Английская Википедия:Cadamosto Seamount
Шаблон:Short description Шаблон:Infobox mountain
Cadamosto Seamount is a seamount in the Cape Verde islands, Шаблон:Convert southwest of Brava. It rises to a depth of Шаблон:Convert and partially overlaps with Brava. The seamount appears to be one of the recently active volcanic centres of the Cape Verde islands and has produced phonolite. The seamount has had intense volcanic eruptions in the late Pleistocene, and recent seismic activity indicates that volcanism is ongoing.
Geography and geomorphology
Cadamosto Seamount lies about Шаблон:Convert southwest of the island of Brava in the Cape Verde islands.Шаблон:Sfn Its name refers to Alvise Cadamosto, who discovered the Cape Verde islands in 1456.Шаблон:Sfn
The seamount is Шаблон:Circa Шаблон:Convert wide at its footШаблон:Sfn and partially overlaps with Brava.Шаблон:Sfn Cadamosto and Brava may be part of a larger northeast-southwest trending alignment of volcanoes.Шаблон:Sfn It rises from a depth of Шаблон:Convert to about Шаблон:Convert depthШаблон:Sfn and has a summit with three separate, well-preserved volcanic centres. Sediment cover is sparse and there is evidence of hydrothermal alterationШаблон:Sfn and of recent activity in the form of spatter deposits. Agglutinates and lavas form most of the seamount,Шаблон:Sfn with sheet and pillow lavas cropping out in the summit region.Шаблон:Sfn Numerous cratersШаблон:Sfn and small volcanic cones dot its flanksШаблон:Sfn which bear evidence of sector collapses.Шаблон:Sfn
Geology
The Cape Verde islands lie about Шаблон:Convert west of Senegal and feature nine main islands, as well as a number of islets and seamounts.Шаблон:EfnШаблон:Sfn Unusually for a hotspot volcanic system, Cape Verde has two separate chains of volcanoes.Шаблон:Sfn The islands lie on the Cape Verde Rise, a 130-to-150-million-year-old sector of seafloor covered by a Шаблон:Convert high volcanic plateau. The Rise is associated with a geoid anomalyШаблон:Sfn and may have formed through the activity of a mantle plume/hotspot. On some islands, Jurassic seafloor is exposed.Шаблон:Sfn
The Cape Verde hotspot is responsible for volcanic activity in the Cape Verde islands. Owing to the slow movement of the African Plate, there is only little evidence of migrating volcanism. It appears that the oldest volcanism occurred 16–12 million years ago at Maio and Sal, while activity in the last 500,000 years has been concentrated at Fogo and Santo Antao at the western end of the Cape Verde islands. Of these, Fogo has displayed the most recent activity with eruptions during historical timeШаблон:Sfn such as in 1769, 1785, 1799, 1847, 1853, 1857, 1951, 1995Шаблон:Sfn and 2014/2015,Шаблон:Sfn and marine records show evidence of past sub-Plinian and Plinian eruptions.Шаблон:Sfn However, a more intense seismic activity occurs at Brava,Шаблон:Sfn where it appears to correlate with eruptions on Fogo, and at Cadamosto Seamount which appears to have a different magma source.Шаблон:Sfn Based on plate motion models, the Cape Verde hotspot is expected to move southwestward, in the direction of Cadamosto Seamount,Шаблон:Sfn and may currently underlie Brava, Fogo and Cadamosto.[1] Apart from Cadamosto Seamount, Nola and Sodade Seamounts are also seismically active.Шаблон:Sfn
Unlike the rest of the Cape Verde islands which have mainly erupted mafic rocks, Cadamosto Seamount and Brava feature felsic rocks.Шаблон:Sfn The dominant volcanic rock is phonolite and phonotephriteШаблон:Sfn although clinopyroxene nephelinite has also been recorded.Шаблон:Sfn Volcanic samples dredged from Cadamosto Seamount contain crystals of aegirine, apatite, augite, biotite, diopside, haüyne, iron-titanium oxides, leucite, nepheline, nosean, pyrite, sanidine, sodalite and titanite.Шаблон:Sfn Calcite, clay and iron oxyhydroxides formed through the alteration of volcanic rocks by seawater.Шаблон:Sfn
The genesis of the magmas erupted by Cadamosto Seamount involves the ascent of mantle melts into the crust, where storage and clinopyroxene crystallization take place. Only small amounts of crustal material and sediments are absorbed by the ascending magma,Шаблон:Sfn but mixing of the felsic magma with more mafic one has been inferred from dredged volcanic rocks.Шаблон:Sfn The formation of the phonolitic magma might take place within large magma chambers.[2]
Eruption history
Ages of crystals found in dredge samples indicate that the magmatic system of Cadamosto Seamount is about 1.52 million years old.Шаблон:Sfn Dredged rocks themselves have yielded ages of 97,000 ± 14,000, 51,800 ± 2,400 and 21,140 ± 620 years by argon-argon dating.Шаблон:Sfn Volcanic activity appears to have been influenced by sea level variations, with eruptions occurring during the last glacial maximum when sea levels were lower.Шаблон:Sfn
Despite its great depth, Cadamosto Seamount appears to be capable of large explosive eruptions.Шаблон:Sfn Tephra layers attributed to Cadamosto Seamount are about 40,000 and 17,000 years old.Шаблон:Sfn These eruptions produced a minimum volume of Шаблон:Convert and Шаблон:Convert tephra, respectively, equivalent of category 4 on the volcanic explosivity index.Шаблон:Sfn The eruptions dispersed volcanic ash over areas of Шаблон:Convert and Шаблон:Convert, respectively,Шаблон:Sfn through submarine volcanic ash plumes.Шаблон:Sfn
There is no indication of historical activityШаблон:Sfn but Cadamosto Seamount is the most seismically active seamount on the Cape Verde Rise.Шаблон:Sfn During the 21st century, earthquakes with intensities of over Шаблон:M have been recorded at Cadamosto Seamount.Шаблон:Sfn The seismic activity may be related to the movement of magma in dykes,Шаблон:Sfn a magmatic system spanning Cadamosto, Brava and Fogo,Шаблон:Sfn and to a normal fault system between Brava and Cadamosto Seamount.Шаблон:Sfn The volcanic activity at Cadamosto Seamount may presage the future formation of a new island there.Шаблон:Sfn This might take up to 100,000 years.[2]
Life
Octocorals grow on Cadamosto Seamount and are populated by crabs, fish and other animals.[3]
Notes
References
Citations
General sources
- Шаблон:Cite journal
- Шаблон:Cite journal
- Шаблон:Cite journal
- Шаблон:Cite book
- Шаблон:Cite journal
- Шаблон:Cite journal
