The geology of

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, ...

is a function of its location on the leading edge of the

North American continent North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

. The mountainous

physiography Physical geography (also known as physiography) is one of the three main branches of geography. Physical geography is the branch of natural science which deals with the processes and patterns in the natural environment such as the atmosphere, h ...

and the diversity of rock types and ages hint at the complex

geology Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Ear ...

, which is still undergoing revision despite a century of exploration and mapping. The country's most prominent geological features are

mountain range A mountain range or hill range is a series of mountains or hills arranged in a line and connected by high ground. A mountain system or mountain belt is a group of mountain ranges with similarity in form, structure, and alignment that have arise ...

s, including the North American Cordillera, which stretches from Southern

Mexico Mexico (Spanish: México), officially the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States; to the south and west by the Pacific Ocean; to the southeast by Guatema ...

Alaska Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U.S., ...

Terrane theory

Terrane In geology, a terrane (; in full, a tectonostratigraphic terrane) is a crust fragment formed on a tectonic plate (or broken off from it) and accreted or " sutured" to crust lying on another plate. The crustal block or fragment preserves its own ...

theory was first proposed by Jim Monger of the

Geological Survey of Canada The Geological Survey of Canada (GSC; french: Commission géologique du Canada (CGC)) is a Canadian federal government agency responsible for performing geological surveys of the country, developing Canada's natural resources and protecting the en ...

and Charlie Rouse in 1971 as an explanation for a set of

fusulinid The Fusulinida is an extinct order within the Foraminifera in which the tests are traditionally considered to have been composed of microgranular calcite. Like all forams, they were single-celled organisms. In advanced forms the test wall was di ...

fossils found in central British Columbia. Rather than use

facies In geology, a facies ( , ; same pronunciation and spelling in the plural) is a body of rock with specified characteristics, which can be any observable attribute of rocks (such as their overall appearance, composition, or condition of formatio ...

changes or seaways (which were common explanations at the time), the two geologists proposed that the fossils in question had been part of an assemblage of rocks that had migrated across the

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continen ...

to their present location. This theory was then developed by Porter Irwin and Davy Jones of the

US Geological Survey The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, an ...

to its common definition of "fault bounded regional geologic entities, each characterized by a different geologic history than its neighbours". Terranes are most commonly associated with different

tectonic Tectonics (; ) are the processes that control the structure and properties of the Earth's crust and its evolution through time. These include the processes of mountain building, the growth and behavior of the strong, old cores of continents ...

elements such as

island arcs Island arcs are long chains of active volcanoes with intense seismic activity found along convergent tectonic plate boundaries. Most island arcs originate on oceanic crust and have resulted from the descent of the lithosphere into the mantle alon ...

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 ...

s, subduction zones,

continental margin A continental margin is the outer edge of continental crust abutting oceanic crust under coastal waters. It is one of the three major zones of the ocean floor, the other two being deep-ocean basins and mid-ocean ridges. The continental margin ...

mid-oceanic ridge A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics. It typically has a depth of about and rises about above the deepest portion of an ocean basin. This feature is where seafloor spreading takes place along a dive ...

s and

continental fragment Continental crustal fragments, partly synonymous with microcontinents, are pieces of continents that have broken off from main continental masses to form distinct islands that are often several hundred kilometers from their place of origin. Caus ...

s. These terranes are gradually joined together by elements such as

overlap formation In geology, a terrane (; in full, a tectonostratigraphic terrane) is a crust fragment formed on a tectonic plate (or broken off from it) and accreted or " sutured" to crust lying on another plate. The crustal block or fragment preserves its own ...

s and

stitching pluton In geology, an igneous intrusion (or intrusive body or simply intrusion) is a body of intrusive igneous rock that forms by crystallization of magma slowly cooling below the surface of the Earth. Intrusions have a wide variety of forms and com ...

s and are then accreted to the continent. In some cases, a terrane can contain multiple tectonic elements. The

Cache Creek Terrane The Cache Creek Terrane (alternately known as Cache Creek Melange ) is a geologic terrane in British Columbia and southern Yukon, Canada. The Cache Creek Terrane consists of Carboniferous to Lower Jurassic volcanic rocks, carbonate rocks, coarse c ...

is composed of a massive

carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate g ...

component, an oceanic floor component and a

subduction Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the ...

mélange In geology, a mélange is a large-scale breccia, a mappable body of rock characterized by a lack of continuous bedding and the inclusion of fragments of rock of all sizes, contained in a fine-grained deformed matrix. The mélange typically cons ...

component.

Architecture and composition

There are five morphogeological belts that define the geology of British Columbia from east to west: the Foreland, Omineca, Intermontane, Coast and Insular Belt. Each has a separate geology, including different metamorphic, physiographic, metallogenic and tectonic histories. The Foreland Belt is composed of weakly

metamorphosed Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causi ...

sedimentary rocks Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles t ...

which are 1.4 billion to 33 million years old, and the belt represents a

rift In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics. Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-grabe ...

sequence followed by a

passive margin A passive margin is the transition between oceanic and continental lithosphere that is not an active plate margin. A passive margin forms by sedimentation above an ancient rift, now marked by transitional lithosphere. Continental rifting creat ...

that was turned into a retro arc

fold and thrust belt A fold and thrust belt (FTB) is a series of mountainous foothills adjacent to an orogenic belt, which forms due to contractional tectonics. Fold and thrust belts commonly form in the forelands adjacent to major orogens as deformation propagates o ...

with synorogenic sedimentation. The region is very rugged except in the northeast of the province where the earth flattens out to a wide plain. The Omineca Belt is composed of highly metamorphosed, pericratonic (near craton) terranes and fragments of North America that are 2 billion to 180 million years old. Terranes in the belt include the

Slide Mountain Terrane The Slide Mountain Terrane is a late Paleozoic terrane made of a complex of oceanic rocks in northern and southern British Columbia, Canada. The rocks of the terrane include Carboniferous limestones, fine grained quartz rich clastics, conglomer ...

, the Yukon–Tanana Terrane and the

Cassiar Terrane The Cassiar Terrane is a long Cretaceous terrane located in the British Columbia Interior, Northern Interior of British Columbia and southern Yukon. It consists of Miogeocline, miogeoclinal stratum, strata and contains the Cassiar Batholith, a 100 ...

. This belt goes from low hills to high mountains across its length, with the majority of the region being extremely rugged. The

Intermontane Belt The Intermontane Belt is a physiogeological region in the Pacific Northwest of North America, stretching from northern Washington into British Columbia, Yukon, and Alaska. It comprises rolling hills, high plateaus and deeply cut valleys. The ro ...

is a flatter, more rounded region composed of three terranes, Stikinia,

Quesnellia Quesnellia, or the Quesnel terrane, is a terrane in British Columbia, Canada; constituent of the Canadian Cordillera. It formed volcanic arc during the Mesozoic era, in the Triassic and Jurassic The Jurassic ( ) is a geologic period and strati ...

and the

. The belt has a lower metamorphic grade than the Omineca Belt and ranges from 400 million to within 10,000 years old. Volcanic activity has been recorded as occurring in the past 10,000 years, including at

Nazko Cone Nazko Cone is a small potentially active basaltic cinder cone in central British Columbia, Canada, located 75 km west of Quesnel and 150 kilometers southwest of Prince George. It is considered the easternmost volcano in the Anahim Volcanic ...

and in the Satah Mountain volcanic field. The Coast Belt is the single largest outpouring of

granite Granite () is a coarse-grained (phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies undergro ...

and

granodiorite Granodiorite () is a coarse-grained (phaneritic) intrusive igneous rock similar to granite, but containing more plagioclase feldspar than orthoclase feldspar. The term banatite is sometimes used informally for various rocks ranging from gra ...

in the

Phanerozoic The Phanerozoic Eon is the current geologic eon in the geologic time scale, and the one during which abundant animal and plant life has existed. It covers 538.8 million years to the present, and it began with the Cambrian Period, when anima ...

. It contains heavily metamorphosed fragments of both the terranes of the

Insular Belt The Insular Belt is a physical geography, physiogeological region on the north western North American coast. It consists of three major island groups and many smaller islands and stretches from southern British Columbia into Alaska and the Yukon. I ...

and the Intermontane Belt. In the southeast there is a series of small terranes of both oceanic (

Bridge River Vent The Bridge River Vent is a volcanic crater in the Pacific Ranges of the Coast Mountains in southwestern British Columbia, Canada. It is located west of Bralorne on the northeastern flank of the Mount Meager massif. With an elevation of , it lies ...

and

Chilliwack Batholith The Chilliwack Batholith is a large batholith that forms much of the North Cascades in southwestern British Columbia, Canada and the U.S. state of Washington. The geological structure is named after the Chilliwack River Valley, where it outcrops ...

) and continental affinity (Jack Konat Mountain, Ladner). The hard-weathering granite is extensively rugged throughout the belt. The

is composed of the outboard terrane with no connection to North America before accretion. There are two main terranes— Wrangellia and the Alexander—and a few smaller ones such as the Pacific Rim terrane. Because the Insular Belt is the most tectonically active of the belts, it has the greatest relief differences from the depths of the Queen Charlotte Sound to the heights of the Wrangell–

St. Elias Mountains The Saint Elias Mountains (french: Chaîne Saint-Élie) are a subgroup of the Pacific Coast Ranges, located in southeastern Alaska in the United States, Southwestern Yukon and the very far northwestern part of British Columbia in Canada. The range ...

. The ages are from 600 million years to recent, with metamorphic grades depending on the age and host of the rock type.

References

External links

Government of British Columbia: Geology of BCEvolution of the Pacific Northwest
Good text on the geology of Cascadia. {{DEFAULTSORT:Geology Of British Columbia

Terrane theory

Architecture and composition

See also

References

External links