Gondwana
Gondwana was a large landmass, sometimes referred to as a supercontinent. The remnants of Gondwana make up around two-thirds of today's continental area, including South America, Africa, Antarctica, Australia, Zealandia, Arabia, and the Indian subcontinent.
Gondwana was formed by the accretion of several cratons, beginning with the East African Orogeny, the collision of India and Madagascar with East Africa, and culminating in with the overlapping Brasiliano and Kuunga orogenies, the collision of South America with Africa, and the addition of Australia and Antarctica, respectively. Eventually, Gondwana became the largest piece of continental crust of the Paleozoic Era, covering an area of some, about one-fifth of the Earth's surface. It fused with Laurasia during the Carboniferous to form Pangaea.
Gondwana began to separate from northern Pangea during the Triassic, and started to fragment during the Early Jurassic. The final stages of break-up saw the fragmentation of the Antarctic land bridge, which occurred during the Paleogene. Gondwana was not considered a supercontinent by the earliest definition, since the landmasses of Baltica, Laurentia, and Siberia were separated from it. To differentiate it from the Indian region of the same name, it is also commonly called Gondwanaland.
Regions that were part of Gondwana shared floral and faunal elements that persist to the present day.
Name
The continent of Gondwana was named by the Austrian scientist Eduard Suess after the Indian region of the same name, which is derived from Sanskrit गोण्डवन . The name had been previously used in a geological context, first by H. B. Medlicott in 1872, from which the Gondwana sedimentary sequences are also described.Some scientists prefer the term "Gondwanaland" for the supercontinent to make a clear distinction between the region and the supercontinent.
Formation
The assembly of Gondwana was a protracted process during the Neoproterozoic and Paleozoic, which remains incompletely understood because of the lack of paleo-magnetic data. Several orogenies, collectively known as the Pan-African orogeny, caused the continental fragments of a much older supercontinent, Rodinia, to amalgamate. One of those orogenic belts, the Mozambique Belt, formed and was originally interpreted as the suture between East and West Gondwana. Three orogenies were recognised during the 1990s as a result of data sets compiled on behalf of oil and mining companies: the East African Orogeny and Kuunga orogeny , the collision between East Gondwana and East Africa in two steps, and the Brasiliano orogeny, the successive collision between South American and African cratons.The last stages of Gondwanan assembly overlapped with the opening of the Iapetus Ocean between Laurentia and western Gondwana. During this interval, the Cambrian explosion occurred. Laurentia was docked against the western shores of a united Gondwana for a brief period near the Precambrian and Cambrian boundary, forming the short-lived and still disputed supercontinent Pannotia.
The Mozambique Ocean separated the Congo–Tanzania–Bangweulu Block of central Africa from Neoproterozoic India. The Azania continent was an island in the Mozambique Ocean.
The continents of Australia and East Antarctica were still separated from India, eastern Africa, and Kalahari by , when most of western Gondwana had already been amalgamated. By 550 Ma, India had reached its Gondwanan position, which initiated the Kuunga orogeny. Meanwhile, on the other side of the newly forming Africa, Kalahari collided with Congo and Rio de la Plata which closed the Adamastor Ocean. 540–530 Ma, the closure of the Mozambique Ocean brought India next to Australia–East Antarctica, and both North China and South China were in proximity to Australia.
As the rest of Gondwana formed, a complex series of orogenic events assembled the eastern parts of Gondwana . First, the Arabian-Nubian Shield collided with eastern Africa in the East African Orogeny. Then Australia and East Antarctica were merged with the remaining Gondwana in the Kuunga Orogeny.
The later Malagasy orogeny at about 550–515 Mya affected Madagascar, eastern East Africa and southern India. In it, Neoproterozoic India collided with the already combined Azania and Congo–Tanzania–Bangweulu Block, suturing along the Mozambique Belt.
The Terra Australis Orogen developed along Gondwana's western, southern, and eastern margins. Proto-Gondwanan Cambrian arc belts from this margin have been found in eastern Australia, Tasmania, New Zealand, and Antarctica. Though these belts formed a continuous arc chain, the direction of subduction was different between the Australian-Tasmanian and New Zealand-Antarctica arc segments.
Peri-Gondwana development: Paleozoic rifts and accretions
Many terranes were accreted to Eurasia during Gondwana's existence, but the Cambrian or Precambrian origin of many of these terranes remains uncertain. For example, some Paleozoic terranes and microcontinents that now make up Central Asia, often called the "Kazakh" and "Mongolian terranes", were progressively amalgamated into the continent Kazakhstania in the late Silurian. Whether these blocks originated on the shores of Gondwana is not known.In the Early Paleozoic, the Armorican terrane, which today form large parts of France, was part of Peri-Gondwana; the Rheic Ocean closed in front of it and the Paleo-Tethys Ocean opened behind it. Precambrian rocks from the Iberian Peninsula suggest that it, too, formed part of core Gondwana before its detachment as an orocline in the Variscan orogeny close to the Carboniferous–Permian boundary.
South-east Asia was made of Gondwanan and Cathaysian continental fragments that were assembled during the Mid-Paleozoic and Cenozoic. This process can be divided into three phases of rifting along Gondwana's northern margin: first, in the Devonian, North and South China, together with Tarim and Quidam rifted, opening the Paleo-Tethys behind them. These terranes accreted to Asia during Late Devonian and Permian. Second, in the Late Carboniferous to Early Permian, Cimmerian terranes opened Meso-Tethys Ocean; Sibumasu and Qiangtang were added to south-east Asia during Late Permian and Early Jurassic. Third, in the Late Triassic to Late Jurassic, Lhasa, Burma, Woyla terranes opened the Neo-Tethys Ocean; Lhasa collided with Asia during the Early Cretaceous, and Burma and Woyla during the Late Cretaceous.
Gondwana's long, northern margin remained a mostly passive margin throughout the Paleozoic. The Early Permian opening of the Neo-Tethys Ocean along this margin produced a long series of terranes, many of which were and still are being deformed in the Himalayan orogeny. These terranes are, from Turkey to north-eastern India: the Taurides in southern Turkey; the Lesser Caucasus Terrane in Georgia; the Sanand, Alborz, and Lut terranes in Iran; the Mangysglak Terrane in the Caspian Sea; the Afghan Terrane; the Karakorum Terrane in northern Pakistan; and the Lhasa and Qiangtang terranes in Tibet. The Permian–Triassic widening of the Neo-Tethys pushed all these terranes across the Equator and over to Eurasia.
Southwestern accretions
During the Neoproterozoic to Paleozoic phase of the Terra Australis Orogen, a series of terranes were rafted from the proto-Andean margin when the Iapetus Ocean opened, to be added back to Gondwana during the closure of that ocean. During the Paleozoic, some blocks which helped to form parts of the Southern Cone of South America, include a piece transferred from Laurentia when the west edge of Gondwana scraped against southeast Laurentia in the Ordovician. This is the Cuyania or Precordillera terrane of the Famatinian orogeny in northwest Argentina which may have continued the line of the Appalachians southwards. Chilenia terrane accreted later against Cuyania. The collision of the Patagonian terrane with the southwestern Gondwanan occurred in the late Paleozoic. Subduction-related igneous rocks from beneath the North Patagonian Massif have been dated at 320–330 million years old, indicating that the subduction process initiated in the early Carboniferous. This was relatively short-lived, and initial contact of the two landmasses occurred in the mid-Carboniferous, with broader collision during the early Permian. In the Devonian, an island arc named Chaitenia accreted to Patagonia in what is now south-central Chile.Gondwana as part of Pangaea: Late Paleozoic to Early Mesozoic
Gondwana and Laurasia formed the Pangaea supercontinent during the Carboniferous. Pangaea began to break up in the Mid-Jurassic when the Central Atlantic opened.In the western end of Pangaea, the collision between Gondwana and Laurasia closed the Rheic and Paleo-Tethys oceans. The obliquity of this closure resulted in the docking of some northern terranes in the Marathon, Ouachita, Alleghanian, and Variscan orogenies, respectively. Southern terranes, such as Chortis and Oaxaca, on the other hand, remained largely unaffected by the collision along the southern shores of Laurentia. Some Peri-Gondwanan terranes, such as Yucatán and Florida, were buffered from collisions by major promontories. Other terranes, such as Carolina and Meguma, were directly involved in the collision. The final collision resulted in the Variscan-Appalachian Mountains, stretching from present-day Mexico to southern Europe. Meanwhile, Baltica collided with Siberia and Kazakhstania which resulted in the Uralian orogeny and Laurasia. Pangaea was finally amalgamated in the Late Carboniferous-Early Permian, but the oblique forces continued until Pangaea began to rift in the Triassic.
In the eastern end, collisions occurred slightly later. The North China, South China, and Indochina blocks rifted from Gondwana during the middle Paleozoic and opened the Proto-Tethys Ocean. North China docked with Mongolia and Siberia during the Carboniferous–Permian, followed by South China. The Cimmerian blocks then rifted from Gondwana to form the Paleo-Tethys and Neo-Tethys oceans in the Late Carboniferous, and docked with Asia during the Triassic and Jurassic. Western Pangaea began to rift while the eastern end was still being assembled.
The formation of Pangaea and its mountains had a tremendous impact on global climate and sea levels, which resulted in glaciations and continent-wide sedimentation. In North America, the base of the Absaroka sequence coincides with the Alleghanian and Ouachita orogenies and are indicative of a large-scale change in the mode of deposition far away from the Pangaean orogenies. Ultimately, these changes contributed to the Permian–Triassic extinction event and left large deposits of hydrocarbons, coal, evaporite, and metals.
The breakup of Pangaea began with the Central Atlantic magmatic province between South America, Africa, North America, and Europe. CAMP covered more than seven million square kilometres over a few million years, reached its peak at , and coincided with the Triassic–Jurassic extinction event. The reformed Gondwanan continent was not precisely the same as that which had existed before Pangaea formed; for example, most of Florida and southern Georgia and Alabama is underlain by rocks that were originally part of Gondwana, but this region stayed attached to North America when the Central Atlantic opened.