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The Samoan archipelago is a chain of 16 islands and numerous seamounts covering 3,123 km2 (1,206 sq mi) in the central South Pacific, south of the equator, about halfway between Hawaii and New Zealand, forming part of Polynesia and of the wider region of Oceania. The islands are Savaiʻi, Upolu, Tutuila, ’Uvea, Taʻū, Ofu, Olosega, Apolima, Manono, Nuʻutele, Niulakita, Nuʻulua, Namua, Fanuatapu, Rose Atoll, Nu'ulopa, as well as the submerged Vailuluʻu, Pasco banks, and Alexa Bank.
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.
Subduction is a geological process in which the oceanic lithosphere and some continental 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 rates of convergence as high as 11 cm/year.
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.
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 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.
Frederick John Vine FRS is an English marine geologist and geophysicist. He made key contributions to the theory of plate tectonics, helping to show that the seafloor spreads from mid-ocean ridges with a symmetrical pattern of magnetic reversals in the basalt rocks on either side.
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 Azores hotspot is a volcanic hotspot in the Northern Atlantic Ocean. The Azores is relatively young and is associated with a bathymetric swell, a gravity anomaly and ocean island basalt geochemistry. The Azores hotspot lies just east of the Mid-Atlantic Ridge
The Southwest Indian Ridge (SWIR) is a mid-ocean ridge located along the floors of the south-west Indian Ocean and south-east Atlantic Ocean. A divergent tectonic plate boundary separating the Somali Plate to the north from the Antarctic Plate to the south, the SWIR is characterised by ultra-slow spreading rates (only exceeding those of the Gakkel Ridge in the Arctic) combined with a fast lengthening of its axis between the two flanking triple junctions, Rodrigues (20°30′S70°00′E) in the Indian Ocean and Bouvet (54°17′S1°5′W) in the Atlantic Ocean.
The Marquesas hotspot is a volcanic hotspot in the southern Pacific Ocean. It is responsible for the creation of the Marquesas Islands – a group of eight main islands and several smaller ones – and a few seamounts. The islands and seamounts formed between 5.5 and 0.4 million years ago and constitute the northernmost volcanic chain in French Polynesia.
The Society hotspot is a volcanic hotspot in the south Pacific Ocean which is responsible for the formation of the Society Islands, an archipelago of fourteen volcanic islands and atolls spanning around 720 km of the ocean which formed between 4.5 and <1 Ma.
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.
The Fifteen-Twenty or 15°20' Fracture Zone (FTFZ), also known as the Cabo Verde Fracture Zone, is a fracture zone located on the Mid-Atlantic Ridge (MAR) in the central Atlantic Ocean between 14–16°N. It is the current location of the migrating triple junction marking the boundaries between the North American, South American, and Nubian plates. The FTFZ is roughly parallel to the North and South America—Africa spreading direction and has a broad axial valley produced over the last ten million years by the northward-migrating triple junction. Offsetting the MAR by some 175 km, the FTFZ is located on one of the slowest portions of the MAR where the full spreading rate is 25 km/Myr.
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.
Catherine Chauvel is a geochemist at the Institut de Physique du Globe de Paris known for her research on the impact of volcanic activity on the chemistry of the mantle, continental crust, and island arc geochemistry.
Mathilde Cannat is a French geologist known for her research on the formation of oceanic crust and the tectonic and magmatic changes of mid-ocean ridges.
References
- ↑ Andal, Eric S.; Arai, Shoji; Yumul, Graciano P. (1 September 2005). "Complete mantle section of a slow-spreading ridge-derived ophiolite: An example from the Isabela ophiolite in the Philippines". Island Arc. 14 (3): 272–294. doi:10.1111/j.1440-1738.2005.00471.x. hdl: 2297/19546 . ISSN 1440-1738. S2CID 128460236.
- ↑ Shervais, John W. (1 January 2001). "Birth, death, and resurrection: The life cycle of suprasubduction zone ophiolites". Geochemistry, Geophysics, Geosystems. 2 (1): 1010. Bibcode:2001GGG.....2.1010S. doi: 10.1029/2000GC000080 . ISSN 1525-2027.
- ↑ Miyashiro, Akiho (1 June 1973). "The Troodos ophiolitic complex was probably formed in an island arc". Earth and Planetary Science Letters. 19 (2): 218–224. Bibcode:1973E&PSL..19..218M. doi:10.1016/0012-821X(73)90118-0.
- ↑ Bernoulli, Daniel; Jenkyns, Hugh C. (1 May 2009). "Ophiolites in ocean–continent transitions: From the Steinmann Trinity to sea-floor spreading". Comptes Rendus Geoscience. 341 (5): 363–381. Bibcode:2009CRGeo.341..363B. doi:10.1016/j.crte.2008.09.009.
- ↑ Mohriak, edited by W.U.; Danforth, A.; Post, P.J.; Brown, D.E.; Tari, G.C.; Nemčok, M.; Sinha, S.T. (2013). Conjugate divergent margins. London: Geological Society of London. ISBN 978-1862393493.
{{cite book}}:|first1=has generic name (help) - ↑ Michael, P. J.; Langmuir, C. H.; Dick, H. J. B.; Snow, J. E.; Goldstein, S. L.; Graham, D. W.; Lehnert, K.; Kurras, G.; Jokat, W.; Mühe, R.; Edmonds, H. N. (26 June 2003). "Magmatic and amagmatic seafloor generation at the ultraslow-spreading Gakkel ridge, Arctic Ocean". Nature. 423 (6943): 956–961. Bibcode:2003Natur.423..956M. doi:10.1038/nature01704. ISSN 0028-0836. PMID 12827193. S2CID 4312652.
- ↑ Snow, Jonathan E.; Hellebrand, Eric; von der Handt, Anette; Nauret, Francois; Gao, Yongjun; Schenke, Hans Werner (1 October 2011). "Oblique nonvolcanic seafloor spreading in Lena Trough, Arctic Ocean". Geochemistry, Geophysics, Geosystems. 12 (10): Q10009. Bibcode:2011GGG....1210009S. doi: 10.1029/2011GC003768 . ISSN 1525-2027.
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