The Wopmay orogen is a Paleoproterozoic orogenic belt in northern

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...

which formed during the collision between the Hottah terrane (north of the

Hottah Lake Hottah Lake is the sixth largest lake in the Northwest Territories, Canada. Plane crash On 8 November 1972, a medical evacuation aircraft piloted by Marten Hartwell crashed on a hillside near the lake. Hartwell broke both legs while the nurse, Ju ...

), a continental

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

, and the Archean Slave Craton at about 1.88 Ga (billion years). The collision lead to the short-lived Calderian orogeny. The formation was named for Wilfrid Reid "Wop" May,

OBE The Most Excellent Order of the British Empire is a British order of chivalry, rewarding contributions to the arts and sciences, work with charitable and welfare organisations, and public service outside the civil service. It was established o ...

, DFC (April 20, 1896 – June 21, 1952), a

Canadian Canadians (french: Canadiens) are people identified with the country of Canada. This connection may be residential, legal, historical or cultural. For most Canadians, many (or all) of these connections exist and are collectively the source of ...

flying ace A flying ace, fighter ace or air ace is a military aviator credited with shooting down five or more enemy aircraft during aerial combat. The exact number of aerial victories required to officially qualify as an ace is varied, but is usually co ...

in the

First World War World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, the United States, and the Ottoman Empire, with fightin ...

and a leading post-war

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. It is approximately 500 km along the north–south axis, and 200 km along the east–west axis at its widest point, tapering at both the northern and southern ends.

Geological setting

The Wopmay orogen can be subdivided into (east to west): a passive continental margin, the Wopmay fault zone, the

Great Bear magmatic zone The Great Bear Magmatic Zone (GBMZ) is a Paleoproterozoic (1.875–1.86 Ga) multi-collisional orogenic belt of which is exposed in the northwestern Canadian Shield east of Great Bear Lake, Northwest Territories. Covering , the GBMZ forms ...

, and the Hottah terrane. The passive margin developed around 1970–1890 Ma on-top of the Slave Craton. The Wopmay fault zone is probably a suture between the Slave craton and the Hottah terrane. No Archean crust have been found west of this suture. The Great Bear magmatic zone is the result of arc magmatism around 1875–1840 Ma when these rocks were deposited on and intruded into the Hottah terrane and Slave craton. The magmatic arc now forms a 3–4.5 km thick basin overlying the Hottah-Slave transition. The cryptic Hottah terrane is a magmatic arc which consists of a 1936–1890 Ma-old suite of

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 intruded into 2.0–2.4 Ga metamorphosed sedimentary and volcanic rocks. It probably extends east beneath the Great Bear magmatic zone.

Tectonic evolution

The Wopmay orogen formed 1882±4 Ma when the Coronation paleocean (named after the Arctic

Coronation Gulf Coronation Gulf lies between Victoria Island and mainland Nunavut in Canada. To the northwest it connects with Dolphin and Union Strait and thence the Beaufort Sea and Arctic Ocean; to the northeast it connects with Dease Strait and thence Queen M ...

) closed between the western margin of the Slave craton and Hottah terrane. The Great Bear magmatic arc remained active 1.88–1.84 Ma while subduction still occurred and still bisects the Hottah terrane north to south. The Coronation margin final closure occurred at 1.74 Ga. The date for the opening of the Coronation Ocean is uncertain, but isotopic studies indicate that initial rifting must be older than about 1.97 Ga. The Hottah arc formed 2.4–2.0 Ga on cryptic crust, probably coeval with sedimentation of Coronation margin. The closure of Coronation Ocean saw an initial phase of westward-directed subduction of oceanic crust beneath the Hottah terrane. This process was followed by an interrupted eastward subduction around 1.885 Ga during which the Coronation margin and Hottah terrane were translated eastward and partially thrust over the Slave craton.

Significance

Sites such as the Wopmay Orogen provide evidence for early and ongoing

plate tectonics Plate tectonics (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large ...

. Traces of old

oceanic crust Oceanic crust is the uppermost layer of the oceanic portion of the tectonic plates. It is composed of the upper oceanic crust, with pillow lavas and a dike complex, and the lower oceanic crust, composed of troctolite, gabbro and ultramafic cumu ...

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 ...

, and colliding continents indicate that the same forces at work today have been at work in the early Proterozoic and probably earlier. Alignments of magnetic particles in rocks demonstrate that continents were drifting across the surface of the Earth relative to the magnetic poles then as now, and that the ocean floor was rifting and subducting, all at least 1.5 billion years ago. Retrieved May 2016. This crust cycling is referred to as the supercontinent cycle.

References

Notes

Sources

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External links

* {{cite web, title=Geological map showing the Slave Craton and the Wopmay Orogen , url=http://esp.cr.usgs.gov/info/gmna/canada.html , work=usgs.gov , publisher=

United States 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, ...

, url-status=dead , archive-url=https://web.archive.org/web/20120909022343/http://esp.cr.usgs.gov/info/gmna/canada.html , archive-date=September 9, 2012 Orogenies of North America Paleoproterozoic orogenies Geology of the Northwest Territories