Late archaic super event

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The late archaic super event represents the most significant episodic magma pulse of all time in the history of the earth . It occurred 2,700 million years ago BP in the end of the Neoarchaic .

introduction

That during the Methaniums takes place in the time interval 2780-2630 million a BP Late Archaic Super event ( Engl. Late Archean great event ) provided the undoubtedly important, Magmenvolumen ever produced in the history of the earth. As a consequence of the increased magma activity, a supercontinent ( Kenorland or Superia ) was created, to which another possibly ( Sclavia ) had been added.

characterization

Area share of new crust formation in the course of the earth's history (in percent of the total crust), according to Condie (2006). Clearly recognizable is the absolute maximum at 2,700 million years BP.

Age distributions

Radiometric age distributions based on igneous and detritic zirconia show a clear, absolute maximum at 2,700 million years BP. Continent and craton-specific analyzes confirm this maximum for Laurentia , Europe , Australia (2680 million years BP), Antarctica (2670 million years BP) and Siberia (2650 million years BP). For Africa and South America the maximum was already at 2,750 million years BP (the detritic ages for South America are again at 2,700 million years BP). East Asia and India show a different behavior , which only reach their maximum at 2500 million years.

As can already be seen from this list, the Late Archaic super event was not limited to a narrowly limited maximum at 2,700 million years BP. Thus, in the time interval 2760 to 2650 million years BP 10 further secondary maxima can be distinguished. The importance of the main maximum is emphasized by the fact that it can be detected on 6 cratons. The secondary maximum at 2680 million years BP can be found on 5 cratons and the secondary maxima at 2760, 2730 and 2650 million years BP can only be made out on three cratons. The most precise analyzes come from the superior kraton , which, in addition to the main maximum , reveals at least four other secondary maxima in both greenstone belts and TTG complexes (at 2729, 2720, 2690 and 2682 million years BP).

For detritic zircons, important maxima are at 2700 million years BP (for Africa, Laurentia, Australia and South America), at 2680 million years BP (for Europe), at 2720 million years BP (for Africa, Europe and Antarctica), at 2665 million years BP (for Australia) and at 2650 million years BP (for South America, Europe and Africa).

intensity

The intensity of this event can be estimated well by comparing it with the secondary maximum at 1900 million years BP. For magmatic zircons, around 250 measurements were recorded at 2,700 million years BP, but only 175 at 1,900 million years BP. Detritic zircons provided 900 measurements at 2,680 million years BP and only 475 measurements at 1,900 million years BP.

Condie (2000) gives around 1 billion cubic kilometers for the volume of the newly formed crust. Taylor and McLennan (1985) estimate the new growth of the crust to be around 40% of the current crust. In the course of the methanium, according to them, the earth's crust expanded from 30% of its current value at 2700 million years BP to 70% at 2500 million years BP. Other model calculations even come to the astonishing result that around 2500 million years BP or even a little earlier 100% of the earth's crust had already been formed. Further, later growth was then balanced out by the combined action of erosion and subduction .

root cause

The cause of the drastically increased magma production is assumed to be a catastrophic overturn of the earth's mantle , which was triggered by an instability in the outflow velocity of the submerged part of a convection cell (flush instability).

Individual evidence

  1. ↑ Bleeker, W .: The Late Archean record: a puzzle in approx. 35 pieces . In: Lithos . tape 71 , 2003, p. 99-134 .
  2. ↑ a b Condie, KC et al .: Granitoid events in space and time: Constraints from igneous and detrital age spectra . In: Gondwana Research . tape 15 , 2009, p. 228-242 .
  3. ↑ Percival, JA et al .: Crustal growth through successive arc magmatism: reconnaissance U-Pb SHRIMP data from the northeastern Superior Province, Canada . In: Precambrian Research . tape 109 , 2001, p. 203-238 .
  4. ^ Taylor, SR and McLennan, SM: The Continental Crust: Composition and Evolution . Blackwell Scientific Publications, 1985, ISBN 0-632-01148-3 .
  5. ^ Armstrong, RI: The persistent myth of crustal growth . In: Australian Journal of Earth Sciences . tape 38 , 1991, pp. 613-630 .
  6. ^ Hawkesworth, CJ et al .: The generation and evolution of continental crust . In: Journal of the Geological Society . tape 167 . London 2010, p. 229-248 .
  7. ↑ Safanova, I. et al .: LA ICP MS U-Pb ages of detrital zircons from Russia's largest rivers: Implications for major granitoid events in Eurasia and global episodes of supercontinent formation . In: Journal of Geodynamics . tape 50 , 2010, p. 134-153 .