Columbia (supercontinent)

Columbia, also known as Nuna and Hudsonland, was one of Earth's ancient supercontinents. It was first proposed by J.J.W. Rogers and M. Santosh (2002) and is thought to have existed approximately 2.5 to 1.6 billion years (Ga) ago in the Paleoproterozoic Era. Zhao et al. (2002) proposed that the assembly of the supercontinent Columbia (Nuna) was completed by global-scale collisional events during 2.1–1.8 Ga.

The Columbia continent consisted of the proto-cratons that made up the former continents of Laurentia, Baltica, Ukrainian Shield, Amazonian Shield, Australia, and possibly Siberia, North China, and Kalaharia as well.

The evidence of Columbia's existence is based upon geological and paleomagnetic data.

Size and location

Columbia is estimated to have been about 12,900 kilometres from North to South, and about 4,800 km across at its broadest part.

The eastern coast of India was attached to western North America, with southern Australia against western Canada.

In this era most of South America was rotated such that the western edge of modern-day Brazil lined up with eastern North America, forming a continental margin that extended into the southern edge of Scandinavia.

Assembly

Columbia was assembled along global-scale 2.1–1.8 Ga collisional orogens and contained almost all of Earth’s continental blocks. The cratonic blocks in South America and West Africa were welded by the 2.1–2.0 Ga Transamazonian and Eburnean Orogens; the Kaapvaal and Zimbabwe cratons in southern Africa were collided along the c. 2.0 Ga Limpopo Belt; the cratonic blocks of Laurentia were sutured along the 1.9–1.8 Ga Trans-Hudson, Penokean, Taltson–Thelon, Wopmay, Ungava, Torngat, and Nagssugtoqidain Orogens; the Kola, Karelia, Volgo-Uralia, and Sarmatia cratons in Baltica (Eastern Europe) were joined by the 1.9–1.8 Ga Kola–Karelia, Svecofennian, Volhyn-Central Russian, and Pachelma Orogens; the Anabar and Aldan Cratons in Siberia were connected by the 1.9–1.8 Ga Akitkan and Central Aldan Orogens; the East Antarctica and an unknown continental block were joined by the Transantarctic Mountains Orogen; the South and North Indian Blocks were amalgamated along the Central Indian Tectonic Zone; and the Eastern and Western Blocks of the North China Craton were welded together by the c. 1.85 Ga Trans-North China Orogen.

Outgrowth

Following its final assembly at c. 1.8 Ga, the supercontinent Columbia underwent long-lived (1.8–1.3 Ga), subduction-related growth via accretion at key continental margins, forming a 1.8–1.3 Ga great magmatic accretionary belt along the present-day southern margin of North America, Greenland, and Baltica. It includes the 1.8–1.7 Ga Yavapai, Central Plains and Makkovikian Belts, 1.7–1.6 Ga Mazatzal and Labradorian Belts, 1.5–1.3 Ga St. Francois and Spavinaw Belts, and 1.3–1.2 Ga Elzevirian Belt in North America; the 1.8–1.7 Ga Ketilidian Belt in Greenland; and the 1.8–1.7 Transscandinavian Igneous Belt, 1.7–1.6 Ga Kongsberggian-Gothian Belt, and 1.5–1.3 Ga Southwest Sweden Granitoid Belt in Baltica. Other cratonic blocks also underwent marginal outgrowth at about the same time.

In South America, a 1.8–1.3 Ga accretionary zone occurs along the western margin of the Amazonia Craton, represented by the Rio Negro, Juruena, and Rondonian Belts. In Australia, 1.8–1.5 Ga accretionary magmatic belts, including the Arunta, Mount Isa, Georgetown, Coen, and Broken Hill Belts, occur surrounding the southern and eastern margins of the North Australia Craton and the eastern margin of the Gawler Craton. In China, a 1.8–1.4 Ga accretionary magmatic zone, called the Xiong’er belt (Group), extends along the southern margin of the North China Craton.

Fragmentation

Columbia began to fragment about 1.6 Ga ago, associated with continental rifting along the western margin of Laurentia (Belt-Purcell Supergroup), eastern India (Mahanadi and the Godavari), southern margin of Baltica (Telemark Supergroup), southeastern margin of Siberia (Riphean aulacogens), northwestern margin of South Africa (Kalahari Copper Belt), and northern margin of the North China Block (Zhaertai-Bayan Obo Belt).

The fragmentation corresponded with widespread anorogenic magmatic activity, forming anorthosite-mangerite-charnockite-granite (AMCG) suites in North America, Baltica, Amazonia, and North China, and continued until the final breakup of the supercontinent at about 1.3–1.2 Ga, marked by the emplacement of the 1.27 Ga Mackenzie and 1.24 Ga Sudbury mafic dike swarms in North America

Configuration

In the initial configuration of Rogers and Santosh (2002), South Africa, Madagascar, India, Australia, and attached parts of Antarctica are placed adjacent to the western margin of North America, whereas Greenland, Baltica (Northern Europe), and Siberia are positioned adjacent to the northern margin of North America, and South America is placed against West Africa. In the same year (2002), Zhao et al. (2002) proposed an alternative configuration of Columbia, in which the fits of Baltica and Siberia with Laurentia and the fit of South America with West Africa are similar to those of the Rogers and Santosh (2002) configuration, whereas the fits of India, East Antarctica, and Australia with Laurentia are similar to their corresponding fits in the configuration of Rodinia.

This continental configuration is based on the available geological reconstructions of 2.1–1.8 Ga orogens and related Archean cratonic blocks, especially on those reconstructions between South America vs West Africa, Western Australia vs South Africa, Laurentia vs Baltica, Siberia vs Laurentia, Laurentia vs Central Australia, East Antarctica vs Laurentia, and North China vs India. Of these reconstructions, the fits of Baltica and Siberia with Laurentia, South America with West Africa, and Southern Africa with Western Australia are also consistent with paleomagnetic data.

The new configuration of the Columbia supercontinent was reconstructed by Guiting Hou (2008) based on the reconstruction of giant radiating dike swarms.

See also

• Plate tectonics
• Supercontinent cycle
• List of supercontinents