Volcanic belt
Avolcanic beltis a largevolcanicallyactive region. Other terms are used for smaller areas of activity, such asvolcanic fieldsor volcanic systems. Volcanic belts are found above zones of unusually high temperature (700 to 1,400 °C (1,292 to 2,552 °F)) wheremagmais created by partial melting of solid material in the Earth's crust andupper mantle.These areas usually form alongtectonic plateboundaries at depths of 10 to 50 kilometres (6.2 to 31.1 mi). For example, volcanoes inMexicoand westernNorth Americaare mostly in volcanic belts, such as theTrans-Mexican Volcanic Beltthat extends 900 kilometres (560 mi) from west to east across central-southern Mexico and theNorthern Cordilleran Volcanic Provincein westernCanada.In the case of Iceland, the geologist G.G. Bárdarson in 1929 identified clusters of volcanic belts while studying theReykjanes Peninsula.[1]
The deeply deformed and eroded remnants of ancient volcanic belts are found in volcanically inactive regions such as theCanadian Shield.It contains over 150 volcanic belts (now deformed and eroded down to nearly flatplains) that range from 600 to 1,200 million years old.[citation needed]These are zones of variablymetamorphosedmafictoultramaficvolcanic sequences with associatedsedimentary rocksthat form what are known asgreenstone belts.They are thought to have formed at ancient oceanic spreading centers andisland arcterranes.TheAbitibi greenstone beltinOntarioandQuebec,Canadais one of the world's largest greenstone belts.
Volcanic belts are similar to amountain range,but the mountains within the mountain range are volcanoes, not mountains that are formed byfaultingandfoldingby the collision oftectonic plates.[2]
Formation[edit]
Volcanic belts may be formed by multiple tectonic settings. They may be formed bysubduction zones,which is an area onEarthwhere twotectonic platesmeet and move towards one another, with one sliding underneath the other and moving down into themantle,at rates typically measured in centimeters per year. Anoceanic plateordinarily slides underneath a continental plate; this often creates anorogeniczone with many volcanoes andearthquakes.In a sense, subduction zones are the opposite ofdivergent boundaries,areas where material rises up from the mantle and plates are moving apart. An example of a subduction-zone related volcanic belt is theOkhotsk-Chukotka Volcanic Beltin northeasternEurasia,which is one of the largest subduction-zone related volcanic provinces in the world, stretching some 3,200 kilometres (2,000 mi) and comprising about 2×106cubic kilometres (4.8×105cu mi) of volcanic and plutonic material.[3]
Volcanic belts may also be formed byhotspots,which is a location on the Earth's surface that has experienced activevolcanismfor a long period of time. These volcanic belts are called volcanic chains. CanadiangeologistJohn Tuzo Wilsoncame up with the idea in 1963 that volcanic chains like theHawaiian 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 ofhotmantleconvecting up from the mantle-core boundary called amantle plume.[4]But more recently some geologists, such asGillian Foulgerview upper-mantle convection as a cause.[5][6][7]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.[8]Geologists have identified some 40-50 such hotspots around the globe, withHawaii,Réunion,Yellowstone,Galápagos,andIcelandoverlying the most currently active. An example of a hotspot volcanic belt is theAnahim Volcanic BeltinBritish Columbia,Canada,which was formed as a result of theNorth American Platesliding westward over theAnahim hotspot.[9]
Most hotspot volcanoes arebasalticbecause they erupt through oceaniclithosphere(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, theYellowstone Calderawas formed by some of the most powerful volcanic explosions in geologic history.
Examples[edit]
See also[edit]
References[edit]
- ^Thordarson, T.; Larsen, G. (2007). "Volcanism in Iceland in historical time: volcano types, eruption styles and eruptive history".Journal of Geodynamics.43(1): 118–152.Bibcode:2007JGeo...43..118T.doi:10.1016/j.jog.2006.09.005.: 123
- ^Volcano World - What is a volcano belt?Archived2007-05-26 at theWayback MachineRetrieved on 2007-07-08
- ^Ispolatov, V. O.; Tikhomirov, P. L.; Heizler, M.; Cherepanova, I. Yu. (May 2004). "New40Ar/39Ar Ages of Cretaceous Continental Volcanics from Central Chukotka: Implications for Initiation and Duration of Volcanism within the Northern Part of the Okhotsk Chukotka Volcanic Belt (Northeastern Eurasia) ".The Journal of Geology.112(3): 369–377.Bibcode:2004JG....112..369I.doi:10.1086/382765.S2CID129022397.
- ^"Hotspots [This Dynamic Earth, USGS]".pubs.usgs.gov.Archivedfrom the original on 3 February 2006.Retrieved23 March2018.
- ^Foulger, Gillian."The Great Plumes Debate 2003".Archived fromthe originalon 2007-09-06.Retrieved2008-02-10.
- ^Wright, Laura."Geotimes - November 2000: New Notes".www.geotimes.org.Archivedfrom the original on 8 August 2017.Retrieved23 March2018.
- ^"Gillian R. Foulger"(PDF).Archived(PDF)from the original on 2007-07-03.Retrieved2007-07-08.
- ^"Antipodal hotspots and bipolar catastrophes: Were oceanic large-body impacts the cause?"(PDF).Archived(PDF)from the original on 2007-11-28.Retrieved2008-02-02.
- ^Volcanoes of Canada - Map of Canadian volcanoesArchived2008-06-02 at theWayback MachineRetrieved on 2007-07-08
