The Labrador Trough or the New Quebec Orogen is a long and wide geologic belt in

Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...

, extending south-southeast from Ungava Bay through

Quebec Quebec is Canada's List of Canadian provinces and territories by area, largest province by area. Located in Central Canada, the province shares borders with the provinces of Ontario to the west, Newfoundland and Labrador to the northeast, ...

and

Labrador Labrador () is a geographic and cultural region within the Canadian province of Newfoundland and Labrador. It is the primarily continental portion of the province and constitutes 71% of the province's area but is home to only 6% of its populatio ...

. The trough is a linear belt of

sedimentary Sedimentary rocks are types of rock formed by the cementation of sediments—i.e. particles made of minerals (geological detritus) or organic matter (biological detritus)—that have been accumulated or deposited at Earth's surface. Sedime ...

and

volcanic rock Volcanic rocks (often shortened to volcanics in scientific contexts) are rocks formed from lava erupted from a volcano. Like all rock types, the concept of volcanic rock is artificial, and in nature volcanic rocks grade into hypabyssal and me ...

s which developed in an Early

Proterozoic The Proterozoic ( ) is the third of the four geologic eons of Earth's history, spanning the time interval from 2500 to 538.8 Mya, and is the longest eon of Earth's geologic time scale. It is preceded by the Archean and followed by the Phanerozo ...

rift basin. To the west is the

Archean The Archean ( , also spelled Archaean or Archæan), in older sources sometimes called the Archaeozoic, is the second of the four geologic eons of Earth's history of Earth, history, preceded by the Hadean Eon and followed by the Proterozoic and t ...

Superior Craton The Superior Craton is a stable fault block, 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 ...

. To the east are the rocks of the Archean Rae Craton. The sedimentary rocks and volcanics of the Labrador Trough were intensely deformed and subjected to high grade

metamorphism Metamorphism is the transformation of existing Rock (geology), rock (the protolith) to rock with a different mineral composition or Texture (geology), texture. Metamorphism takes place at temperatures in excess of , and often also at elevated ...

along with the Churchill terrain during the

Trans-Hudson orogeny The Trans-Hudson orogeny or Trans-Hudsonian orogeny was the major mountain building event (orogeny) that formed the Precambrian Canadian Shield and the North American Craton (also called Laurentia), forging the initial North American conti ...

. It is a northeast extension of the Circum-Superior Belt and is terminated to the south by the Grenville Front Tectonic Zone. Radiometric dates of 1883-1870 Ma are reported for

mafic A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks include ...

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 usua ...

carbonatite Carbonatite () is a type of intrusive rock, intrusive or extrusive rock, extrusive igneous rock defined by mineralogic composition consisting of greater than 50% carbonate minerals. Carbonatites may be confused with marble and may require geoche ...

and

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 o ...

intrusions within the Trough. It is a large

iron ore Iron ores are rocks and minerals from which metallic iron can be economically extracted. The ores are usually rich in iron oxides and vary in color from dark grey, bright yellow, or deep purple to rusty red. The iron is usually found in the f ...

belt developed on

banded iron formation Banded iron formations (BIFs; also called banded ironstone formations) are distinctive units of sedimentary rock consisting of alternating layers of iron oxides and iron-poor chert. They can be up to several hundred meters in thickness and e ...

s and has had mining operations since 1954. At least two large magmatic events occurred in the Labrador Trough. The first event 2,170 million years ago engulfed an area of and the second 1,880 million years ago covered a similar area of .

Geological history

The geological history of the Labrador Trough spans several tens of millions of years ranging from around 2.2 Ga to 1.74 Ga: # Following rifting along the

margin of the

Superior craton The Superior Craton is a stable fault block, 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 ...

about 2.2 billion years ago, rocks of the western part of the Labrador Trough were deposited. This period corresponds to the onset of first-cycle sedimentation and is characterized by the deposition of immature sediments, slightly alkaline volcanics, and the intrusion of mafic dykes. # Deposition of passive margin sediments, MORB-like mafic volcanism and intrusion of mafic sills characterize most of the first cycle between approximately 2.17 and 2.14 Ga. The end of the cycle (<2.06 Ga) is marked by the deposition of dolomite and chert on a restored platform. # Second-cycle platform and basin sedimentation occurred from 1.88 to 1.87 Ga and is associated with a new rifting episode or development of a fore-trough basin. This period is characterized by the intrusion of mafic-ultramafic sills, meimechite and carbonatite deposition, and MORB-like mafic volcanism corresponding to the formation of a transitional continental-oceanic crust. # A deformation and high-grade metamorphism phase occurs in the hinterland near Kuujjuaq from 1.84 to 1.83 Ga. A regional-scale granitic and charnockitic intrusion, the De Pas Supersuite (formerly De Pas Batholith), was also emplaced during the same period and up to 1.81 Ga. This supersuite is interpreted by several authors as being associated with a Proterozoic magmatic arc environment connected to a subduction zone developed during the orogenesis. This supersuite may also be associated with a syncollisional component in the hinterland. # There would have been an oblique collision between the Superior craton and the Core Zone of the Churchill Province during the orogenesis from 1.82 to 1.77 Ga. This event resulted in transpressure-type deformation and the formation of a western-verging thrust and fold belt, now known as the Labrador Trough. Molasse-type sediments were deposited on the Superior Province margin in the third cycle during this period. # Undeformed and likely post-tectonic small intrusions of monzonite occurred in the Labrador Trough around 1.81 Ga. # The hinterland near Kuujjuaq is characterized by pegmatite intrusion and hydrothermal activity followed by a cooling period from 1.77 to 1.74 Ga.

References

External links

Geological Survey of Quebec on the Labrador Trough
{{coord, 56.0, N, 67.5, W, display=title Geology of Newfoundland and Labrador Geology of Quebec Volcanism of Newfoundland and Labrador Volcanism of Quebec

Geological history

See also

References

External links