Lineament

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See also Line (geometry)

A lineament is a linear feature in a landscape which is an expression of an underlying geological structure such as a fault. Typically a lineament will appear as a fault-aligned valley, a series of fault or fold-aligned hills, a straight coastline or indeed a combination of these features. Fracture zones, shear zones and igneous intrusions such as dykes can also be expressed as geomorphic lineaments.

Landscape visible features of an area of land

A landscape is the visible features of an area of land, its landforms, and how they integrate with natural or man-made features. A landscape includes the physical elements of geophysically defined landforms such as (ice-capped) mountains, hills, water bodies such as rivers, lakes, ponds and the sea, living elements of land cover including indigenous vegetation, human elements including different forms of land use, buildings, and structures, and transitory elements such as lighting and weather conditions. Combining both their physical origins and the cultural overlay of human presence, often created over millennia, landscapes reflect a living synthesis of people and place that is vital to local and national identity.

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 information about the history of deformation (strain) in the rocks, and ultimately, to understand the stress field that resulted in the observed strain and geometries. This understanding of the dynamics of the stress field can be linked to important events in the geologic past; a common goal is to understand the structural evolution of a particular area with respect to regionally widespread patterns of rock deformation due to plate tectonics.

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 movement. Large faults within the Earth's crust result from the action of plate tectonic forces, with the largest forming the boundaries between the plates, such as subduction zones or transform faults. Energy release associated with rapid movement on active faults is the cause of most earthquakes.

Lineaments are often apparent in geological or topographic maps and can appear obvious on aerial or satellite photographs. There are for example, several instances within Great Britain. In Scotland the Great Glen Fault and Highland Boundary Fault give rise to lineaments as does the Malvern Line in western England and the Neath Disturbance in South Wales.

Great Britain island in the North Atlantic off the north-west coast of continental Europe

Great Britain is an island in the North Atlantic Ocean off the northwest coast of continental Europe. With an area of 209,331 km2 (80,823 sq mi), it is the largest of the British Isles, the largest European island, and the ninth-largest island in the world. In 2011, Great Britain had a population of about 61 million people, making it the world's third-most populous island after Java in Indonesia and Honshu in Japan. The island of Ireland is situated to the west of Great Britain, and together these islands, along with over 1,000 smaller surrounding islands, form the British Isles archipelago.

Scotland Country in Europe, part of the United Kingdom

Scotland is a country that is part of the United Kingdom. Sharing a border with England to the southeast, Scotland is otherwise surrounded by the Atlantic Ocean to the north and west, by the North Sea to the northeast and by the Irish Sea to the south. In addition to the mainland, situated on the northern third of the island of Great Britain, Scotland has over 790 islands, including the Northern Isles and the Hebrides.

Great Glen Fault Geological fault in Scotland

The Great Glen Fault is a long strike-slip fault that runs through its namesake the Great Glen in Scotland.

The term 'megalineament' has been used to describe such features on a continental scale. The trace of the San Andreas Fault might be considered an example. [1] The Trans Brazilian Lineament and the Trans-Saharan Belt, taken together, form perhaps the longest coherent shear zone on the Earth, extending for about 4,000 km. [2]

San Andreas Fault A continental transform fault through California between the Pacific Plate and the North American Plate

The San Andreas Fault is a continental transform fault that extends roughly 1,200 kilometers (750 mi) through California. It forms the tectonic boundary between the Pacific Plate and the North American Plate, and its motion is right-lateral strike-slip (horizontal). The fault divides into three segments, each with different characteristics and a different degree of earthquake risk. The slip rate along the fault ranges from 20 to 35 mm /yr.

The Trans Brazilian Lineament (TBL), or Transbrasiliano Lineament, is a major shear zone that developed in the Precambrian period, and that has been reactivated several times since then, mostly recently during the Mesozoic. Movement along the shear zone helps explain how the South American continent could have fitted tightly to the African continent before the breakup of Gondwana.

Lineaments have also been identified on other planets and their moons. Their origins may be radically different from those of terrestrial lineaments due to the differing tectonic processes involved.

Planet Class of astronomical body directly orbiting a star or stellar remnant

A planet is an astronomical body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.

Natural satellite astronomical body that orbits a planet

A natural satellite or moon is, in the most common usage, an astronomical body that orbits a planet or minor planet.

Related Research Articles

Shear zone structural discontinuity surface in the Earths crust and upper mantle

A shear zone is a very important structural discontinuity surface in the Earth's crust and upper mantle. It forms as a response to inhomogeneous deformation partitioning strain into planar or curviplanar high-strain zones. Intervening (crustal) blocks stay relatively unaffected by the deformation. Due to the shearing motion of the surrounding more rigid medium, a rotational, non co-axial component can be induced in the shear zone. Because the discontinuity surface usually passes through a wide depth-range, a great variety of different rock types with their characteristic structures are produced.

In structural geology, a suture is a joining together along a major fault zone, of separate terranes, tectonic units that have different plate tectonic, metamorphic and paleogeographic histories. The suture is often represented on the surface by an orogen or mountain range. The term was borrowed from surgery where it describes the sewing together of two pieces of tissue, but the sutures of the skull, where separate plates of bone have fused, may be a better metaphor.

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.

Walker Lane geologic trough

The Walker Lane is a geologic trough roughly aligned with the California/Nevada border southward to where Death Valley intersects the Garlock Fault, a major left lateral, or sinistral, strike-slip fault. The north-northwest end of the Walker Lane is between Pyramid Lake in Nevada and California's Lassen Peak where the Honey Lake Fault Zone meets the transverse tectonic zone forming the southern boundary of the Modoc Plateau and Columbia Plateau provinces. The Walker Lane takes up 15 to 25 percent of the boundary motion between the Pacific Plate and the North American Plate, the other 75 percent being taken up by the San Andreas Fault system to the west. The Walker Lane may represent an incipient major transform fault zone which could replace the San Andreas as the plate boundary in the future.

Olympic-Wallowa Lineament

The Olympic-Wallowa lineament (OWL) – first reported by cartographer Erwin Raisz in 1945 on a relief map of the continental United States – is a physiographic feature of unknown origin in the state of Washington running approximately from the town of Port Angeles, on the Olympic Peninsula to the Wallowa Mountains of eastern Oregon.

The Philippine Fault System is a major inter-related system of faults throughout the whole of the Philippine Archipelago, primarily caused by tectonic forces compressing the Philippines into what geophysicists call the Philippine Mobile Belt.

Brothers Fault Zone

The Brothers Fault Zone (BFZ) is the most notable of a set of northwest-trending fault zones including the Eugene–Denio, McLoughlin, and Vale zones that dominate the geological structure of most of Oregon. These are also representative of a regional pattern of generally northwest-striking geological features ranging from Walker Lane on the California–Nevada border to the Olympic–Wallowa Lineament in Washington; these are generally associated with the regional extension and faulting of the Basin and Range Province, of which the BFZ is considered the northern boundary.

Puget Sound faults

The Puget Sound faults under the heavily populated Puget Sound region of Washington state form a regional complex of interrelated seismogenic (earthquake-causing) geologic faults. These include the:

Central African Shear Zone

The Central African Shear Zone (CASZ) is a wrench fault system extending in an ENE direction from the Gulf of Guinea through Cameroon into Sudan. The structure is not well understood. As of 2008, there was still no general agreement about how the individual shears along the lineament link up.

The Pharusian Ocean is an ancient ocean that existed from 800 to 635 million years ago, between the break-up of the Rodinia supercontinent and the start of formation of the Gondwana supercontinent.

The Kandi fault zone is a southern extension of the Hoggar fault zone in West Africa, with splays in Benin, Togo and southeastern Ghana. It lies at the southern end of the Trans Saharan belt, a lineament that extends in a southwest direction from Algeria to Benin. The Kandi fault zone is identified with the Sobral fault in northeastern Brazil, considered to be the northern section of the Trans Brazilian Lineament.

The Sobral fault is a major fault in the Borborema geological province of northeastern Brazil, a part of the Transbrasiliano lineament. It is commonly correlated with the Kandi fault in Benin, east of the West African craton. The fault lies in the northwest of Ceará state. It appears to have formed late in the orogeny when the West African craton engaged with the Congo craton, and to have allowed significant dextral strike-slip movement. It was reactivated when South America was breaking away from Africa. In this later phase, a sinistral shear movement of about 100 km seems to have taken place during and after the break-up.

The Foumban Shear Zone, or Central Cameroon Shear Zone (CCSZ), is a fault zone in Cameroon that has been correlated with the Pernambuco fault in northeastern Brazil, which splays from the Trans-Brazilian Lineament. It is part of the Central African Shear Zone (CASZ) and dates to at least 640 million years ago. The zone was rejuvenated several times, usually with a dextral movement, before and during the opening of the South Atlantic in the Cretaceous period.

The Pernambuco Fault or Pernambuco Shear Zone in northeastern Brazil is a fault radiating from the Trans Brazilian Lineament eastwards to the coast, a major geological feature.

Aswa Dislocation

The Aswa Dislocation, also called the Aswa mylonite belt, Aswa Lineament or Aswa Shear Zone is a north-west trending ductile shear zone that runs to the east of Lake Victoria in East Africa.

The Central Wales Lineament is a north-south aligned zone of geological faults and folds which runs for scores of miles through Wales and which gives rise to a number of landscape features. The lineament lies along the axis of the Central Wales Syncline, both following the generally northeast-southwest Caledonide trend though its central section is more north-south aligned.

Yakima Fold Belt

The Yakima Fold Belt of south-central Washington, also called the Yakima fold-and-thrust belt, is an area of topographical folds raised by tectonic compression. It is a 14,000 km2 (5,400 sq mi) structural-tectonic sub province of the western Columbia Plateau Province resulting from complex and poorly understood regional tectonics. The folds are associated with geological faults whose seismic risk is of particular concern to the nuclear facilities at the Hanford Nuclear Reservation and major dams on the Columbia and Snake Rivers.

Romeral Fault System

The Romeral Fault System is a megaregional system of major parallel and anastomosing faults in the Central Ranges of the Colombian Andes and the Cauca, Amagá, and Sinú-San Jacinto Basins. The system spans across ten departments of Colombia, from northeast to south Bolívar, Sucre, Córdoba, Antioquia, Caldas, Risaralda, Quindío, Valle del Cauca, Cauca and Nariño. The fault zone extends into Ecuador where it is known as the Peltetec Fault System. The in detail described part of the Romeral Fault System south of Córdoba has a total length of 697.4 kilometres (433.3 mi) with a cumulative length of 1,787.9 kilometres (1,110.9 mi) and runs along an average north to south strike of 017.6 ± 16, cross-cutting the central-western portion of Colombia.

References

  1. Whitten & Brooks, The Penguin Dictionary of Geology 1972
  2. Attoh, K.; Brown, L. D. (2008). "The Neoproterozoic Trans-Saharan/Trans-Brasiliano shear zones: Suggested Tibetan Analogs". American Geophysical Union. American Geophysical Union. 51. Bibcode:2008AGUSM.S51A..04A.