Related Research Articles
Plate tectonics is the scientific theory that Earth's lithosphere comprises a number of large tectonic plates, which have been slowly moving since 3–4 billion years ago. The model builds on the concept of continental drift, an idea developed during the first decades of the 20th century. Plate tectonics came to be accepted by geoscientists after seafloor spreading was validated in the mid-to-late 1960s. The processes that result in plates and shape Earth's crust are called tectonics. Tectonic plates also occur in other planets and moons.
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.
A lithosphere is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust and the lithospheric mantle, the topmost portion of the upper mantle that behaves elastically on time scales of up to thousands of years or more. The crust and upper mantle are distinguished on the basis of chemistry and mineralogy.
The asthenosphere is the mechanically weak and ductile region of the upper mantle of Earth. It lies below the lithosphere, at a depth between c. 80 and 200 km below the surface, and extends as deep as 700 km (430 mi). However, the lower boundary of the asthenosphere is not well defined.
Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second plate, the heavier plate dives beneath the other and sinks into the mantle. A region where this process occurs is known as a subduction zone, and its surface expression is known as an arc-trench complex. The process of subduction has created most of the Earth's continental crust. Rates of subduction are typically measured in centimeters per year, with rates of convergence as high as 11 cm/year.
Obduction is a geological process whereby denser oceanic crust is scraped off a descending ocean plate at a convergent plate boundary and thrust on top of an adjacent plate. When oceanic and continental plates converge, normally the denser oceanic crust sinks under the continental crust in the process of subduction. Obduction, which is less common, normally occurs in plate collisions at orogenic belts or back-arc basins.
Isostasy or isostatic equilibrium is the state of gravitational equilibrium between Earth's crust and mantle such that the crust "floats" at an elevation that depends on its thickness and density. This concept is invoked to explain how different topographic heights can exist at Earth's surface. Although originally defined in terms of continental crust and mantle, it has subsequently been interpreted in terms of lithosphere and asthenosphere, particularly with respect to oceanic island volcanoes, such as the Hawaiian Islands.
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.
A convergent boundary is an area on Earth where two or more lithospheric plates collide. One plate eventually slides beneath the other, a process known as subduction. The subduction zone can be defined by a plane where many earthquakes occur, called the Wadati–Benioff zone. These collisions happen on scales of millions to tens of millions of years and can lead to volcanism, earthquakes, orogenesis, destruction of lithosphere, and deformation. Convergent boundaries occur between oceanic-oceanic lithosphere, oceanic-continental lithosphere, and continental-continental lithosphere. The geologic features related to convergent boundaries vary depending on crust types.
Island arcs are long chains of active volcanoes with intense seismic activity found along convergent tectonic plate boundaries. Most island arcs originate on oceanic crust and have resulted from the descent of the lithosphere into the mantle along the subduction zone. They are the principal way by which continental growth is achieved.
Earth's mantle is a layer of silicate rock between the crust and the outer core. It has a mass of 4.01×1024 kg (8.84×1024 lb) and makes up 67% of the mass of Earth. It has a thickness of 2,900 kilometers (1,800 mi) making up about 46% of Earth's radius and 84% of Earth's volume. It is predominantly solid but, on geologic time scales, it behaves as a viscous fluid, sometimes described as having the consistency of caramel. Partial melting of the mantle at mid-ocean ridges produces oceanic crust, and partial melting of the mantle at subduction zones produces continental crust.
The outer trench swell, outer trench high, or outer rise is a subtle ridge on the seafloor near an oceanic trench, where a descending plate begins to flex and fault in preparation for its descent into the mantle at a subduction zone. The lithosphere is bent upwards by plate stresses, and is not in isostatic equilibrium.
The Farallon Trench was a subduction related tectonic formation located off the coast of the western California continental margin during the late to mid Cenozoic era, around 50 miles southeast of modern-day Monterey Bay. The time duration of subduction began from around 165 Ma when the Farallon Plate replaced the Mezcalera promontory, until the San Andreas Fault straightening around 35 Ma. As data accumulated over time, a common view developed that one large oceanic plate, the Farallon Plate, acted as a conveyor belt, conveying accreted terranes onto the North American west coast. As the continent overran the subducting Farallon Plate, the denser plate became subducted into the mantle below the continent. When the plates converged, the dense oceanic plate sank into the mantle to form a slab below the lighter continent. Rapid subduction under the southwestern North America continent began 40 to 60 million years ago (Ma), during the mid Paleocene to mid Eocene epochs. This convergent subduction margin created a distinctive geomorphologic feature called an oceanic trench, which occurs at a convergent plate boundaries as a heavy metal rich, lithospheric plate moves below a light silica rich continental plate. The trench marks the position at which the flexed subducting slab begins to descend beneath and deform the continental plate margin. By 43 Ma, during the Eocene, worldwide plate motions changed and the Pacific Plate began to move away from North America and subduction of the Farallon Plate slowed dramatically. By around 36 Ma, the easternmost part of the East Pacific Rise, located between the Pioneer and Murray fracture zones at that time, approached the trench and the young, hot, buoyant lithosphere appears to have clogged part of the subduction zone, resulting in widespread dramatic uplift on land. The eventual complete subduction of this plate, consequential contact of the Pacific Plate with the California continental margin, and creation of the Mendocino triple junction (MTJ), took place around 30 to 20 Ma. The partial complete subduction and division of the Farallon Plate by the Pacific Plate, created the Juan de Fuca Plate to the north and the Cocos Plate to the south. The final stages of the evolution of California's continental margin was the growth of the San Andreas transform fault system, which formed as the Pacific Plate came into contact with the continental margin and the MTJ was formed. As subduction of the Pacific Plate continued along this margin, and the contact zone grew, the San Andreas proportionally grew as well.
The Izu–Bonin–Mariana (IBM) arc system is a tectonic plate convergent boundary in Micronesia. The IBM arc system extends over 2800 km south from Tokyo, Japan, to beyond Guam, and includes the Izu Islands, the Bonin Islands, and the Mariana Islands; much more of the IBM arc system is submerged below sealevel. The IBM arc system lies along the eastern margin of the Philippine Sea plate in the Western Pacific Ocean. It is the site of the deepest gash in Earth's solid surface, the Challenger Deep in the Mariana Trench.
In geodynamics, delamination refers to the loss and sinking (foundering) of the portion of the lowermost lithosphere from the tectonic plate to which it was attached.
Non-volcanic passive margins (NVPM) constitute one end member of the transitional crustal types that lie beneath passive continental margins; the other end member being volcanic passive margins (VPM). Transitional crust welds continental crust to oceanic crust along the lines of continental break-up. Both VPM and NVPM form during rifting, when a continent rifts to form a new ocean basin. NVPM are different from VPM because of a lack of volcanism. Instead of intrusive magmatic structures, the transitional crust is composed of stretched continental crust and exhumed upper mantle. NVPM are typically submerged and buried beneath thick sediments, so they must be studied using geophysical techniques or drilling. NVPM have diagnostic seismic, gravity, and magnetic characteristics that can be used to distinguish them from VPM and for demarcating the transition between continental and oceanic crust.
Cape Verde is a volcanic archipelago situated above an oceanic rise that puts the base of the islands 2 kilometers (1.2 mi) above the rest of the seafloor. Cape Verde has been identified as a hotspot and the majority of geoscientists have argued that the archipelago is underlain by a mantle plume and that this plume is responsible for the volcanic activity and associated geothermal anomalies.
The subcontinental lithospheric mantle (SCLM) is the uppermost solid part of Earth's mantle associated with the continental lithosphere.
The plate theory is a model of volcanism that attributes all volcanic activity on Earth, even that which appears superficially to be anomalous, to the operation of plate tectonics. According to the plate theory, the principal cause of volcanism is extension of the lithosphere. Extension of the lithosphere is a function of the lithospheric stress field. The global distribution of volcanic activity at a given time reflects the contemporaneous lithospheric stress field, and changes in the spatial and temporal distribution of volcanoes reflect changes in the stress field. The main factors governing the evolution of the stress field are:
- Changes in the configuration of plate boundaries.
- Vertical motions.
- Thermal contraction.
Intraplate volcanism is volcanism that takes place away from the margins of tectonic plates. Most volcanic activity takes place on plate margins, and there is broad consensus among geologists that this activity is explained well by the theory of plate tectonics. However, the origins of volcanic activity within plates remains controversial.
References
- ↑ National Science Foundation (May 27, 2009). "Dripping 'Blob' Under Western U.S.: A Hidden Drip, Drip, Drip Beneath Earth's Surface". Science Daily. Retrieved January 12, 2016.
- ↑ West, John D.; Fouch, Matthew J.; Roth, Jeffrey B.; Elkins-Tanton, Linda T. (2009). "Vertical mantle flow associated with a lithospheric drip beneath the Great Basin" (PDF). Nature Geoscience. 2 (6): 439–444. Bibcode:2009NatGe...2..439W. doi:10.1038/ngeo526. ISSN 1752-0894 . Retrieved January 12, 2016.
- ↑ Saleeby, Jason; Foster, Zorka (2004). "Topographic response to mantle lithosphere removal in the southern Sierra Nevada region, California". Geology. 32 (3): 245. Bibcode:2004Geo....32..245S. doi:10.1130/G19958.1. ISSN 0091-7613 . Retrieved January 12, 2016.
 | This geophysics-related article is a stub. You can help Wikipedia by expanding it. |