Northern Cordilleran volcanic province
Encyclopedia
The Northern Cordilleran Volcanic Province (NCVP), formerly known as the Stikine Volcanic Belt, is a geologic province
defined by the occurrence of Miocene to Holocene volcano
es in the Pacific Northwest
of North America
. This belt of volcanoes extends roughly north-northwest from northwestern British Columbia
and the Alaska Panhandle
through Yukon
to the Southeast Fairbanks Census Area
of far eastern Alaska
, in a corridor hundreds of kilometres wide. It is the most recently defined volcanic province in the Western Cordillera. It has formed due to extensional cracking
of the North American continent—similar to other on-land extensional volcanic zones, including the Basin and Range Province and the East African Rift
. Although taking its name from the Western Cordillera, this term is a geologic grouping rather than a geographic one. The southmost part of the NCVP has more, and larger, volcanoes than does the rest of the NCVP; further north it is less clearly delineated, describing a large arch that sways westward through central Yukon.
At least four large volcanoes are grouped with the Northern Cordilleran Volcanic Province, including Hoodoo Mountain
in the Boundary Ranges
, the Mount Edziza volcanic complex
on the Tahltan Highland
, and the Level Mountain Range
and Heart Peaks
on the Nahlin Plateau
. These four volcanoes have volumes of more than 15 km³ (3.6 cu mi), the largest and oldest which is the Level Mountain Range with an area of 1800 square kilometre and a volume of more than 860 km³ (206.3 cu mi). Apart from the large volcanoes, several smaller volcanoes exist throughout the Northern Cordilleran Volcanic Province, including cinder cone
s which are widespread throughout the volcanic zone. Most of these small cones have been sites of only one volcanic eruption; this is in contrast to the larger volcanoes throughout the volcanic zone, which have had more than one volcanic eruption throughout their history.
The Northern Cordilleran Volcanic Province is part of an area of intensive earthquake
and volcanic activity around the Pacific Ocean
called the Pacific Ring of Fire
. However, the Northern Cordilleran Volcanic Province is commonly interpreted to be part of a gap in the Pacific Ring of Fire between the Cascade Volcanic Arc
further south and the Aleutian Arc
further north. But the Northern Cordilleran Volcanic Province is recognized to include over 100 independent volcanoes that have been active in the past 1.8 million years. At least three of them have erupted in the past 360 years, making it the most active volcanic area in Canada. Nevertheless the dispersed population within the volcanic zone has witnessed few eruptions due to remoteness and the infrequent volcanic activity.
The Northern Cordilleran Volcanic Province has been a zone of active volcanism
since it began to form 20 million years ago. Unlike other parts of the Pacific Ring of Fire, the Northern Cordilleran Volcanic Province has its origins in continental rift
ing—an area where the Earth's crust
and lithosphere
is being pulled apart. This differs from other portions of the Pacific Ring of Fire as it consists largely of volcanic arc
s formed by subducting
oceanic crust
at oceanic trench
es along continental margin
s circling the Pacific Ocean
. The continental crust
at the Northern Cordilleran Volcanic Province is being stretched at a rate of about 2 cm (0.78740157480315 in) per year. This incipient rifting formed as a result of the Pacific Plate
sliding northward along the Queen Charlotte Fault
, on its way to the Aleutian Trench
, which extends along the southern coastline of Alaska and the adjacent waters off the southern coast of the Kamchatka Peninsula
. As a result, volcanism in the Northern Cordilleran Volcanic Province is also not related to back-arc basin
volcanism. When the stored energy is suddenly released by slippage across the fault at irregular intervals, it can create very large earthquake
s, such as the magnitude
8.1 Queen Charlotte Islands earthquake of 1949
. As these far-field forces stretch the North American crust, the near surface rocks fracture along steeply dipping faults parallel to the rift zone. Hot magma rises between these fractures to create passive or effusive eruption
s. Volcanoes within the Northern Cordilleran Volcanic Province are located along short northerly trending segments which in the northern part of the volcanic province are unmistakenably involved with north-trending rift structures, including synvolcanic graben
s and grabens with one major fault line along only one of the boundaries (half-grabens). Grabens are indicative of tensional forces and crustal stretching.
Two major north-trending faults hundreds of kilometres long extend along the Northern Cordilleran Volcanic Province. These two rock fractures, known as the Tintina
and Denali
fault systems, have been tectonically
active since the Cretaceous
period as strike-slip faults. The Denali fault to the west and the Tintina fault to the east are nearly 2000 km (1,242.7 mi) long, extending from northern British Columbia to central Alaska. Other mechanisms suggested for triggering volcanism in the Northern Cordilleran Volcanic Province include mantle plume
s, deglaciation and slab window
s, although continental rifting is the most accurrate mechanism for activating volcanism in the volcanic zone. Further evidence for continental rifting in the Northern Cordilleran Volcanic Province is magmas are mainly alkaline, it includes highly alkaline and peralkaline
rock types, the main spatial-temporal pattern of volcanism is in the middle of the volcanic province followed by movement to the south, north and possibly northeast, heat flow in the Northern Cordilleran Volcanic Province is high, seismic activity is largely absent in the volcanic province and the largest period of volcanism correlates with an interval of net extension between the Pacific and North American plates.
A range of more heavily alkaline rock types not commonly found in the Western Cordillera are regionally widespread in the Northern Cordilleran Volcanic Province. These include nephelinite
, basanite
and peralkaline phonolite
, trachyte
, and comendite
lavas. The most magnesium oxide
-rich nephelinites, basanites and alkaline basalts all through the Northern Cordilleran Volcanic Province display trace element abundances and isotopic compositions that are logical with an asthenospheric
source like those for average oceanic island basalt and for alkaline basalts younger than five million years in the rift-related Basin and Range Province of southwestern United States and northwestern Mexico
. One hypothesized explanation for oceanic island basalt in the Earth's upper mantle under the Northern Cordilleran Volcanic Province is the existence of a slab window. However, not much of a noticeable evidence linking the production of magma in the upper mantle to a possible tectonic system has been stated.
The existence of a fault next to the western flank of the Mount Edziza volcanic complex is normally considered to be the prime structural evidence for continental rifting in the Northern Cordilleran Volcanic Province. However, more recent mapping and seismic studies in the Coast Mountains have documented the presence of brittle rift-related faults southwest of the small community of Stewart
in northwestern British Columbia. But these faults were in a matter of dispute in 1997 by geologists, stating these faults were last active between 20 and five million years ago. In 1999, a sequence of north-trending faults were mapped that seem to represent young rifting events parallel with the southwestern boundary of the Northern Cordilleran Volcanic Province. These rift-related faults might have been active as recently as five million years ago and they might have connections with adjacent Miocene and younger volcanic activity in the southern part of the Northern Cordilleran Volcanic Province. In addition, brittle faults with similar north-trending directions might enlarge as far north as the fault next to the western flank of the Mount Edziza volcanic complex. These tectonic events might have helped form the structure the Northern Cordilleran Volcanic Province.
Subduction
beside the northern portion of the Western Cordillera deceased between 43 and 40 million years ago. This finally caused the formation of a slab window under the northern portion of the Western Cordillera 10 million years ago, supporting an entrance to relatively undepleted upper mantle. A switch in relative plate motions at the Queen Charlotte Fault 10 million years ago produced consequent strain throughout the northern portion of the Western Cordillera, resulting in crustal thinning and decompression melting of oceanic island basalt-like mantle to create alkaline volcanism. Several plate motion models indicate a rebound to net compression throughout the Queen Charlotte Fault sometime after four million years ago. Although extensive rifting has not yet been recognized in the Northern Cordilleran Volcanic Province, volcanism throughout the past 1.6 million years is possibly due to repetitive upper mantle upwelling and adjacent transtension
throughout the Queen Charlotte Fault, accommodated partly by numerous east-west trending fault zones that extend all through the Northern Cordilleran Volcanic Province.
The volcanics comprising the Northern Cordilleran Volcanic Province are conistent with the rifting environment. Alkaline basalt, lesser hawaiite
and basanite magmas from effusive eruptions create the massive shield volcanoes and small cinder cones throughout the volcanic province, several of which comprise lherzolite
magma. Felsic magmas from more viscous eruptions create the massive central volcanoes and largely consist of trachyte, pantellerite
and comendite lavas. These felsic volcanics are understood to have been created by fractionation of mainly alkali basalt magma in crustal reservoirs. An area of continental rifting, such as the Northern Cordilleran Volcanic Province, would aid the formation of high-level reservoirs of capable size and thermal activity to maintain long-lived fractionation.
s throughout the Northern Cordilleran Volcanic Province indicate that a narrow lithosphere
lies under the northern portion of the volcanic province and a more dense lithosphere lies under the southern portion of the volcanic province. This indication is further provided if the geothermal gradient inside the lithosphere under the northern portion of the Northern Cordilleran Volcanic Province is greater than that in the southern portion of the province. A greater geothermal gradient would indicate that a xenolith recording a temperature of 900 °C (1,652 °F) was collected from a shallower depth than one from a zone with a reduced geothermal gradient that also records a temperature of 900 °C (1,652 °F).
Further evidence that indicate lithospheric thickening beneath the middle portion of Stikinia include the increased profusion of cognate inclusion and plagioclase megacrysts in volcanic rocks from the southern portion of the volcanic province, which might be evidence of magma ponding and magma crystallization in the lithosphere before a volcanic eruption, and the restricted existence of petrologically
evolved rock types in the southern half of the Northern Cordilleran Volcanic Province. If the developed magmas originated from fractionation of mafic magmas, fractionation associated with lithospheric contamination, or entirely from melting of the associated lithosphere, their existence suggests more dense lithosphere lies under the southern portion of the Northern Cordilleran Volcanic Province.
In the Llangorse section of the Atlin Volcanic Field in northwestern British Columbia, a suite of xenoliths confines the thickness of the Northern Cordilleran Volcanic Province mantle lithosphere to as thin as 18 km (11.2 mi) and a thickness no more than 39 km (24.2 mi). Analysis of recent data related to earthquake
s in the southwestern portion of the volcanic province indicates that the crust under Stikinia, which comprises the bedrock
underlying a large number of volcanoes in the southern portion of the Northern Cordilleran Volcanic Province, is also more dense than the crust under the nearby Coast Plutonic Complex, which consists of a broad belt of granitic
and dioritic
intrusive rocks that collectively represent more than 140 million years of nearly continuous subduction-related magmatism.
Hot spring
s are present throughout the Northern Cordilleran Volcanic Province, indicating magmatic heat is present under the Northern Cordilleran Volcanic Province. They are formed if water percolates deeply through the crust and heats up from the primal magmatic heat under the surface. After the groundwater is heated, the heated groundwater rises to the surface as a hot spring. In some cases, the heated groundwater may rise along extensional faults related to rifting in the Northern Cordilleran Volcanic Province. The Lakelse Hot Springs
near Lakelse Lake Provincial Park
in northern British Columbia is interpreted to be one such example. With a temperature of 89 °C (192.2 °F), the springs are the hottest in Canada. It is also possible the magma associated with the Nass Valley eruption 250 years ago to the north rose along the same north trending fault lines fueling the Lakelse Hot Springs. Hot springs are also present in Iskut River Hot Springs Provincial Park
and Choquette Hot Springs Provincial Park
in northwestern British Columbia.
Xenolith
s, rock fragments that become enveloped in a larger igneous rock
, are widespread in the Northern Cordilleran Volcanic Province. Xenoliths that originated in the Earth's crust include rich metamorphic rock
s and felsic intrusive rocks. Granulite
xenoliths exist mainly at the Fort Selkirk Volcanic Field
in central Yukon, Prindle Volcano in easternmost Alaska and at Castle Rock
and the Iskut River
in northern British Columbia. Felsic intrusive xenoliths are a lot more common and usually originate from adjacent granitic intrusions, including those that form the Coast Mountains. More than 14 volcanic zones throughout the Northern Cordilleran Volcanic Province comprise xenoliths that originated from the Earth's mantle and are located mainly at the Yukon-Tanana Terrane, the Cache Creek Terrane and at volcanoes occupying the Paleozoic
and Mesozoic
Stikinia
terrane. They consist of lherzolite, harzburgite
, wehrlite, dunite
, websterite and garnet
composed pyroxenite
. The highest and lowest temperatures recorded by mantle xenoliths increase to the south and decrease to the north. Mantle xenoliths at Prindle Volcano in easternmost Alaska record the minimum temperature of 860 °C (1,580 °F) and mantle xenoliths from the Fort Selkirk Volcanic Field in central Yukon record the minimum temperature range from 960 to 1050 °C (1,760 to 1,922 F). At Castle Rock in northern British Columbia, mantle xenoliths record the maximum temperature of 1260 °C (2,300 °F), as well as the maximum temperature range from 1000 to 1260 °C (1,832 to 2,300 F). The minimum xenolith temperatures indicate that the boundary between the Earth's crust and mantle
is shallowest beneath the northern portion of the Northern Cordilleran Volcanic Province. Therefore, the temperature ranges for the northernmost xenolith series is about one-half the temperature range found in xenoliths at the southern portion of the volcanic province.
Megacryst
s, crystals or grains that are considerably larger than the encircling matrix
, are commonly found in lava flows throughout the Northern Cordilleran Volcanic Province. They consist of three different groups, including kaersutitic
amphibole
megacrysts, clinopyroxene megacrysts and plagioclase
megacrysts. Megacrysts made of kaersutite are known to be found mainly at Llangorse Mountain
in northern British Columbia. Black glassy clinopyroxene megacrysts are widespread throughout the Northern Cordilleran Volcanic Province, suggesting their creation is independent of lithosphere structure. In contrast, clear glassy plagioclase megacrysts are found largely at the southern end of the Northern Cordilleran Volcanic Province and largely within the boundaries of the Stikinia terrane. This suggests the plagioclase megacrysts have a source that is sensitive to the Earth's lithosphere, including contamination or magma ponding. Megacrysts made of plagioclase and clinopyroxene regionally show significant evidence of reaction with the associated magma, including sieve-textured cores and random, resorbed and embayed outer margins wherever they are located.
Lava tube
s are widespread in the Northern Cordilleran Volcanic Province, and are typically basaltic in composition. At the Level Mountain Range, lava tubes reach diameters of 1 m (3.3 ft) to 2 m (6.6 ft). These owed their origin to highly fluid lavas with temperatures of at least 1200 °C (2,192 °F). In Nisga'a Memorial Lava Beds Provincial Park of northwestern British Columbia, lava tubes are present that were formed during one of Canada's most recent volcanic eruptions in the 18th century. Lava Fork
at the British Columbia-Alaska border is influenced by lava flows from a recent volcanic eruption that later collapsed into underlying lava tubes after the lava solidified. Sections of these collapsed lava tubes now form volcanic pits.
Extensive areas of nearly flat-lying lava flows throughout the Northern Cordilleran Volcanic Province can cover areas of at least 100 square kilometre and are generally composed of highly-fluid basaltic lava. However, lava plains that pre-date the last glacial period have been eroded and overridden by glacial ice, affording a less distinctive form to these older landforms. For example, lava beds at least a million years old in central Yukon contain unconsolidated glacial deposits that were deposited when glacial ice rode on top of the lava flows comprising the lava beds.
Subvolcanic
intrusion
s in the Northern Cordilleran Volcanic Province are exposed in areas of high relief. This includes volcanic plug
s found at the Mount Edziza volcanic complex, the Level Mountain Range, Hoodoo Mountain and in the Atlin and Maitland areas. Volcanic plugs in the Atlin and Maitland areas consist of olivine nephelinite and basanite magmas. Minor plugs made of gabbro
ic and granitic
magma are associated with volcanic stratigraphy
at the Mount Edziza volcanic complex and Level Mountain Range.
s, known as Stikinia, Cache Creek
, Yukon-Tanana
and Cassiar
. Stikinia is a sequence of late Paleozoic and Mesozoic aged volcanic, plutonic and sedimentary rocks interpreted to have been created in an island arc environment that were later placed along a pre-existing continental margin
. The Cache Creek Terrane is believed to have formed widely in a pre-existing oceanic basin
. It comprises late Paleozoic to Mesozoic aged oceanic melange and abyssal peridotites intruded by younger granitic intrusions. The Yukon-Tanana and Cassiar terranes consist of shifted sedimentary and metamorphic rocks that were derived from the North American continent.
The southern boundary of the Northern Cordilleran Volcanic Province is parallel with southwestern Stikinia and is characterized by separate volcanic vents and erosional remains of lavas south of the small community of Stewart
. The southern boundary of the Northern Cordilleran Volcanic Province also parallels with a gap in modern volcanism and the supposed northern boundary of the Cascadia subduction zone
, defined by the eastward extension of the northern edge of the subducting Juan de Fuca Plate
. These two zones divide the Northern Cordilleran Volcanic Province from modern volcanic zones further south, including the broad Chilcotin Plateau
, the east-west trending Anahim Volcanic Belt
and the monogenetic Wells Gray-Clearwater volcanic field
in the British Columbia Interior
. The eastern boundary of the Northern Cordilleran Volcanic Province is bounded by the Cassiar Terrane and is adjoined by a cluster of volcanic plug
s in central British Columbia. The northern and western boundaries are adjoined by the Yukon-Tanana and Cache Creek terranes where there lies volcanics in eastern Alaska and weathered remains of lava flows just north and west of Dawson City in west-central Yukon.
, which is the northern extension of the Northern Rocky Mountain Trench. The fastest rates of strike-slip movement along the Tintina Fault likely occurred during two pulses in the Mid-Cretaceous and early Cenozoic periods, respectively, with the latter probably occurring during the Eocene
epoch. Since the Cretaceous, the Tintina Fault has offset 450 km (279.6 mi) of the surface, although some evidence suggest as much as 1200 km (745.6 mi) of offset. The end result is that the Northern Cordilleran Volcanic Province and the terrains of which the volcanic province occupies have moved northwards. In the context of plate tectonics, strip-slip movement of the Tintina Fault is also related to strike-slip movement along the San Andreas Fault
and other extensional or strike-slip fault systems of western North America.
To the west, the Denali Fault is the source of minor earthquakes that extend along the length of the fault. In contrast to the Tintina Fault, strike-slip movement along the Denali Fault has offset at least 370 km (229.9 mi) of the surface. The fault separates mountains of the Insular Belt
from mountains east of the fault. Tectonic events in the Insular Belt are also related to movement along the Denali Fault.
in northwestern British Columbia. As more mapping and dating of volcanic deposits was completed in the Western Cordillera, the Stikine Volcanic Belt was expanded to include volcanic deposits further and further from the geographic area associated with the name Stikine. In part for this reason, scientists Ben Edwards and James Russell redefined this area of volcanism as the Northern Cordilleran Volcanic Province. As a geographic descriptor, application of the name Stikine to volcanic rocks exposed along the Yukon River
seems a bit odd and confusing. As well, a much older group of totally unrelated volcanic rock
s comprise the Stikine Assemblage, which also mainly occurs within the geographic area informally referred to as Stikine Country
. The Northern Cordilleran Volcanic Province is a broader name, to encompass a broader geographic area, in which the most recent volcanism has a similar character (mainly alkaline, mafic volcanic rocks), a similar age range (Miocene
to Holocene
), and a similar tectonic setting (transtension).
Geologic province
A geologic or geomorphic province is a spatial entity with common geologic or geomorphic attributes. A province may include a single dominant structural element such as a basin or a fold belt, or a number of contiguous related elements...
defined by the occurrence of Miocene to Holocene volcano
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...
es in the Pacific Northwest
Pacific Northwest
The Pacific Northwest is a region in northwestern North America, bounded by the Pacific Ocean to the west and, loosely, by the Rocky Mountains on the east. Definitions of the region vary and there is no commonly agreed upon boundary, even among Pacific Northwesterners. A common concept of the...
of North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
. This belt of volcanoes extends roughly north-northwest from northwestern British Columbia
British Columbia
British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...
and the Alaska Panhandle
Alaska Panhandle
Southeast Alaska, sometimes referred to as the Alaska Panhandle, is the southeastern portion of the U.S. state of Alaska, which lies west of the northern half of the Canadian province of British Columbia. The majority of Southeast Alaska's area is part of the Tongass National Forest, the United...
through Yukon
Yukon
Yukon is the westernmost and smallest of Canada's three federal territories. It was named after the Yukon River. The word Yukon means "Great River" in Gwich’in....
to the Southeast Fairbanks Census Area
Southeast Fairbanks Census Area, Alaska
Southeast Fairbanks Census Area is a census area located in the state of Alaska, United States. As of the 2000 census, the population was 6,174. It is part of the unorganized borough and therefore has no borough seat...
of far eastern Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
, in a corridor hundreds of kilometres wide. It is the most recently defined volcanic province in the Western Cordillera. It has formed due to extensional cracking
Rift
In geology, a rift or chasm is a place where the Earth's crust and lithosphere are being pulled apart and is an example of extensional tectonics....
of the North American continent—similar to other on-land extensional volcanic zones, including the Basin and Range Province and the East African Rift
East African Rift
The East African Rift is an active continental rift zone in eastern Africa that appears to be a developing divergent tectonic plate boundary. It is part of the larger Great Rift Valley. The rift is a narrow zone in which the African Plate is in the process of splitting into two new tectonic plates...
. Although taking its name from the Western Cordillera, this term is a geologic grouping rather than a geographic one. The southmost part of the NCVP has more, and larger, volcanoes than does the rest of the NCVP; further north it is less clearly delineated, describing a large arch that sways westward through central Yukon.
At least four large volcanoes are grouped with the Northern Cordilleran Volcanic Province, including Hoodoo Mountain
Hoodoo Mountain
Hoodoo Mountain is a potentially active flat-topped stratovolcano in the Stikine Country of northwestern British Columbia, Canada, located northeast of Wrangell, Alaska on the north side of the lower Iskut River and east of its junction with the Stikine River...
in the Boundary Ranges
Boundary Ranges
The Boundary Ranges, also known in the singular and as the Alaska Boundary Range, are the largest and most northerly subrange of the Coast Mountains...
, the Mount Edziza volcanic complex
Mount Edziza volcanic complex
The Mount Edziza volcanic complex is a large and potentially active north-south trending complex volcano in Stikine Country, northwestern British Columbia, Canada, located southeast of the small community of Telegraph Creek...
on the Tahltan Highland
Tahltan Highland
The Tahltan Highland is an upland area of plateau and relatively lower mountain ranges in British Columbia, Canada, lying east of the Boundary Ranges and south of the Inklin River...
, and the Level Mountain Range
Level Mountain Range
The Level Mountain Range, also known as Level Mountain, is a mountain range in Cassiar Country, northwestern British Columbia, Canada, located just northeast of Callison Ranch, southwest of Dease Lake and about north of Mount Edziza. It consists of a massive shield volcano and lies on the Nahlin...
and Heart Peaks
Heart Peaks
Heart Peaks, originally known as the Heart Mountains, is a mountain massif in the Northern Interior of British Columbia, Canada. It is located northwest of the small community of Telegraph Creek and just southwest of Callison Ranch. With a maximum elevation of , it rises above the surrounding...
on the Nahlin Plateau
Nahlin Plateau
The Nahlin Plateau is a plateau in northwestern British Columbia, Canada, located between the Sheslay River and Tuya River on the west and east and the Nahlin River and the Stikine River to the north and south...
. These four volcanoes have volumes of more than 15 km³ (3.6 cu mi), the largest and oldest which is the Level Mountain Range with an area of 1800 square kilometre and a volume of more than 860 km³ (206.3 cu mi). Apart from the large volcanoes, several smaller volcanoes exist throughout the Northern Cordilleran Volcanic Province, including cinder cone
Cinder cone
According to the , Cinder Cone is the proper name of 1 cinder cone in Canada and 7 cinder cones in the United States:In Canada: Cinder Cone In the United States:...
s which are widespread throughout the volcanic zone. Most of these small cones have been sites of only one volcanic eruption; this is in contrast to the larger volcanoes throughout the volcanic zone, which have had more than one volcanic eruption throughout their history.
The Northern Cordilleran Volcanic Province is part of an area of intensive earthquake
Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...
and volcanic activity around the Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
called the Pacific Ring of Fire
Pacific Ring of Fire
The Pacific Ring of Fire is an area where large numbers of earthquakes and volcanic eruptions occur in the basin of the Pacific Ocean. In a horseshoe shape, it is associated with a nearly continuous series of oceanic trenches, volcanic arcs, and volcanic belts and/or plate movements...
. However, the Northern Cordilleran Volcanic Province is commonly interpreted to be part of a gap in the Pacific Ring of Fire between the Cascade Volcanic Arc
Cascade Volcanoes
The Cascade Volcanoes are a number of volcanoes in a volcanic arc in western North America, extending from southwestern British Columbia through Washington and Oregon to Northern California, a distance of well over 700 mi ...
further south and the Aleutian Arc
Aleutian Arc
The Aleutian Arc is a large volcanic arc in the U.S. state of Alaska. It consists of a number of active and dormant volcanoes that have formed as a result of subduction along the Aleutian Trench...
further north. But the Northern Cordilleran Volcanic Province is recognized to include over 100 independent volcanoes that have been active in the past 1.8 million years. At least three of them have erupted in the past 360 years, making it the most active volcanic area in Canada. Nevertheless the dispersed population within the volcanic zone has witnessed few eruptions due to remoteness and the infrequent volcanic activity.
Origins and chemistry
Volcanism
Volcanism is the phenomenon connected with volcanoes and volcanic activity. It includes all phenomena resulting from and causing magma within the crust or mantle of a planet to rise through the crust and form volcanic rocks on the surface....
since it began to form 20 million years ago. Unlike other parts of the Pacific Ring of Fire, the Northern Cordilleran Volcanic Province has its origins in continental rift
Rift
In geology, a rift or chasm is a place where the Earth's crust and lithosphere are being pulled apart and is an example of extensional tectonics....
ing—an area where the Earth's crust
Crust (geology)
In geology, the crust is the outermost solid shell of a rocky planet or natural satellite, which is chemically distinct from the underlying mantle...
and lithosphere
Lithosphere
The lithosphere is the rigid outermost shell of a rocky planet. On Earth, it comprises the crust and the portion of the upper mantle that behaves elastically on time scales of thousands of years or greater.- Earth's lithosphere :...
is being pulled apart. This differs from other portions of the Pacific Ring of Fire as it consists largely of volcanic arc
Volcanic arc
A volcanic arc is a chain of volcanoes positioned in an arc shape as seen from above. Offshore volcanoes form islands, resulting in a volcanic island arc. Generally they result from the subduction of an oceanic tectonic plate under another tectonic plate, and often parallel an oceanic trench...
s formed by subducting
Subduction
In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...
oceanic crust
Oceanic crust
Oceanic crust is the part of Earth's lithosphere that surfaces in the ocean basins. Oceanic crust is primarily composed of mafic rocks, or sima, which is rich in iron and magnesium...
at oceanic trench
Oceanic trench
The oceanic trenches are hemispheric-scale long but narrow topographic depressions of the sea floor. They are also the deepest parts of the ocean floor....
es along continental margin
Continental margin
The continental margin is the zone of the ocean floor that separates the thin oceanic crust from thick continental crust. Continental margins constitute about 28% of the oceanic area....
s circling the Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
. The continental crust
Continental crust
The continental crust is the layer of igneous, sedimentary, and metamorphic rocks which form the continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called sial due to more felsic, or granitic, bulk composition, which lies in...
at the Northern Cordilleran Volcanic Province is being stretched at a rate of about 2 cm (0.78740157480315 in) per year. This incipient rifting formed as a result of the Pacific Plate
Pacific Plate
The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At 103 million square kilometres, it is the largest tectonic plate....
sliding northward along the Queen Charlotte Fault
Queen Charlotte Fault
The Queen Charlotte Fault is an active transform fault, located between the North American Plate and the Pacific Plate, Canada's equivalent of the San Andreas Fault. The Queen Charlotte Fault forms a triple junction on its south with the Cascadia subduction zone and the Explorer Ridge...
, on its way to the Aleutian Trench
Aleutian Trench
The Aleutian Trench is a subduction zone and oceanic trench which runs along the southern coastline of Alaska and the adjacent waters of northeastern Siberia off the coast of Kamchatka Peninsula. It is classified as a "marginal trench" in the east as it runs along the margin of the continent, and...
, which extends along the southern coastline of Alaska and the adjacent waters off the southern coast of the Kamchatka Peninsula
Kamchatka Peninsula
The Kamchatka Peninsula is a peninsula in the Russian Far East, with an area of . It lies between the Pacific Ocean to the east and the Sea of Okhotsk to the west...
. As a result, volcanism in the Northern Cordilleran Volcanic Province is also not related to back-arc basin
Back-arc basin
Back-arc basins are geologic features, submarine basins associated with island arcs and subduction zones.They are found at some convergent plate boundaries, presently concentrated in the Western Pacific ocean. Most of them result from tensional forces caused by oceanic trench rollback and the...
volcanism. When the stored energy is suddenly released by slippage across the fault at irregular intervals, it can create very large earthquake
Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...
s, such as the magnitude
Moment magnitude scale
The moment magnitude scale is used by seismologists to measure the size of earthquakes in terms of the energy released. The magnitude is based on the seismic moment of the earthquake, which is equal to the rigidity of the Earth multiplied by the average amount of slip on the fault and the size of...
8.1 Queen Charlotte Islands earthquake of 1949
1949 Queen Charlotte earthquake
The Queen Charlotte Islands earthquake of 1949 was a magnitude 8.1 interplate earthquake that struck the sparsely populated Queen Charlotte Islands and the Pacific Northwest coast on August 22, 1949. It is one of the world's greatest earthquakes. The main shock epicenter began in the ocean bottom...
. As these far-field forces stretch the North American crust, the near surface rocks fracture along steeply dipping faults parallel to the rift zone. Hot magma rises between these fractures to create passive or effusive eruption
Effusive eruption
An effusive eruption is a volcanic eruption characterized by the outpouring of lava onto the ground...
s. Volcanoes within the Northern Cordilleran Volcanic Province are located along short northerly trending segments which in the northern part of the volcanic province are unmistakenably involved with north-trending rift structures, including synvolcanic graben
Graben
In geology, a graben is a depressed block of land bordered by parallel faults. Graben is German for ditch. Graben is used for both the singular and plural....
s and grabens with one major fault line along only one of the boundaries (half-grabens). Grabens are indicative of tensional forces and crustal stretching.
Two major north-trending faults hundreds of kilometres long extend along the Northern Cordilleran Volcanic Province. These two rock fractures, known as the Tintina
Tintina Fault
The Tintina Fault is a large strike-slip fault in western North America, extending from northwestern British Columbia, Canada to the U.S. state of central Alaska. It represents the northern extension of the Rocky Mountain Fault in the northern United States....
and Denali
Denali Fault
The Denali Fault is a major intracontinental dextral strike-slip fault in western North America, extending from northwestern British Columbia, Canada to the U.S. state of central Alaska. It was the main fault along which the 2002 Denali earthquake occurred, which was measured as a magnitude of 7.9...
fault systems, have been tectonically
Tectonics
Tectonics is a field of study within geology concerned generally with the structures within the lithosphere of the Earth and particularly with the forces and movements that have operated in a region to create these structures.Tectonics is concerned with the orogenies and tectonic development of...
active since the Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
period as strike-slip faults. The Denali fault to the west and the Tintina fault to the east are nearly 2000 km (1,242.7 mi) long, extending from northern British Columbia to central Alaska. Other mechanisms suggested for triggering volcanism in the Northern Cordilleran Volcanic Province include mantle plume
Mantle plume
A mantle plume is a hypothetical thermal diapir of abnormally hot rock that nucleates at the core-mantle boundary and rises through the Earth's mantle. Such plumes were invoked in 1971 to explain volcanic regions that were not thought to be explicable by the then-new theory of plate tectonics. Some...
s, deglaciation and slab window
Slab window
In geology, a slab window is a gap that forms in a subducted oceanic plate when a mid-ocean ridge meets with a subduction zone. They are commonly associated with the formation of convergent plate boundaries and they have had significant effects on the formation of the North American Cordillera.A...
s, although continental rifting is the most accurrate mechanism for activating volcanism in the volcanic zone. Further evidence for continental rifting in the Northern Cordilleran Volcanic Province is magmas are mainly alkaline, it includes highly alkaline and peralkaline
Peralkaline
Peralkaline rocks include those igneous rocks which have a deficiency of aluminium such that sodium and potassium are in excess of that needed for feldspar. The presence of aegerine and riebeckite are indicative of peralkaline conditions....
rock types, the main spatial-temporal pattern of volcanism is in the middle of the volcanic province followed by movement to the south, north and possibly northeast, heat flow in the Northern Cordilleran Volcanic Province is high, seismic activity is largely absent in the volcanic province and the largest period of volcanism correlates with an interval of net extension between the Pacific and North American plates.
Nephelinite
Nephelinite is a fine-grained or aphanitic igneous rock made up almost entirely of nepheline and clinopyroxene . If olivine is present, the rock may be classified as an olivine nephelinite. Nephelinite is dark in color and may resemble basalt in hand specimen...
, basanite
Basanite
Basanite is an igneous, volcanic rock with aphanitic to porphyritic texture.The mineral assembly is usually abundant feldspathoids , plagioclase, and augite, together with olivine and lesser iron-titanium oxides such as ilmenite and magnetite-ulvospinel; minor alkali feldspar may be present, as...
and peralkaline phonolite
Phonolite
Phonolite is a rare igneous, volcanic rock of intermediate composition, with aphanitic to porphyritic texture....
, trachyte
Trachyte
Trachyte is an igneous volcanic rock with an aphanitic to porphyritic texture. The mineral assemblage consists of essential alkali feldspar; relatively minor plagioclase and quartz or a feldspathoid such as nepheline may also be present....
, and comendite
Comendite
Comendite is a hard, peralkaline igneous rock, a type of light blue grey rhyolite. Phenocrysts are sodic sanidine with minor albite and bipyrimidal quartz. Comendite occurs in the mountains Tibrogargan, Coonowrin, Tunbubudla, Coochin, Saddleback, Tibberoowuccum and Ngungun in the Glass House...
lavas. The most magnesium oxide
Magnesium oxide
Magnesium oxide , or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium . It has an empirical formula of and consists of a lattice of Mg2+ ions and O2– ions held together by ionic bonds...
-rich nephelinites, basanites and alkaline basalts all through the Northern Cordilleran Volcanic Province display trace element abundances and isotopic compositions that are logical with an asthenospheric
Asthenosphere
The asthenosphere is the highly viscous, mechanically weak and ductilely-deforming region of the upper mantle of the Earth...
source like those for average oceanic island basalt and for alkaline basalts younger than five million years in the rift-related Basin and Range Province of southwestern United States and northwestern Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
. One hypothesized explanation for oceanic island basalt in the Earth's upper mantle under the Northern Cordilleran Volcanic Province is the existence of a slab window. However, not much of a noticeable evidence linking the production of magma in the upper mantle to a possible tectonic system has been stated.
The existence of a fault next to the western flank of the Mount Edziza volcanic complex is normally considered to be the prime structural evidence for continental rifting in the Northern Cordilleran Volcanic Province. However, more recent mapping and seismic studies in the Coast Mountains have documented the presence of brittle rift-related faults southwest of the small community of Stewart
Stewart, British Columbia
Stewart is a small town, incorporated as a district municipality at the head of the Portland Canal in northwestern British Columbia, Canada. In 2006, its population was about 496.-History:...
in northwestern British Columbia. But these faults were in a matter of dispute in 1997 by geologists, stating these faults were last active between 20 and five million years ago. In 1999, a sequence of north-trending faults were mapped that seem to represent young rifting events parallel with the southwestern boundary of the Northern Cordilleran Volcanic Province. These rift-related faults might have been active as recently as five million years ago and they might have connections with adjacent Miocene and younger volcanic activity in the southern part of the Northern Cordilleran Volcanic Province. In addition, brittle faults with similar north-trending directions might enlarge as far north as the fault next to the western flank of the Mount Edziza volcanic complex. These tectonic events might have helped form the structure the Northern Cordilleran Volcanic Province.
Subduction
Subduction
In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...
beside the northern portion of the Western Cordillera deceased between 43 and 40 million years ago. This finally caused the formation of a slab window under the northern portion of the Western Cordillera 10 million years ago, supporting an entrance to relatively undepleted upper mantle. A switch in relative plate motions at the Queen Charlotte Fault 10 million years ago produced consequent strain throughout the northern portion of the Western Cordillera, resulting in crustal thinning and decompression melting of oceanic island basalt-like mantle to create alkaline volcanism. Several plate motion models indicate a rebound to net compression throughout the Queen Charlotte Fault sometime after four million years ago. Although extensive rifting has not yet been recognized in the Northern Cordilleran Volcanic Province, volcanism throughout the past 1.6 million years is possibly due to repetitive upper mantle upwelling and adjacent transtension
Transtension
Transtension is the term used to describe a rock mass or area of the Earth's crust that experiences both extensive and transtensive shear. As such, transtensional regions are characterised by both extensional structures and wrench structures ....
throughout the Queen Charlotte Fault, accommodated partly by numerous east-west trending fault zones that extend all through the Northern Cordilleran Volcanic Province.
The volcanics comprising the Northern Cordilleran Volcanic Province are conistent with the rifting environment. Alkaline basalt, lesser hawaiite
Hawaiite
Hawaiite is an olivine basalt with intermediate composition between alkali olivine and mugearite. It was first described at the island of Hawaii. In gemology, hawaiite is a colloquial term for Hawaii-originated peridot,which is gem-quality olivine mineral....
and basanite magmas from effusive eruptions create the massive shield volcanoes and small cinder cones throughout the volcanic province, several of which comprise lherzolite
Lherzolite
Lherzolite is a type of ultramafic igneous rock. It is a coarse grained rock consisting of 40 to 90% olivine along with significant orthopyroxene and lesser calcic chromium rich clinopyroxene. Minor minerals include chromium and aluminium spinels and garnets. Plagioclase can occur in lherzolites...
magma. Felsic magmas from more viscous eruptions create the massive central volcanoes and largely consist of trachyte, pantellerite
Pantellerite
Pantellerite is a peralkaline rhyolite. It has a higher iron and lower aluminium composition than comendite. It is named after Pantelleria, a volcanic island in the Strait of Sicily and the type location for this rock. On Pantelleria the rock is usually found as a vitrophyre containing phenocrysts...
and comendite lavas. These felsic volcanics are understood to have been created by fractionation of mainly alkali basalt magma in crustal reservoirs. An area of continental rifting, such as the Northern Cordilleran Volcanic Province, would aid the formation of high-level reservoirs of capable size and thermal activity to maintain long-lived fractionation.
Lithosphere thickness
The variety of different temperature ranges from xenolithXenolith
A xenolith is a rock fragment which becomes enveloped in a larger rock during the latter's development and hardening. In geology, the term xenolith is almost exclusively used to describe inclusions in igneous rock during magma emplacement and eruption...
s throughout the Northern Cordilleran Volcanic Province indicate that a narrow lithosphere
Lithosphere
The lithosphere is the rigid outermost shell of a rocky planet. On Earth, it comprises the crust and the portion of the upper mantle that behaves elastically on time scales of thousands of years or greater.- Earth's lithosphere :...
lies under the northern portion of the volcanic province and a more dense lithosphere lies under the southern portion of the volcanic province. This indication is further provided if the geothermal gradient inside the lithosphere under the northern portion of the Northern Cordilleran Volcanic Province is greater than that in the southern portion of the province. A greater geothermal gradient would indicate that a xenolith recording a temperature of 900 °C (1,652 °F) was collected from a shallower depth than one from a zone with a reduced geothermal gradient that also records a temperature of 900 °C (1,652 °F).
Further evidence that indicate lithospheric thickening beneath the middle portion of Stikinia include the increased profusion of cognate inclusion and plagioclase megacrysts in volcanic rocks from the southern portion of the volcanic province, which might be evidence of magma ponding and magma crystallization in the lithosphere before a volcanic eruption, and the restricted existence of petrologically
Petrology
Petrology is the branch of geology that studies rocks, and the conditions in which rocks form....
evolved rock types in the southern half of the Northern Cordilleran Volcanic Province. If the developed magmas originated from fractionation of mafic magmas, fractionation associated with lithospheric contamination, or entirely from melting of the associated lithosphere, their existence suggests more dense lithosphere lies under the southern portion of the Northern Cordilleran Volcanic Province.
In the Llangorse section of the Atlin Volcanic Field in northwestern British Columbia, a suite of xenoliths confines the thickness of the Northern Cordilleran Volcanic Province mantle lithosphere to as thin as 18 km (11.2 mi) and a thickness no more than 39 km (24.2 mi). Analysis of recent data related to earthquake
Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...
s in the southwestern portion of the volcanic province indicates that the crust under Stikinia, which comprises the bedrock
Bedrock
In stratigraphy, bedrock is the native consolidated rock underlying the surface of a terrestrial planet, usually the Earth. Above the bedrock is usually an area of broken and weathered unconsolidated rock in the basal subsoil...
underlying a large number of volcanoes in the southern portion of the Northern Cordilleran Volcanic Province, is also more dense than the crust under the nearby Coast Plutonic Complex, which consists of a broad belt of granitic
Granite
Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...
and dioritic
Diorite
Diorite is a grey to dark grey intermediate intrusive igneous rock composed principally of plagioclase feldspar , biotite, hornblende, and/or pyroxene. It may contain small amounts of quartz, microcline and olivine. Zircon, apatite, sphene, magnetite, ilmenite and sulfides occur as accessory...
intrusive rocks that collectively represent more than 140 million years of nearly continuous subduction-related magmatism.
Geologic features
Hot spring
A hot spring is a spring that is produced by the emergence of geothermally heated groundwater from the Earth's crust. There are geothermal hot springs in many locations all over the crust of the earth.-Definitions:...
s are present throughout the Northern Cordilleran Volcanic Province, indicating magmatic heat is present under the Northern Cordilleran Volcanic Province. They are formed if water percolates deeply through the crust and heats up from the primal magmatic heat under the surface. After the groundwater is heated, the heated groundwater rises to the surface as a hot spring. In some cases, the heated groundwater may rise along extensional faults related to rifting in the Northern Cordilleran Volcanic Province. The Lakelse Hot Springs
Lakelse Hot Springs
The Lakese Hot Springs, also known as the Mount Layton Hot Springs, are a group of hot springs in the Kalum-Kitimat valley of northern British Columbia, Canada, located on the eastern shore of Lakelse Lake in Lakelse Lake Provincial Park south of Terrace along Highway 37...
near Lakelse Lake Provincial Park
Lakelse Lake Provincial Park
Lakelse Lake Provincial Park is a provincial park in British Columbia, Canada located just west of Highway 37 between Terrace and Kitimat. The name is derived from the Coast Tsimshian language word "LaxGyels"....
in northern British Columbia is interpreted to be one such example. With a temperature of 89 °C (192.2 °F), the springs are the hottest in Canada. It is also possible the magma associated with the Nass Valley eruption 250 years ago to the north rose along the same north trending fault lines fueling the Lakelse Hot Springs. Hot springs are also present in Iskut River Hot Springs Provincial Park
Iskut River Hot Springs Provincial Park
Iskut River Hot Springs Provincial Park is a small provincial park in British Columbia, Canada, located on the western side of the Iskut River....
and Choquette Hot Springs Provincial Park
Choquette Hot Springs Provincial Park
Choquette Hot Springs Provincial Park is a provincial park in the Stikine Country region of northwestern British Columbia, Canada. Despite the park's name, the official and most commonly used name of the springs it was established to protect is Stikine River Hot Springs...
in northwestern British Columbia.
Xenolith
Xenolith
A xenolith is a rock fragment which becomes enveloped in a larger rock during the latter's development and hardening. In geology, the term xenolith is almost exclusively used to describe inclusions in igneous rock during magma emplacement and eruption...
s, rock fragments that become enveloped in a larger igneous rock
Igneous rock
Igneous rock is one of the three main rock types, the others being sedimentary and metamorphic rock. Igneous rock is formed through the cooling and solidification of magma or lava...
, are widespread in the Northern Cordilleran Volcanic Province. Xenoliths that originated in the Earth's crust include rich metamorphic rock
Metamorphic rock
Metamorphic rock is the transformation of an existing rock type, the protolith, in a process called metamorphism, which means "change in form". The protolith is subjected to heat and pressure causing profound physical and/or chemical change...
s and felsic intrusive rocks. Granulite
Granulite
Granulites are medium to coarse–grained metamorphic rocks that have experienced high temperature metamorphism, composed mainly of feldspars sometimes associated with quartz and anhydrous ferromagnesian minerals, with granoblastic texture and gneissose to massive structure...
xenoliths exist mainly at the Fort Selkirk Volcanic Field
Fort Selkirk Volcanic Field
The Fort Selkirk volcanic field is a monogenetic volcanic field in the Northern Cordilleran Volcanic Province, Yukon Territory, Canada. It is the northernmost Holocene age volcanic field in Canada, located close to the connection of the Yukon and Pelly rivers. The youngest eruptions within the...
in central Yukon, Prindle Volcano in easternmost Alaska and at Castle Rock
Castle Rock (volcano)
Castle Rock is a volcanic neck located west of Iskut and 8 km northwest of Tuktsayda Mountain in British Columbia, Canada. It is part of the Pacific Ring of Fire that includes over 160 active volcanoes and is in the Klastline Group, Northern Cordilleran Volcanic Province and last erupted in...
and the Iskut River
Iskut River
The Iskut River is the largest tributary of the Stikine River in northwestern British Columbia, Canada, entering it a few miles above its entry into Alaska....
in northern British Columbia. Felsic intrusive xenoliths are a lot more common and usually originate from adjacent granitic intrusions, including those that form the Coast Mountains. More than 14 volcanic zones throughout the Northern Cordilleran Volcanic Province comprise xenoliths that originated from the Earth's mantle and are located mainly at the Yukon-Tanana Terrane, the Cache Creek Terrane and at volcanoes occupying the Paleozoic
Paleozoic
The Paleozoic era is the earliest of three geologic eras of the Phanerozoic eon, spanning from roughly...
and Mesozoic
Mesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...
Stikinia
Stikinia
Stikinia is the name of a tectonostratigraphic terrane in the Canadian Cordillera of British Columbia, Canada. It was formed in a volcanic arc environment during the Paleozoic and Mesozoic periods...
terrane. They consist of lherzolite, harzburgite
Harzburgite
The ultramafic igneous rock, harzburgite, is a variety of peridotite consisting mostly of the two minerals, olivine and low-calcium pyroxene ; it is named for occurrences in the Harz Mountains of Germany. It commonly contains a few percent chromium-rich spinel as an accessory mineral...
, wehrlite, dunite
Dunite
Dunite is an igneous, plutonic rock, of ultramafic composition, with coarse-grained or phaneritic texture. The mineral assemblage is greater than 90% olivine, with minor amounts of other minerals such as pyroxene, chromite and pyrope. Dunite is the olivine-rich end-member of the peridotite group...
, websterite and garnet
Garnet
The garnet group includes a group of minerals that have been used since the Bronze Age as gemstones and abrasives. The name "garnet" may come from either the Middle English word gernet meaning 'dark red', or the Latin granatus , possibly a reference to the Punica granatum , a plant with red seeds...
composed pyroxenite
Pyroxenite
Pyroxenite is an ultramafic igneous rock consisting essentially of minerals of the pyroxene group, such as augite and diopside, hypersthene, bronzite or enstatite. They are classified into clinopyroxenites, orthopyroxenites, and the websterites which contain both pyroxenes...
. The highest and lowest temperatures recorded by mantle xenoliths increase to the south and decrease to the north. Mantle xenoliths at Prindle Volcano in easternmost Alaska record the minimum temperature of 860 °C (1,580 °F) and mantle xenoliths from the Fort Selkirk Volcanic Field in central Yukon record the minimum temperature range from 960 to 1050 °C (1,760 to 1,922 F). At Castle Rock in northern British Columbia, mantle xenoliths record the maximum temperature of 1260 °C (2,300 °F), as well as the maximum temperature range from 1000 to 1260 °C (1,832 to 2,300 F). The minimum xenolith temperatures indicate that the boundary between the Earth's crust and mantle
Mohorovičić discontinuity
The Mohorovičić discontinuity , usually referred to as the Moho, is the boundary between the Earth's crust and the mantle. Named after the pioneering Croatian seismologist Andrija Mohorovičić, the Moho separates both the oceanic crust and continental crust from underlying mantle...
is shallowest beneath the northern portion of the Northern Cordilleran Volcanic Province. Therefore, the temperature ranges for the northernmost xenolith series is about one-half the temperature range found in xenoliths at the southern portion of the volcanic province.
Megacryst
In geology, a megacryst is a crystal or grain that is considerably larger than the encircling matrix. They are found in igneous and metamorphic rocks.- Notes :*...
s, crystals or grains that are considerably larger than the encircling matrix
Matrix (geology)
The matrix or groundmass of rock is the finer grained mass of material in which larger grains, crystals or clasts are embedded.The matrix of an igneous rock consists of finer grained, often microscopic, crystals in which larger crystals are embedded. This porphyritic texture is indicative of...
, are commonly found in lava flows throughout the Northern Cordilleran Volcanic Province. They consist of three different groups, including kaersutitic
Kaersutite
Kaersutite is a dark brown to black amphibole mineral with formula: NaCa2Si6Al2O232.It occurs as phenocrysts in alkalic volcanic rocks; in nodules of peridotite and gabbro in alkalic basalts; in syenites, monzonites and carbonatite tuffs...
amphibole
Amphibole
Amphibole is the name of an important group of generally dark-colored rock-forming inosilicate minerals, composed of double chain tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium in their structures.-Mineralogy:...
megacrysts, clinopyroxene megacrysts and plagioclase
Plagioclase
Plagioclase is an important series of tectosilicate minerals within the feldspar family. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a solid solution series, more properly known as the plagioclase feldspar series...
megacrysts. Megacrysts made of kaersutite are known to be found mainly at Llangorse Mountain
Llangorse Mountain
Llangorse Mountain is a mountain in northern British Columbia, Canada, located southeast of Atlin on the eastern side of the head of the Gladys River...
in northern British Columbia. Black glassy clinopyroxene megacrysts are widespread throughout the Northern Cordilleran Volcanic Province, suggesting their creation is independent of lithosphere structure. In contrast, clear glassy plagioclase megacrysts are found largely at the southern end of the Northern Cordilleran Volcanic Province and largely within the boundaries of the Stikinia terrane. This suggests the plagioclase megacrysts have a source that is sensitive to the Earth's lithosphere, including contamination or magma ponding. Megacrysts made of plagioclase and clinopyroxene regionally show significant evidence of reaction with the associated magma, including sieve-textured cores and random, resorbed and embayed outer margins wherever they are located.
Lava tube
Lava tube
Lava tubes are natural conduits through which lava travels beneath the surface of a lava flow, expelled by a volcano during an eruption. They can be actively draining lava from a source, or can be extinct, meaning the lava flow has ceased and the rock has cooled and left a long, cave-like...
s are widespread in the Northern Cordilleran Volcanic Province, and are typically basaltic in composition. At the Level Mountain Range, lava tubes reach diameters of 1 m (3.3 ft) to 2 m (6.6 ft). These owed their origin to highly fluid lavas with temperatures of at least 1200 °C (2,192 °F). In Nisga'a Memorial Lava Beds Provincial Park of northwestern British Columbia, lava tubes are present that were formed during one of Canada's most recent volcanic eruptions in the 18th century. Lava Fork
Lava Fork
Lava Fork is a creek in northwestern British Columbia, Canada and of the Alaska Panhandle, United States. It lies west of the Unuk River and northwest of Stewart...
at the British Columbia-Alaska border is influenced by lava flows from a recent volcanic eruption that later collapsed into underlying lava tubes after the lava solidified. Sections of these collapsed lava tubes now form volcanic pits.
Extensive areas of nearly flat-lying lava flows throughout the Northern Cordilleran Volcanic Province can cover areas of at least 100 square kilometre and are generally composed of highly-fluid basaltic lava. However, lava plains that pre-date the last glacial period have been eroded and overridden by glacial ice, affording a less distinctive form to these older landforms. For example, lava beds at least a million years old in central Yukon contain unconsolidated glacial deposits that were deposited when glacial ice rode on top of the lava flows comprising the lava beds.
Subvolcanic
Subvolcanic rock
A subvolcanic rock, also known as a hypabyssal rock, is an igneous rock that originates at medium to shallow depths within the crust and contain intermediate grain size and often porphyritic texture. They have textures between volcanic and plutonic rocks. Subvolcanic rocks include diabase and...
intrusion
Intrusion
An intrusion is liquid rock that forms under Earth's surface. Magma from under the surface is slowly pushed up from deep within the earth into any cracks or spaces it can find, sometimes pushing existing country rock out of the way, a process that can take millions of years. As the rock slowly...
s in the Northern Cordilleran Volcanic Province are exposed in areas of high relief. This includes volcanic plug
Volcanic plug
A volcanic plug, also called a volcanic neck or lava neck, is a volcanic landform created when magma hardens within a vent on an active volcano. When forming, a plug can cause an extreme build-up of pressure if volatile-charged magma is trapped beneath it, and this can sometimes lead to an...
s found at the Mount Edziza volcanic complex, the Level Mountain Range, Hoodoo Mountain and in the Atlin and Maitland areas. Volcanic plugs in the Atlin and Maitland areas consist of olivine nephelinite and basanite magmas. Minor plugs made of gabbro
Gabbro
Gabbro refers to a large group of dark, coarse-grained, intrusive mafic igneous rocks chemically equivalent to basalt. The rocks are plutonic, formed when molten magma is trapped beneath the Earth's surface and cools into a crystalline mass....
ic and granitic
Granite
Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...
magma are associated with volcanic stratigraphy
Stratigraphy
Stratigraphy, a branch of geology, studies rock layers and layering . It is primarily used in the study of sedimentary and layered volcanic rocks....
at the Mount Edziza volcanic complex and Level Mountain Range.
Terranes and boundaries
The bedrock of the Northern Cordilleran Volcanic Province consists of four large terraneTerrane
A terrane in geology is short-hand term for a tectonostratigraphic terrane, which is a fragment of crustal material formed on, or broken off from, one tectonic plate and accreted or "sutured" to crust lying on another plate...
s, known as Stikinia, Cache Creek
Cache Creek Terrane
The Cache Creek Terrane is a geologic terrane in British Columbia and southern Yukon, Canada. It consists of volcanics, carbonate rocks, coarse clastic rocks and small amounts of ultramafic rock, chert and argillite....
, Yukon-Tanana
Yukon-Tanana Terrane
The Yukon-Tanana Terrane is a tectonic terrane that extends from central Alaska through central Yukon and into northern British Columbia, Canada and Southeast Alaska, USA. Extending over 2000 km, the YTT is the largest tectonostratigraphic terrane in the northern North American Cordillera...
and Cassiar
Cassiar Terrane
The Cassiar Terrane is a long Cretaceous terrane located in the Northern Interior British Columbia and southern Yukon. It consists of miogeoclinal strata and contains the Cassiar Batholith, a 100 million year old igneous intrusion and the single largest intrusive body in the hinterland of the...
. Stikinia is a sequence of late Paleozoic and Mesozoic aged volcanic, plutonic and sedimentary rocks interpreted to have been created in an island arc environment that were later placed along a pre-existing continental margin
Continental margin
The continental margin is the zone of the ocean floor that separates the thin oceanic crust from thick continental crust. Continental margins constitute about 28% of the oceanic area....
. The Cache Creek Terrane is believed to have formed widely in a pre-existing oceanic basin
Oceanic basin
Hydrologically, an oceanic basin may be anywhere on Earth that is covered by seawater, but geologically ocean basins are large geologic basins that are below sea level...
. It comprises late Paleozoic to Mesozoic aged oceanic melange and abyssal peridotites intruded by younger granitic intrusions. The Yukon-Tanana and Cassiar terranes consist of shifted sedimentary and metamorphic rocks that were derived from the North American continent.
The southern boundary of the Northern Cordilleran Volcanic Province is parallel with southwestern Stikinia and is characterized by separate volcanic vents and erosional remains of lavas south of the small community of Stewart
Stewart, British Columbia
Stewart is a small town, incorporated as a district municipality at the head of the Portland Canal in northwestern British Columbia, Canada. In 2006, its population was about 496.-History:...
. The southern boundary of the Northern Cordilleran Volcanic Province also parallels with a gap in modern volcanism and the supposed northern boundary of the Cascadia subduction zone
Cascadia subduction zone
The Cascadia subduction zone is a subduction zone, a type of convergent plate boundary that stretches from northern Vancouver Island to northern California. It is a very long sloping fault that separates the Juan de Fuca and North America plates.New ocean floor is being created offshore of...
, defined by the eastward extension of the northern edge of the subducting Juan de Fuca Plate
Juan de Fuca Plate
The Juan de Fuca Plate, named after the explorer of the same name, is a tectonic plate, generated from the Juan de Fuca Ridge, and subducting under the northerly portion of the western side of the North American Plate at the Cascadia subduction zone...
. These two zones divide the Northern Cordilleran Volcanic Province from modern volcanic zones further south, including the broad Chilcotin Plateau
Chilcotin Plateau
The Chilcotin Plateau is part of the Fraser Plateau, a major subdivision of the Interior Plateau of British Columbia. The Chilcotin Plateau is physically near-identical with the region of the same name, i.e...
, the east-west trending Anahim Volcanic Belt
Anahim Volcanic Belt
The Anahim Volcanic Belt is a 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. The volcanoes generally become younger eastward at a rate of to ...
and the monogenetic Wells Gray-Clearwater volcanic field
Wells Gray-Clearwater volcanic field
The Wells Gray-Clearwater volcanic field, also called the Clearwater Cone Group, is a potentially active monogenetic volcanic field in east-central British Columbia, Canada, located approximately north of Kamloops. It is situated in the Cariboo Mountains of the Columbia Mountains and on the...
in the British Columbia Interior
British Columbia Interior
The British Columbia Interior or BC Interior or Interior of British Columbia, usually referred to only as the Interior, is one of the three main regions of the Canadian province of British Columbia, the other two being the Lower Mainland, which comprises the overlapping areas of Greater Vancouver...
. The eastern boundary of the Northern Cordilleran Volcanic Province is bounded by the Cassiar Terrane and is adjoined by a cluster of volcanic plug
Volcanic plug
A volcanic plug, also called a volcanic neck or lava neck, is a volcanic landform created when magma hardens within a vent on an active volcano. When forming, a plug can cause an extreme build-up of pressure if volatile-charged magma is trapped beneath it, and this can sometimes lead to an...
s in central British Columbia. The northern and western boundaries are adjoined by the Yukon-Tanana and Cache Creek terranes where there lies volcanics in eastern Alaska and weathered remains of lava flows just north and west of Dawson City in west-central Yukon.
Tintina and Denali fault zones
The Tintina and Denali faults are the largest fault zones associated with the Northern Cordilleran Volcanic Province rift zone, with all volcanism occurring west of the Tintina Fault and east of the Denali Fault. Physiographically, the Tintina Fault forms the Northern Rocky Mountain Trench and the Tintina TrenchTintina Trench
The Tintina Trench is a large valley extending through Yukon, Canada. It is the northern extension of the Northern Rocky Mountain Trench in British Columbia and it has its origin from the Tintina Fault. Much of the valley serves as the path through which flows the Pelly River, a tributary of the...
, which is the northern extension of the Northern Rocky Mountain Trench. The fastest rates of strike-slip movement along the Tintina Fault likely occurred during two pulses in the Mid-Cretaceous and early Cenozoic periods, respectively, with the latter probably occurring during the Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
epoch. Since the Cretaceous, the Tintina Fault has offset 450 km (279.6 mi) of the surface, although some evidence suggest as much as 1200 km (745.6 mi) of offset. The end result is that the Northern Cordilleran Volcanic Province and the terrains of which the volcanic province occupies have moved northwards. In the context of plate tectonics, strip-slip movement of the Tintina Fault is also related to strike-slip movement along the San Andreas Fault
San Andreas Fault
The San Andreas Fault is a continental strike-slip fault that runs a length of roughly through California in the United States. The fault's motion is right-lateral strike-slip...
and other extensional or strike-slip fault systems of western North America.
To the west, the Denali Fault is the source of minor earthquakes that extend along the length of the fault. In contrast to the Tintina Fault, strike-slip movement along the Denali Fault has offset at least 370 km (229.9 mi) of the surface. The fault separates mountains of the Insular Belt
Insular Belt
The Insular Belt is a physiogeological region on the north western North American coast. It consist of three major island groups and many smaller islands and stretches from southern British Columbia into Alaska and the Yukon...
from mountains east of the fault. Tectonic events in the Insular Belt are also related to movement along the Denali Fault.
Human history
The term Stikine Volcanic Belt was originally defined by Jack Souther and Christopher Yorath of the Geological Survey of Canada in 1991 as a group of volcanic deposits centered around the Stikine RiverStikine River
The Stikine River is a river, historically also the Stickeen River, approximately 610 km long, in northwestern British Columbia in Canada and southeastern Alaska in the United States...
in northwestern British Columbia. As more mapping and dating of volcanic deposits was completed in the Western Cordillera, the Stikine Volcanic Belt was expanded to include volcanic deposits further and further from the geographic area associated with the name Stikine. In part for this reason, scientists Ben Edwards and James Russell redefined this area of volcanism as the Northern Cordilleran Volcanic Province. As a geographic descriptor, application of the name Stikine to volcanic rocks exposed along the Yukon River
Yukon River
The Yukon River is a major watercourse of northwestern North America. The source of the river is located in British Columbia, Canada. The next portion lies in, and gives its name to Yukon Territory. The lower half of the river lies in the U.S. state of Alaska. The river is long and empties into...
seems a bit odd and confusing. As well, a much older group of totally unrelated volcanic rock
Volcanic rock
Volcanic rock is a rock formed from magma erupted from a volcano. In other words, it is an igneous rock of volcanic origin...
s comprise the Stikine Assemblage, which also mainly occurs within the geographic area informally referred to as Stikine Country
Stikine Country
The Stikine Country, also referred to as the Stikine District or simply "the Stikine" , is one of the historical geographic regions of the Canadian province of British Columbia, located inland from the central Alaska Panhandle and comprising the basin of the Stikine River and its tributaries...
. The Northern Cordilleran Volcanic Province is a broader name, to encompass a broader geographic area, in which the most recent volcanism has a similar character (mainly alkaline, mafic volcanic rocks), a similar age range (Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
to Holocene
Holocene
The Holocene is a geological epoch which began at the end of the Pleistocene and continues to the present. The Holocene is part of the Quaternary period. Its name comes from the Greek words and , meaning "entirely recent"...
), and a similar tectonic setting (transtension).
See also
- Volcanic history of the Northern Cordilleran Volcanic ProvinceVolcanic history of the Northern Cordilleran Volcanic ProvinceThe volcanic history of the Northern Cordilleran Volcanic Province presents a record of volcanic activity in northwestern British Columbia, central Yukon and the U.S. state of easternmost Alaska. The volcanic activity lies in the northern part of the Western Cordillera of the Pacific Northwest...
- List of Northern Cordilleran volcanoes
- List of volcanoes in Canada
- List of volcanoes in the United States
- Geology of the Pacific NorthwestGeology of the Pacific NorthwestThe geology of the Pacific Northwest refers to the study of the composition , structure, physical properties and the processes that shape the Pacific Northwest region of the United States and Canada...
- Volcanism of Canada
- Volcanism of Western CanadaVolcanism of Western CanadaVolcanism of Western Canada produces lava flows, lava plateaus, lava domes, cinder cones, stratovolcanoes, shield volcanoes, submarine volcanoes, calderas, diatremes and maars, along with examples of more less common volcanic forms such as tuyas and subglacial mounds.-Volcanic belts:*Anahim...
- Volcanism of Northern CanadaVolcanism of Northern CanadaVolcanism of Northern Canada has led to the formation of hundreds of volcanic areas and extensive lava formations across Northern Canada, indicating volcanism played a major role in shaping its surface...