The North Atlantic Craton (NAC) is an Archaean

craton A craton (, , or ; from grc-gre, κράτος "strength") is an old and stable part of the continental lithosphere, which consists of Earth's two topmost layers, the crust and the uppermost mantle. Having often survived cycles of merging an ...

exposed in southern

West Greenland Kitaa, originally Vestgrønland ("West Greenland"), is a former administrative division of Greenland. It was by far the most populated of the divisions, being home to almost 90% of the total population. The divisions were de facto replaced by st ...

, the Nain Province in

Labrador , nickname = "The Big Land" , etymology = , subdivision_type = Country , subdivision_name = Canada , subdivision_type1 = Province , subdivision_name1 ...

, and the

Lewisian complex The Lewisian complex or Lewisian gneiss is a suite of Precambrian metamorphic rocks that outcrop in the northwestern part of Scotland, forming part of the Hebridean Terrane and the North Atlantic Craton. These rocks are of Archaean and Paleopr ...

in northwestern Scotland. The NAC is bounded by the Nagssugtoqidian orogen to the north and the 1.8–1.87 Ga Ketilidan–

Makkovik Makkovik (Inuit: ''Maggovik'') is a town in Labrador in eastern Canada. It had 365 residents in 2021. The main industry is snow crabbing and there is a fishing cooperative. Makkovik is only accessible by air or sea. History The Makkovik area has ...

mobile belt to the south. The latter can be linked to the Lewisian- Malin boundary in Scotland, which in turn can be linked to the Transscandinavian Igneous Belt in

Baltica Baltica is a paleocontinent that formed in the Paleoproterozoic and now constitutes northwestern Eurasia, or Europe north of the Trans-European Suture Zone and west of the Ural Mountains. The thick core of Baltica, the East European Craton, ...

Palaeoproterozoic 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 ...

mobile belts surround the

continental Continental may refer to: Places * Continent, the major landmasses of Earth * Continental, Arizona, a small community in Pima County, Arizona, US * Continental, Ohio, a small town in Putnam County, US Arts and entertainment * ''Continental'' ( ...

blocks and cratonic fragments of the NAC. Throughout the

Mesoproterozoic The Mesoproterozoic Era is a geologic era that occurred from . The Mesoproterozoic was the first era of Earth's history for which a fairly definitive geological record survives. Continents existed during the preceding era (the Paleoproterozoic), ...

Neoproterozoic The Neoproterozoic Era is the unit of geologic time from 1 billion to 538.8 million years ago. It is the last era of the Precambrian Supereon and the Proterozoic Eon; it is subdivided into the Tonian, Cryogenian, and Ediacaran periods. It is prec ...

, and

Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretace ...

(1350–550 ), when these blocks still formed a coherent craton, repeated continental extension resulted in lithospheric thinning. The NAC finally broke up at 60 Ma with the opening of the

Labrador Sea The Labrador Sea (French: ''mer du Labrador'', Danish: ''Labradorhavet'') is an arm of the North Atlantic Ocean between the Labrador Peninsula and Greenland. The sea is flanked by continental shelves to the southwest, northwest, and northeast. It ...

Ultramafic Ultramafic rocks (also referred to as ultrabasic rocks, although the terms are not wholly equivalent) are igneous and meta-igneous rocks with a very low silica content (less than 45%), generally >18% MgO, high FeO, low potassium, and are composed ...

magmatism Magmatism is the emplacement of magma within and at the surface of the outer layers of a terrestrial planet, which solidifies as igneous rocks. It does so through magmatic activity or igneous activity, the production, intrusion and extrusion of ...

has occurred continuously in the NAC for almost 3 billion years, but

kimberlite Kimberlite is an igneous rock and a rare variant of peridotite. It is most commonly known to be the main host matrix for diamonds. It is named after the town of Kimberley in South Africa, where the discovery of an diamond called the Star of S ...

-producing magmatism has only occurred in two stages: in the Neoproterozoic () in the northern NAC and in the

Jurassic The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...

() in the southern NAC. Magmatism during the Neoproterozoic was caused by either the opening of the Iapetus Ocean, lithospheric thinning along a fracture zone, or the appearance of a

mantle plume A mantle plume is a proposed mechanism of convection within the Earth's mantle, hypothesized to explain anomalous volcanism. Because the plume head partially melts on reaching shallow depths, a plume is often invoked as the cause of volcanic hot ...

. A rift system that developed during the Mesozoic began to fraction the NAC, and the initial stages of the break-up of the NAC produced the kimberlite and carbonatite deposits along the Labrador Sea. In Greenland the NAC is primarily made of

tonalite–trondhjemite–granodiorite Tonalite–trondhjemite–granodiorite (TTG) rocks are intrusive rocks with typical granitic composition (quartz and feldspar) but containing only a small portion of potassium feldspar. Tonalite, trondhjemite, and granodiorite often occur togethe ...

orthogneiss 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 ...

es separated and obscured by

supracrustal Supracrustal rocks (''supra'' (Latin for "above")) are rocks that were deposited on the existing basement rocks of the crust, hence the name. They may be further metamorphosed from both sedimentary and volcanic rocks. The oldest minerals on Ear ...

belts,

anorthosite Anorthosite () is a phaneritic, intrusive igneous rock characterized by its composition: mostly plagioclase feldspar (90–100%), with a minimal mafic component (0–10%). Pyroxene, ilmenite, magnetite, and olivine are the mafic minerals most ...

complexes, and granite intrusions. A series of

terrane In geology, a terrane (; in full, a tectonostratigraphic terrane) is a crust (geology), crust fragment formed on a tectonic plate (or broken off from it) and Accretion (geology), accreted or "Suture (geology), sutured" to crust lying on another pla ...

s have been distinguished in Greenland: north of the Frederikshåb Isblink Glacier. The Akia, Isukasia, and Kapisilik terranes probably collided in the Isukasia orogeny, although events are masked by

Neoarchaean The Neoarchean (; also spelled Neoarchaean) is the last geologic era in the Archean eon that spans from 2800 to 2500 million years ago—the period being defined chronometrically and not referencing a specific level in a rock section on Earth. ...

overprinting. The Færingehavn, Tre Brødre, and Tasiusarsuaq terranes merged in the Tasiusarsuaq orogeny, although these terranes were affected by Neoarchaean folding and deformation. In the Kapisilik orogeny terranes around the Godthåbsfjord, mostly north of Nuuk, were accreted along the Iivinnguit fault. South of Frederikshåb Isblink the Paamiut and Neria blocks probably collided in the Paamiut orogeny. They in turn collided with the Sioraq block and Tasiusarsuaq terranes 2760–270 Ma in the Tasiusarsuaq orogeny.

References

Notes

Sources

* * * * * Cratons Geology of Canada Geology of Greenland Geology of Scotland {{geology-stub