The geology of the
Northwest Territories
The Northwest Territories (abbreviated ''NT'' or ''NWT''; french: Territoires du Nord-Ouest, formerly ''North-Western Territory'' and ''North-West Territories'' and namely shortened as ''Northwest Territory'') is a federal territory of Canada. ...
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
The Hearne Craton is a craton in northern Canada which, together with the Rae Craton, forms the Western Churchill Province. Hearne is one of the six Archaean cratons of the Canadian Shield (the other being Slave, Rae, Wyoming, Superior, Na ...
. These rocks form the
Archean and
Proterozoic
The Proterozoic () is a geological eon spanning the time interval from 2500 to 538.8million years ago. It is the most recent part of the Precambrian "supereon". It is also the longest eon of the Earth's geologic time scale, and it is subdivided ...
Precambrian
The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the ...
basement rock of the region and are the subject of extensive research to understand continental crust and tectonic conditions on the early Earth.
Geologic History, Stratigraphy & Tectonics
The
Hearne Craton
The Hearne Craton is a craton in northern Canada which, together with the Rae Craton, forms the Western Churchill Province. Hearne is one of the six Archaean cratons of the Canadian Shield (the other being Slave, Rae, Wyoming, Superior, Na ...
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
The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the ...
rocks. The Ennadai-Rankin greenstone belt is the second largest in Canada and displays
felsic
In geology, felsic is a modifier describing igneous rocks that are relatively rich in elements that form feldspar and quartz.Marshak, Stephen, 2009, ''Essentials of Geology,'' W. W. Norton & Company, 3rd ed. It is contrasted with mafic rocks, whi ...
volcanic and volcaniclastic rocks, as well as
mafic rocks reaching
greenschist grade on the sequence of
metamorphic facies
A metamorphic facies is a set of mineral assemblages in metamorphic rocks formed under similar pressures and temperatures.Essentials of Geology, 3rd Edition, Stephen Marshak The assemblage is typical of what is formed in conditions corresponding ...
. 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.
In the late
Proterozoic
The Proterozoic () is a geological eon spanning the time interval from 2500 to 538.8million years ago. It is the most recent part of the Precambrian "supereon". It is also the longest eon of the Earth's geologic time scale, and it is subdivided ...
, the region was affected by the
Wopmay orogeny
The Wopmay orogen is a Paleoproterozoic orogenic belt in northern Canada which formed during the collision between the Hottah terrane (north of the Hottah Lake), a continental volcanic arc, magmatic arc, and the Archean Slave Craton at about 1.88& ...
. 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
In geology, felsic is a modifier describing igneous rocks that are relatively rich in elements that form feldspar and quartz.Marshak, Stephen, 2009, ''Essentials of Geology,'' W. W. Norton & Company, 3rd ed. It is contrasted with mafic rocks, whi ...
than
mafic rocks, more potassium-rich granite and gold and base-metal mineralization.
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.
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
Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from '' shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology. ...
turbidites, some of the earliest evidence of life, forming in the shallows around volcanic islands.
Around 1.27 billion years ago in the
Proterozoic
The Proterozoic () is a geological eon spanning the time interval from 2500 to 538.8million years ago. It is the most recent part of the Precambrian "supereon". It is also the longest eon of the Earth's geologic time scale, and it is subdivided ...
, a series of major magmatic events affected the region, referred to as "Mackenzie magmatic event," by some geologists. In the Coppermine River Province,
tholeiite
The tholeiitic magma series is one of two main magma series in subalkaline igneous rocks, the other being the calc-alkaline series. A magma series is a chemically distinct range of magma compositions that describes the evolution of a mafic magma i ...
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.
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.
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
The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...
fed by nutrients from eroding
Canadian Shield
The Canadian Shield (french: Bouclier canadien ), also called the Laurentian Plateau, is a geologic shield, a large area of exposed Precambrian igneous and high-grade metamorphic rocks. It forms the North American Craton (or Laurentia), the anc ...
rocks and offshore upwelling in the ocean.
The Selwyn Basin, which now spans into the Yukon Territory formed at the same time and accumulated
graptolite fossils and
bitumen
Asphalt, also known as bitumen (, ), is a sticky, black, highly viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product, and is classed as a pitch. Before the 20th century, the term a ...
.
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.
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.
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.
Cenozoic (66 million years ago-present)
In the early
Cenozoic
The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configura ...
, changes in regional structural geology led to widespread erosion and fission track analysis of
apatite
Apatite is a group of phosphate minerals, usually hydroxyapatite, fluorapatite and chlorapatite, with high concentrations of OH−, F− and Cl− ions, respectively, in the crystal. The formula of the admixture of the three most common e ...
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.
The Northwest Territories was heavily glaciated during the
Pleistocene. In the Mackenzie Mountains,
moraine
A moraine is any accumulation of unconsolidated debris (regolith and rock), sometimes referred to as glacial till, that occurs in both currently and formerly glaciated regions, and that has been previously carried along by a glacier or ice shee ...
glacial till overlies older Paleogene gravel, paleosols and different till shed off of mountains.
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.
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.
References
{{DEFAULTSORT:Geology Of the Northwest Territories
NorthWest
The points of the compass are a set of horizontal, radially arrayed compass directions (or azimuths) used in navigation and cartography. A compass rose is primarily composed of four cardinal directions—north, east, south, and west—each sep ...
Clathrate hydrates
Methane
Natural gas