- Volcanic belt
Trans-Mexican Volcanic Beltin Mexico] A volcanic belt is a large volcanically active region. Other terms are used for smaller areas of activity, such as volcanic fields. Volcanic belts are found above zones of unusually high temperature (700-1400°C) where magmais created by partial melting of solid material in the Earth's crust and upper mantle. These areas usually form along tectonic plate boundaries at depths of 10-50 km. For example, volcanoes in Mexicoand western North Americaare mostly in volcanic belts, such as the Trans-Mexican Volcanic Beltthat extends 900 km from west to east across central-southern Mexico and the Northern Cordilleran Volcanic Provincein western Canada.
The deeply deformed and eroded remnants of ancient volcanic belts are found in volcanically inactive regions such as the
Canadian Shield. It contains over 150 volcanic belts (now deformed and eroded down to nearly flat plains) that range from 600 to 1200 million years old. These are zones of variably metamorphosed maficto ultramaficvolcanic sequences with associated sedimentary rocks that form what are known as greenstone belts. They are thought to have formed at ancient oceanic spreading centers and island arc terranes. The Abitibi greenstone beltin Ontarioand Quebec, Canadais one of the world's largest greenstone belts.
Volcanic belts are similar to a
mountain range, but the mountains within the mountain range are volcanoes, not actual mountains that are formed by faulting and folding by the collision of tectonic plates. [ [http://volcano.und.edu/vwdocs/frequent_questions/grp9/question2990.html Volcano World - What is a volcano belt?] Retrieved on 2007-07-08]
Volcanic belts may be formed by multiple tectonic settings. They may be formed by subduction zones, which is an area on
Earthwhere two tectonic plates meet and move towards one another, with one sliding underneath the other and moving down into the mantle, at rates typically measured in centimeters per year. An oceanic plateordinarily slides underneath a continental plate; this often creates an orogeniczone with many volcanoes and earthquakes. In a sense, subduction zones are the opposite of divergent boundaries, areas where material rises up from the mantle and plates are moving apart. An example of a subduction-zone related volcanic belt is the Okhotsk-Chukotka Volcanic Beltin northeastern Eurasia, which is one of the largest subduction-zone related volcanic provinces in the world, stretching some 3200 km and comprising about 2 million km3 of volcanic and plutonic material. [ [http://sbmg.geol.msu.ru/pp/Tikhomirov/Ocvb2/text_final.htm New 40Ar/39Ar ages of Cretaceous continental volcanics from central Chukotka: implications for initiation and duration of volcanism within northern part of the Okhotsk Chukotka Volcanic Belt (northeastern Eurasia)] , by V. O. Ispolatov, P. L. Tikhomirov, M. Heizler, and I. Yu. Cherepanova. Retrieved on 2007-07-08]
Volcanic belts may also be formed by hotspots, which is a location on the Earth's surface that has experienced active volcanism for a long period of time. These volcanic belts are called volcanic chains. Canadian
geologist John Tuzo Wilsoncame up with the idea in 1963 that volcanic chains like the Hawaiian Islandsresult from the slow movement of a tectonic plate across a "fixed" hot spot deep beneath the surface of the planet, thought to be caused by a narrow stream of hot mantle convecting up from the mantle-core boundary called a mantle plume. [ [http://pubs.usgs.gov/publications/text/hotspots.html Hotspots [This Dynamic Earth, USGS ] ] But more recently some geologists, such as Gillian Foulgerview upper-mantle convection as a cause. [cite web|last=Foulger|first=Gillian|authorlink=Gillian Foulger|url=http://www.geolsoc.org.uk/gsl/views/debates/page1060.html|title= The Great Plumes Debate 2003|accessdate=2008-02-10] [ [http://www.geotimes.org/nov00/hotspot.html Geotimes - November 2000: New Notes ] ] [http://www.dur.ac.uk/g.r.foulger/Offprints/Yellowstone.pdf] This in turn has re-raised the antipodal pair impact hypothesis, the idea that pairs of opposite hot spots may result from the impact of a large meteor. [http://www.mantleplumes.org/WebDocuments/Antip_hot.pdf] Geologists have identified some 40-50 such hotspots around the globe, with Hawaii, Réunion, Yellowstone, Galápagos, and Icelandoverlying the most currently active. An example of a hotspot volcanic belt is the Anahim Volcanic Beltin British Columbia, Canada, which was formed as a result of the North American Platesliding westward over the Anahim hotspot. [ [http://gsc.nrcan.gc.ca/volcanoes/map/index_e.php Volcanoes of Canada - Map of Canadian volcanoes] Retrieved on 2007-07-08]
Most hotspot volcanoes are
basalticbecause they erupt through oceanic lithosphere(e.g., Hawaii, Tahiti). As a result, they are less explosive than subduction zone volcanoes, which have high water contents. Where hotspots occur under continental crust, basaltic magma is trapped in the less dense continental crust, which is heated and melts to form rhyolites. These rhyolites can be quite hot and form violent eruptions, despite their low water content. For example, the Yellowstone Calderawas formed by some of the most powerful volcanic explosions in geologic history.
Andean Volcanic Belt
Garibaldi Volcanic Belt
Taupo Volcanic Zone
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Garibaldi Volcanic Belt — The Garibaldi Volcanic Belt is a north south range of volcanoes in southwestern British Columbia, Canada. It is the northern extension of the Cascade Volcanic Arc, a chain of volcanoes of major andesitic to dacitic stratovolcanoes extending… … Wikipedia
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Anahim Volcanic Belt — The Anahim Volcanic Belt is a 600 kilometre long volcanic belt, stretching from just north of Vancouver Island to near Quesnel, British Columbia, Canada. The Anahim Volcanic Belt has had three main magmatic episodes: 15–13 Ma, 9–6 Ma, and 3–1 Ma … Wikipedia
Pemberton Volcanic Belt — The Pemberton Volcanic Belt is an eroded Miocene volcanic belt at a low angle near Mount Meager, British Columbia, Canada. The Garibaldi and Pemberton volcanic belts appear to merge into a single belt, although the Pemberton is older then the… … Wikipedia
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Okhotsk-Chukotka Volcanic Belt — The Okhotsk Chukotka Volcanic Belt (OCVB) is a Cretaceous volcanic belt in northeastern Eurasia. It is one of the largest subduction zone related volcanic provinces in the world, stretching some 3200 km and comprising about 2 million km3 of… … Wikipedia
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