Napier complex

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The Napier complex is a crustalized block of crust of archaic age. It is characterized by metamorphoses under ultra-high temperatures and multiple strong deformations. This complex is located on the northern edge of the Rayner Province of East Antarctica . The earliest protoliths (parent rocks) date to 3850 mya . They are the oldest rocks in East Antarctica and, along with the Canadian Acasta gneiss, are among the oldest in the world. In the rock spectrum, ultra-high temperature metamorphosed tonalitic - granodioritic orthogneiss predominate .

The archaic plate tectonic formation of the Napier complex is still poorly understood. This collided with the Rayner Province during the Grenville orogeny, which led to the formation of the supercontinent Rodinia , for the first time with the south-eastern fringes of Greater India. The separation occurred around 124 mya during the disintegration of Eastern Gondwana , making them part of what is now East Antarctica.

Extension

The Napier Complex emerges on the edges of the Enderbyland and is there in front of the orogenic belt of the Rayner Province. It is open over an area of ​​approx. 400 by 200 square kilometers.

Protoliths and rocks

The Napier complex represents a crustal block that has been highly metamorphosed over a long period of time and has been severely deformed several times under high pressure. The oldest rocks were formed in the Eoarchean more than 3850 mya, which emerged from protoliths (parent rocks) of tonalite - trondhjemite - granodiorite crustal complexes (see → TTG complex ). The age was determined using zirconium samples . It represents the oldest rock in Antarctica. These consist of tonalitic orthogneiss . They developed during Felsic magmatic activities and possibly the first regional tectono-thermal events.

The protoliths of the Napier complex consisted of mantle rocks such as serpentinites and depleted peridotites as well as igneous tonalite-trondhjemite-granodiorites (TTG complexes). Next were basaltic to komatiitische rocks and slightly Anorthosite represented. The sediment protoliths consisted of sediments of various compositions, contaminated quartzites , ribbon ores and calcareous silicate rocks . This spectrum of protoliths, especially the Komatiit-TTG associations with the anorthosites, is reminiscent of archaic greenstone belts .

The rock spectrum evolved from the Protolithen existed alongside the prevailing tonalitic and granodioritic pryroxenhaltigen orthogneisses also Enderbiten , garnet leading granitic gneisses, mafic to ultramafic granulites and paragneisses of various compositions.

Chronology of rock formations and metamorphoses

The igneous protoliths of the oldest orthogneiss crystallized between 3850 and 3770 mya. The zircons come from Mount Sones and Gage Ridge in the Tula Mountains and the Fyfe Hills in Casey Bay . The paragneiss around Mount Sones, in Casey Bay and in Khmara Bay , whose orthogneiss there probably formed the sediment delivery areas, are of a similar age .

Around 3270 mya tonal- granodioritic magmatism arose in the area around Mount Riiser-Larsen , which rises on the edge of the Tula Mountains in the coastal region of the Amundsen Bay .

Even before 2980 mya a supracrustal sequence was formed, which was formed from older igneous orthogneiss.

Around 2980 mya, the Charnockites crystallized in Proclamation Island with local deformations and moderate metamorphoses. This metamorphosis documents what is probably the oldest demonstrable tectono-thermal process. Deformations with wrinkles developed throughout the Napier complex . They covered areas of around 200 by 100 kilometers. In the Napier Mountains and possibly other areas of rocks at ultra-high temperatures of 900 to 1100 ° C were metamorphic overprinted with formation of granulite facies .

The Napier crust was exhumed from 2980 to 2840 mya with the accompanying deposit of further supracrustal sequences.

Between 2840 and 2820 mya, deformations with folds and metamorphoses of older crust occurred under ultra-high temperature conditions as well as the deposition of new supracrustal sequences in the Tula Mountains and Scott Mountains . Furthermore, intrusions of orthogneiss of different ages arose.

At 2840 mya, granitoids took place in the Napier Mountains .

Between 2840 and 2480 mya, partial areas of the crust cooled under almost isobaric pressures between 0.7 and 1.0 gigapascals .

At around 2630 mya, tonal- granodioritic magmatism occurred on Tonagh Island in the Amundsen Bay .

From 2480 to 2450 mya, tectono-thermal processes followed with the formation of folds and metamorphoses with the formation of amphibolite facies to granulite facies . Pegmatites also rose .

At 2410 mya the last granites formed at the Simmers Peaks .

Around 2530 mya and between 1900 and 1200 mya tholeiitic dykes penetrated the existing rock packages. In the former Dyke event, tholeiites were deposited at considerable crustal depths during decreasing phases of granulite facies metamorphoses. They have a comatose affinity and may come from sources with more highly enriched incompatible elements . These dykes were found in Amundsen Bay . The dykes of the second phase correspond to typical continental tholeiites. Their geochemical signature is similar to that of oceanic island basalt (OIB) or enriched mid-ocean ridge basalt (E-MORB) (see also basalt formation ). These Dykes developed along the transition zone between the Napier Complex and Rayner Province.

Tectonic evolution

The petrographic diversity of the rocks, their placement and metamorphoses suggests a complex, protracted and progressive geodynamic development of different TTG terrans of different ages. Their accretion to the current rock complex is still unknown, as such archaic processes are poorly understood (see also → Greenstone belt and TTG complex ). However, crustal constituents in the Napier Complex show a joint geodynamic development after the first major regional igneous-metamorphic event around 2980 mya.

Geological framework

Some hypotheses suggest that the Napier Complex with the Rayner Province adjoining it originally had tectonic contact with the archaic to Proterozoic amphibolitic-granulitic south Indian terranos of the Dharwar craton, Nilgiri-Madras block and the Eastern Ghats . This is derived from the similarly old tonalite magmatism around 3300 mya and the high-grade metamorphism around 2500 mya. Although there are several similarities or similarities in this regard, some inconsistencies or differences have not yet been resolved. In comparison, Rayner Province formed during an accretion regime between 2400 and 1500 mya.

The plate tectonic and orogenic processes that led to the formation of the supercontinent Rodinias and later Eastern Gondwana are better documented . Between 1050 and 1000 mya, the Napier Complex and Rayner Province collided with the southeastern edges of Proto-India. This period corresponds roughly to the Grenville orogeny . The Indian and East Antarctic margins involved were tectono-thermally embossed. A quasi-continuous orogenic belt formed on the East Antarctic side, stretching from Queen Maud Land in the west to Queen Marie Land in the east. After the disintegration of Rodinia, Eastern Gondwana and Proto-Eastern Antarctica and Greater India collided during the Kuunga orogeny.

Their separation took place during the disintegration of East Gondwana with the separation of Proto-East Antarctica from Greater India. Proto-Australia also separated in a timely manner. The separation began around 160 mya with a strike-slip fault (strike-slip fault) between today's Madagascar and India, which also Proto-East Antarctica has been postponed, including proto-Australia. Ocean floor spreading began from 130 mya, and up to 124 mya a new lithospheric plate boundary was formed between Proto-East Antarctica and Greater India. The Enderby Plain and the northeastern Proto- Indian Ocean opened. The Napier complex with Rayner Province was separated from the Eastern Ghats and remained as part of Proto- Eastern Gondwana.

Web links

  • CW Fitzsimons: A review of tectonic events in the East Antarctic Shield and their implications for Gondwana and earlier supercontinents. In: Journal of African Earth Sciences, Volume 31, Issue 1, July 2000, Pages 3-23. doi: 10.1016 / S0899-5362 (00) 00069-5 , alternatively
  • SL Harley: Archaean-Cambrian crustal development of East Antarctica: metamorphic characteristics and tectonic implications. In: Geological Society, London, Special Publications, 206, 203-230, January 1, 2003. doi: 10.1144 / GSL.SP.2003.206.01.11 , alternative
  • C. Diana, RD Müller, BJ Brown and T. Ishihara: Microcontinent formation around Australia. In: Geol.Soc.Australia Spec.Publ. 22, and Geol.Soc.America Spec.Pap. 372: 405-416 (2003). Online article
  • M. Seton, RD Müller, S. Zahirovic, C. Gaina and others: Global continental and ocean basin reconstructions since 200 Ma. In: Earth Science Reviews 113 (2012) 212-270. doi: 10.1016 / j.earscirev.2012.03.002 , alternatively

Individual evidence

  1. ↑ M. Satish-Kumar, T. Hokada, T. Kawakami and Daniel J. Dunkley: Geosciences research in East Antarctica (0 ° E – 60 ° E): present status and future perspectives. In: Geological Society, London, Special Publications, 308, 1-20, November 21, 2008. doi: 10.1144 / SP308.1 , alternative
  2. ^ SL Harley and LP Black: A revised Archaean chronology for the Napier Complex, Enderby Land, from SHRIMP ion-microprobe studies. In: Antarctic Science, Article 9, Volume 8, Issue 1, March 1977, pp. 74 - 91. doi: 10.1017 / S0954102097000102 , alternatively
  3. ^ Hideo Ishizuka: Protoliths of the Napier Complex in Enderby Land, East Antarctica; an overview and implication for crustal formation of Archaean continents. In: Journal of Mineralogical and Petrological Sciences, 2008, Volume 103 Issue 4 Pages 218-225. doi: 10.2465 / jmps.080328 , alteranitv
  4. ^ JW Sheraton and LP Black: Geochemistry and geochronology of proterozoic tholeiite dykes of east antarctica: evidence for mantle metasomatism. In: Contributions to Mineralogy and Petrology, January 1982, Volume 78, Issue 3, pp 305-317. doi: 10.1007 / BF00398925 , alternatively
  5. ↑ Tomokazu Hokada, Keiji Misawa, Kazuyuki Shiraishi and Satoko Suzuki: Mid to late Archaean (3.3–2.5 Ga) tonalitic crustal formation and high-grade metamorphism at Mt. Riiser-Larsen, Napier Complex, East Antarctica. In: Precambrian Research 127 (2003) 215-228. doi: 10.1016 / S0301-9268 (03) 00188-8 , alternatively
  6. ↑ EV Mikhalsky and JW Sheraton: The Rayner tectonic Province of East Antarctica: compositional features and Geodynamic setting. In: Geotectonics, November 2011, Volume 45, Issue 6, pp 496-512. doi: 10.1134 / S0016852111060057 , alternatively
  7. ↑ GH Granthama, PH Macey, K. Horie, T. Kawakami, M. Ishikawa, M. Satish-Kumar and others: Comparison of the metamorphic history of the Monapo Complex, northern Mozambique and Balchenfjella and Austhameren areas, Sør Rondane, Antarctica: Implications for the Kuunga Orogeny and the amalgamation of N and S. Gondwana. In: Precambrian Research Volume 234, September 2013, Pages 85-135. doi: 10.1016 / j.precamres.2012.11.012 , alternatively
  8. ↑ Carmen Gaina, R. Dietmar Müller, Belinda Brown, Takemi Ishihara and Sergey Ivanov: Breakup and early seafloor spreading between India and Antarctica. In: Geophysical Journal International, Volume 170, Issue 1, July 2007, Pages 151-169. doi: 10.1111 / j.1365-246X.2007.03450.x , alternatively