplift of a sedimentary basin or similar structure as a result of crustal shortening

In structural geology inversion or basin inversion relates to the relative uplift of a sedimentary basin or similar structure as a result of crustal shortening. This normally excludes uplift developed in the footwalls of later extensional faults, or uplift caused by mantle plumes. "Inversion" can also refer to individual faults, where an extensional fault is reactivated in the opposite direction to its original movement.

Accretionary wedge The sediments accreted onto the non-subducting tectonic plate at a convergent plate boundary

An accretionary wedge or accretionary prism forms from sediments accreted onto the non-subducting tectonic plate at a convergent plate boundary. Most of the material in the accretionary wedge consists of marine sediments scraped off from the downgoing slab of oceanic crust, but in some cases the wedge includes the erosional products of volcanic island arcs formed on the overriding plate.

Fold and thrust belt

A fold and thrust belt is a series of mountainous foothills adjacent to an orogenic belt, which forms due to contractional tectonics. Fold and thrust belts commonly form in the forelands adjacent to major orogens as deformation propagates outwards. Fold and thrust belts usually comprise both folds and thrust faults, commonly interrelated. They are commonly also known as thrust-and-fold belts, or simply thrust-fold belts.

Fold mountains Mountains formed by compressive crumpling of the layers of rock

Fold mountains are mountains that form mainly by the effects of folding on layers within the upper part of the Earth's crust. Before either plate tectonic theory developed, or the internal architecture of thrust belts became well understood, the term was used for most mountain belts, such as the Himalayas. The term is still fairly common in physical geography literature but has otherwise generally fallen out of use except as described below. The forces responsible for formation of fold mountains are called orogenic movements. The term orogenic has derived from a Greek word meaning mountain building. These forces act at tangent to the surface of the earth and are primarily a result of plate tectonics.

Thin-skinned deformation

Thin-skinned deformation is a style of deformation in plate tectonics at a convergent boundary which occurs with shallow thrust faults that only involves cover rocks, and not deeper basement rocks.

Zagros fold and thrust belt zone of deformed crustal rocks, formed in the foreland of the collision between the Arabian Plate and the Eurasian Plate

The Zagros fold and thrust belt is an approximately 1,800-kilometre (1,100 mi) long zone of deformed crustal rocks, formed in the foreland of the collision between the Arabian Plate and the Eurasian Plate. It is host to one of the world's largest petroleum provinces, containing about 49% of the established hydrocarbon reserves in fold and thrust belts and about 7% of all reserves globally.

Tectonic subsidence is the sinking of the Earth's crust on a large scale, relative to crustal-scale features or the geoid. The movement of crustal plates and accommodation spaces created by faulting create subsidence on a large scale in a variety of environments, including passive margins, aulacogens, fore-arc basins, foreland basins, intercontinental basins and pull-apart basins. Three mechanisms are common in the tectonic environments in which subsidence occurs: extension, cooling and loading.

Tectonics of the Tian Shan

The Tian Shan is a mountain range in central Asia that extends through western China, Kazakhstan, and Kyrgyzstan. The Tian Shan is 2,800 kilometres (1,700 mi) long, and up to 7,400 metres (24,300 ft) high. Throughout the Tian Shan there are several intermontane basins separated by high ranges. Plate tectonic theory makes the assumption that deformation is concentrated along plate boundaries. However, active deformation is observed in the Tian Shan, far from plate boundaries. This apparent contradiction of plate tectonic theory makes the Tian Shan a key place to study the dynamics of intracontinental deformation.

Thick-skinned deformation is a geological term which refers to crustal shortening that involves basement rocks and deep-seated faults as opposed to only the upper units of cover rocks above the basement which is known as thin-skinned deformation. While thin-skinned deformation is common in many different localities, thick-skinned deformation requires much more strain to occur and is a rarer type of deformation.

References

  1. Shiner, P (2004). "Thin-skinned versus thick-skinned structural models for Apulian carbonate reservoirs: constraints from the Val d'Agri Fields, S Apennines, Italy". Marine and Petroleum Geology . 21 (7): 805. doi:10.1016/j.marpetgeo.2003.11.020.
  2. Hatcher, R.D. 2007. Confirmation of Thin-skinned Thrust Faulting in Foreland Fold-Thrust Belts and Its Impact on Hydrocarbon Exploration: Bally, Gordy, and Stewart, Bulletin of Canadian Petroleum Geology, 1966. First in the AAPG History of Petroleum Geology Series on Papers Having a Major Impact on Petroleum Geology: A contribution of the AAPG History of Petroleum Geology Committee
  3. Butler, R. W. H., S. Mazzoli, S. Corrado, M. De Donatis, D. Di Bucci, R. Gambini, G. Naso, C. Nicolai, D. Scrocca, P. Shiner, and V. Zucconi, 2004, Applying thick-skinned tectonic models to the Apennine thrust belt of Italy—Limitations and implications, in K. R. McClay, ed., Thrust tectonics and hydrocarbon systems: AAPG Memoir 82, p. 647– 667.
  4. Timothy Briggs Byrne; Char-Shine Liu (2002). Geology and Geophysics of an Arc-continent Collision, Taiwan. Special Paper 358. Geological Society of America. ISBN   978-0-8137-2358-7.
  5. Rust, D. 1998. Contractional and extensional structures in the transpressive ‘Big Bend’ of the San Andreas fault, southern California. Geological Society, London, Special Publications; 135; p. 119-126
  6. Gomez, F., Nemer, T., Tabet, C., Meghraoui, M. & Barazangi, M. 2007. Strain partitioning of active transpression within the Lebanese restraining bend of the Dead Sea Fault (Lebanon and SW Syria). Geological Society, London, Special Publications; 290; 285–303
  7. Bilotti, F. & Shaw, J.H. 2005. Deep-water Niger Delta fold and thrust belt modeled as a critical taper wedge: The influence of elevated basal fluid pressure on structural styles. AAPG Bulletin; 89; 11; 1475–1491
  8. Marton, G, & Schoenborn, G. 2008. Salt Tectonics of the Continent-Ocean Transition, Deep-Water Angola. MAPG conference abstract