Geology of Enderby Land

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Enderby Land
Stratigraphic range: Archean to Paleozoic
Enderby Land, Antarctica.jpg
Enderby Land, Antarctica. NASA MODIS image, 2011.
Type Geological formation
Unit ofNapier Complex, Rayner Complex, Lützow-Holm Complex, Yamato–Belgica Complex
Location
Coordinates 68°16′S31°34′E / 68.27°S 31.57°E / -68.27; 31.57
RegionNortheastern Antarctica
Type section
Named for Samuel Enderby & Sons
Named byJohn Briscoe and Whaling brig Tula [1]
Year defined1831
Region East Antarctica
Country Antarctica
The four distinct metamorphic complexes Enderby Land, Antarctica Geology.jpg
The four distinct metamorphic complexes
Garnet gneiss Garnet gneiss.jpg
Garnet gneiss

Enderby Land is a region of Northeastern Antarctica which extends into the Southern Indian Ocean. The area is claimed by Australia as part of the Australian Antarctic Territory. The unique and diverse geological features of this region have been associated with the evolution and development of the supercontinent Gondwana. Multiple distinct geological formations are located in this region. The most prominent and important are the

Contents

  1. Napier Complex (Archaean)
  2. Rayner Complex (late-Proterozoic)
  3. Lützow-Holm Complex (LHC) (early-Paleozoic)
  4. Yamato–Belgica Complex (early-Paleozoic)

Both the Proterozoic and Paleozoic structures present in this region have become visible due to the initial uplift and exposure of the Archaean Napier Complex, where the oldest metamorphic rocks (4000 Ma) were found in the expanding Archaean blocks. [2] [3]

Metamorphism

The high‐grade metamorphic rocks of Enderby Land, which form part of the East Antarctic Shield, have been subdivided into three major metamorphic core complexes. These are the

The Napier Complex contains primarily pyroxene‐quartz‐feldspar gneiss and garnet‐quartz‐feldspar gneiss, with minor amounts of both pyroxene and mafic granulite. There are also a variety of siliceous and aluminous metasediments present. Multiple mafic dykes are also present in the area which intrude into the gneisses. [4] [5] The ultra-high-temperature (UHT) Napier metamorphic complex is noteworthy and distinctive due to the presence of the highest grades of metamorphism seen in rocks of any continental crust. The early predecessors of tonalitic and granitic gneisses range in age locally up to 3800 Ma, and therefore are the oldest rocks documented from Antarctica. It is generally agreed upon that all the high-grade and ultra-high-temperature metamorphism in the area was finished by the end of the Archean. Effects of the metamorphism are mostly restricted to regions of retrogression and localized shear zones in the area. [6] [7]

The Rayner Complex consists predominately of re‐metamorphosed Napier Complex rocks, and mafic dykes that occur only as metamorphosed remnants. The rocks of the Rayner Complex are generally of a lower metamorphic grade (upper amphibolite to granulite facies) than those found in the Napier Complex. There are however, high-pressure granulites that can be found locally. [4] Higher water pressures were inferred from observation of relatively abundant migmatitic gneisses and hydrous minerals such as biotite and hornblende, as well as the lack of mesoperthite. [5] [8]

The Lützow-Holm Complex experienced regional metamorphism in the early Paleozoic. This metamorphic complex contains metamorphic ages associated with the Pan-African orogeny (520 and 560 Ma). The main regional metamorphism in the LHC is related to continent-continent collision between portions of the Gondwana supercontinent. This area may include remains of a potential suture between East and West Gondwana. The metamorphic grade increases gradually from the Prince Olav Coast (amphibolite facies; eastern part of the LHC) to the Soya Coast (granulite facies; western part of the LHC). [3] [9]

Tectonic evolution

Two major tectonic processes could have influenced the formation of the present structures seen in Enderby Land.

As evidenced by the figure visible below, there are multiple viable examples of occurrences and structures which could relate to the hypothesis described.

Tectonic Model of structures in Antarctica.jpg

The Pan-African orogenic event is linked with NE-SW compression in Western and Eastern Gondwana. This compression could have possibly produced the strong seismic reflections which were detected in the Lützow-Holm Complex (LHC), as well as the neighboring Princess Elizabeth Land (PEL). After Gondwana broke up there seemed to be NW-SE extension which affected the graben structure found in the Prince Charles Mountains (PCM) and the diversity found around the Moho. [3] [10]

There is a general consensus that the Napier Complex could be a nucleus during the amalgamation of East-West Gondwanaland. The Rayner Complex is thought to be a rim of the Napier nucleus, and the western part of this complex seems to have been reworked at the Pan-African age. Surface structures in this area contain near right angles in a generally N-S trending East African/Antarctic Orogen as verified by the presence of discovered magnetic anomalies. [3]

Recent scientific studies

Multiple countries including Australia, Russia, and Japan have conducted recent marine surveys over the past several decades which have collected integrated data sets from seismic, gravitational, and magnetic studies in the southern Indian Ocean surrounding Enderby Land. This data was combined and compiled in order to create an improved definition of crustal magnetic anomaly patterns and to help further understand the igneous activity and breakup processes associated with the creation of the East Antarctic passive margin. [11]

Two recent deep seismic surveys were carried out on the continental ice-sheet of the Lützow-Holm Complex in 2000 and 2002. The two surveys were carried out as a program of the “Structure and Evolution of the East Antarctic Lithosphere” (SEAL) by the Japanese Antarctic expeditions. Crustal velocity models and simple reflection sections were taken and data was compiled. [12]

1. SEAL-2000

2. SEAL-2002

Enderby Land is known to have higher seismic velocities than other neighboring regions, with its center around the Napier Complex, as determined by surface wave tomographic studies. Additionally, the depth of the lithospheric rock body beneath the Napier complex acquired from the seismic body wave tomography is found to be about 250 km. [3]

See also

Related Research Articles

Gneiss Common high-grade metamorphic rock

Gneiss is a common and widely distributed type of metamorphic rock. Gneiss is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. Gneiss forms at higher temperatures and pressures than schist. Gneiss nearly always shows a banded texture characterized by alternating darker and lighter colored bands and without a distinct cleavage.

Migmatite Mixture of metamorphic rock and igneous rock

Migmatite is a composite rock found in medium and high-grade metamorphic environments. It consists of two or more constituents often layered repetitively; one layer was formerly paleosome, a metamorphic rock that was reconstituted subsequently by partial melting; the alternate layer has a pegmatitic, aplitic, granitic or generally plutonic appearance. Commonly, migmatites occur below deformed metamorphic rocks that represent the base of eroded mountain chains, commonly within Precambrian cratonic blocks,

The Napier Mountains are a group of close set peaks, the highest being Mount Elkins, at about 2,300 meters above sea level. This mountain range is located in Enderby Land, in the claimed Australian Antarctic Territory, East Antarctica.

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The Yilgarn Craton is a large craton that constitutes the bulk of the Western Australian land mass. It is bounded by a mixture of sedimentary basins and Proterozoic fold and thrust belts. Zircon grains in the Jack Hills, Narryer Terrane have been dated at ~4.27 Ga, with one detrital zircon dated as old as 4.4 Ga.

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Mount Elkins

Mount Elkins, also known as Jökelen is a dark, steep-sided mountain with three major peaks, the highest 2,300 meters (7,500 ft) above sea level, in the Napier Mountains of Enderby Land. Enderby Land is part of East Antarctica, and is claimed by Australia as part of the Australian Antarctic Territory. The mountain was named after Terence James Elkins, an ionospheric physicist with the Australian National Antarctic Research Expeditions at Mawson Station in 1960.

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Lewisian complex

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References

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  3. 1 2 3 4 5 6 Kanao, Masaki; Suvorov, Vladimir D.; Yamashita, Mikiya; Mishenkin, Boris (2014-07-13). "Crustal structure and tectonic evolution of Enderby Land, East Antarctica, as revealed by deep seismic surveys". Tectonophysics. 627: 38–47. doi:10.1016/j.tecto.2014.04.014.
  4. 1 2 Tingey, R.J.; Ellis, D.J. (September 1980). "Enderby land, Antarctica-an unusual Precambrian high grade metamorphic terrane". Journal of the Geological Society of Australia. 27 (1–2): 1–18. doi:10.1080/00167618008729114.
  5. 1 2 Mikhalsky, E.V.; Sheraton, J.W. (2011). "The Rayner tectonic Province of East Antarctica: Compositional features and geodynamic setting" (PDF). Geotectonics. 45 (6): 496–512. doi:10.1134/s0016852111060057. S2CID   128752229 . Retrieved 19 November 2014.
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  7. Mikhalsky, E.V.; Henjes-Kunst, F.; Belyatsky, B.V.; Roland, N.W. "Mafic dykes in the southern Prince Charles Mountains: A tale of Pan-African amalgamation of East Antarctica questioned" (PDF). USGS. Retrieved 19 November 2014.
  8. Tingey, R.J.; Ellis, D.J. (1980). "Enderby land, Antarctica-an unusual Precambrian high grad metamorphic terrain". Journal of the Geological Society of Australia. 27 (1–2): 1–18. doi:10.1080/00167618008729114.
  9. Satish-Kumar, M.; Motoyoshi, Y.; Osanai, Y.; Hiroi, Y.; Shiraishi, K. (2008). Geodynamic Evolution of East Antarctica "A key to East-West Gondwana Connection". The Geological Society of London. ISBN   9781862392687.
  10. Mikhalsky, E.V. "The Tectogenesis Stages of the Antarctic Shield: Review of Geochronological Data" (PDF). Retrieved 21 November 2014.
  11. Golynsky, A.V.; Ivanov, S.V.; Kazankov, A.Ju.; Jokat, W.; Masolov, V.N.; von Frese, R.R.B. (2013-02-11). "New continental margin magnetic anomalies of East Antarctica". Tectonophysics. 585 (RECENT ADVANCES IN ANTARCTIC GEOMAGNETISM AND LITHOSPHERE STUDIES): 172–184. doi:10.1016/j.tecto.2012.06.043.
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