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Plate tectonics is a scientific theory describing the large-scale motion of seven large plates and the movements of a larger number of smaller plates of Earth's lithosphere, since tectonic processes began on Earth between 3.3 and 3.5 billion years ago. The model builds on the concept of continental drift, an idea developed during the first decades of the 20th century. The geoscientific community accepted plate-tectonic theory after seafloor spreading was validated in the late 1950s and early 1960s.
The Rio Grande rift is a north-trending continental rift zone. It separates the Colorado Plateau in the west from the interior of the North American craton on the east. The rift extends from central Colorado in the north to the state of Chihuahua, Mexico, in the south. The rift zone consists of four basins that have an average width of 50 kilometers. The rift can be observed on location at Rio Grande National Forest, White Sands National Park, Santa Fe National Forest, and Cibola National Forest, among other locations.
Seafloor spreading is a process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge.
A lithosphere is the rigid, outermost shell of a terrestrial-type planet or natural satellite. On Earth, it is composed of the crust and the portion of the upper mantle that behaves elastically on time scales of thousands of years or greater. The crust and upper mantle are distinguished on the basis of chemistry and mineralogy.
The asthenosphere is the highly viscous, mechanically weak and ductile region of the upper mantle of Earth. It lies below the lithosphere, at depths between approximately 80 and 200 km below the surface. The lithosphere–asthenosphere boundary is usually referred to as LAB. The asthenosphere is almost solid, although some of its regions could be molten. The lower boundary of the asthenosphere is not well defined. The thickness of the asthenosphere depends mainly on the temperature. However, the rheology of the asthenosphere also depends on the rate of deformation, which suggests that the asthenosphere could be also formed as a result of a high rate of deformation. In some regions the asthenosphere could extend as deep as 700 km (430 mi). It is considered the source region of mid-ocean ridge basalt (MORB).
Subduction is a geological process in which oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the heavier plate dives beneath the second plate 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 the average rate of convergence being approximately two to eight centimeters per year along most plate boundaries.
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.
In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics.
Post-glacial rebound is the rise of land masses after the removal of the huge weight of ice sheets during the last glacial period, which had caused isostatic depression. Post-glacial rebound and isostatic depression are phases of glacial isostasy, the deformation of the Earth's crust in response to changes in ice mass distribution. The direct raising effects of post-glacial rebound are readily apparent in parts of Northern Eurasia, Northern America, Patagonia, and Antarctica. However, through the processes of ocean siphoning and continental levering, the effects of post-glacial rebound on sea level are felt globally far from the locations of current and former ice sheets.
The Oceanic crust is the uppermost layer of the oceanic portion of a tectonic plate. It is composed of the upper oceanic crust, with pillow lavas and a dike complex, and the lower oceanic crust, composed of troctolite, gabbro and ultramafic cumulates. The crust overlies the solidified and uppermost layer of the mantle. The crust and the solid mantle layer together constitute oceanic lithosphere.
The Iceland hotspot is a hotspot which is partly responsible for the high volcanic activity which has formed the Iceland Plateau and the island of Iceland.
A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics. It typically has a depth of ~ 2,600 meters (8,500 ft) and rises about two kilometers above the deepest portion of an ocean basin. This feature is where seafloor spreading takes place along a divergent plate boundary. The rate of seafloor spreading determines the morphology of the crest of the mid-ocean ridge and its width in an ocean basin. The production of new seafloor and oceanic lithosphere results from mantle upwelling in response to plate separation. The melt rises as magma at the linear weakness between the separating plates, and emerges as lava, creating new oceanic crust and lithosphere upon cooling. The first discovered mid-ocean ridge was the Mid-Atlantic Ridge, which is a spreading center that bisects the North and South Atlantic basins; hence the origin of the name 'mid-ocean ridge'. Most oceanic spreading centers are not in the middle of their hosting ocean basis but regardless, are traditionally called mid-ocean ridges. Mid-ocean ridges around the globe are linked by plate tectonic boundaries and the trace of the ridges across the ocean floor appears similar to the seam of a baseball. The mid-ocean ridge system thus is the longest mountain range on Earth, reaching about 65,000 km (40,000 mi).
A Wadati–Benioff zone is a planar zone of seismicity corresponding with the down-going slab in a subduction zone. Differential motion along the zone produces numerous earthquakes, the foci of which may be as deep as about 670 km (420 mi). The term was named for the two seismologists, Hugo Benioff of the California Institute of Technology and Kiyoo Wadati of the Japan Meteorological Agency, who independently discovered the zones.
Dan Peter McKenzie is a Professor of Geophysics at the University of Cambridge, and one-time head of the Bullard Laboratories of the Cambridge Department of Earth Sciences. He wrote the first paper defining the mathematical principles of plate tectonics on a sphere, and his early work on mantle convection created the modern discussion of planetary interiors.
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.
The low-velocity zone (LVZ) occurs close to the boundary between the lithosphere and the asthenosphere in the upper mantle. It is characterized by unusually low seismic shear wave velocity compared to the surrounding depth intervals. This range of depths also corresponds to anomalously high electrical conductivity. It is present between about 80 and 300 km depth. This appears to be universally present for S waves, but may be absent in certain regions for P waves. A second low-velocity zone has been detected in a thin ≈50 km layer at the core-mantle boundary. These LVZs may have important implications for plate tectonics and the origin of the Earth's crust.
The lithosphere–asthenosphere boundary represents a mechanical difference between layers in Earth's inner structure. Earth's inner structure can be described both chemically and mechanically. The lithosphere–asthenosphere boundary lies between Earth's cooler, rigid lithosphere and the warmer, ductile asthenosphere. The actual depth of the boundary is still a topic of debate and study, although it is known to vary according to the environment.
The gravity of Mars is a natural phenomenon, due to the law of gravity, or gravitation, by which all things with mass around the planet Mars are brought towards it. It is weaker than Earth's gravity due to the planet's smaller mass. The average gravitational acceleration on Mars is 3.72076 ms−2 and it varies laterally. In general, topography-controlled isostasy drives the short wavelength free-air gravity anomalies. At the same time, convective flow and finite strength of the mantle lead to long-wavelength planetary-scale free-air gravity anomalies over the entire planet. Variation in crustal thickness, magmatic and volcanic activities, impact-induced Moho-uplift, seasonal variation of polar ice caps, atmospheric mass variation and variation of porosity of the crust could also correlate to the lateral variations. Over the years models consisting of an increasing but limited number of spherical harmonics have been produced. Maps produced have included free-air gravity anomaly, Bouguer gravity anomaly, and crustal thickness. In some areas of Mars there is a correlation between gravity anomalies and topography. Given the known topography, higher resolution gravity field can be inferred. Tidal deformation of Mars by the Sun or Phobos can be measured by its gravity. This reveals how stiff the interior is, and shows that the core is partially liquid. The study of surface gravity of Mars can therefore yield information about different features and provide beneficial information for future landing projects.
Ridge push or sliding plate force is a proposed driving force for plate motion in plate tectonics that occurs at mid-ocean ridges as the result of the rigid lithosphere sliding down the hot, raised asthenosphere below mid-ocean ridges. Although it is called ridge push, the term is somewhat misleading; it is actually a body force that acts throughout an ocean plate, not just at the ridge, as a result of gravitational pull. The name comes from earlier models of plate tectonics in which ridge push was primarily ascribed to upwelling magma at mid-ocean ridges pushing or wedging the plates apart.
References
- ↑ Parro, Laura M.; Jiménez-Díaz, Alberto; Mansilla, Federico; Ruiz, Javier (2017). "Present-day heat flow model of Mars". Scientific Reports. 7: 45629. Bibcode:2017NatSR...745629P. doi:10.1038/srep45629. PMC 5377363 . PMID 28367996.
- ↑ Zamani, Ahmad; Samiee, Jafar; Kirby, Jon F. (2014). "The effective elastic thickness of the lithosphere in the collision zone between Arabia and Eurasia in Iran". Journal of Geodynamics. 81: 30–40. Bibcode:2014JGeo...81...30Z. doi:10.1016/j.jog.2014.06.002.
- ↑ "CORDIS (European Commission)". cordis.europa.eu. Europa (web portal) . Retrieved 2019-03-08.
- ↑ McKenzie, D.; Jackson, J.; Priestley, K. (2005). "Thermal structure of oceanic and continental lithosphere". Earth and Planetary Science Letters. 233 (3–4): 337–349. doi:10.1016/j.epsl.2005.02.005.
- ↑ Watts, A. B.; Taiwani, M. (1974). "Gravity Anomalies Seaward of Deep-Sea Trenches and their Tectonic Implications". Geophysical Journal. 36 (1): 57. Bibcode:1974GeoJ...36...57W. doi: 10.1111/j.1365-246X.1974.tb03626.x .
- ↑ Burov, Evgene B.; Diament, Michel (1995). "The effective elastic thickness (Te) of continental lithosphere: What does it really mean?" (PDF). Journal of Geophysical Research: Solid Earth. 100: 3905–3927. doi:10.1029/94JB02770.
- ↑ McNutt, Marcia (1980). "Implications of regional gravity for state of stress in the Earth's crust and upper mantle". Journal of Geophysical Research: Solid Earth. 85 (B11): 6377–6396. Bibcode:1980JGR....85.6377M. doi:10.1029/JB085iB11p06377.
- ↑ Tesauro, Magdala; Audet, Pascal; Kaban, Mikhail K.; Bürgmann, Roland; Cloetingh, Sierd (2012). "The effective elastic thickness of the continental lithosphere: Comparison between rheological and inverse approaches". Geochemistry, Geophysics, Geosystems. 13 (9): Q09001. Bibcode:2012GGG....13.9001T. doi: 10.1029/2012GC004162 .