The Chilcotin Group, also called the Chilcotin Plateau Basalts, is a large area of

basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...

ic lava that forms a

volcanic plateau A volcanic plateau is a plateau produced by volcanic activity. There are two main types: lava plateaus and pyroclastic plateaus. Lava plateau Lava plateaus are formed by highly fluid basaltic lava during numerous successive eruptions thro ...

running parallel with the

Garibaldi Volcanic Belt The Garibaldi Volcanic Belt is a northwest–southeast trending volcanic chain in the Pacific Ranges of the Coast Mountains that extends from Watts Point in the south to the Ha-Iltzuk Icefield in the north. This chain of volcanoes is located in s ...

in south-central

British Columbia British Columbia is the westernmost Provinces and territories of Canada, province of Canada. Situated in the Pacific Northwest between the Pacific Ocean and the Rocky Mountains, the province has a diverse geography, with rugged landscapes that ...

, Canada. Predominantly, during

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

and

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58Interior Plateau. The distribution is assumed to engulf up to 50,000 km² of the

Pacific Northwest The Pacific Northwest (PNW; ) is a geographic region in Western North America bounded by its coastal waters of the Pacific Ocean to the west and, loosely, by the Rocky Mountains to the east. Though no official boundary exists, the most common ...

, forming a medium-sized

large igneous province A large igneous province (LIP) is an extremely large accumulation of igneous rocks, including intrusive ( sills, dikes) and extrusive (lava flows, tephra deposits), arising when magma travels through the crust towards the surface. The format ...

, of volume 3300 km³.Regional stratigraphy and age of Chilcotin Group basalts, south-central British Columbia
Retrieved on 2012-09-22 Volcanism occurred as late as Oligocene time, but continues sporadically up to present. Eruptions were most vigorous 6-10 million years ago and 2-3 million years ago, when most of the basalt was released. Less extensive eruptions continued 0.01 to 1.6 million years ago.National Resources Canada - Catalogue of Canadian volcanoes: Chilcotin Plateau basalts
Retrieved on 2008-03-15 These lava flows have been dominantly exposed by erosion resulting from the great floods that flowed in this region throughout the past ice ages, which laid bare many layers of the basalt flows along the

Fraser Canyon The Fraser Canyon is a major landform of the Fraser River where it descends rapidly through narrow rock gorges in the Coast Mountains en route from the Interior Plateau of British Columbia to the Fraser Valley. Colloquially, the term "Fraser Ca ...

from Soda Creek south to Canoe Creek elsewhere along the Chilcotin, Chilko, Chilanko and Taseko Rivers, and also to the east of the Fraser River at Chasm Provincial Park and along the Upper Deadman River. Prior to Late Pleistocene glacial erosion these centers formed a series of coalesced, low-profile

shield volcano A shield volcano is a type of volcano named for its low profile, resembling a shield lying on the ground. It is formed by the eruption of highly fluid (low viscosity) lava, which travels farther and forms thinner flows than the more viscous lava ...

es of unknown volume and distribution. The Chilcotin Group were thought to potentially be linked to the partly coeval Columbia River Basalt Group. However, its morphology and geochemistry have been proven much similar to other volcanic plateaus such as the Snake River Plain in Idaho and parts of

Iceland Iceland is a Nordic countries, Nordic island country between the Atlantic Ocean, North Atlantic and Arctic Oceans, on the Mid-Atlantic Ridge between North America and Europe. It is culturally and politically linked with Europe and is the regi ...

(Bevier, 1983).

Formation of the Chilcotin Plateau Basalts

The distribution and volume of the Chilcotin Group is unknown due to extensive Pleistocene glacial cover. This presumably glacial "drift" is very thick, and in most regions completely obscures the volcanism. Individual vents for

volcanism include small

cinder cone A cinder cone or scoria cone is a steep, volcanic cone, conical landform of loose pyroclastic rock, pyroclastic fragments, such as volcanic ash, clinkers, or scoria that has been built around a volcanic vent. The pyroclastic fragments are forme ...

volcanic plug A volcanic plug, also called a volcanic neck or lava neck, is a volcano, volcanic object created when magma hardens within a Volcanic vent, vent on an active volcano. When present, a plug can cause an extreme build-up of high gas pressure if risi ...

s, and

gabbro Gabbro ( ) is a phaneritic (coarse-grained and magnesium- and iron-rich), mafic intrusive igneous rock formed from the slow cooling magma into a holocrystalline mass deep beneath the Earth's surface. Slow-cooling, coarse-grained gabbro is ch ...

ic feeders, which locally crosscut lava flows. Recent studies indicate that the volume of the Chilcotin Group is much less than previously thought, and that the "Plateau" is likely Eocene in age. This means that the Chilcotin is likely composed of many local volcanic vents, that were of small volumes that fed into the paleo-landscape, and subsequently are found in the major river systems that we see at present. Prior to 16 million years ago, the western

Cascade Volcanic Arc The Cascade Volcanoes (also known as the Cascade Volcanic Arc or the Cascade Arc) are a number of volcanoes in a continental volcanic arc in western North America, extending from southwestern British Columbia through Washington and Oregon to No ...

stratovolcanoes erupted with periodic regularity for over 27 million years, even as they do today. The ultimate cause of this volcanism is still up for debate, however, the most widely accepted idea is that a

back-arc basin A back-arc basin is a type of geologic Structural basin, basin, found at some convergent boundary, convergent plate boundaries. Presently all back-arc basins are submarine features associated with island arcs and subduction zones, with many found ...

behind the Cascadia subduction zone initiated the widespread and voluminous basaltic volcanism. Some centers erupted along pre-existing brittle fault systems while volcanism along its northern portion is most widely believed to have been related to a centre of upwelling

magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma (sometimes colloquially but incorrectly referred to as ''lava'') is found beneath the surface of the Earth, and evidence of magmatism has also ...

called the Anahim hotspot (similar to that associated with present-day Hawaii), creating the

Rainbow A rainbow is an optical phenomenon caused by refraction, internal reflection and dispersion of light in water droplets resulting in a continuous spectrum of light appearing in the sky. The rainbow takes the form of a multicoloured circular ...

, Ilgachuz and Itcha Range

es which also in turn form part of the Anahim Volcanic Belt. The exact nature of the relationship between the Anahim hotspot and the Chilcotin Group is unknown, however.

Notable vents

Volcanoes of the Chilcotin Group include: * Alixton Creek * Browns Lake * Crows Bar * Prentice Gulch * Thaddeus Lake * Alkali Lake * Canoe Creek * Dog Creek * Leon Creek * Lambly Creek * Missezula Lake * Nicola (Chester) * Quilchena Creek * West Kettle River * Hydraulic Lake * Chilcotin Creek Cone * Lightning Peak * Black Dome Mountain * Skoatl Point * Alasla Mountain * Tin Cup Mountain * Mount Begbie * Forestry Hill * Lone Butte

References

{{Reflist

External links

The Cheslatta Lake suite:Miocene mafic, alkaline magmatism in central British Columbia
Canadian Cascade Arc Plateaus of British Columbia Miocene volcanism Pliocene volcanism Pleistocene volcanism Landforms of the Chilcotin Geologic groups of British Columbia Flood basalts Neogene British Columbia Basalt groups

Formation of the Chilcotin Plateau Basalts

Notable vents

See also

References

External links