East Antarctic Shield

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Map of East and West Antarctica
Figure 1. Map of East and West Antarctica separated by the Transantarctic Mountain Range

The East Antarctic Shield or Craton is a

Mawson craton
) that occupies most of the continental interior and various other marginal cratons that are exposed along the coast.

Background

The blue line represents the path traveled by the East Antarctic Shield over the past 550 million years. Red numbers indicate the time (millions of years ago); the yellow dot represents the south pole.

Over the past 1 billion years,

plutonic and volcanic rocks.[1]
This knowledge of the shield's structural features and compositions leads to the development of a tectonic history. The traditional models of East Antarctic Shield geology typically involve a three-stage tectonic history that includes:

Interaction with supercontinents

Rodinia: 1100–750 Ma

Mawson continent) and the marginal cratons that make up most of southern Africa, India and western Australia.[3] This tectonism continued until 900 Ma and by 750 Ma, the supercontinent Rodinia had begun to break up. The rupture might have resulted from the opening of an equatorial ocean basin between West Laurentia and West Australia-East Antarctica.[2]

Gondwana: 550–320 Ma

The configuration of the continents during the time of Gondwana. The location of the Pan-African Orogeny, Lutzow Holm belt and many other features caused by the interaction between the East Antarctic Shield and the surrounding plates.

Then came

Arabia, India and East Antarctica along with most of South America and Australia.[2] In the late Cambrian, Gondwana stretched from polar (NW Africa) to subtropical southerly latitudes with East Antarctica around the equator. The Pan-African orogenies that stabilized the East Antarctic Shield took place in two main zones; a broad region between the Shackleton Mountain Range, caused by the collision with South Africa, and India, and along the Transantarctic Mountains (Ross Orogeny).[2]

The Ross Orogen comprises a deformed sequence of Neoproterozoic to Cambrian sediments.[9] These sediments were deposited at a passive margin that likely developed during the rifting of North America from the East Antarctic Shield, and were subsequently deformed and metamorphosed at a low- to medium-grade and intruded by syn- and post-tectonic granitoids.[3] Plutonism and metamorphism commenced at about 550 Ma with peak metamorphism at 540-535 Ma.[10] At this time, two more high-grade Cambrian mobile belts formed in East Antarctica, the Lutzow Holm Belt and the Prydz Belt. Tectonism was relatively synchronous between the two from 550 to 515 Ma and both belts overprinted late Mesoproterozoic to early Neoproterozoic, Grenville-age magmatic and metamorphosed rocks. The Lutzow Holm Belt separates the Grenville-age Maud and Rayner Provinces and is the southernmost segment of the East African Orogeny, which extended from East Africa to the Shackleton Range.[3] Evidence for ocean closure is well-documented in the East African Orogen and this is supported by the occurrence of ophiolite material in the Shackleton Range.[11] Further evidence for ocean closure along the Lutzow Holm Belt is provided by the different ages of Grenville-age tectonism in the Maud and Rayner Provinces of either side of the inferred suture. The climax of activity in both the Lutzow Holm and Prydz Belts was at 530 Ma, but the possibility of two-near-simultaneous collisions cannot be discounted and would mean that East Antarctica comprise three major crustal fragments that did not combine until the Cambrian.[12]

Pangea: 320–160 Ma

Animation of the rifting of Pangaea

From 320 Ma onward, Gondwana,

Pangea.[2] Pangea's main amalgamation occurred during the Carboniferous but continents continued to be added and rifted away in the Late Paleozoic to Early Mesozoic.[13] Pangea ruptured during the Jurassic, preceded by and associated with widespread magmatic activity, including the Karoo flood basalts and related dyke swarms in South Africa and the Ferrar Province in East Antarctica.[14]

Post Pangea: 160 Ma–Present

In the Late Jurassic and Early Cretaceous, the East Antarctic Shield began to move southward at a faster rate than Africa and South America, resulting in seafloor spreading between the two sub-blocks of Gondwana in the Weddell Sea, Riiser-Larsen Sea, Mozambique and Somali basins.[2] A long phase of extension and rifting took place in the southern Weddell Sea before the onset of seafloor spreading, dated around 147 Ma.[15] During the mid-Cretaceous, seafloor spreading propagated eastward from the Riiser-Larsen Sea to the Enderby basin between East Antarctica and India.[16] At 50 Ma, the inception of rapid northward drift of the Australian plate caused rapid accretion of oceanic crust on the East Antarctic Shield.[17] Relative extension between West Australia and East Antarctica commenced in the Late Cretaceous to Early Tertiary, but oceanic crust between these two plates was formed only between 45 and 30 Ma in the Adare Trough of the Ross Sea.[18]

See also

References

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  7. ^ a b Kamanev, E. N. (1993). "Structure and evolution of the Antarctic shield in Precambrian". Gondwana Eight: Assembly, Evolution and Dispersal: 141–151.
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  14. doi:10.1111/j.1365-246X.2006.03158.x
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  15. doi:10.1029/2005JB004035
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  16. doi:10.1111/j.1365-246X.2007.03450.x
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  17. S2CID 129191964
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  18. S2CID 4399729
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