Geology of the Northwest Territories

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The geology of the Northwest Territories has been mapped in different quadrangles by the Canadian government. The region has some of the oldest rocks in the world and among the oldest in North America, formed from several sections of stable craton continental crust, including the Slave Craton, Rae Craton and Hearne Craton. These rocks form the Archean and Proterozoic Precambrian basement rock of the region and are the subject of extensive research to understand continental crust and tectonic conditions on the early Earth.

Contents

Geologic History, Stratigraphy & Tectonics

The Hearne Craton and Rae Craton are underlain by Archean metasedimentary and metavolcanic rocks. Quartz arenite in the Rae Craton has been interpreted as possible passive margin or rift deposits. Around the world, greenstone belts are a hallmark of ancient Precambrian rocks. The Ennadai-Rankin greenstone belt is the second largest in Canada and displays felsic volcanic and volcaniclastic rocks, as well as mafic rocks reaching greenschist grade on the sequence of metamorphic facies. Laminations in ironstone and pelite formations suggest that the mafic volcanic rocks deposited on the low energy slope of a volcanic plateau, away from wave action. Because of the enormous time distance from the Archean, exact interpretations are less reliable. [1]

In the late Proterozoic, the region was affected by the Wopmay orogeny. Along the edge of the Archean Slave Craton, a 1.1 kilometre thick wedge of carbonates formed the Rocknest Formation, which thins to the east. The Slave Craton (also known as the Slave Province) is smaller than the vast neighboring Superior Province, which extends southward to the Great Lakes. By contrast with the Superior Province, the Slave Province has more sedimentary rocks, more felsic than mafic rocks, more potassium-rich granite and gold and base-metal mineralization. [2] Geologists have inferred ancient sea floor spreading in the western part of the province from dikes and mafic lava flows, overlain by deep ocean turbidite deposits. These rocks are believed to be the remains of oceanic crust that ended up preserved, surrounded on all sides by felsic volcanic rocks and granitoid plutons. [3] In the area of Snofleld Lake in the northern part of the Slave Province, the remains of Archean stromatolites are preserved in a dolomite unit between felsic volcanic and greywacke-mudstone turbidites, some of the earliest evidence of life, forming in the shallows around volcanic islands. [4]

Around 1.27 billion years ago in the Proterozoic, a series of major magmatic events affected the region, referred to as "Mackenzie magmatic event," by some geologists. In the Coppermine River Province, tholeiite flood basalts emplaced at the same time over a rapid span of five million years. Strontium-neodymium-lead analysis indicates that the rocks included older, partially melted basement rocks. [5]

In the Neoproterozoic, the four kilometre thick Mackenzie Mountains Supergroup deposited in a poorly understood basin. Hydrothermal fluids emplaced base metals into these deposits, likely during rifting that lasted into the Paleozoic. [6]

Paleozoic (541-251 million years ago)

Marine deposition was common across much of the area in the Paleozoic. Within the Mackenzie Basin, tabulate and rugose corals grew formed the Horn Plateau Formation—a group of isolated reefs from the Devonian fed by nutrients from eroding Canadian Shield rocks and offshore upwelling in the ocean. [7] The Selwyn Basin, which now spans into the Yukon Territory formed at the same time and accumulated graptolite fossils and bitumen. [8]

The siliclastic, fossiliferous wackestone and mudstone of the Ordovician Bad Cache Rapids Formation record a shallow shelf environment on Southampton Island. This unit is overlain by the Ashgill Boas River Formation carbonaceous mudstone and oil shale, Churchill River Formation coral-bearing wackestone and the Sixteen Mile Brook oil shale. [9]

Mesozoic (251-66 million years ago)

In the Mesozoic, kimberlite pipes intruded Archean basement rock in places beginning around 75 million years ago and continuing into the Cenozoic in the Ekati area. [10]

Sedimentation continued in many areas into the Mesozoic. On Banks Island, manganese spherulites with rhodochrosite, iron-manganese oxides and dolomite mark the boundary between the Christopher and Kanguk sedimentary formations from the Cretaceous. [11]

Cenozoic (66 million years ago-present)

In the early Cenozoic, changes in regional structural geology led to widespread erosion and fission track analysis of apatite indicates that in the Beaufort-Mackenzie area, rocks cooled from temperatures around 110 degrees Celsius after one mile of rock eroded above them in the early Eocene. [12] The Northwest Territories was heavily glaciated during the Pleistocene. In the Mackenzie Mountains, moraine glacial till overlies older Paleogene gravel, paleosols and different till shed off of mountains. [13]

In the vicinity of the Mackenzie River delta and Sitidgi Lake till and sediments formed into the unglaciated Eskioma Lakes area. The Mackenzie delta formed as alluvium drowned valleys. Thermokarst and an ice-cored landscape took shape in the early Holocene. [14]

Gas Hydrates

Northern Canada and the Northwest Territories are famous for gas hydrates, also known as methane clathrate—methane gas frozen in thick sediments, which might hypothetically lead to intense climate change if they melted. Recognized from bore holes, gas flow during drilling or seismic data, it was not until March and April, 1993 that samples were recovered from a 451 meter deep hole in the Mackenzie Delta. [15]

Related Research Articles

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Kenorland was one of the earliest known supercontinents on Earth. It is thought to have formed during the Neoarchaean Era c. 2.72 billion years ago by the accretion of Neoarchaean cratons and the formation of new continental crust. It comprised what later became Laurentia, Baltica, Western Australia and Kalaharia.

<span class="mw-page-title-main">Greenstone belt</span> Zone of variably metamorphosed rocks occurring in Archaean and Proterozoic cratons

Greenstone belts are zones of variably metamorphosed mafic to ultramafic volcanic sequences with associated sedimentary rocks that occur within Archaean and Proterozoic cratons between granite and gneiss bodies.

<span class="mw-page-title-main">Yilgarn Craton</span> Large craton in Western Australia

The Yilgarn Craton is a large craton that constitutes the bulk of the Western Australian land mass. It is bounded by a mixture of sedimentary basins and Proterozoic fold and thrust belts. Zircon grains in the Jack Hills, Narryer Terrane have been dated at ~4.27 Ga, with one detrital zircon dated as old as 4.4 Ga.

<span class="mw-page-title-main">Slave Craton</span> Archaean craton in the north-western Canadian Shield, in Northwest Territories and Nunavut

The Slave Craton is an Archaean craton in the north-western Canadian Shield, in Northwest Territories and Nunavut. The Slave Craton includes the 4.03 Ga-old Acasta Gneiss which is one of the oldest dated rocks on Earth. Covering about 300,000 km2 (120,000 sq mi), it is a relatively small but well-exposed craton dominated by ~2.73–2.63 Ga greenstones and turbidite sequences and ~2.72–2.58 Ga plutonic rocks, with large parts of the craton underlain by older gneiss and granitoid units. The Slave Craton is one of the blocks that compose the Precambrian core of North America, also known as the palaeocontinent Laurentia.

<span class="mw-page-title-main">Kaapvaal Craton</span> Archaean craton, possibly part of the Vaalbara supercontinent

The Kaapvaal Craton, along with the Pilbara Craton of Western Australia, are the only remaining areas of pristine 3.6–2.5 Ga crust on Earth. Similarities of rock records from both these cratons, especially of the overlying late Archean sequences, suggest that they were once part of the Vaalbara supercontinent.

<span class="mw-page-title-main">Churchill Craton</span> Northwest section of the Canadian Shield from southern Saskatchewan and Alberta to northern Nunavut

The Churchill Craton is the northwest section of the Canadian Shield and stretches from southern Saskatchewan and Alberta to northern Nunavut. It has a very complex geological history punctuated by at least seven distinct regional tectonometamorphic intervals, including many discrete accretionary magmatic events. The Western Churchill province is the part of the Churchill Craton that is exposed north and west of the Hudson Bay. The Archean Western Churchill province contributes to the complicated and protracted tectonic history of the craton and marks a major change in the behaviour of the Churchill Craton with many remnants of Archean supracrustal and granitoid rocks.

<span class="mw-page-title-main">Temagami Greenstone Belt</span> Greenstone belt in Northeastern Ontario, Canada

The Temagami Greenstone Belt (TGB) is a small 2.7 billion year old greenstone belt in the Temagami region of Northeastern Ontario, Canada. It represents a feature of the Superior craton, an ancient and stable part of the Earth's lithosphere that forms the core of the North American continent and Canadian Shield. The belt is composed of metamorphosed volcanic rocks that range in composition from basalt to rhyolite. These form the east-northeast trend of the belt and are overlain by metamorphosed sedimentary rocks. They were created during several volcanic episodes involving a variety of eruptive styles ranging from passive lava eruptions to viscous explosive eruptions.

<span class="mw-page-title-main">Trans-Hudson orogeny</span> Mountain-building event in North America

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<span class="mw-page-title-main">Algoman orogeny</span> Late Archaean episode of mountain building in what is now North America

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<span class="mw-page-title-main">Wopmay orogen</span> Mountain-building event in northern Canada

The Wopmay orogen is a Paleoproterozoic orogenic belt in northern Canada which formed during the collision between the Hottah terrane, a continental magmatic arc, and the Archean Slave Craton at about 1.88 Ga. The collision lead to the short-lived Calderian orogeny. The formation was named for Wilfrid Reid "Wop" May, OBE, DFC, a Canadian flying ace in the First World War and a leading post-war aviator.

<span class="mw-page-title-main">Geology of Zimbabwe</span>

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<span class="mw-page-title-main">Tectonic evolution of the Barberton greenstone belt</span> Evolutionary history of ancient continental crust remnant located in southeastern Africa

The Barberton greenstone belt (BGB) is located in the Kapvaal craton of southeastern Africa. It characterizes one of the most well-preserved and oldest pieces of continental crust today by containing rocks in the Barberton Granite Greenstone Terrain (3.55–3.22 Ga). The BGB is a small, cusp-shaped succession of volcanic and sedimentary rocks, surrounded on all sides by granitoid plutons which range in age from >3547 to <3225 Ma. It is commonly known as the type locality of the ultramafic, extrusive volcanic rock, the komatiite. Greenstone belts are geologic regions generally composed of mafic to ultramafic volcanic sequences that have undergone metamorphism. These belts are associated with sedimentary rocks that occur within Archean and Proterozoic cratons between granitic bodies. Their name is derived from the green hue that comes from the metamorphic minerals associated with the mafic rocks. These regions are theorized to have formed at ancient oceanic spreading centers and island arcs. In simple terms, greenstone belts are described as metamorphosed volcanic belts. Being one of the few most well-preserved Archean portions of the crust, with Archean felsic volcanic rocks, the BGB is well studied. It provides present geologic evidence of Earth during the Archean (pre-3.0 Ga). Despite the BGB being a well studied area, its tectonic evolution has been the cause of much debate.

<span class="mw-page-title-main">Eastern Pilbara Craton</span> Carton in Western Australia

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<span class="mw-page-title-main">Eoarchean geology</span> Study of the oldest crustal fragments on Earth

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<span class="mw-page-title-main">Archean felsic volcanic rocks</span> Felsic volcanic rocks formed in the Archean Eon

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The geology of Nunavut began to form nearly three billion years ago in the Archean and the territory preserves some of the world's oldest rock units.

<span class="mw-page-title-main">Eastern Block of the North China Craton</span>

The Eastern Block of the North China Craton is one of the Earth's oldest pieces of continent. It is separated from the Western Block by the Trans-North China Orogen. It is situated in northeastern China and North Korea. The Block contains rock exposures older than 2.5 billion years. It serves as an ideal place to study how the crust was formed in the past and the related tectonic settings.

The Superior Craton is a stable crustal block covering Quebec, Ontario, and southeast Manitoba in Canada, and northern Minnesota in the United States. It is the biggest craton among those formed during the Archean period. A craton is a large part of the Earth's crust that has been stable and subjected to very little geological changes over a long time. The size of Superior Craton is about 1,572,000 km2. The craton underwent a series of events from 4.3 to 2.57 Ga. These events included the growth, drifting and deformation of both oceanic and continental crusts.

<span class="mw-page-title-main">Geology of the Kimberley (Western Australia)</span> Overview of geology of the Kimberley

The geology of the Kimberley, a region of Western Australia, is a rock record of early Proterozoic plate collision, orogeny and suturing between the Kimberley Craton and the Northern Australia Craton, followed by sedimentary basin formation from Proterozoic to Phanerozoic.

References

  1. ↑ Aspler, Lawrence B.; Chiarenzelli, Jeffrey R. (1996). "Stratigraphy, sedimentology and physical volcanology of the Henik Group, central Ennadai-Rankin greenstone belt, Northwest Territories, Canada: late Archean paleogeography of the Hearne Province and tectonic implications". Precambrian Research. 77 (1–2): 59–89. doi:10.1016/0301-9268(95)00045-3.
  2. ↑ Padgham, W. A.; Fyson, W. K. (1992). "The Slave Province: a distinct Archean craton". Canadian Journal of Earth Sciences. 29 (10): 2072–2086. doi:10.1139/e92-165.
  3. ↑ Fyson, W. K.; Helmstaedt, H. (1988). "Structural patterns and tectonic evolution of supracrustal domains in the Archean Slave Province, Canada". Canadian Journal of Earth Sciences. 25 (2): 301–315. doi:10.1139/e88-032.
  4. ↑ Henderson, John B. (1975). "Archean Stromatolites in the Northern Slave Province, Northwest Territories, Canada". Canadian Journal of Earth Sciences. 12 (9): 1619–1630. doi:10.1139/e75-144.
  5. ↑ Dupuy, C.; Michard, A.; Dostal, J.; Dautel, D.; Baragar, W. R. A. (1992). "Proterozoic flood basalts from the Coppermine River area, Northwest Territories: isotope and trace element geochemistry". Canadian Journal of Earth Sciences. 29 (9): 1937–1943. doi:10.1139/e92-151.
  6. ↑ Turner, Elizabeth C.; Long, Darrel G.F. (2008). "Basin architecture and syndepositional fault activity during deposition of the Neoproterozoic Mackenzie Mountains supergroup, Northwest Territories, CanadaNorthwest Territories Geoscience Office Contribution 0040". Canadian Journal of Earth Sciences. 45 (10): 1159–1184. doi:10.1139/E08-062.
  7. ↑ Corlett, Hilary; Jones, Brian (2011). "Ecological controls on Devonian stromatoporoid-dominated and coral-dominated reef growth in the Mackenzie Basin, Northwest Territories, Canada". Canadian Journal of Earth Sciences. 48 (12): 1543–1560. doi:10.1139/e11-056.
  8. ↑ Riediger, C.; Goodarzi, F.; MacQueen, R. W. (1989). "Graptolites as indicators of regional maturity in lower Paleozoic sediments, Selwyn Basin, Yukon and Northwest Territories, Canada". Canadian Journal of Earth Sciences. 26 (10): 2003–2015. doi:10.1139/e89-169.
  9. ↑ Dewing, Keith; Copper, Paul (1991). "Upper Ordovician stratigraphy of Southampton Island, Northwest Territories". Canadian Journal of Earth Sciences. 28 (2): 283–291. doi:10.1139/e91-027.
  10. ↑ Nowicki, Tom; Crawford, Barbara; Dyck, Darren; Carlson, Jon; McElroy, Ross; Oshust, Peter; Helmstaedt, Herb (2004). "The geology of kimberlite pipes of the Ekati property, Northwest Territories, Canada". Lithos. 76 (1–4): 1–27. doi:10.1016/j.lithos.2004.03.020.
  11. ↑ Miall, Andrew D. (1974). "Manganese Spherulites at an Intra-Cretaceous Disconformity, Banks Island, Northwest Territories". Canadian Journal of Earth Sciences. 11 (12): 1704–1716. doi:10.1139/e74-168.
  12. ↑ O'Sullivan, Paul B.; Lane, Larry S. (1997). "Early Tertiary thermotectonic history of the northern Yukon and adjacent Northwest Territories, Arctic Canada". Canadian Journal of Earth Sciences. 34 (10): 1366–1378. doi:10.1139/e17-109.
  13. ↑ Duk-Rodkin, A.; Barendregt, R. W.; Tarnocai, C.; Phillips, F. M. (1996). "Late Tertiary to late Quaternary record in the Mackenzie Mountains, Northwest Territories, Canada: stratigraphy, paleosols, paleomagnetism, and chlorine - 36". Canadian Journal of Earth Sciences. 33 (6): 875–895. doi:10.1139/e96-066.
  14. ↑ "Quaternary geology of the Tuktoyaktuk coastlands, Northwest Territories (Technical Report) | ETDEWEB". osti.gov. Retrieved 2018-11-10.
  15. ↑ Dallimore, S. R.; Collett, T. S. (1995). "Intrapermafrost gas hydrates from a deep core hole in the Mackenzie Delta, Northwest Territories, Canada | Geology". Geology. 23 (6): 527. doi:10.1130/0091-7613(1995)023<0527:IGHFAD>2.3.CO;2.

The following five timelines show the geologic time scale to scale. The first shows the entire time from the formation of the Earth to the present, but this gives little space for the most recent eon. The second timeline shows an expanded view of the most recent eon. In a similar way, the most recent era is expanded in the third timeline, the most recent period is expanded in the fourth timeline, and the most recent epoch is expanded in the fifth timeline.

SiderianRhyacianOrosirianStatherianCalymmianEctasianStenianTonianCryogenianEdiacaranEoarcheanPaleoarcheanMesoarcheanNeoarcheanPaleoproterozoicMesoproterozoicNeoproterozoicPaleozoicMesozoicCenozoicHadeanArcheanProterozoicPhanerozoicPrecambrianGeology of the Northwest Territories
CambrianOrdovicianSilurianDevonianCarboniferousPermianTriassicJurassicCretaceousPaleogeneNeogeneQuaternaryPaleozoicMesozoicCenozoicPhanerozoicGeology of the Northwest Territories
PaleoceneEoceneOligoceneMiocenePliocenePleistoceneHolocenePaleogeneNeogeneQuaternaryCenozoicGeology of the Northwest Territories
GelasianCalabrian (stage)ChibanianPleistocenePleistoceneHoloceneQuaternaryGeology of the Northwest Territories
GreenlandianNorthgrippianMeghalayanHoloceneGeology of the Northwest Territories
Millions of Years (1st, 2nd, 3rd, and 4th)
Thousands of years (5th)
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