The geology of

Nunavut Nunavut ( , ; iu, ᓄᓇᕗᑦ , ; ) is the largest and northernmost Provinces and territories of Canada#Territories, territory of Canada. It was separated officially from the Northwest Territories on April 1, 1999, via the ''Nunavut Act'' ...

began to form nearly three billion years ago in the

Archean The Archean Eon ( , also spelled Archaean or Archæan) is the second of four geologic eons of Earth's history, representing the time from . The Archean was preceded by the Hadean Eon and followed by the Proterozoic. The Earth Earth ...

and the territory preserves some of the world's oldest rock units.

Geologic History, Stratigraphy & Tectonics

Archean

Archean rocks dominate much of the territory's surface and places with overlying rock.

Greenstone belts 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. The name comes from the green h ...

are common together with

migmatite Migmatite is a composite rock found in medium and high-grade metamorphic environments, commonly within Precambrian cratonic blocks. It consists of two or more constituents often layered repetitively: one layer is an older metamorphic rock tha ...

gneiss Gneiss ( ) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. Gneiss forms at higher temperatures an ...

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 ...

, and

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical form ...

monzonite Monzonite is an igneous intrusive rock, formed by slow cooling of underground magma that has a moderate silica content and is enriched in alkali metal oxides. Monzonite is composed mostly of plagioclase and alkali feldspar. Syenodiorite is an o ...

, on the Melville Peninsula and northern

Baffin Island Baffin Island (formerly Baffin Land), in the Canadian territory of Nunavut, is the largest island in Canada and the fifth-largest island in the world. Its area is , slightly larger than Spain; its population was 13,039 as of the 2021 Canadia ...

, as well as the southwest mainland. Lenses and bands of

amphibolite Amphibolite () is a metamorphic rock that contains amphibole, especially hornblende and actinolite, as well as plagioclase feldspar, but with little or no quartz. It is typically dark-colored and dense, with a weakly foliated or schistose (flaky ...

granitoid A granitoid is a generic term for a diverse category of coarse-grained igneous rocks that consist predominantly of quartz, plagioclase, and alkali feldspar. Granitoids range from plagioclase-rich tonalites to alkali-rich syenites and from quartz ...

and metasedimentary rocks are common in these areas, along with less common ultramafic rocks. Gold and other base metals are widespread as mineralization in siliclastic, felsic, mafic and ironstone rocks of the greenstone belts. The George Lake, Boston and Ulu deposits are all hosted in the Yellowknife Supergroup of the

Slave Craton 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 , ...

in the west as well as the Lupin gold mine. In the western Churchill Province of south-central Nunavut are the Noomut, Heninga Lake and Meliadine gold deposits, and the Victory Lake and Ferguson Lake base metals deposits. Ultramafic volcanic rocks,

quartzite Quartzite is a hard, non- foliated metamorphic rock which was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usually related to tect ...

and iron formations in the northern Churchill Province hold the Woodhurn, Prince Albert and Meadowbank gold deposits. The Churchill Province experienced widespread metamorphism 2.5 billion years ago. Baffin Island represents the eastern margin of the Canadian Shield and the long-term thermal history of southern Baffin suggests temperatures remained high (above 400C) following Trans-Hudson Orogeny peak metamorphism at c. 1.85 billion years ago, slow cooling and minor reheating ensued throughout the Proterozoic, followed by episodic sedimentary burial during the Paleozoic through Mesozoic of <3-4 km.

Paleozoic (539-251 million years ago)

Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...

rocks cover one-third of the territory, northwest of Fury and Hecla Strait, forming part of the Arctic Platform and continuing north to

Ellesmere Island Ellesmere Island ( iu, script=Latn, Umingmak Nuna, lit=land of muskoxen; french: île d'Ellesmere) is Canada's northernmost and List of Canadian islands by area, third largest island, and the List of islands by area, tenth largest in the world. ...

. In the southeast, they are continuation of the

Hudson Platform Hudson may refer to: People * Hudson (given name) * Hudson (surname) * Henry Hudson, English explorer * Hudson (footballer, born 1986), Hudson Fernando Tobias de Carvalho, Brazilian football right-back * Hudson (footballer, born 1988), Hudson R ...

beneath the

Foxe Basin Foxe Basin is a shallow oceanic basin north of Hudson Bay, in Nunavut, Canada, located between Baffin Island and the Melville Peninsula. For most of the year, it is blocked by sea ice (fast ice) and drift ice made up of multiple ice floes. Th ...

. Subsidence and craton rifting are recorded in

Cambrian The Cambrian Period ( ; sometimes symbolized C with bar, Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million ...

strata, with clastic sequences left by a

marine transgression A marine transgression is a geologic event during which sea level rises relative to the land and the shoreline moves toward higher ground, which results in flooding. Transgressions can be caused by the land sinking or by the ocean basins filling ...

. A stable platform developed from the Cambrian through the

Silurian The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the shortest period of the Paleozo ...

and thick carbonates with high oil and gas potential deposited. The

Caledonian orogeny The Caledonian orogeny was a mountain-building era recorded in the northern parts of the British Isles, the Scandinavian Mountains, Svalbard, eastern Greenland and parts of north-central Europe. The Caledonian orogeny encompasses events that occ ...

brought uplift and erosion from the Silurian through the

Early Devonian The Early Devonian is the first of three Epoch (geology), epochs comprising the Devonian period, corresponding to the Lower Devonian Series (stratigraphy), series. It lasted from and began with the Lochkovian Stage , which was followed by the P ...

, generating potential red bed related copper deposits in a thick clastic wedge. The Ellesmerian orogeny produced Mississippi-valley type zinc-lead mineralization in the Polaris district of the Canadian Arctic Archipelago. Thick clastic and carbonate sediments deposited in the Sverdrup Basin in the north during the

Carboniferous The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carbonifero ...

Proterozoic (2.5 billion-539 million years ago)

Hurwitz Group In mathematics, Hurwitz's automorphisms theorem bounds the order of the group of automorphisms, via orientation-preserving conformal mappings, of a compact Riemann surface of genus ''g'' > 1, stating that the number of such automorphisms ...

strata and other units from 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 ...

cover much of the Churchill Province. Continental margin sediments deposited in central Baffin Island as the Piling Group and as the Penrhyn Group on the southern Melville Peninsula. The units include

and feldspathic quartzite, overlain by

dolomite Dolomite may refer to: *Dolomite (mineral), a carbonate mineral *Dolomite (rock), also known as dolostone, a sedimentary carbonate rock *Dolomite, Alabama, United States, an unincorporated community *Dolomite, California, United States, an unincor ...

marble Marble is a metamorphic rock composed of recrystallized carbonate minerals, most commonly calcite or Dolomite (mineral), dolomite. Marble is typically not Foliation (geology), foliated (layered), although there are exceptions. In geology, the ...

and

, together with

schist Schist ( ) is a medium-grained metamorphic rock showing pronounced schistosity. This means that the rock is composed of mineral grains easily seen with a low-power hand lens, oriented in such a way that the rock is easily split into thin flakes o ...

and iron formations with sulfur geochemistry. Gray, weathered psammitic rocks are common in the upper part of the basin, with high potential for base metals and gold. The former Black Angel zinc and lead mine is located within the Karrat Group carbonates on the coast of West Greenland. Ultramafic sills are found in the southern Baffin Island Lake Harbour Group. On the Belcher Islands in Hudson Bay are clastic rocks overlain by volcanic and carbonate rocks, which record subsidence and rifting at the western edge of the Superior Craton. Thermal overprinting and deformation from the

Paleoproterozoic The Paleoproterozoic Era (;, also spelled Palaeoproterozoic), spanning the time period from (2.5–1.6 Ga), is the first of the three sub-divisions (eras) of the Proterozoic Eon. The Paleoproterozoic is also the longest era of the Earth's ...

have been found in these rocks, dating to the Trans-Hudson Orogeny 1.8 billion years ago. The Bylot Supergroup in Baffin Island and Bylot Island is six kilometers thick with a combination of undeformed volcanic, clastic and carbonate rocks deposited during a phase of renewed rifting. The Borden Peninsula is divided into

horst and graben In geology, horst and graben (or range and valley) refers to topography consisting of alternating raised and lowered fault blocks known as horsts and grabens. The features are created by normal faulting and rifting caused by crustal extension ...

structures by normal faults from local rifting and subsidence 1.27 billion years ago. The Nanisivik Mine extracts zinc and lead from these carbonates. The Bylot Supergroup is known as the Fury Group and Hecla Group along the Fury and Hecla Strait, where it overlies Archean and Paleoproterozoic rocks with nearly six kilometers of material, likely deposited over the span of 75 million years.

Mesozoic (251-66 million years ago)

Through the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...

, sedimentation continued in the Sverdrup Basin, producing oil and gas forming conditions and Bent Horn light crude field. Rifting and alkaline volcanism in the Cretaceous began the process of siliclastic deposition in northern Baffin Island and northern Ellesmere Island. Diamond-bearing

kimberlite pipes Volcanic pipes or volcanic conduits are subterranean geological structures formed by the violent, supersonic eruption of deep-origin volcanoes. They are considered to be a type of ''diatreme''. Volcanic pipes are composed of a deep, narrow cone o ...

formed on Somerset Island, exposed along the

Brodeur Peninsula The Brodeur Peninsula is an uninhabited headland on Baffin Island in the Qikiqtaaluk Region of Nunavut, Canada. It is located in the northwestern part of the island and is bounded by Prince Regent Inlet to the west, Lancaster Sound to the nort ...

and northwest Baffin Island. The Jericho diamond pipes are part of a northern continuation of Lac de Gras field in the northern Slave Province. There are also kimberlite pipes on Victoria Island.

Cenozoic (66 million years ago-present)

In the far north, compression and strike-slip faulting affected the Canadian Arctic Archipelago throughout the Eureakan orogeny. The tectonic event happened in parallel with the siliclastic sedimentation and opened Baffin Bay and the Labrador Sea.

References

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