Neo-Archean

Aeonothem	Arathem	system	Age ( mya )
later	later	later
A r c h a i k u m Duration: 1500 Ma	Neo-Archaic Duration: 300 Ma		2500 ⬍ 2800
	Mesoarchean Duration: 400 Ma		2800 ⬍ 3200
	Paleoarchean Duration: 400 Ma		3200 ⬍ 3600
	Eoarchic Duration: 400 Ma		3600 ⬍ 4000
formerly: Hadaikum

The Neo-Archean is a geological age . It represents the last of four eras (Neoarchean = new Archean ) within the geological eon of the Archean . It begins about 2800 million years ago with the end of the Mesoarchean and ends about 2500 million years ago with the beginning of the Paleoproterozoic .

Redefinition of the Neo-Archean

In the course of moving away from period boundaries determined purely by radiometry, the GSSP principle should now be applied as far as possible in the Precambrian, according to Gradstein et al. (2012) . The periods are thus defined on the basis of significant geological events and no longer on arbitrary radiometric ages.

For the Neo-Archaic, Gradstein propose the following new classification:

“The Neo-Archean is divided into the two periods Methanium and Siderium . Methanium begins at 2,780 million years BP with the first appearance of continental flood basalts and a positive d ¹³ C value in hydrocarbons for the first time . It is followed by the siderium around 2630 million years BP with the first appearance of ribbon ores , which ends around 2420 million years BP with the first paleoproterozoic, glacial deposits . The GSSP for the methanium is at the base of the Mount Roe Basalt of the Fortescue Group ( Mount Bruce Supergroup ) in Western Australia , that of the siderium at the base of the Marra Mamba Iron Formation of the Hamersley Group (also Mount Bruce Supergroup, Western Australia) "

The newly defined Neo-Archean lasts 360 million years; the Mesoarchean-Neoarchean boundary tapers by 20 million years and the Archean-Proterozoan boundary by 80 million years.

characterization

Ribbon ore in the Dales Gorge, Hamersley Range

Recent research suggests that the prerequisites for the formation of higher mountains were given for the first time in the Neo-Archean . In the ages before that, the continental lithosphere was not yet sufficiently stable for topographical elevations of more than 2,500 meters due to its lower viscosity (high temperature and insufficient thickness) .

A pulse of magmatic activity , the so-called late archaic super event, is unique in the history of the earth . In the period from 2700 to 2500 million years BP it led to enormous crustal growth and probably to the formation of one or more supercontinents ( Kenorland or Superia and Sclavia ). Maxima in the zircon age and in the frequency distribution of greenstone belts and associated orogenic gold deposits underline the importance of this event.

The last period of the Neo-Archean, the Siderium, is characterized by the worldwide formation of ribbon ores . A large part of the iron dissolved in the oceans was thereby precipitated, so that from the Paleoproterozoic the oxygen concentration in the sea ​​water and finally also in the earth's atmosphere could increase (see also Great Oxygen Disaster ).

Events

• 2960 to 2760 million years BP:
  • Eruption of the Blake River Megacaldera , a super volcano in Ontario / Quebec ( Superior Kraton )
• Around 2700 million years BP:
  • A total of 15 diamond horizons document glaciation in the more than 500 meters thick, around 2700 million year old Talya Conglomerate of the Vanivilas Formation in southern India . Simultaneous icing is also documented directly below the intrusion contact of the Stillwater Complex in Montana .
• Between 2530 and 2510 million years BP:
  • Penetration of the Closepet granite into the Peninsular Gneiss Complex (PGC) in the South Indian Dharwar Kraton .
• Around 2500 to 2475 million years ago BP:
  • Penetration of the tholeiitic and komatiitic Mistassini gang swarm into the superior kraton.
• 2473 to 2446 million years BP:
  • Matachewan gang swarm in the Superior Kraton. Four times the size of its predecessor, it is the oldest known superplume ( giant mantle diapir ).
• Around 2400 million years BP:
  • The oldest known meteorite crater of Suavjärvi was possibly formed in Karelia .

stratigraphy

Significant sedimentary basins and geological formations

• Hamersley Basin with Hamersley Group in Western Australia - 2715 to about 2400 million years BP
• Dharwar Supergroup in the south of India :
  • Chitrapura Group - 2,700 to 2,600 million years BP
  • Bababudan Group - 2910 to 2700 million years BP
• Yellowknife Supergroup in Canada - 2,700 to 2,600 million years BP
• South Pass Greenstone Belt in Wyoming - 2700 to 2600 million years BP
• Ventersdorp Supergroup on the Kaapvaal Craton in South Africa - 2740 to 2690 million years BP
• Transvaal Basin in South Africa - 2670 to 1900 million years BP
  • Transvaal Supergroup :
    • Ghaap Group in the Griqualand West Area - 2669 ± 5 to 2450 million years BP
    • Chuniespoort Group in the Transvaal area - 2588 ± 6 to 2460 million years BP
• Minas Supergroup in Eastern Brazil - 2610/2580 to 2420 million years BP
• Eastern block of what will later become the North China Craton - 2800 to 2600 million years BP with:
  • Taishan Group in western Shandong - 2,767 to 2,671 million years old BP
  • Upper Anshan Group in Anshan - 2724 to 2610 million years BP
  • In addition, Jiaodong Group in eastern Shandong, Jiapigou Group in southern Jilin , Jianping Group in western Liaoning and Qianxi Group / Zhunhua Group / Dantazi Group / Badaohe Group / Miyun Group in eastern Hebei

Deposits

• Iron (ribbon ores):
  • Michipicoten Iron Formation , Canada - 2744 to 2696 million years old BP
  • Marra Mamba Iron Formation in Western Australia - 2,630 million years old
  • Cauê Banded Iron Formation of the Itabira Group , Minas Supergroup in Brazil - 2580 to 2420 million years BP
  • Asbestos Hills subgroup of the Ghaap Group in South Africa - 2,489 to 2,480 million years ago
  • Penge formation of the Chuniesport Group in South Africa - around 2,480 million years BP
  • Brockman Iron Formation in the Hamersley Basin, Western Australia - 2,469 million years BP
  • Kuruman Iron Formation of the Campbellrand Subgroup in South Africa - around 2,465 million years BP
• Gold :
  • Witwatersrand Basin , South Africa (multiple deposits) - 3,074 to 2,714 million years BP
  • Ventersdorp Contact Reef in South Africa - 2729 ± 19 million years BP
  • Eastern Goldfields Province near Kalgoorlie , Yilgarn Craton , Western Australia - 2640 to 2600 million years BP
  • Southern Abitibi Greenstone Belt in Canada - <2670 million years BP
  • Eastern Dharwar Craton -> 2550 million years BP
  • Sukumaland greenstone belt of the Tanzania craton - <2640 million years BP
  • Rio das Velhas greenstone belt of the São Francisco craton in Brazil - <2710 million years BP
• Chromium , platinum and palladium :
  • Stillwater Complex , Montana - 2,700 million years old BP

Geodynamics

• Baltic shield :
  • Formation of the Karelids - 3100 to 2600 million years BP
• Kaapvaal Kraton and Zimbabwe Kraton :
  • Northward thrust of greenstone belts on the northern edge of the Kapvaal craton - 2729 ± 19 million years BP
  • Limpopo belt
    • Thrust of the Southern Marginal Zone to the south onto the Kaapvaal Craton (granulite facial metamorphism) - 2691 ± 7 million years BP
• Superior Kraton :
  • In North America the Algoman Orogeny (also Kenoran Orogeny) comes to an end around 2500 million years BP.
• East Antarctica :
  • Retromorphosis and anatexis in the Mawson Craton ( Adélieland , Georg-V-Land ) - 2500 to 2420 million years BP.

See also

• Geological timescale

Individual evidence

1. ^ Felix M. Gradstein et al .: On the Geologic Time Scale . In: Newsletters on Stratigraphy . tape 45/2 , 2012, p. 171-188 .
2. ↑ P. Rey, N. Coltitce: Neoarchean lithospheric strengthening and the coupling of Earth's geochemical reservoirs. ( Memento of the original from June 9, 2013 in the Internet Archive ) Info: The  archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. In: Geology. Volume 36, 2008, pp. 635-638.
3. ↑ RW Ojakangas et al: The Talya Conglomerate: an Archean (~ 2.7 Ga) Glaciomarine Formation, Western Dharwar Craton, Southern India . In: Current Science . tape 106 , N ° 3, 2014, p. 387-396 .
4. ^ NJ Page: The Precambrian diamictite below the base of the Stillwater Complex, Montana . In: MJ Hambrey, NB Harland (Ed.): Earth's Pre-Pleistocene Glacial Record . Cambridge University Press, Cambridge 1981, pp. 821-823 .
5. ↑ LM Heaman: 2.45 Ga global mafic magmatism: Earth's oldest superplume? In: Eighth International Conference on Geochronology, Cosmochronology & Isotope Geology, Program with Abstracts, US Geol. Surv. Circular 1107 . Berkeley, California 1994, pp. 132 .