Thrust tectonics

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Cross-section diagram of the frontal part of a thin-skinned thrust zone Compressional decollement.svg
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. It is one of the three main types of tectonic regime, the others being extensional tectonics and strike-slip tectonics. These match the three types of plate boundary, convergent (thrust), divergent (extensional) and transform (strike-slip). There are two main types of thrust tectonics, thin-skinned and thick-skinned, depending on whether or not basement rocks are involved in the deformation. The principle geological environments where thrust tectonics is observed are zones of continental collision, restraining bends on strike-slip faults and as part of detached fault systems on some passive margins. [1]


Deformation styles

In areas of thrust tectonics, two main processes 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. [2]

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. [3]

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. [4]

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. [5]

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, [6] and parts of the Dead Sea Transform. [7]

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) [8] and the Angola margin (with a salt detachment). [9]

Related Research Articles

<span class="mw-page-title-main">Orogeny</span> The formation of mountain ranges

Orogeny is a mountain-building process that takes place at a convergent plate margin when plate motion compresses the margin. An orogenic belt or orogen develops as the compressed plate crumples and is uplifted to form one or more mountain ranges. This involves a series of geological processes collectively called orogenesis. These include both structural deformation of existing continental crust and the creation of new continental crust through volcanism. Magma rising in the orogen carries less dense material upwards while leaving more dense material behind, resulting in compositional differentiation of Earth's lithosphere. A synorogenic process or event is one that occurs during an orogeny.

<span class="mw-page-title-main">Thrust fault</span> 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.

<span class="mw-page-title-main">Tectonics</span> Process of evolution of the Earths crust

Tectonics are the processes that result in the structure and properties of the Earth's crust and its evolution through time.

<span class="mw-page-title-main">Caledonian orogeny</span> Mountain building event caused by the collision of Laurentia, Baltica and Avalonia

The Caledonian orogeny was a mountain-building cycle recorded in the northern parts of the British Isles, the Scandinavian Caledonides, Svalbard, eastern Greenland and parts of north-central Europe. The Caledonian orogeny encompasses events that occurred from the Ordovician to Early Devonian, roughly 490–390 million years ago (Ma). It was caused by the closure of the Iapetus Ocean when the Laurentia and Baltica continents and the Avalonia microcontinent collided.

<span class="mw-page-title-main">Nappe</span> 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 klippes.

<span class="mw-page-title-main">Sevier orogeny</span> Mountain-building episode in North America

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

<span class="mw-page-title-main">Shear (geology)</span> Response of rock to deformation

In geology, shear is the response of a rock to deformation usually by compressive stress and forms particular textures. Shear can be homogeneous or non-homogeneous, and may be pure shear or simple shear. Study of geological shear is related to the study of structural geology, rock microstructure or rock texture and fault mechanics.

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 59-75 million years ago that drove a several mile thick wedge of Precambrian rock 50 mi (80 km) eastwards, causing it to overlie softer Cretaceous age rock that is 1300 to 1400 million years younger.

<span class="mw-page-title-main">Foreland basin</span> 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.

<span class="mw-page-title-main">Décollement</span> Geological feature

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.

<span class="mw-page-title-main">Transpression</span> Type of strike-slip deformation

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 or wrench tectonics is a type of tectonics that is dominated by lateral (horizontal) movements within the Earth's crust. Where a zone of strike-slip tectonics forms the boundary between two tectonic plates, this is known as a transform or conservative plate boundary. Areas of strike-slip tectonics are characterised by particular deformation styles including: stepovers, Riedel shears, flower structures and strike-slip duplexes. Where the displacement along a zone of strike-slip deviates from parallelism with the zone itself, the style becomes either transpressional or transtensional 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 zones of continental collision.

<span class="mw-page-title-main">Inversion (geology)</span> 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.

<span class="mw-page-title-main">Accretionary wedge</span> 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.

<span class="mw-page-title-main">Fold mountains</span> Mountains formed by compressive crumpling of the layers of rock

Fold mountains are formed by the effects of folding on layers within the upper part of the Earth's crust. Before the development of the theory of plate tectonics and before the internal architecture of thrust belts became well understood, the term was used to describe most mountain belts but has otherwise fallen out of use.

<span class="mw-page-title-main">Thin-skinned deformation</span>

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.

<span class="mw-page-title-main">Zagros fold and thrust belt</span> Geologic zone

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 (FTBs) and about 7% of all reserves globally.

<span class="mw-page-title-main">Tectonics of the Tian Shan</span>

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.

<span class="mw-page-title-main">Geology of Myanmar</span>

The geology of Myanmar is shaped by dramatic, ongoing tectonic processes controlled by shifting tectonic components as the Indian plate slides northwards and towards Southeast Asia. Myanmar spans across parts of three tectonic plates separated by north-trending faults. To the west, a highly oblique subduction zone separates the offshore Indian plate from the Burma microplate, which underlies most of the country. In the center-east of Myanmar, a right lateral strike slip fault extends from south to north across more than 1,000 km (620 mi). These tectonic zones are responsible for large earthquakes in the region. The India-Eurasia plate collision which initiated in the Eocene provides the last geological pieces of Myanmar, and thus Myanmar preserves a more extensive Cenozoic geological record as compared to records of the Mesozoic and Paleozoic eras. Myanmar is physiographically divided into three regions: the Indo-Burman Range, Myanmar Central Belt and the Shan Plateau; these all display an arcuate shape bulging westwards. The varying regional tectonic settings of Myanmar not only give rise to disparate regional features, but they also foster the formation of petroleum basins and a diverse mix of mineral resources.


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