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 throu ...

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 ...

in south-central

British Columbia British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, ...

, Canada. Predominantly, during

Miocene The Miocene ( ) is the first 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 means "less recen ...

and

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Interior Plateau The Interior Plateau comprises a large region of the Interior of British Columbia, and lies between the Cariboo and Monashee Mountains on the east, and the Hazelton Mountains, Coast Mountains and Cascade Range on the west.''Landforms of British C ...

. The distribution is assumed to engulf up to 50,000 km² of the

Pacific Northwest The Pacific Northwest (sometimes Cascadia, or simply abbreviated as 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 ...

, 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 formation ...

, 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 Soda Creek is a rural subdivision 38 km north of Williams Lake in British Columbia, Canada. Located on the east bank of the Fraser River, Soda Creek was originally the home of the Xat'sull First Nation. Soda Creek Indian Reserve No. 1 is ...

south to Canoe Creek elsewhere along the Chilcotin, Chilko, Chilanko and

Taseko River The Taseko River or Dasiqox in the original Chilcotin, is a tributary of British Columbia's Chilko River, a tributary of the Chilcotin River which joins the Fraser near the city of Williams Lake. The Taseko has its origins at Taylor Pass in ...

s, 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 warrior's 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 v ...

es of unknown volume and distribution. The Chilcotin Group were thought to potentially be linked to the partly coeval

Columbia River Basalt Group The Columbia River Basalt Group is the youngest, smallest and one of the best-preserved continental flood basalt province on Earth, covering over mainly eastern Oregon and Washington, western Idaho, and part of northern Nevada. The basalt grou ...

. However, its morphology and geochemistry have been proven much similar to other volcanic plateaus such as the

Snake River Plain image:Snake River view near Twin Falls, Idaho.jpg, The Snake River cutting through the plain leaves many canyons and Canyon#List of gorges, gorges, such as this one near Twin Falls, Idaho The Snake River Plain is a geology, geologic feature ...

in Idaho and parts of

Iceland Iceland ( is, Ísland; ) is a Nordic island country in the North Atlantic Ocean and in the Arctic Ocean. Iceland is the most sparsely populated country in Europe. Iceland's capital and largest city is Reykjavík, which (along with its s ...

(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 conical hill of loose pyroclastic fragments, such as volcanic clinkers, volcanic ash, or scoria that has been built around a volcanic vent. The pyroclastic fragments are formed by explosive eruptions o ...

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

s, and

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

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 volcanic arc in western North America, extending from southwestern British Columbia through Washington and Oregon to Northern Calif ...

stratovolcano A stratovolcano, also known as a composite volcano, is a conical volcano built up by many layers (strata) of hardened lava and tephra. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile with a summit crater and per ...

es 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 basin, found at some convergent plate boundaries. Presently all back-arc basins are submarine features associated with island arcs and subduction zones, with many found in the western Pacific Ocean. Most of ...

behind the

Cascadia subduction zone The Cascadia subduction zone is a convergent plate boundary that stretches from northern Vancouver Island in Canada to Northern California in the United States. It is a very long, sloping subduction zone where the Explorer, Juan de Fuca, and ...

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 center of upwelling

magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural sa ...

called the

Anahim hotspot The Anahim hotspot is a hypothesized hotspot in the Central Interior of British Columbia, Canada. It has been proposed as the candidate source for volcanism in the Anahim Volcanic Belt, a long chain of volcanoes and other magmatic features tha ...

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

Rainbow A rainbow is a meteorological phenomenon that is caused by reflection, refraction and dispersion of light in water droplets resulting in a spectrum of light appearing in the sky. It takes the form of a multicoloured circular arc. Rainbows c ...

, Ilgachuz and

Itcha Range The Itcha Range, also known as the Itchas, is a small isolated mountain range in the West-Central Interior of British Columbia, Canada. It is located northeast of the community of Anahim Lake. With a maximum elevation of , it is the lowest of ...

es which also in turn form part of the

Anahim Volcanic Belt The Anahim Volcanic Belt (AVB) is a west–east trending chain of volcanoes and related magmatic features in British Columbia, Canada. It extends from Athlone Island on the Central Coast, running eastward through the strongly uplifted and deeply ...

. The exact nature of the relationship between the Anahim hotspot and the Chilcotin Group is, however, unknown.

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 Leon Creek is a tributary stream of the Medina River, in Bexar County, Texas, Bexar County, Texas. Leon Creek has its source seven miles northeast of Leon Springs, Texas, Leon Springs in northwestern Bexar County. The creek runs southeast throug ...

* Lambly Creek * Missezula Lake * Nicola (Chester) * Quilchena Creek *

West Kettle River The West Kettle River is a tributary of the Kettle River in the Canadian province of British Columbia. It is part of the Columbia River basin, as the Kettle River is a tributary of the Columbia River. Course The West Kettle River originates in St ...

* Hydraulic Lake * Chilcotin Creek Cone * Lightning Peak *

Black Dome Mountain Black Dome Mountain is the northernmost summit of the Camelsfoot Range, which lies along the west side of the Fraser River, north of Lillooet, British Columbia, Canada. It is an ancient butte-like volcano located in the formation known as the Chi ...

Skoatl Point Skoatl Point is a volcanic plug located in the formation known as the Chilcotin Group, which lie between the Pacific Ranges of the Coast Mountains and the mid-Fraser River in British Columbia, Canada. See also * List of volcanoes in Canada Lis ...

* Alasla Mountain * Tin Cup Mountain *

Mount Begbie Mount Begbie is a mountain summit located in the Gold Range of the Monashee Mountains in British Columbia, Canada. Situated west of the Columbia River high above the shore of Upper Arrow Lake, this prominent peak is visible from the Trans-Ca ...

* 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 Volcanic belts Landforms of the Chilcotin