The Hearne Craton is a craton in northern Canada which, together with the Rae Craton, forms the Western Churchill Province. Hearne is one of the six Archaean cratons of the Canadian Shield (the other being Slave, Rae, Wyoming, Superior, Nain) that are bound together by Palaeoproterozoic orogenic belts. Before being merged these six cratons formed independent microcontinents. [1]
The Hearne Craton is separated from the Rae Craton by the 2,000 km (1,200 mi)-long Snowbird Tectonic Zone (STZ). During the Neoarchaean and Palaeoproterozoic the STZ played a major role when the Western Churchill Province was first assembled and then reworked. The STZ is a record of Neoarchaean plate tectonics similar in scale to modern orogenic belts. [2]
When Laurentia formed at 2.0–1.7 Ga Hearne and Rae formed a central strip to which the Slave, Superior, Sask, and Wyoming cratons were accreted. This strip is bounded by a series of orogens: the 1.92–1.69 Ga Trans-Hudson to the south, the 2.0–1.9 Ga Taltson–Thelon and the 1.97–1.84 Ga Wopmey to the west. Hearne and Rae were extensively reworked during the assembly of Laurentia and overlain by Palaeoproterozoic cover sequences. On Hearne the most extensive such cover sequence is a series of continental and marine deposits known as the Hurwitz Group, a series of north-east-trending belts that cover 150,000 km2 (58,000 sq mi). A synclinoria infolded with Archaean basement in central Hearne has a fold-train with a wavelength of 35–45 km (22–28 mi). In the south-western Hearne continental siliciclastic rocks known as the Kiyuk Group overlie the Hurwitz Group. Both groups are covered by a thick cover of thrusts and folds. [3]
The Manikewan Ocean, a palaeocean named by Stauffer 1984, started to open along the south-east margin of Hearne at 2.075 Ga and had reached a width of 5,000 km (3,100 mi) after a hundred million years. Intra-oceanic arc collision resulted in the Amisk Collage and the Flin Flon – Glennie Complex around 1.92–1.88 Ga. [4] Today these Palaeoproterzoic structures in the Trans-Hudson Orogen welds the Archaean Hearne and the Superior cratons. [5] As the ocean continued to close, an Andean-style arc pluton known as the Wathaman Batholith formed 1.86–1.85 Ga. The subduction of the Manikewan Ocean stopped when the La Ronge Arc collided with Hearne. The final closure of the ocean around 1.83 Ga, when Hearne, Superior, and Sask cratons merged with the Flin Flon – Glennie Complex, was followed by a period of metamorphism that peaked around 1.82–1.8 Ga. [4] The Manikewan Mobile Belt now covers an area of 600,000 km2 (230,000 sq mi) but is overlain by Middle Proterozoic Athabasca sandstone. [6]
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, is more than three billion years old and formed part of the Rodinia supercontinent at c. 1 Ga.
The Congo Craton, covered by the Palaeozoic-to-recent Congo Basin, is an ancient Precambrian craton that with four others makes up the modern continent of Africa. These cratons were formed between about 3.6 and 2.0 billion years ago and have been tectonically stable since that time. All of these cratons are bounded by younger fold belts formed between 2.0 billion and 300 million years ago.
The Pan-African orogeny was a series of major Neoproterozoic orogenic events which related to the formation of the supercontinents Gondwana and Pannotia about 600 million years ago. This orogeny is also known as the Pan-Gondwanan or Saldanian Orogeny. The Pan-African orogeny and the Grenville orogeny are the largest known systems of orogenies on Earth. The sum of the continental crust formed in the Pan-African orogeny and the Grenville orogeny makes the Neoproterozoic the period of Earth's history that has produced most continental crust.
The East European Craton (EEC) is the core of the Baltica proto-plate and consists of three crustal regions/segments: Fennoscandia to the northwest, Volgo-Uralia to the east, and Sarmatia to the south. Fennoscandia includes the Baltic Shield and has a diversified accretionary Archaean and early Proterozoic crust, while Sarmatia has an older Archaean crust. The Volgo-Uralia region has a thick sedimentary cover, however deep drillings have revealed mostly Archaean crust. There are two shields in the East European Craton: the Baltic/Fennoscandian shield and the Ukrainian shield. The Ukrainian Shield and the Voronezh Massif consists of 3.2-3.8 Ga Archaean crust in the southwest and east, and 2.3-2.1 Ga Early Proterozoic orogenic belts.
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 300,000 km2 (120,000 sq mi), it is a relatively small but well-exposed craton dominated by ~2.73–2.63 Ga greenstones and turbidite sequences and ~2.72–2.58 Ga plutonic rocks, with large parts of the craton underlain by older gneiss and granitoid units. The Slave Craton is one of the blocks that compose the Precambrian core of North America, also known as the palaeocontinent Laurentia.
The Sarmatian Craton or Sarmatia is the southern segment/region of the East European Craton or Baltica, also known as Scythian Plateau. The craton contains Archaean rocks 2.8 to 3.7 billion years old (Ga). During the Carboniferous the craton was rifted apart by the Dnieper-Donets rift. As a result, geomorphologically the cratonic area is split by the Donbas Fold Belt, also known as a part of the large Pripyat-Dniepr-Donets aulacogen, which transects Sarmatia, dividing it into the Ukrainian Massif or shield on the southwest and the Voronezh Massif to the northeast.
The Kaapvaal Craton, along with the Pilbara Craton of Western Australia, are the only remaining areas of pristine 3.6–2.5 Ga crust on Earth. Similarities of rock records from both these cratons, especially of the overlying late Archean sequences, suggest that they were once part of the Vaalbara supercontinent.
The Churchill Craton is the northwest section of the Canadian Shield and stretches from southern Saskatchewan and Alberta to northern Nunavut. It has a very complex geological history punctuated by at least seven distinct regional tectonometamorphic intervals, including many discrete accretionary magmatic events. The Western Churchill province is the part of the Churchill Craton that is exposed north and west of the Hudson Bay. The Archean Western Churchill province contributes to the complicated and protracted tectonic history of the craton and marks a major change in the behaviour of the Churchill Craton with many remnants of Archean supracrustal and granitoid rocks.
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, forging the initial North American continent. It gave rise to the Trans-Hudson orogen (THO), or Trans-Hudson Orogen Transect (THOT), which is the largest Paleoproterozoic orogenic belt in the world. It consists of a network of belts that were formed by Proterozoic crustal accretion and the collision of pre-existing Archean continents. The event occurred 2.0–1.8 billion years ago.
The Wyoming Craton is a craton in the west-central United States and western Canada – more specifically, in Montana, Wyoming, southern Alberta, southern Saskatchewan, and parts of northern Utah. Also called the Wyoming Province, it is the initial core of the continental crust of North America.
The Flin Flon greenstone belt, also referred to as the Flin Flon – Snow Lake greenstone belt, is a Precambrian greenstone belt located in the central area of Manitoba and east-central Saskatchewan, Canada. It lies in the central portion of the Trans-Hudson orogeny and was formed by arc volcanism during the Paleoproterozoic period. The Flin Flon – Snow Lake greenstone belt is 250 km long by 75 km wide and is exposed just north of McClarty Lake. The belt is bounded by metasedimentary gneisses and metavolcanics of the Kisseynew Domain to the north and extends to the south where it is unconformably overlain by Ordovician age dolomite.
Laurentia or the North American Craton is a large continental craton that forms the ancient geological core of North America. Many times in its past, Laurentia has been a separate continent, as it is now in the form of North America, although originally it also included the cratonic areas of Greenland and also the northwestern part of Scotland, known as the Hebridean Terrane. During other times in its past, Laurentia has been part of larger continents and supercontinents and itself consists of many smaller terranes assembled on a network of Early Proterozoic orogenic belts. Small microcontinents and oceanic islands collided with and sutured onto the ever-growing Laurentia, and together formed the stable Precambrian craton seen today.
The Circum-Superior Belt is a widespread Paleoproterozoic large igneous province in the Canadian Shield of Northern, Western and Eastern Canada. It extends more than 3,400 km (2,100 mi) from northeastern Manitoba through northwestern Ontario, southern Nunavut to northern Quebec and into western Labrador. Igneous rocks of the Circum-Superior Belt are mafic-ultramafic in composition, deposited in the Labrador Trough near Ungava Bay, the Cape Smith Belt near the southern shore of Hudson Strait and along the eastern shore of Hudson Bay in its northern portion; the Thompson and Fox River belts in the northwest and the Marquette Range Supergroup in its southern portion. The Circum Superior Belt also hosts a rare example of Proterozoic Komatiite, in the Winnipegosis komatiite belt.
The Winnipegosis komatiite belt is a 150 km (93 mi) long and 30 km (19 mi) wide greenstone belt located in the Lake Winnipegosis area of central Manitoba, Canada. It has no surface exposure and was identified based on geophysical signatures and drilling during mineral exploration by Cominco during the 1990s. The belt has an age of 1870 ± 7 million years and is predominantly composed of basaltic and komatiitic volcanic rocks with minor intrusive and sedimentary rocks. The belt is considered part of the larger Circum-Superior Belt and was likely generated by a mantle plume. The Winnipegosis Komatiite Belt is notable as one of the few examples of komatiite formed during the Proterozoic.
The Svecofennian orogeny is a series of related orogenies that resulted in the formation of much of the continental crust in what is today Sweden and Finland plus some minor parts of Russia. The orogenies lasted from about 2000 to 1800 million years ago during the Paleoproterozoic Era. The resulting orogen is known as the Svecofennian orogen or Svecofennides. To the west and southwest the Svecofennian orogen limits with the generally younger Transscandinavian Igneous Belt. It is assumed that the westernmost fringes of the Svecofennian orogen have been reworked by the Sveconorwegian orogeny just as the western parts of the Transscandinavian Igneous Belt has. The Svecofennian orogeny involved the accretion of numerous island arcs in such manner that the pre-existing craton grew with this new material from what is today northeast to the southwest. The accretion of the island arcs was also related to two other processes that occurred in the same period; the formation of magma that then cooled to form igneous rocks and the metamorphism of rocks.
The Snowbird Tectonic Zone (STZ) is a geological structure in the western Canadian Shield which forms a geophysical boundary between the Hearne Craton and the south-west arm of the Rae Craton. It is enigmatic and has been interpreted as a Proterozoic suture or escape structure, or an Archaean suture reactivated during either the Archaean or Palaeoproterozic. It stretches 2,800 km (1,700 mi) from the Canadian Cordillera north-east to Hudson Bay, diagonally crossing Alberta, Saskatchewan, the Northwest Territories, and Nunavut.
The Nagssugtoqidian orogeny was a late Paleoproterozoic mountain-building event that affected Greenland during the period 1.91 to 1.77 Ga. The orogenic belt formed during this event marks the northern boundary of the mainly Archaean North Atlantic Craton. It was first recognised by Ramberg in 1949, based on its effect on the Kangaamiut dike swarm. The subsequent recognition of magmatic terranes representing past island arcs and two potential sutures representing now vanished subduction zones within the belt, have enabled its interpretation in terms of plate tectonics.
The Ketilidian orogeny was a late Paleoproterozoic mountain-building event that affected southern Greenland during the period 1.85 to 1.72 Ga. The orogenic belt formed during this event, sometimes known as the Ketilidian mobile belt, forms the southern boundary to the mainly Archaean North Atlantic Craton. The belt is 250–350 km wide, much of it covered by ice. It is correlated with the Makkovik Province in Labrador, Canada, which has a similar history.
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 Earth's crust that has been stable and subjected to very little geological changes over a long time. The size of Superior Craton is about 1,572,000 km2. The craton underwent a series of events from 4.3 to 2.57 Ga. These events included the growth, drifting and deformation of both oceanic and continental crusts.
The Dharwar Craton is an Archean continental crust craton formed between 3.6-2.5 billion years ago (Ga), which is located in southern India and considered as the oldest part of the Indian peninsula.