Fault block

Last updated
The Hanging Hills of Connecticut (Metacomet Ridge range); upfaulting (horst) visible from right to left. Hanging Hills.jpg
The Hanging Hills of Connecticut (Metacomet Ridge range); upfaulting (horst) visible from right to left.
Horizontal movement between blocks along a strike-slip fault Strikeslip-fault.gif
Horizontal movement between blocks along a strike-slip fault

Fault blocks are very large blocks of rock, sometimes hundreds of kilometres in extent, created by tectonic and localized stresses in Earth's crust. Large areas of bedrock are broken up into blocks by faults. Blocks are characterized by relatively uniform lithology. The largest of these fault blocks are called crustal blocks. Large crustal blocks broken off from tectonic plates are called terranes. [1] Those terranes which are the full thickness of the lithosphere are called microplates. Continent-sized blocks are called variously microcontinents, continental ribbons, H-blocks, extensional allochthons and outer highs. [2]

Contents

Because most stresses relate to the tectonic activity of moving plates, most motion between blocks is horizontal, that is parallel to the Earth's crust by strike-slip faults. However vertical movement of blocks produces much more dramatic results. Landforms (mountains, hills, ridges, lakes, valleys, etc.) are sometimes formed when the faults have a large vertical displacement. Adjacent raised blocks (horsts) and down-dropped blocks (grabens) can form high escarpments. Often the movement of these blocks is accompanied by tilting, due to compaction or stretching of the crust at that point.

Fault-block mountains

Lifted fault-block geology Fault-Horst-Graben.svg
Lifted fault-block geology
Tilted fault-block formation in the Teton Range Teton fault block.jpg
Tilted fault-block formation in the Teton Range
Belasitsa, Rila - Rhodope massif, Bulgaria Rhodopen 14.png
Belasitsa, Rila - Rhodope massif, Bulgaria

Fault-block mountains often result from rifting, an indicator of extensional tectonics. These can be small or form extensive rift valley systems, such as the East African Rift zone. Death Valley in California is a smaller example. There are two main types of block mountains; uplifted blocks between two faults and tilted blocks mainly controlled by one fault.

Lifted type block mountains have two steep sides exposing both sides scarps, leading to the horst and graben terrain seen in various parts of Europe including the Upper Rhine valley, a graben between two horsts - the Vosges mountains (in France) and the Black Forest (in Germany), and also the Rila - Rhodope Massif in Bulgaria, Southeast Europe, including the well defined horsts of Belasitsa (linear horst), Rila mountain (vaulted domed shaped horst) and Pirin mountain - a horst forming a massive anticline situated between the complex graben valleys of Struma and that of Mesta. [3] [4] [5]

Tilted type block mountains have one gently sloping side and one steep side with an exposed scarp, and are common in the Basin and Range region of the western United States.

Example of graben is the basin of the Narmada River in India, between the Vindhya and Satpura horsts.

See also

Notes

  1. A crustal block may or may not also comprise a tectonostratigraphic terrane that has a specific geologic definition. Bulter, Robert F. (1992) "Chapter 11: Applications to Regional Tectonics" Paleomagnetism: Magnetic Domains to Geologic Terranes Blackwell, pp. 205223, page 205, archived here by Internet Archive on 26 October 2004
  2. Péron-Pinvidic1, Gwenn and Manatschal, Gianreto (2010). "From microcontinents to extensional allochthons: witnesses of how continents rift and break apart?". Petroleum Geoscience. 16 (3): 189–197. doi:10.1144/1354-079309-903. S2CID   131142997.CS1 maint: multiple names: authors list (link) page 189
  3. Geographic Dictionary of Bulgaria 1980 , p. 368
  4. Dimitrova & al 2004 , p. 53
  5. Donchev & Karakashev 2004 , pp. 128–129

Related Research Articles

Basin and Range Province Geologic province extending through much of the western United States and Mexico

The Basin and Range Province is a vast physiographic region covering much of the inland Western United States and northwestern Mexico. It is defined by unique basin and range topography, characterized by abrupt changes in elevation, alternating between narrow faulted mountain chains and flat arid valleys or basins. The physiography of the province is the result of tectonic extension that began around 17 million years ago in the early Miocene epoch.

Graben Depressed block of planetary crust bordered by parallel faults

In geology, a graben is a depressed block of the crust of a planet bordered by parallel faults.

Horst (geology) A raised fault block bounded by normal faults

In physical geography and geology, a horst is a raised fault block bounded by normal faults. A horst is a raised block of the Earth's crust that has lifted, or has remained stationary, while the land on either side (graben) has subsided. The word Horst in Dutch and German means heap – cognate with English "hurst".

Rift A linear zone where the Earths crust is being pulled apart, and is an example of extensional tectonics

In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics.

Mountain formation The geological processes that underlie the formation of mountains

Mountain formation refers to the geological processes that underlie the formation of mountains. These processes are associated with large-scale movements of the Earth's crust. Folding, faulting, volcanic activity, igneous intrusion and metamorphism can all be parts of the orogenic process of mountain building. The formation of mountains is not necessarily related to the geological structures found on it.

Slave Craton An Archaean craton in the north-western Canadian Shield, in Northwest Territories and Nunavut

The Slave Craton is an Archaean craton in the north-western Canadian Shield, in Northwest Territories and Nunavut. The Slave Craton includes the 4.03 Ga-old Acasta Gneiss which is one of the oldest dated rocks on Earth. Covering about 300,000 km2 (120,000 sq mi), it is a relatively small but well-exposed craton dominated by ~2.73–2.63 Ga greenstones and turbidite sequences and ~2.72–2.58 Ga plutonic rocks, with large parts of the craton underlain by older gneiss and granitoid units. The Slave Craton is one of the blocks that compose the Precambrian core of North America, also known as the palaeocontinent Laurentia.

Extensional tectonics is concerned with the structures formed by, and the tectonic processes associated with, the stretching of a planetary body's crust or lithosphere.

Basin and range topography

Basin and range topography is an alternating landscape of parallel mountain ranges and valleys. It is a result of crustal extension/stretching of the lithosphere due to mantle upwelling, gravitational collapse, crustal thickening, or relaxation of confining stresses. Crustal extension causes the thinning and deformation of the upper crust in an orientation perpendicular to the direction of extension. As the plates pull apart, they thin allowing the hot mantle to rise close to the surface. When the crust is extended it fractures along a fault plane, creating a series of long parallel normal faults. Between these normal faults are blocks, which subside, get uplifted or tilted. This is known as block faulting. Basins are formed due to subsidence of a block, while the blocks adjacent to the subsidence gets uplifted creating ranges. Normal faults are on both sides of the blocks; creating alternating elevated or subsided blocks, otherwise known as horst and graben. Basins and ranges can also be formed by blocks that are tilted causing one side to subside while the other side gets uplifted. These only have one side with a normal fault, this is known as tilted block faulting. Extension causes the plate to stretch, fracture and thin. Mountains rise and valleys drop, over a long period of time creating what we see as basin and range topography.

Geology of Norway

The geology of Norway encompasses the history of earth that can be interpreted by rock types found in Norway, and the associated sedimentological history of soils and rock types.

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.

This is a list of articles related to plate tectonics and tectonic plates.

The geological structure of Great Britain is complex, resulting as it does from a long and varied geological history spanning more than two billion years. This piece of the Earth's crust has experienced several episodes of mountain building or 'orogenies', each of which has added further complexity to the picture.

Geology of Russia Overview of the geology of Russia

The geology of Russia, the world's largest country, which extends over much of northern Eurasia, consists of several stable cratons and sedimentary platforms bounded by orogenic (mountain) belts.

Geology of Massachusetts

The geology of Massachusetts includes numerous units of volcanic, intrusive igneous, metamorphic and sedimentary rocks formed within the last 1.2 billion years. The oldest formations are gneiss rocks in the Berkshires, which were metamorphosed from older rocks during the Proterozoic Grenville orogeny as the proto-North American continent Laurentia collided against proto-South America. Throughout the Paleozoic, overlapping the rapid diversification of multi-cellular life, a series of six island arcs collided with the Laurentian continental margin. Also termed continental terranes, these sections of continental rock typically formed offshore or onshore of the proto-African continent Gondwana and in many cases had experienced volcanic events and faulting before joining the Laurentian continent. These sequential collisions metamorphosed new rocks from sediments, created uplands and faults and resulted in widespread volcanic activity. Simultaneously, the collisions raised the Appalachian Mountains to the height of the current day Himalayas.

Half-graben

A half-graben is a geological structure bounded by a fault along one side of its boundaries, unlike a full graben where a depressed block of land is bordered by parallel faults.

Tilted block faulting

Tilted block faulting, also called rotational block faulting, is a mode of structural evolution in extensional tectonic events, a result of tectonic plates stretching apart. When the upper lithospheric crust experiences extensional pressures, the brittle crust fractures, creating detachment faults. These normal faults express themselves on a regional scale; upper crust fractures into tilted fault blocks, and ductile lower crust ascends. This results in uplift, cooling, and exhumation of ductily deformed deeper crust. The large unit of tilted blocks and associated crust can help form an integral part of metamorphic core complexes and can occur on both continental and oceanic crust.

Tectonic evolution of Patagonia

Patagonia comprises the southernmost region of South America, portions of which lie either side of the Chile–Argentina border. It has traditionally been described as the region south of the Rio Colorado, although the physiographic border has more recently been moved southward to the Huincul fault. The region's geologic border to the north is composed of the Rio de la Plata craton and several accreted terranes comprising the La Pampa province. The underlying basement rocks of the Patagonian region can be subdivided into two large massifs: the North Patagonian Massif and the Deseado Massif. These massifs are surrounded by sedimentary basins formed in the Mesozoic that underwent subsequent deformation during the Andean orogeny. Patagonia is known for their vast earthquakes and the damage.

The geology of Nevada began to form in the Proterozoic at the western margin of North America. Terranes accreted to the continent as a marine environment dominated the area through the Paleozoic and Mesozoic periods. Intense volcanism, the horst and graben landscape of the Basin and Range Province originating from the Farallon Plate, and both glaciers and valley lakes have played important roles in the region throughout the past 66 million years.

The geology of Mongolia is made up a complicated array of microcontinents and island chains accreted together over the past half billion years, producing varied terrain and tectonics.

References