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Seafloor spreading, or seafloor spread, 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.
An ophiolite is a section of Earth's oceanic crust and the underlying upper mantle that has been uplifted and exposed, and often emplaced onto continental crustal rocks.
The Explorer Plate is an oceanic tectonic plate beneath the Pacific Ocean off the west coast of Vancouver Island, Canada, which is partially subducted under the North American Plate. Along with the Juan de Fuca Plate and Gorda Plate, the Explorer Plate is a remnant of the ancient Farallon Plate, which has been subducted under the North American Plate. The Explorer Plate separated from the Juan de Fuca Plate roughly 4 million years ago. In its smoother, southern half, the average depth of the Explorer plate is roughly 2,400 metres (7,900 ft) and rises up in its northern half to a highly variable basin between 1,400 metres (4,600 ft) and 2,200 metres (7,200 ft) in depth.
Oceanic crust is the uppermost layer of the oceanic portion of the tectonic plates. 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 rigid uppermost layer of the mantle. The crust and the rigid upper mantle layer together constitute oceanic lithosphere.
Eclogite is a metamorphic rock containing garnet (almandine-pyrope) hosted in a matrix of sodium-rich pyroxene (omphacite). Accessory minerals include kyanite, rutile, quartz, lawsonite, coesite, amphibole, phengite, paragonite, zoisite, dolomite, corundum and, rarely, diamond. The chemistry of primary and accessory minerals is used to classify three types of eclogite. The broad range of eclogitic compositions has led to a longstanding debate on the origin of eclogite xenoliths as subducted, altered oceanic crust.
A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics. It typically has a depth of about 2,600 meters (8,500 ft) and rises about 2,000 meters (6,600 ft) 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.
A back-arc basin is a type of geologic basin, found at some convergent plate boundaries. Presently all back-arc basins are submarine features associated with island arcs and subduction zones, with many found in the western Pacific Ocean. Most of them result from tensional forces, caused by a process known as oceanic trench rollback, where a subduction zone moves towards the subducting plate. Back-arc basins were initially an unexpected phenomenon in plate tectonics, as convergent boundaries were expected to universally be zones of compression. However, in 1970, Dan Karig published a model of back-arc basins consistent with plate tectonics.
A sheeted dyke complex, or sheeted dike complex, is a series of sub-parallel intrusions of igneous rock, forming a layer within the oceanic crust. At mid-ocean ridges, dykes are formed when magma beneath areas of tectonic plate divergence travels through a fracture in the earlier formed oceanic crust, feeding the lavas above and cooling below the seafloor forming upright columns of igneous rock. Magma continues to cool, as the existing seafloor moves away from the area of divergence, and additional magma is intruded and cools. In some tectonic settings slices of the oceanic crust are obducted (emplaced) upon continental crust, forming an ophiolite.
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.
The Troodos Ophiolite on the island of Cyprus represents a Late Cretaceous spreading axis that has since been uplifted due to its positioning on the overriding Anatolian plate at the Cyprus arc and ongoing subduction to the south of the Eratosthenes Seamount.
In geology, the term exhumation refers to the process by which a parcel of rock, approaches Earth's surface.
Flat slab subduction is characterized by a low subduction angle beyond the seismogenic layer and a resumption of normal subduction far from the trench. A slab refers to the subducting lower plate. A broader definition of flat slab subduction includes any shallowly dipping lower plate, as in western Mexico. Flat slab subduction is associated with the pinching out of the asthenosphere, an inland migration of arc magmatism, and an eventual cessation of arc magmatism. The coupling of the flat slab to the upper plate is thought to change the style of deformation occurring on the upper plate's surface and form basement-cored uplifts like the Rocky Mountains. The flat slab also may hydrate the lower continental lithosphere and be involved in the formation of economically important ore deposits. During the subduction, a flat slab itself may deform or buckle, causing sedimentary hiatus in marine sediments on the slab. The failure of a flat slab is associated with ignimbritic volcanism and the reverse migration of arc volcanism. Multiple working hypotheses about the cause of flat slabs are subduction of thick, buoyant oceanic crust (15–20 km) and trench rollback accompanying a rapidly overriding upper plate and enhanced trench suction. The west coast of South America has two of the largest flat slab subduction zones. Flat slab subduction is occurring at 10% of subduction zones.
Kenneth Craig Macdonald is an American oceanographer and marine geophysicist born in San Francisco, California in 1947. As of 2018 he is professor emeritus at the Department of Earth Science and the Marine Sciences Institute at the University of California, Santa Barbara (UCSB). His work focuses on the tectonics and geophysics of the global mid-oceanic ridge including its spreading centers and transform faults, two of the three types of plate boundaries central to the theory of plate tectonics. His work has taken him to the north and south Atlantic oceans, the north and south Pacific oceans, the Indian Ocean, the Red Sea and the Sea of Cortez, as well as to the deep seafloor on over 50 dives in the research submersible ALVIN. Macdonald has participated in over 40 deep sea expeditions, and was chief- or co-chief scientist on 31 expeditions.
The lower oceanic crust is the lower part of the oceanic crust and represents the major part of it. It is generally located 4–8 km below the ocean floor and the major lithologies are mafic which derive from melts rising from the Earth's mantle. This part of the oceanic crust is an important zone for processes such as melt accumulation and melt modification. And the recycling of this part of the oceanic crust, together with the upper mantle has been suggested as a significant source component for tholeiitic magmas in Hawaiian volcanoes. Although the lower oceanic crust builds the link between the mantle and the MORB, and can't be neglected for the understanding of MORB evolution, the complex processes operating in this zone remain unclear and there is an ongoing debate in Earth Sciences about this. It is 6KM long.
Overlapping spreading centers are a feature of spreading centers at mid-ocean ridges.
Project FAMOUS was the first-ever marine scientific exploration by manned submersibles of a diverging tectonic plate boundary on a mid-ocean ridge. It took place between 1971 and 1974, with a multi-national team of scientists concentrating numerous underwater surveys on an area of the Mid-Atlantic Ridge about 700 kilometers west of the Azores. By deploying new methods and specialized equipment, scientists were able to look at the sea floor in far greater detail than ever before. The project succeeded in defining the main mechanisms of creation of the median rift valley on the Mid-Atlantic Ridge, and in locating and mapping the zone of oceanic crustal accretion.
Marine geophysics is the scientific discipline that employs methods of geophysics to study the world's ocean basins and continental margins, particularly the solid earth beneath the ocean. It shares objectives with marine geology, which uses sedimentological, paleontological, and geochemical methods. Marine geophysical data analyses led to the theories of seafloor spreading and plate tectonics.
Suzanne Carbotte is a marine geophysicist known for her research on the formation of new oceanic crust.
Rachel Haymon is a marine geologist known for her work linking geological and biological processes occurring at deep-sea hydrothermal vents. In 2005 she was elected a fellow of the Geological Society of America.
Roger Clive Searle is an English geophysicist, known for using sonar imaging in research on the geology and geophysics of the ocean floor. In particular, he has made important contributions to understanding the oceanic spreading system and the mid-ocean spreading centres.
References
- ↑ Cannat, Mathilde (1983). Cinématique de charriages ophiolitiques (Klamath, Semail, Groix) et convergence océanique (Thesis) (in French). S.l.: [s.n.] OCLC 490574002.
- 1 2 3 "Mathilde Cannat reçoit la médaille d'argent 2009 du CNRS | INSU". www.insu.cnrs.fr (in French). December 30, 2009. Retrieved 2021-09-14.
- 1 2 Fernández-Blanco, David (December 7, 2018). "Meeting Plate Tectonics – Mathilde Cannat". Tectonics and Structural Geology. Retrieved 2021-09-14.
- 1 2 "Cannat". Honors Program. Retrieved 2021-09-14.
- ↑ Boudier, F.; Bouchez, J.L.; Nicolas, A.; Cannat, M.; Ceuleneer, G.; Misseri, M.; Montigny, R. (1985-10-01). "Kinematics of oceanic thrusting in the Oman ophiolite: model of plate convergence". Earth and Planetary Science Letters. 75 (2–3): 215–222. Bibcode:1985E&PSL..75..215B. doi:10.1016/0012-821X(85)90103-7. ISSN 0012-821X.
- ↑ Cannat, Mathilde (1989). "Late Caledonian northeastward ophiolite thrusting in the Shetland Islands, U.K." Tectonophysics. 169 (4): 257–270. Bibcode:1989Tectp.169..257C. doi:10.1016/0040-1951(89)90090-5.
- ↑ Lagabrielle, Yves; Cannat, Mathilde (1990-04-01). "Alpine Jurassic ophiolites resemble the modern central Atlantic basement". Geology. 18 (4): 319–322. Bibcode:1990Geo....18..319L. doi:10.1130/0091-7613(1990)018<0319:AJORTM>2.3.CO;2. ISSN 0091-7613.
- ↑ Cannat, Mathilde; Mevel, Catherine; Maia, Marcia; Deplus, Christine; Durand, Cecile; Gente, Pascal; Agrinier, Pierre; Belarouchi, Abdel; Dubuisson, Gilles; Humler, Eric; Reynolds, Jennifer (1995-01-01). "Thin crust, ultramafic exposures, and rugged faulting patterns at the Mid-Atlantic Ridge (22°–24°N)". Geology. 23 (1): 49–52. Bibcode:1995Geo....23...49C. doi:10.1130/0091-7613(1995)023<0049:TCUEAR>2.3.CO;2. ISSN 0091-7613.
- ↑ Cannat, Mathilde (1993). "Emplacement of mantle rocks in the seafloor at mid-ocean ridges". Journal of Geophysical Research: Solid Earth. 98 (B3): 4163–4172. Bibcode:1993JGR....98.4163C. doi:10.1029/92JB02221. ISSN 2156-2202.
- ↑ Cannat, Mathilde (1996). "How thick is the magmatic crust at slow spreading oceanic ridges?". Journal of Geophysical Research: Solid Earth. 101 (B2): 2847–2857. Bibcode:1996JGR...101.2847C. doi:10.1029/95JB03116. ISSN 2156-2202.
- 1 2 "Mathilde Cannat". European Geosciences Union (EGU). Retrieved 2021-09-14.
- ↑ "Mathilde Cannat | CNRS". www.cnrs.fr. Retrieved 2021-09-14.
- ↑ "Mathilde Cannat reçoit la Médaille d'argent du CNRS | INSTITUT DE PHYSIQUE DU GLOBE DE PARIS". www.ipgp.fr. Retrieved 2021-09-14.
- ↑ "The Geological Society of London - Geological Society Awards 2023 Winners". www.geolsoc.org.uk.
