The geology of

Quebec Quebec ( ; )According to the Canadian government, ''Québec'' (with the acute accent) is the official name in Canadian French and ''Quebec'' (without the accent) is the province's official name in Canadian English is one of the thirtee ...

involves several different geologic provinces, made up of ancient Precambrian crystalline igneous and metamorphic rock, overlain by younger sedimentary rocks and soils. Most of southern Quebec is dominated by the

Grenville Province The Grenville Province is a tectonically complex region, in Eastern Canada, that contains many different aged accreted terranes from various origins. It exists southeast of the Grenville Front and extends from Labrador southwestern to Lake Huron. ...

, while the vast north is divided between the large Superior Province and the Churchill Province to the east, near Labrador.

Geologic History, Stratigraphy & Tectonics

The Grenville Province, which dominates southern Quebec, particularly the northern shore of the St. Lawrence formed beginning 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 during the Arc ...

, more than 2.5 billion years ago. Geologists subdivide the Grenville Province into the

Allochthon upright=1.6, Schematic overview of a thrust system. The hanging wall block is (when it has reasonable proportions) called a nappe. If an erosional hole is created in the nappe that is called a window (geology)">window. A klippe is a solitary out ...

along the river itself and the more northern Parautochthon. The Parautochthon is a band running parallel to the Grenville Front, which varies in width from Labrador to northeastern

Georgian Bay Georgian Bay (french: Baie Georgienne) is a large bay of Lake Huron, in the Laurentia bioregion. It is located entirely within the borders of Ontario, Canada. The main body of the bay lies east of the Bruce Peninsula and Manitoulin Island. To ...

on Lake Huron. Parautochthonous rocks are made up composed of ancient Archean and Proterozoic rocks that are highly deformed plutonic and metamorphosed supracrustal (metasedimentary and metavolcanic) rocks that reached

greenschist Greenschists are metamorphic rocks that formed under the lowest temperatures and pressures usually produced by regional metamorphism, typically and 2–10 kilobars (). Greenschists commonly have an abundance of green minerals such as chlorite ...

granulite Granulites are a class of high-grade metamorphic rocks of the granulite facies that have experienced high-temperature and moderate-pressure metamorphism. They are medium to coarse–grained and mainly composed of feldspars sometimes associated ...

facies on the sequence of metamorphic facies during the

Grenville orogeny The Grenville orogeny was a long-lived Mesoproterozoic mountain-building event associated with the assembly of the supercontinent Rodinia. Its record is a prominent orogenic belt which spans a significant portion of the North American continent, f ...

. These rocks correlate with the least deformed rocks north of the Grenville Front in the Superior Province and show signs of east-west lateral extension. The Allochthon includes all the lands of the Grenville Province south of the Parautochtone. The Allochthon juxtaposed on the Parautochthon during the Grenville orogeny cycle from 1.09 billion to 985 million years ago. The Allochthon is composed of

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 ...

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), ...

rocks. In the western part, it is mainly

marble Marble is a metamorphic rock composed of recrystallized carbonate minerals, most commonly calcite or dolomite. Marble is typically not foliated (layered), although there are exceptions. In geology, the term ''marble'' refers to metamorphose ...

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 tec ...

, and

pelite A pelite ( Greek: ''pelos'', "clay") or metapelite is a metamorphosed fine-grained sedimentary rock, i.e. mudstone or siltstone. The term was earlier used by geologists to describe a clay-rich, fine-grained clastic sediment or sedimentary rock, ...

platform levels and Mesoproterozoic amphibolite-grade rocks. There are also

charnockite Charnockite () is any orthopyroxene-bearing quartz-feldspar rock formed at high temperature and pressure, commonly found in granulite facies metamorphic regions, ''sensu stricto'' as an endmember of the charnockite series. Charnockite series Th ...

and

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 ...

intrusions that intersect metasediments and

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 ...

. In the center,

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 th ...

, quartzo-feldspathic orthogneisses and mangerites predominate. In its eastern part, it consists mainly of gneissic rocks of varied composition and origin, metasedimentary rocks, granitoid intrusions,

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 ch ...

, gabbronorite and

. There are also several anorthositic intrusions scattered throughout the Allochthon belt. The Canadian Shield spans much of northern Quebec, which is primarily underlain by the Superior Craton, a 160-mile thick section of stable continental crust formed beginning 4.03 billion years ago. In the northwest and at the northern tip of the

Ungava Peninsula The Ungava Peninsula of Nunavik, Quebec, Canada, is bounded by Hudson Bay to the west, Hudson Strait to the north, and Ungava Bay to the east. This peninsula is part of the Labrador Peninsula, and covers about . Its northernmost point is Ca ...

is the large Churchill Craton, which extends into Labrador and Nunavut as the eastern extent of the Canadian Shield. Quebec's northern bedrock is also regionally composed of the Hudson Platform along the shore of

James Bay James Bay (french: Baie James; cr, ᐐᓂᐯᒄ, Wînipekw, dirty water) is a large body of water located on the southern end of Hudson Bay in Canada. Both bodies of water extend from the Arctic Ocean, of which James Bay is the southernmost pa ...

and a small section of the

Nain Province In Labrador, Canada, the North Atlantic Craton is known as the Nain Province. The Nain geologic province was intruded by the Nain Plutonic Suite, which divides the province into the northern Saglek block and the southern Hopedale, Newfoundland an ...

, near the northern tip of Labrador. The St. Lawrence Platform occupies the lowlands where much of Quebec's urban population lives, while the Gaspe Peninsula,

Anticosti Island ; moe, Notiskuan; mic, Natigostec , sobriquet = , image_name = RiviereHuileAnticosti.jpg , image_caption = Salmon fisherman on Rivière à l'Huile , image_map ...

and the Magdalene Islands are part of the Appalachian Province.

Paleozoic (539-251 million years ago)

During the

Taconic orogeny The Taconic orogeny was a mountain building period that ended 440 million years ago and affected most of modern-day New England. A great mountain chain formed from eastern Canada down through what is now the Piedmont of the East coast of the Unit ...

that began the formation of the

Appalachian Mountains The Appalachian Mountains, often called the Appalachians, (french: Appalaches), are a system of mountains in eastern to northeastern North America. The Appalachians first formed roughly 480 million years ago during the Ordovician Period. They ...

, amphibolite,

mica 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 ...

and other metamorphic rocks formed a belt running down the Gaspe Peninsula to

Sherbrooke Sherbrooke ( ; ) is a city in southern Quebec, Canada. It is at the confluence of the Saint-François and Magog rivers in the heart of the Estrie administrative region. Sherbrooke is also the name of a territory equivalent to a regional cou ...

. Muscovite bearing granites and metamorphic rocks around Asbestos formed over a broad span from 468 to 379 million years ago. While slate and plutonic

tonalite Tonalite is an igneous, plutonic ( intrusive) rock, of felsic composition, with phaneritic (coarse-grained) texture. Feldspar is present as plagioclase (typically oligoclase or andesine) with alkali feldspar making up less than 10% of the total ...

formed in the vicinity of Becancour and

Quebec City Quebec City ( or ; french: Ville de Québec), officially Québec (), is the capital city of the Canadian province of Quebec. As of July 2021, the city had a population of 549,459, and the metropolitan area had a population of 839,311. It is t ...

respectively. Around 292 million years ago, volcanism deposited tuff in the Magdalene Islands.

Mesozoic (251-66 million years ago)

Sedimentary deposition and some volcanic activity took place during the

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 ...

, particularly in the lowlands of the St. Lawrence Platform. Central

Montreal Montreal ( ; officially Montréal, ) is the second-most populous city in Canada and most populous city in the Canadian province of Quebec. Founded in 1642 as '' Ville-Marie'', or "City of Mary", it is named after Mount Royal, the triple ...

is underlain by 119 to 117 million year old plutonic basanite,

lamprophyre Lamprophyres () are uncommon, small-volume ultrapotassic igneous rocks primarily occurring as dikes, lopoliths, laccoliths, stocks, and small intrusions. They are alkaline silica- undersaturated mafic or ultramafic rocks with high magnesium ...

and camptonite while to the immediate southeast amphibole gabbro and peralkaline rocks formed from 141 to 123 million years ago.

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 ...

intrusive rocks formed hills housed in the sedimentary rocks of the St. Lawrence Lowlands Platform, notably Mount St. Bruno.

Cenozoic (66 million years ago-present)

Quebec experienced intense erosion during the past 2.5 million years of the Quaternary, which often mobilized older rocks, such as Proterozoic granite boulders found offshore in the moraines which formed parts of the Magdalene Islands. Some of the youngest rocks in Quebec are situated along the western border with Ontario, including the Bedford Hill Rhyolite and dacites which are less than one million years old.

References

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