The Nipissing sills, also called the Nipissing diabase, is a large 2217– to 2210–million year old group of sills in the

Superior craton 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

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 ...

Ontario Ontario ( ; ) is one of the thirteen provinces and territories of Canada.Ontario is located in the geographic eastern half of Canada, but it has historically and politically been considered to be part of Central Canada. Located in Central Ca ...

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 intrude the

Huronian Supergroup The Huronian Supergroup is a Proterozoic assemblage of geologic formations of the Superior craton of the Canadian Shield in Ontario and Quebec. It extends from west of the city of Sault Ste. Marie in the west to the Ontario-Quebec border to the ...

. Nipissing sills intrude all the Huronian sediments and older basement rocks in the northern margin of the

Sudbury Basin The Sudbury Basin (), also known as Sudbury Structure or the Sudbury Nickel Irruptive, is a major geological structure in Ontario, Canada. It is the third-largest known impact crater or astrobleme on Earth, as well as one of the oldest. The cra ...

; they were emplaced after the

faulting In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...

and

folding Fold, folding or foldable may refer to: Arts, entertainment, and media * ''Fold'' (album), the debut release by Australian rock band Epicure * Fold (poker), in the game of poker, to discard one's hand and forfeit interest in the current pot *Abov ...

of Huronian rocks, and are

hornblende Hornblende is a complex inosilicate series of minerals. It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole. Hornblende minerals are common in igneous and metamorphic rocks ...

gabbro Gabbro () is a phaneritic (coarse-grained), mafic intrusive igneous rock formed from the slow cooling of magnesium-rich and iron-rich magma into a holocrystalline mass deep beneath the Earth's surface. Slow-cooling, coarse-grained gabbro is che ...

tholeiitic basalt 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 ...

composition. In the Sudbury–

Elliot Lake Elliot Lake is a city in Algoma District, Ontario, Canada. It is north of Lake Huron, midway between the cities of Sudbury and Sault Ste. Marie in the Northern Ontario region. Once dubbed the "uranium capital of the world," Elliot Lake has since ...

area the Nipissing diabase is deformed; outcrops are parallel to the fold axes of the Huronian sedimentary rocks. Nipissing diabase intrusions are east-northeast trending and are no wider than . The Nipissing sills in the Southern Province of the Superior craton are thought to originate from a radiating

dike swarm A dike swarm (American spelling) or dyke swarm (British spelling) is a large geological structure consisting of a major group of parallel, linear, or radially oriented magmatic dikes intruded within continental crust or central volcanoes ...

area to the northeast. The mantle source for the Nipissing sills did not come from the mantle beneath the Southern Province that had generated the 2500– to 2450–million year old

Matachewan dike swarm The Matachewan dike swarm is a large 2,500 to 2,450 million year old Paleoproterozoic dike swarm of Northern Ontario, Canada. It consists of basaltic dikes that were intruded in greenschist, granite-greenstone, and metamorphosed sedimentary terra ...

. The 2217– to 2210–million year old

Ungava magmatic event The Ungava magmatic event was a widespread magmatic event that began about 2.22 billion years ago during the Proterozoic Eon. Extent With an area of , the Ungava magmatic event caused the formation of a large igneous province. Magmatic feat ...

– located under the

Labrador Trough The Labrador Trough or the New Quebec Orogen is a long and wide geologic belt in Canada, extending south-southeast from Ungava Bay through Quebec and Labrador. The trough is a linear belt of sedimentary and volcanic rocks which developed in an ...

– fed the Nipissing sills; evidence shows the sills were laterally fed from 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 ...

center away via the 2216–million year old Senneterre dikes which form part of the radiating dike swarm.

References

{{coord missing, Ontario Igneous petrology of Ontario Sills (geology) Paleoproterozoic magmatism Landforms of Sudbury District Landforms of Nipissing District Geology of Greater Sudbury Mafic intrusions

See also

References