Hotspot (geology)
In geology, the places known as hotspots or hot spots are volcanic regions thought to be fed by underlying mantle that is anomalously hot compared with the surrounding mantle. Examples include the Hawaii, Iceland and Yellowstone hotspots. A hotspot's position on the Earth's surface is independent of tectonic plate boundaries, and so hotspots may create a chain of volcanoes as the plates move above them.
There are two hypotheses that attempt to explain their origins. One suggests that hotspots are due to mantle plumes that rise as thermal diapirs from the core–mantle boundary. The other hypothesis is that lithospheric extension permits the passive rising of melt from shallow depths. This hypothesis considers the term "hotspot" to be a misnomer, asserting that the mantle source beneath them is not in fact anomalously hot.
Origin
The origins of the concept of hotspots lie in the work of J. Tuzo Wilson, who postulated in 1963 that the formation of the Hawaiian Islands resulted from the slow movement of a tectonic plate across a hot region beneath the surface. It was later postulated that hotspots are fed by narrow streams of hot mantle rising from the Earth's core–mantle boundary in a structure called a mantle plume. Whether or not such mantle plumes exist is the subject of a major controversy in Earth science. Estimates for the number of hotspots postulated to be fed by mantle plumes have ranged from about 20 to several thousands, over the years, with most geologists considering a few tens to exist. Hawaii, Réunion, Yellowstone, Galápagos, and Iceland are some of the most active volcanic regions to which the hypothesis is applied.Composition
Most hotspot volcanoes are basaltic. As a result, they are less explosive than subduction zone volcanoes, in which water is trapped under the overriding plate. Where hotspots occur in continental regions, basaltic magma rises through the continental crust, which melts to form rhyolites. These rhyolites can form violent eruptions. For example, the Yellowstone Caldera was formed by some of the most powerful volcanic explosions in geologic history. However, when the rhyolite is completely erupted, it may be followed by eruptions of basaltic magma rising through the same lithospheric fissures. An example of this activity is the Ilgachuz Range in British Columbia, which was created by an early complex series of trachyte and rhyolite eruptions, and late extrusion of a sequence of basaltic lava flows.The hotspot hypothesis is now closely linked to the mantle plume hypothesis.
Comparison with island arc volcanoes
Hotspot volcanoes are considered to have a fundamentally different origin from island arc volcanoes. The latter form over subduction zones, at converging plate boundaries. When one oceanic plate meets another, the denser plate is forced downward into a deep ocean trench. This plate, as it is subducted, releases water into the base of the over-riding plate, and this water mixes with the rock, thus changing its composition causing some rock to melt and rise. It is this that fuels a chain of volcanoes, such as the Aleutian Islands, near Alaska.Hotspot volcanic chains
The joint mantle plume/hotspot hypothesis envisages the feeder structures to be fixed relative to one another, with the continents and seafloor drifting overhead. The hypothesis thus predicts that time-progressive chains of volcanoes are developed on the surface. Examples are Yellowstone, which lies at the end of a chain of extinct calderas, which become progressively older to the west. Another example is the Hawaiian archipelago, where islands become progressively older and more deeply eroded to the northwest.Geologists have tried to use hotspot volcanic chains to track the movement of the Earth's tectonic plates. This effort has been vexed by the lack of very long chains, by the fact that many are not time-progressive and by the fact that hotspots do not appear to be fixed relative to one another
Postulated hotspot volcano chains
- Hawaiian–Emperor seamount chain
- Louisville Ridge
- Walvis Ridge
- Kodiak–Bowie Seamount chain
- Cobb–Eickelberg Seamount chain
- New England Seamounts
- Anahim Volcanic Belt
- Mackenzie dike swarm
- Great Meteor hotspot track
- St. Helena Seamount Chain–Cameroon Volcanic Line
- Southern Mascarene Plateau–Chagos-Maldives-Laccadive Ridge
- Ninety East Ridge
- Tuamotu–Line Island chain
- Austral–Gilbert–Marshall chain
- Juan Fernández Ridge
- Tasmantid Seamount Chain
List of volcanic regions postulated to be hotspots
Eurasian Plate
- Eifel hotspot
- *, w= 1 az= 082° ±8° rate= 12 ±2 mm/yr
- Iceland hotspot
- *
- ** Eurasian Plate, w=.8 az= 075° ±10° rate= 5 ±3 mm/yr
- ** North American Plate, w=.8 az= 287° ±10° rate= 15 ±5 mm/yr
- * Possibly related to the North Atlantic continental rifting, Greenland.
- Azores hotspot
- *
- ** Eurasian Plate, w=.5 az= 110° ±12°
- ** North American Plate, w=.3 az= 280° ±15°
- Jan Mayen hotspot
- *
- Hainan hotspot
- *, az= 000° ±15°
African Plate
- Mount Etna
- *
- Hoggar hotspot
- *, w=.3 az= 046° ±12°
- Tibesti hotspot
- *, w=.2 az= 030° ±15°
- Jebel Marra/Darfur hotspot
- *, w=.5 az= 045° ±8°
- Afar hotspot
- *, w=.2 az= 030° ±15° rate= 16 ±8 mm/yr
- * Possibly related to the Afar Triple Junction, 30 Ma.
- Cameroon hotspot
- *, w=.3 az= 032° ±3° rate= 15 ±5 mm/yr
- Madeira hotspot
- *, w=.3 az= 055° ±15° rate= 8 ±3 mm/yr
- Canary hotspot
- *, w= 1 az= 094° ±8° rate= 20 ±4 mm/yr
- New England/Great Meteor hotspot
- *, w=.8 az= 040° ±10°
- Cape Verde hotspot
- *, w=.2 az= 060° ±30°
- St. Helena hotspot
- *, w= 1 az= 078° ±5° rate= 20 ±3 mm/yr
- Gough hotspot, at 40°19' S 9°56' W.
- *, w=.8 az= 079° ±5° rate= 18 ±3 mm/yr
- Tristan hotspot, at 37°07′ S 12°17′ W.
- *
- Vema hotspot, at 31°38' S 8°20' E.
- *
- * Related maybe to the Paraná and Etendeka traps through the Walvis Ridge.
- Discovery hotspot
- *, w= 1 az= 068° ±3°
- Bouvet hotspot
- *
- Shona/Meteor hotspot
- *, w=.3 az= 074° ±6°
- Réunion hotspot
- *, w=.8 az= 047° ±10° rate= 40 ±10 mm/yr
- * Possibly related to the Deccan Traps
- Comoros hotspot
- *, w=.5 az=118 ±10° rate=35 ±10 mm/yr
Antarctic Plate
- Marion hotspot
- *, w=.5 az= 080° ±12°
- Crozet hotspot
- *, w=.8 az= 109° ±10° rate= 25 ±13 mm/yr
- * Possibly related to the Karoo-Ferrar geologic province
- Kerguelen hotspot
- *, w=.2 az= 050° ±30° rate= 3 ±1 mm/yr
- * Île Saint-Paul and Île Amsterdam could be part of the Kerguelen hotspot trail
- * Related maybe to the Kerguelen Plateau
- Heard hotspot
- *, w=.2 az= 030° ±20°
- Balleny hotspot
- *, w=.2 az= 325° ±7°
- Erebus hotspot
- *
South American Plate
- Trindade/Martin Vaz hotspot
- *, w= 1 az= 264° ±5°
- Fernando hotspot
- *, w= 1 az= 266° ±7°
- * Possibly related to the Central Atlantic Magmatic Province
- Ascension hotspot
- *
North American Plate
- Bermuda hotspot
- *, w=.3 az= 260° ±15°
- Yellowstone hotspot
- *, w=.8 az= 235° ±5° rate= 26 ±5 mm/yr
- * Possibly related to the Columbia River Basalt Group.
- Raton hotspot
- *, w= 1 az= 240°±4° rate= 30 ±20 mm/yr
- Anahim hotspot
- *
Indo-Australian Plate
- Lord Howe hotspot
- *, w=.8 az= 351° ±10°
- Tasmantid hotspot
- *, w=.8 az= 007° ±5° rate= 63 ±5 mm/yr
- East Australia hotspot
- *, w=.3 az= 000° ±15° rate= 65 ±3 mm/yr
Nazca Plate
- Juan Fernández hotspot
- *, w= 1 az= 084° ±3° rate= 80 ±20 mm/yr
- San Felix hotspot
- *, w=.3 az= 083° ±8°
- Easter hotspot
- *, w= 1 az= 087° ±3° rate= 95 ±5 mm/yr
- Galápagos hotspot
- *
- ** Nazca Plate, w= 1 az= 096° ±5° rate= 55 ±8 mm/yr
- ** Cocos Plate, w=.5 az= 045° ±6°
- * Possibly related to the Caribbean large igneous province.
Pacific Plate
- Louisville hotspot
- *, w= 1 az= 316° ±5° rate= 67 ±5 mm/yr
- * Possibly related to the Ontong Java Plateau.
- Foundation hotspot/Ngatemato seamounts
- *, w= 1 az= 292° ±3° rate= 80 ±6 mm/yr
- Macdonald hotspot
- *, w= 1 az= 289° ±6° rate= 105 ±10 mm/yr
- North Austral/President Thiers
- *, w= azim= 293° ± 3° rate= 75 ±15 mm/yr
- Arago hotspot
- *, w= 1 azim= 296° ±4° rate= 120 ±20 mm/yr
- Maria/Southern Cook hotspot
- *, w= 0.8 az= 300° ±4°
- Samoa hotspot
- *, w=.8 az= 285°±5° rate= 95 ±20 mm/yr
- Crough hotspot
- *, w=.8 az= 284° ± 2°
- Pitcairn hotspot
- *, w= 1 az= 293° ±3° rate= 90 ±15 mm/yr
- Society/Tahiti hotspot
- *, w=.8 az= 295°±5° rate= 109 ±10 mm/yr
- Marquesas hotspot
- *, w=.5 az= 319° ±8° rate= 93 ±7 mm/yr
- Caroline hotspot
- *, w= 1 az= 289° ±4° rate= 135 ±20 mm/yr
- Hawaii hotspot
- *, w= 1 az= 304° ±3° rate= 92 ±3 mm/yr
- Socorro/Revillagigedos hotspot
- *
- Guadalupe hotspot
- *, w=.8 az= 292° ±5° rate= 80 ±10 mm/yr
- Cobb hotspot
- *, w= 1 az= 321° ±5° rate= 43 ±3 mm/yr
- Bowie/Pratt-Welker hotspot
- *, w=.8 az= 306° ±4° rate= 40 ±20 mm/yr
Former hotspots
- Euterpe/Musicians hotspot
- Mackenzie hotspot
- Matachewan hotspot